Toward Reduced Burden in Evidence-Based Assessment of PTSD: A Machine Learning Study

Structured diagnostic interviews involve significant respondent burden and clinician administration time. This study examined whether we can maintain diagnostic accuracy using fewer posttraumatic stress disorder (PTSD) assessment questions. Our study included 1,265 U.S. veterans of the Afghanistan and Iraq conflicts who were assessed for PTSD using the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (SCID-5). We used random forests to assess the importance of each diagnostic item in predicting a SCID-5 PTSD diagnosis. We used variable importance to rank each item and removed the lowest ranking items while maintaining ≥90% accuracy (i.e., efficiency), sensitivity, and other metrics. We eliminated six diagnostic items among the overall sample, four items among male veterans, and six items among female veterans. Our findings demonstrate that we may shorten the SCID-5 PTSD module while maintaining excellent diagnostic performance. These findings have implications for potentially reducing patient and provider burden of PTSD diagnostic assessment.

Resilience is spreading: Mental health within the COVID-19 pandemic

The COVID-19 global pandemic is in many ways unchartered mental health territory, but history would suggest that long-term resilience will be the most common outcome, even for those most directly impacted by the outbreak. We address 4 common myths about resilience and discuss ways to systematically build individual and community resiliency. Actively cultivating social support, adaptive meaning, and direct prosocial behaviors to reach the most vulnerable can have powerful resilience promoting effects. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Peritonitis caused by Blastomyces dermatitidis in a kidney transplant recipient: case report and literature review

Blastomyces dermatitidis is a dimorphic fungus endemic to the midwestern, south-central, and southeastern United States known to cause disseminated infection in immunocompromised individuals. We report a case of B. dermatitidis peritonitis in a renal allograft recipient with new-onset ascites and cytomegalovirus encephalitis. Peritoneal blastomycosis is a rare clinical entity and, to our knowledge, this patient represents the first known case of peritoneal blastomycosis in a solid organ transplant recipient. We review the clinical characteristics of B. dermatitidis peritonitis as well as the literature on fungal peritonitis with emphasis on dimorphic fungal pathogens. Clinical features suggestive of fungal peritonitis include new-onset ascites, abdominal pain, and fevers, especially with antecedent or concomitant pneumonia. A high index of clinical suspicion, along with the use of culture and non-culture diagnostics, is needed for early diagnosis and prompt initiation of therapy.

Development and application of a green fluorescent protein sentinel system for identification of RNA interference in Blastomyces dermatitidis illuminates the role of septin in morphogenesis and sporulation

A high-throughput strategy for testing gene function would accelerate progress in our understanding of disease pathogenesis for the dimorphic fungus Blastomyces dermatitidis, whose genome is being completed. We developed a green fluorescent protein (GFP) sentinel system of gene silencing to rapidly study genes of unknown function. Using Gateway technology to efficiently generate RNA interference plasmids, we cloned a target gene, "X," next to GFP to create one hairpin to knock down the expression of both genes so that diminished GFP reports target gene expression. To test this approach in B. dermatitidis, we first used LACZ and the virulence gene BAD1 as targets. The level of GFP reliably reported interference of their expression, leading to rapid detection of gene-silenced transformants. We next investigated a previously unstudied gene encoding septin and explored its possible role in morphogenesis and sporulation. A CDC11 septin homolog in B. dermatitidis localized to the neck of budding yeast cells. CDC11-silenced transformants identified with the sentinel system grew slowly as flat or rough colonies on agar. Microscopically, they formed ballooned, distorted yeast cells that failed to bud, and they sporulated poorly as mold. Hence, this GFP sentinel system enables rapid detection of gene silencing and has revealed a pronounced role for septin in morphogenesis, budding, and sporulation of B. dermatitidis.

Blastomycosis in solid organ transplant recipients

BACKGROUND

Blastomyces dermatitidis, the etiologic agent of blastomycosis, causes severe disease and substantial mortality in those immunocompromised by acquired immunodeficiency syndrome or malignancy. In solid organ transplant recipients, the epidemiology, clinical features, and outcomes have not been fully described.

METHODS

We conducted a retrospective case-series at the University of Wisconsin Hospital and Clinics. Case patients were solid organ transplant recipients with blastomycosis.

RESULTS

From 1986 to 2004, we identified 11 cases of post-transplant blastomycosis with 64% occurring between 2000 and 2004. Onset of infection occurred a median of 26 months post transplantation with near equal distribution before and after the first year of transplantation. Rejection did not precede any case of post-transplant blastomycosis. Opportunistic co-infections were common, occurring in 36% of patients. Pneumonia was the most common clinical presentation and was frequently complicated by acute respiratory distress syndrome (ARDS). Extrapulmonary disease predominantly involved the skin and spared the central nervous system. The overall mortality rate was 36%; however, this increased to 67% in those with ARDS. None of the surviving patients relapsed or received routine secondary antifungal prophylaxis.

CONCLUSION

Blastomycosis is an uncommon infection following solid organ transplantation that is frequently complicated by ARDS, dissemination, and opportunistic co-infection. After cure, post-transplant blastomycosis may not require lifelong antifungal suppression.

Vision of the hand prior to movement onset allows full motor adaptation to a multi-force environment

In everyday life, because of unexpected mechanical perturbation applied to the hand or to the whole body, hand movements may become suddenly inaccurate. With prolonged exposure to the perturbation, trajectories slowly recover their normal accuracy, which is the mark of motor adaptation. However, full development of this adaptive process in complete darkness has been recently challenged in a multi-force environment. Here, we report on the effectiveness of static hand position information as specified through vision prior to movement onset on the adaptative changes, over trials, of pointing movements performed in a gravitoinertial force field. For this, subjects seated off-center on a platform rotating at constant velocity, were either confined to complete darkness (No Vision Session, NV) or provided with vision of the hand resting on the starting position prior to movement onset (Hand Vision Prior to Movement Session, HVPM). Overall, our results showed that adaptation to the centrifugal force was very rapid, and allowed subjects to demonstrate appropriate motor control as early as of the very first trials performed during the rotation period, even in the NV condition. They also showed that the integration by the Central Nervous System (CNS) of visual and proprioceptive information prior to the execution of a reaching movement allows subjects to reach full motor adaptation in a multi-force environment. Furthermore, our data confirm the existence of differentiated motor adaptive mechanisms for centrifugal and Coriolis forces. Adaptation to the former may fully develop on the basis of an a priori coding of the characteristics of the background force level even without visual information, while the latter needs visual cues about hand position prior to movement onset to take place.

Subtherapeutic Ocular Penetration of Caspofungin and Associated Treatment Failure in Candida albicans Endophthalmitis

Candida endophthalmitis represents the most serious ocular complication of candidemia. The pharmacokinetics and pharmacodynamics of fluconazole, amphotericin B, and flucytosine are fairly well established in endophthalmitis therapy. There remains a paucity of clinical data regarding the utility of new antimycotic agents in the treatment of fungal chorioretinitis and endophthalmitis. We report a case of clinical failure of caspofungin in the management of Candida albicans endophthalmitis associated with poor vitreous penetration.

Accuracy of spatial localization depending on head posture in a perturbed gravitoinertial force field

Spatial orientation is crucial when subjects have to accurately reach memorized visual targets. In previous studies modified gravitoinertial force fields were used to affect the accuracy of pointing movements in complete darkness without visual feedback of the moving limb. Target mislocalization was put forward as one hypothesis to explain this decrease in accuracy of pointing movements. The aim of this study was to test this hypothesis by determining the accuracy of spatial localization of memorized visual targets in a perturbed gravitoinertial force field. As head orientation is involved in localization tasks and carrying relevant sensory systems (visual, vestibular and neck muscle proprioceptive), we also tested the effect of head posture on the accuracy of localization. Subjects (n=10) were seated off-axis on a rotating platform (120 degrees s(-1)) in complete darkness with the head fixed (head-fixed session) or free to move (head-free session). They were required to report verbally the egocentric spatial localization of visual memorized targets. They gave the perceived target location in direction (i.e. left or right) and in amplitude (in centimeters) relative to the direction they thought to be straight ahead. Results showed that the accuracy of visual localization decreased when subjects were exposed to inertial forces. Moreover, subjects localized the memorized visual targets more to the right than their actual position, that was in the direction of the inertial forces. With further analysis, it appeared that this shift of localization was concomitant with a shift of the visual straight ahead (VSA) in the opposite direction. Thus, the modified gravitoinertial force field led to a modification in the orientation of the egocentric reference frame. Furthermore, this shift of localization increased when the head was free to move while the head was tilted in roll toward the center of rotation of the platform and turned in yaw in the same direction. It is concluded that the orientation of the egocentric reference frame was influenced by the gravitoinertial vector.

Galvanic vestibular stimulation in humans produces online arm movement deviations when reaching towards memorized visual targets

Using galvanic vestibular stimulation (GVS), we tested whether a change in vestibular input at the onset of goal-directed arm movements induces deviations in arm trajectory. Eight head-fixed standing subjects were instructed to reach for memorized visual targets in complete darkness. In half of the trials, randomly-selected, a 3 mA bipolar binaural galvanic stimulation of randomly alternating polarity was triggered by the movement onset. Results revealed significant GVS-induced directional shifts of reaching movements towards the anode side. The earliest significant deviations of hand path occurred 240 ms after stimulation onset. The likely goal of these online deviations of arm trajectory was to compensate for a vestibular-evoked apparent change in the spatial relationship between the target and the hand.

Accuracy level of pointing movements performed during slow passive whole-body rotations

Seated observers requested to detect low-velocity passive rotations show a high motion-detection threshold. However, when standing on a slowly rotating platform, their equilibrium is preserved, suggesting that cognitive sensing and sensorimotor reactions do not share the same central processes. The present experiments investigated the ability of observers seated on a slowly rotating chair in total darkness to indicate with their hand the position of briefly flashed targets (Experiment 1) and to indicate the subjective horizon with an outstretched arm (Experiment 2) or with a target driven by a joystick (Experiment 3). The overall hypothesis stated that egocentric coding of the position of a target should not be affected by sensing or not-sensing body rotation (Experiment 1), while geocentric positioning may (Experiments 2 and 3). Our data partially supported the hypothesis. Subjects pointed accurately to the memorized targets (Experiment 1), whereas misperception of body orientation was a source of inaccuracy for actions referred to a geocentric frame (Experiments 2 and 3). More interestingly, subjects' perceptions changed as a single, smooth, and monotonic function of tilt, independent of whether the perception of body orientation was present or not.

Weight estimation in a "deafferented" man and in control subjects: are judgements influenced by peripheral or central signals?

It is not yet certain which sources of information are most important in judging the weight of a held object. In order to study this question further, a "deafferented" man and five controls flexed their wrist to lift a container weighing 1,000 g. Direct vision of the arm and weight was denied; the container's vertical position was displayed to the subjects on an oscilloscope at the start of each trial and, then, in most experimental conditions, this display was removed. The weight was then either gradually increased or decreased over 20 s or left unchanged, on a pseudorandom basis. A verbal judgement of its change was required at the end of each trial, lasting 20 or 40 s. Under these conditions, the "deafferented" subject was unable to correctly judge the weight changes (38% accuracy, n.s. chi2, compared with 77% in control subjects), and even the control subjects, when exposed to muscle vibration, made many errors (54% accuracy). However, in many trials, including those in which the weight was unchanged, the vertical height of the container was not held constant by the subjects, but drifted up or down (mean absolute drift: approximately 2 cm). Hence, the change in muscular activation or stiffness could be estimated by the observers in the majority of trials. This allowed the verbal judgements of both the "deafferented" man and of control subjects undergoing muscle vibration to be correlated with the muscle activation produced, independent of the actual weight being tested. Post-hoc predictions of controls' responses during vibration, based on the direction of the change in muscle activity which these drifts in position implied, were 77% and 66% accurate for +/-750 g and +/-375 g tasks and 73% accurate for forearm-vibration trials (P<0.0001, chi2). Predictions of the "deafferented" subject's responses were 64% accurate (P=0.0002, chi2), even though his own responses were at a chance level with respect to the actual weight change. The judgements made by these subjects might have been based upon a peripheral sensory input, as small afferent fibres are still present in the "deafferented" man and vibration only partly blocked sensory function in the control subjects. Care was taken to minimise all other possible cues to the weight changes, e.g. vestibular, thermal, pressure or pain cues. However, peripheral inputs may not be the only signals used in the subjects' perceptual judgements. They might, instead, be based upon a centrally originating, but illusory changing sense of body position or, possibly, a changing sense of effort. In both cases, a perceived discordance between voluntary muscle activation and body image could underlie the subjects' responses. Our data do not yet allow us to distinguish between these alternative peripheral and central hypotheses, but do highlight the need to include perceptions of body position and motion into judgements of force control.

The role of proprioception and attention in a visuomotor adaptation task

The role of proprioception in the control and adaptation of visuomotor relationships is still unclear. We have studied a deafferented subject, IW, and control subjects in a task in which they used single joint elbow extension to move to a visual target, with visual feedback of the terminal position provided by a cursor displayed in the plane of their movements. We report the differences in movement accuracy between the deafferented subject and controls in the normal task and when challenged with a cognitive load, counting backwards. All subjects were less accurate when counting; this was a small effect for the controls (<10% change) but much greater for the deafferented subject (>60% change). We also examined changes in movement kinematics when the instructed amplitude was altered via a changed gain between final arm position and presentation of the feedback cursor. The deafferented subject maintained temporal movement parameters stable and altered amplitude by scaling force (i.e. changed peak velocity), whereas the controls scaled both movement velocity and duration. Finally, we compared the subjects' adaptation of movement amplitude after a period of exposure to the changed visuomotor gain. The deafferented subject was able to adapt, but his adaptation was severely impaired by the counting task. These results suggest that proprioception is not an absolute requirement for adaptation to occur. Instead, proprioception has a more subtle role to play in the adjustment to visuomotor perturbations. It has an important role in the control of reaching movements, while in the absence of proprioception, attention appears necessary to monitor movements.

Does the oculo-manual co-ordination control system use an internal model of the arm dynamics?

The hypothesis that during self-moved target tracking, the eye-arm co-ordination control system uses an internal model of the arm dynamics was tested. The contribution of arm proprioception to this model was also assessed. Subjects (nine healthy adults and one deafferented subject) were requested to make forearm movements and visually track an arm-driven target. Unexpected changes in mechanical properties of the manipulandum were used to modify the dynamical conditions of arm movement. The smooth pursuit gain (SPG) was computed before and during the perturbation. Results showed a decrease of SPG during perturbation in control subjects only. We propose that an internal model of the arm dynamics may be used to co-ordinate eye and arm movements, and arm proprioception may contribute to this internal model.

Updating visual space during passive and voluntary head-in-space movements

The accuracy of our spatially oriented behaviors largely depends on the precision of monitoring the change in body position with respect to space during self-motion. We investigated observers' capacity to determine, before and after head rotations about the yaw axis, the position of a memorized earth-fixed visual target positioned 21 degrees laterally. The subjects (n=6) showed small errors (mean=-0.6 degrees) and little variability (mean=0.9 degrees) in determining the position of an extinguished visual-target position when the head (and gaze) remained in a straight-ahead position. This accuracy was preserved when subjects voluntary rotated the head by various magnitudes in the direction of the memorized visual target (head rotations ranged between 5 degrees and 60 degrees). However, when the chair on which the subjects were seated was unexpectedly rotated about the yaw axis in the direction of the target (chair rotations ranged between 6 degrees and 36 degrees ) during the head-on-trunk rotations, the performance was markedly decreased, both in terms of spatial precision (mean error=5.6 degrees ) and variability (mean=5.7 degrees). A control experiment showed that the prior knowledge of chair rotation occurrence had no effect on the perceived target position after head-trunk movements. Updating an earth-fixed target position during head-on-trunk rotations could be achieved through both cervical and vestibular signals processing, but, in the present experiment, the vestibular output was the only signal that had the potentiality to contribute to accurate coding of the target position after simultaneous head and trunk movements. Our results therefore suggest that the vestibular output is a noisy signal for the central nervous signal to update the visual space during head-in-space motion.

Role of arm proprioception in calibrating the arm-eye temporal coordination

When subjects track with the eyes an arm-attached target, eye latency is shorter than when tracking an external target. This improved synchrony could result from either a common command addressed to the two systems or from an influence of the arm command on eye motion initiation. According to the first hypothesis, the eyes should start moving long before the arm, because of the difference in dynamics. We recorded arm and eye motion together with biceps muscle activity in controls and a deafferented subject. Data support the second hypothesis. Moreover, the deafferented subject showed a lesser correlation between arm and eye motions than controls, suggesting a role for arm proprioception in the calibration of the temporal relationship between arm and eye movements.

The role of ocular muscle proprioception during modifications in smooth pursuit output

The output of the smooth pursuit (SP) system can be increased by adding a portion of the recorded eye motion onto target motion, producing a situation analogous to that occurring with weakened ocular muscles. This change is most likely the result of alterations in the signals that code eye and target motion. We have assessed the contribution of one such signal, that arising from ocular proprioception, to the modification process during monocular SP by preventing the motion of the non-viewing eye with a suction scleral lens. The large increases normally observed for SP velocity following the modification period were substantially reduced under these conditions. Similar alterations were also observed in a manual tracking task. These results demonstrate that ocular proprioceptive signals serve to stabilize the output of the SP system following perturbations, via the recoding of eye and target motion.

Visual object localization through vestibular and neck inputs. 2: Updating off-mid-sagittal-plane target positions

The vestibular signal plays a significant role in sensing changes in head orientation during rotations and in determining the magnitude of the rotations, but has only minor contributions in updating the internal representation of object positions with respect to the body after body rotations. The small contribution of the vestibular signal in egocentric object localization was evidenced in experiments in which the subjects reported the remembered position of eccentric earth-fixed targets after passive body rotations. The experiment reported here tested whether motor systems, such as the oculomotor system, make use of vestibular signals to generate accurate goal-directed motor responses toward a target whose position needs to be updated with respect to the body during and after whole-body rotations. The results showed that although subjects can produce saccadic eye movements of about the same magnitude as passive whole-body rotations (as previously reported by a number of researchers), they failed to generate accurate saccades toward the position of an extinguished peripheral visual target after the rotation. Overall, these results combined with those found in the literature suggest different central processes for determining changes in body orientation in complete darkness and for updating a target position with respect to the body during and after body rotations.

Self-moved target eye tracking in control and deafferented subjects: roles of arm motor command and proprioception in arm-eye coordination

1. When a visual target is moved by the subject's hand (self-moved target tracking), smooth pursuit (SP) characteristics differ from eye-alone tracking: SP latency is shorter and maximal eye velocity is higher in self-moved target tracking than in eye-alone tracking. The aim of this study was to determine which signals (motor command and/or proprioception) generated during arm motion are responsible for the decreased time interval between arm and eye motion onsets in self-moved target tracking. 2. Six control subjects tracked a visual target whose motion was generated by active or passive movements of the observer's arm in order to determine the role played by arm proprioception in the arm-eye coordination. In a second experiment, the participation of two subjects suffering complete loss of proprioception allowed us to assess the contribution of arm motor command signals. 3. In control subjects, passive movement of the arm led to eye latencies significantly longer (130 ms) than when the arm was actively self-moved (-5 ms:negative values meaning that the eyes actually started to move before the target) but slightly shorter than in eye-alone tracking (150 ms). These observations indicate that active movement of the arm is necessary to trigger short-latency SP of self-moved targets. 4. Despite the lack of proprioceptive information about arm motion, the two deafferented subjects produced early SP (-8 ms on average) when they actively moved their arms. In this respect they did not differ from control subjects. Active control of the arm is thus sufficient to trigger short-latency SP. However, in contrast with control subjects, in deafferented subjects SP gain declined with increasing target motion frequency more rapidly in self-moved target tracking than in eye-alone tracking. 5. The deafferented subjects also tracked a self-moved target while the relationship between arm and target motions was altered either by introducing a delay between arm motion and target motion or by reversing target motion relative to arm motion. As with control subjects, delayed target motion did not affect SP latency. Furthermore, the deafferented subjects adapted to the reversed arm-target relationship faster than control subjects. 6. The results suggest that arm motor command is necessary for the eye-to-arm motion onset synchronization, because eye tracking of the passively moved arm was performed by control subjects with a latency comparable with that of eye-alone tracking of an external target. On the other hand, as evidenced by the data from the deafferented subjects, afferent information does not appear to be necessary for reducing the time between arm motion and SP onsets. However, afferent information appears to contribute to the parametric adjustment between arm motor command and visual information about arm motion.

The relative contribution of retinal and extraretinal signals in determining the accuracy of reaching movements in normal subjects and a deafferented patient

This experiment investigated the relative extent to which different signals from the visuo-oculomotor system are used to improve accuracy of arm movements. Different visuo-oculomotor conditions were used to produce various retinal and extraretinal signals leading to a similar target amplitude: (a) fixating a central target while pointing to a peripheral visual target, (b) tracking a target through smooth pursuit movement and then pointing to the target when its excursion ceased, and (c) pointing to a target reached previously by a saccadic eye movement. The experiment was performed with a deafferented subject and control subjects. For the deafferented patient, the absence of proprioception prevented any comparison between internal representations of target and limb (through proprioception) positions during the arm movement. The deafferented patient's endpoint therefore provided a good estimate of the accuracy of the target coordinates used by the arm motor system. The deafferented subject showed relatively good accuracy by producing a saccade prior to the pointing, but large overshooting in the fixation condition and undershooting in the pursuit condition. The results suggest that the deafferented subject does use oculomotor signals to program arm movement and that signals associated with fast movements of the eyes are better for pointing accuracy than slow ramp movements. The inaccuracy of the deafferented subject when no eye movement is allowed (the condition in which the controls were the most accurate) suggests that, in this condition, a proprioceptive map is involved in which both the target and the arm are represented.

Perception of passive whole-body rotations in the absence of neck and body proprioception

1. This study investigated whether accurate perception of body rotation after passive horizontal whole-body rotations in the dark requires the integration of both vestibular and neck-body proprioceptive signals. 2. In the first experiment, the gain of the vestibuloocular reflex (VOR) of normal subjects ("controls") and of a patient without proprioception of the neck and body muscles was assessed by the use of pulse and sinusoidal stimulation. In the second experiment, the subjects reported verbally the magnitude of the body rotations. Finally, in the third experiment, they shifted gaze to the position fixated before the rotation ("vestibular memory-contingent saccades" paradigm). 3. The VOR gain of the patient was similar to that of controls, although the body rotations of the patient were largely overestimated, regardless of whether the patient reported the perceived magnitude verbally or through a gaze shift toward the position gazed at before the rotation. 4. These results suggest that neck muscle proprioception contributes to the vestibular signal calibration at the perceptual level necessary for determining body orientation accurately after rotations in the dark.

Evaluation of saccadic eye movements as an objective test of recovery from anaesthesia

Saccadic eye movements have been previously used to assess residual effect of anaesthetics, but this test is seldom compared to other psychomotor tests. The aim of the present study was to validate saccades as a recovery index in relation to frequently referred subjective and psychometric tests. Eight healthy subjects were tested before and after intra-muscular injection of either placebo or 0.15 mg.kg-1 of midazolam. Each session consisted of a saccadic test (recorded by electro-oculography), a choice-reaction-time test (CRT), a subjective state-of-alertness test (11 visual analogic scales) and blood sampling (to monitor midazolam plasma concentration), before and 30 (t30), 60 (t60), 120 (t120), 180 (t180), 240 (t240) minutes after drug administration. In the placebo group, there was no change in subjective assessment, saccade characteristics (latency, peak velocity and duration) or CRT results. In the midazolam group, 6 subjective items changed with different time-courses, when compared to baseline: from t30 to t120 (drowsy, in shape, tired, clumsy, strong) and t120 (woolly). Saccade latency and duration were significantly different from t30 to t120 and until t180 for peak velocity. CRT performance was significantly altered from t30 to t120. Midazolam plasma concentration decreased from 177 +/- 33 ng.ml-1 at t30 to 47 +/- 12 ng.ml-1 at t240. At this latter time, sensorimotor functions returned to the baseline. All subjects fulfilled the clinical conditions for home discharge 4 hours after administration. These results suggest that a saccadic eye movement test is a sensitive and reliable tool for the assessment of residual effect of anaesthetics. This test was found to be more sensitive than CRT test since peak saccadic velocity was the last psychometric parameter to be returned to baseline after midazolam injection. This study also confirms the poor reliability of subjective assessment, as subjects tended to underestimate the alteration of their performance immediately following drug injection.

Influence of eye motion on adaptive modifications of the vestibulo-ocular reflex in the rat

While sustained retinal slip is assumed to be the basic conditioning stimulus in adaptive modifications of the vestibulo-ocular reflex (VOR) gain, several observations suggest that eye motion-related signals might also be involved. We oscillated pigmented rats over periods of 20 min around the vertical axis, at 0.3 Hz and 20 degrees/s peak velocity, in different retinal slip and/or eye motion conditions in order to modify their VOR gain. The positions of both eyes were recorded by means of a phase-detection coil system with the head restrained. The main findings came from the comparison of two basic conditions--including their respective controls--in which one or both eyes were reversibly immobilised by threads sutured to the eyes. In the first condition the animals were rotated in the light with one eye immobilised and the other eye free to move but covered. Rotation in the light in this open-loop condition immediately elicited high-gain compensatory eye movements of the non-impeded, covered eye. At the end of this training procedure, the VOR gain increased by 43.2%. In the second condition, both eyes were immobilised and one eye was covered. The result was an increase in the VOR gain of 26.3%. These two conditions were similar as to the visuo-vestibular drive during the exposure, but different as to the resulting--and allowed--eye motion, showing that the condition where the larger eye movements occurred yielded the larger VOR gain change. Our data support the idea proposed by Collewijn and Grootendorst (1979, p. 779) and Collewijn (1981, p. 146) that "[retinal] slip and eye movements seem to be relevant signals for the adaptation of the rabbit's visuo-vestibular oculomotor reflexes".(ABSTRACT TRUNCATED AT 250 WORDS)

Failure to update the egocentric representation of the visual space through labyrinthine signal

The present study evaluated the capacity to compare retinal and vestibular signals in a heterosensorial matching task. In the first experiment, subjects evaluated the magnitude of passive whole-body rotations in relation to the eccentricity of a visual target briefly presented before rotation. Such a task elicits multimodal sensory stimulations experienced by a subject during normal goal-oriented head movements, i.e., retinal and vestibular stimulations. A good capacity to evaluate vestibular signals in relation with retinal inputs might suggest that the labyrinthine output is part of a cognitive feedback-loop controlling active head movements oriented toward a visual target and/or that the labyrinthine signal might make a major contribution to judging the position of the target in space after goal-directed head movements. Results showed that body rotation magnitudes had to exceed the amplitude of the visual target by about 120 and 89% to be perceived as having a similar magnitude to a 10 degree and an 18 degree visual target, respectively. A second experiment was designed to test whether this major discrepancy originated either from (a) an overestimation of the peripheral visual target locations, (b) an underestimation of the labyrinthine signal, (c) a deficiency in matching sensory signals from different modalities, or (d) any combination of (a), (b), and (c). In the second experiment, the actual perception of retinal and labyrinthine signals, as indicated by verbal responses, was quantified. Results from this experiment showed that most of the large underestimation of the vestibular stimulation found in Experiment I ought to emerge from a poor capacity to integrate heterogeneous sensory signals by the perceptual system rather than from pure misperception of the retinal and/or labyrinthine signals. Overall, results from Experiments I and II argue for a deficiency of the CNS to integrate labyrinthine signals for updating the egocentric representation of the peripheral visual target during passive body (head) rotations.

Egocentric visual target position and velocity coding: role of ocular muscle proprioception

Limited knowledge is available regarding the processes by which the brain codes the velocity of visual targets with respect to the observer. Two models have been previously proposed to describe the visual target localization mechanism. Both assume that the necessary information is derived from the coding of the position of the eye in the orbit, either through a copy of the muscular activation (out flow model) or through eye muscle proprioception (in flow model). Eye velocity coding might be derived from velocity sensitive ocular muscle proprioceptors or from position coding signals through differentiation. We used techniques based on manual pointing and manual tracking of visual target, combined with passive deviation of one covered eye, to demonstrate that ocular muscle proprioception is involved in (i) eye-in-head position coding, hence in target localization function; (ii) long-term maintenance of ocular alignment (phoria); and (iii) sensing of visual target velocity with respect to the head. These observations support other data now available, describing the processes by which the brain codes position and velocity of visual targets. Such findings might interest engineers in the field of robotics who are facing the problem of providing robots with the ability to sense object position and velocity in order to create an internal model of their working environment.

Encoding the position of a flashed visual target after passive body rotations

The capacity of the central nervous system (CNS) for processing vestibular signals during passive whole-body rotations to update the internal representation of a visual target position in relation to the body was assessed. Results showed that subjects mislocalized previously presented visual targets after body rotations in complete darkness. Detailed analysis of the results suggested that the large target mislocalization stemmed not only from a systematic underestimation of rotation magnitude but also from the incapacity of the CNS to use the vestibular signals to accurately update the internal representation of the target position in relation to the body after passive rotations.

Oculo-manual coordination control: respective role of visual and non-visual information in ocular tracking of self-moved targets

We evaluated the role of visual and non-visual information in the control of smooth pursuit movements during tracking of a self-moved target. Previous works have shown that self-moved target tracking is characterised by shorter smooth pursuit latency and higher maximal velocity than eye-alone tracking. In fact, when a subject tracks a visual target controlled by his own arm, eye movement and arm movement are closely synchronised. In the present study, we showed that, in a condition where the direction of motion of a self-moved visual target was opposite to that of the arm (same amplitude, same velocity, but opposite direction of movement), the resulting smooth pursuit eye movements occurred with low latency, and continued for about 140 ms in the direction of the arm movement rather than in the direction of the actual visual target movement. After 140 ms, the eye movement direction reversed through a combination of smooth pursuit and saccades. Subsequently, while arm and visual target still moved in opposite directions, smooth pursuit occurred in pace with the visual target motion. Subjects were also submitted to a series of 60 tracking trials, for which the arm-to-target motion relationship was systematically reversed. Under these conditions subjects were able to initiate early smooth pursuit in the actual direction of the visual target. Overall, these results confirm that non-visual information produced by the arm motor system can trigger and control smooth pursuit. They also demonstrate the plasticity of the neuronal network handling eye-arm coordination control.

Internal representation of gaze direction with and without retinal inputs in man

The contribution of retinal and extraretinal signals to the coding of eye position in the head was studied in human subjects (Ss). Horizontal saccades were produced in darkness. For some trials, before returning gaze direction to the starting position, a visual signal briefly stimulated the foveal retina. Results showed that this retinal input helped Ss to perceive gaze orientation more accurately after the saccade suggesting that the internal representation of eye position was improved when both extraretinal and retinal signals were available.

Changes in ocular alignment and pointing accuracy after sustained passive rotation of one eye

We have investigated the contribution of ocular muscle proprioception (OMP) to the long-term maintenance of ocular alignment in normal human beings. Using a scleral suction lens, one eye was rotated laterally 30 deg away from the position of the other eye. This procedure selectively affects OMP without altering the efferent copy of the ocular motor command. The passively displaced eye was covered while the unimpeded eye fixed upon a stationary target. The suction lens was removed after 6 or 10 min and the measures of alignment begun immediately. Three tests were used to determine the effects of the deviation on ocular alignment: the Lancaster red-green test; saccadic eye movement responses to stepping targets; and hand pointing to monocularly presented targets. All three tests indicated a change of ocular alignment of about 2-4 deg, lasting 5-10 min: sustained temporal deviation resulted in exophoria (relative divergence of the visual axis), and sustained nasal deviation induced esophoria (relative convergence). Binocular viewing rapidly abolished the effect. The hand pointing test showed a large shift in the perceived position of a target during monocular viewing with either eye and its amplitude was correlated with the change of ocular alignment. These results indicate that a sustained passive rotation of one eye can lead to a persistent change in ocular alignment even after the eye is released, without any disparity cues. We further suggest that central mechanisms, based upon ocular motor afferents, rather than passive orbital mechanical factors, are the main cause of this phenomenon.

Eye-head-hand coordination in pointing at visual targets: spatial and temporal analysis

This study investigated whether the execution of an accurate pointing response depends on a prior saccade orientation towards the target, independent of the vision of the limb. A comparison was made between the accuracy of sequential responses (in which the starting position of the hand is known and the eye centred on the target prior to the onset of the hand pointing movement) and synergetic responses (where both hand and gaze motions are simultaneously initiated on the basis of unique peripheral retinal information). The experiments were conducted in visual closed-loop (hand visible during the pointing movement) and in visual open-loop conditions (vision of hand interrupted as the hand started to move). The latter condition eliminated the possibility of a direct visual evaluation of the error between hand and target during pointing. Three main observations were derived from the present work: (a) the timing of coordinated eye-head-hand pointing at visual targets can be modified, depending on the executed task, without a deterioration in the accuracy of hand pointing; (b) mechanical constraints or instructions such as preventing eye, head or trunk motion, which limit the redundancy of degrees of freedom, lead to a decrease in accuracy; (c) the synergetic movement of eye, head and hand for pointing at a visible target is not trivially the superposition of eye and head shifts added to hand pointing. Indeed, the strategy of such a coordinated action can modify the kinematics of the head in order to make the movements of both head and hand terminate at approximately the same time. The main conclusion is that eye-head coordination is carried out optimally by a parallel processing in which both gaze and hand motor responses are initiated on the basis of a poorly defined retinal signal. The accuracy in hand pointing is not conditioned by head movement per se and does not depend on the relative timing of eye, head and hand movements (synergetic vs sequential responses). However, a decrease in the accuracy of hand pointing was observed in the synergetic condition, when target fixation was not stabilised before the target was extinguished. This suggests that when the orienting saccade reaches the target before hand movement onset, visual updating of the hand motor control signal may occur. A rapid processing of this final input allows a sharper redefinition of the hand landing point.

Dynamic analysis of human visuo-oculo-manual coordination control in target tracking tasks

Human subjects tracked a visual target controlled either by a function generator (sine wave at different frequencies) or directly by the observer's arm. Gain and phase curves of the oculomotor response as a function of target frequency were determined. Data show that the upper frequency limit of smooth pursuit is higher when the target is driven by the observer's hand, confirming previous reports that smooth pursuit can reach higher velocities when tracking self-moved targets. Comparative analysis of ocular tracking with and without manual target control showed that subjects could be classified into two groups. One group exhibited an increase in gain at high frequency, but showed no significant phase changes. Conversely, the reverse was found in the other group: a significant decrease of phase lag at high frequency and no change in gain. These results demonstrate the existence, within the oculo-manual coordination control system, of at least two separate mechanisms (or strategies), tending either to synchronize the eye and arm motor activities (timing coordination) or to adjust their gain (spatial coordination).

Oculo-manual coordination control: ocular and manual tracking of visual targets with delayed visual feedback of the hand motion

The aim of this study was to examine coordination control in eye and hand tracking of visual targets. We studied eye tracking of a self-moved target, and simultaneous eye and hand tracking of an external visual target moving horizontally on a screen. Predictive features of eye-hand coordination control were studied by introducing a delay (0 to 450 ms) between the Subject's (S's) hand motion and the motion of the hand-driven target on the screen. In self-moved target tracking with artificial delay, the eyes started to move in response to arm movement while the visual target was still motionless, that is before any retinal slip had been produced. The signal likely to trigger smooth pursuit in that condition must be derived from non-visual information. Candidates are efference copy and afferent signals from arm motion. When tracking an external target with the eyes and the hand, in a condition where a delay was introduced in the visual feedback loop of the hand, the Ss anticipated with the arm the movement of the target in order to compensate the delay. After a short tracking period, Ss were able to track with a low lag, or eventually to create a lead between the hand and the target. This was observed if the delay was less than 250-300 ms. For larger delays, the hand lagged the target by 250-300 ms. Ss did not completely compensate the delay and did not, on the average, correct for sudden changes in movement of the target (at the direction reversal of the trajectory). Conversely, in the whole range of studied delays (0-450 ms), the eyes were always in phase with the visual target (except during the first part of the first cycle of the movement, as seen previously). These findings are discussed in relation to a scheme in which both predictive (dynamic nature of the motion) and coordination (eye and hand movement system interactive signals) controls are included.

Ocular muscle proprioception and visual localization of targets in man

Passive deviation of one eye through 18 degrees, 30 degrees and 42 degrees, achieved by force applied to a sucked-on contact lens, caused the direction of visual targets seen by the other eye to be misjudged in the direction of the passive movement by an amount roughly one-sixth of the angle of passive deviation. The result was the same when the perceived direction was indicated by hand, as when the instant at which a moving target seemed straight ahead was signalled. This result is interpreted by considering that muscular efferents were identical in normal and eye-deviated subjects. The main difference between the two target localization conditions results from the proprioceptor output of the deviated eye. Our data demonstrate that the assessment of the direction of a target seen by an eye that is free to move depends in part on information received by the brain from proprioceptors in the orbit (in our case the contralateral orbit). It would be surprising if the ipsilateral orbit did not contribute as much or more. We therefore consider that this constitutes clear evidence against the pure outflow theory of visual direction judgement (Helmholz, 1867), additional to that provided by the all-or-nothing situation of complete versus incomplete oculomotor paralysis. Two models have previously been proposed to describe the function of the visual localization mechanism. Both assume that the necessary information is derived from the coding of the position of the eye in the orbit, either through a copy of the muscular activation or through eye muscle proprioception. We propose an alternative model in which both afferent and efferent signals from all actively contracted or stretched muscles provide the necessary information to the CNS. The data gathered so far from normal subjects made strabismic with a suction lens, and from a fair proportion of strabismic patients, support our model describing the mechanism of localization of a single punctate target in darkness.

The role of ocular muscle proprioception in visual localization of targets

The role of ocular muscle proprioception in the localization of visual targets has been investigated in normal humans by deviating one eye to create an experimental strabismus. The passively deviated eye was covered and the other eye viewed the target. With a hand-pointing task, targets were systematically mislocalized in the direction of the deviated nonviewing eye. A 4- to 6-degree error resulted when the nonviewing eye was offset 30 degrees from straight ahead. When the eye was deviated, the perceived "straight-ahead" was also displaced, by a similar amount, in the same direction. Since the efferent motor commands to the displaced and to the nondisplaced eyes are presumably identical by the law of equal innervation, the mislocalization of visual objects must be attributed to the change in proprioceptive information issued from the nonviewing, deviated eye. Thus proprioception contributes to the localization of objects in space.

Visual vestibular interaction: vestibulo-ocular reflex suppression with head-fixed target fixation

In order to maintain clear vision, the images on the retina must remain reasonably stable. Head movements are generally dealt with successfully by counterrotation of the eyes induced by the combined actions of the vestibulo-ocular reflex (VOR) and the opto-kinetic reflex. We have studied how, in humans, the VOR gain (VORG) is modulated to provide appropriate eye movements in two situations: 1. fixation of a stationary object of the visual space while the head moves. This requires a visuo-vestibulo-ocular reaction to induce eye movements opposite in direction, and equal in velocity to head movements, and 2. fixation of an object moving with the head. Here, the visuo-vestibulo-ocular reaction should be totally suppressed. These two situations were compared to a basic condition in which, to induce "pure" VOR, the subjects (Ss) in darkness were not allowed a visual target. Eye movements were recorded in seated Ss during constant amplitude sinusoidal and pulse-like passive rotations applied around the vertical axis. Subjects were in total darkness (DARK condition) and performing mental arithmetic. Alternatively, they were provided with a small target, either stationary with respect to earth (earth-fixed target: EFT), or moving with them (chair-fixed-target: CFT). The sinusoidal rotation experiment was used as baseline for the ensuing experiments and yielded control data in agreement with the literature. In particular, rotation in the dark showed a VORG of 0.6. With, for example, 0.8 s passive pulse rotations, typical responses in all three visual conditions were rigorously identical during the first 150 to 180 ms. They showed a delay of about 16 ms of the eye behind the head with no significant difference between passive whole-body and passive head-alone rotations. In all conditions, once the eyes had started to move, a rapid increase in eye velocity was observed during 75 to 80 ms, after which, the average VORG was 0.9 +/- 0.15. During the following 50 to 100 ms, the gain remained around 0.9 in all three conditions. Beyond 180 ms, the VORG remained around 0.9 in DARK, increased slowly towards 1 or decreased towards zero in the EFT and CFT conditions, respectively. The time-course of these later events suggests that visual tracking mechanisms came into play to reduce retinal slip through smooth pursuit. Sinusoidal rotations, extensively used in VOR studies, do not seem to be a satisfactory stimulus to rapidly and precisely characterize VOR function, particularly in pathological cases. Our data suggest that rapid transient rotations are more appropriate.

Pyridostigmine-induced inhibition of blood acetylcholinesterase (AChE) and resulting effects on manual ocular tracking performance in the trained baboon

A method was developed to determine the effects of pyridostigmine on sensory-motor control in baboons trained to perform visuo-oculo-manual tracking tasks. The performance was evaluated in terms of accuracy, maximum smooth pursuit velocity, and gain. Administration of pyridostigmine (0.4-0.7 mg/kg intramuscularly) induced a dose-related decrease in smooth pursuit performance which appeared 10 to 30 min after injection and lasted about 1 h. If the animal was allowed to track the target with its hand or to move the target itself, the smooth pursuit performance increased significantly, returning to near normal values. The movement of the hand was not altered. The effect of intramuscular injections of pyridostigmine (0.5 mg/kg) was studied on blood acetylcholinesterase activity in alert baboons. Maximum inhibition of about 60% of baseline activity was observed 10 min after pyridostigmine injection. Subsequently the activity slowly tended to return to control level. Three hours after drug administration, acetylcholinesterase activity inhibition was still 34.1% of control value. In the baboon, the time-course of acetylcholinesterase activity recovery after injection is similar to that recorded in human. The similarity of the time-course of blood acetylcholinesterase activity and changes in smooth pursuit performance suggests a causal relationship between the two factors. A further experiment showed that pyridostigmine administered per os at a dose normally used as a prophylactic against organophosphates does not significantly alter sensorimotor performance as evaluated at the oculomanual tracking system level. When compared to the literature, our results suggest that the baboon can be used as a human experimental analog for pharmacological studies such as the action of acetylcholinesterase inhibitors.

Ultrasonic two-axis rotation detector

A two-axis rotation monitor is described which determines the relative displacement between a pair of ultrasonic detectors using the phase difference of a continuous ultrasound wave generated by a single, distant source. The monitor has been used to measure head rotations around the vertical and horizontal axes, but can easily be adopted to other body segment rotations or translations. The device produces high sensitivity recordings of wide spatial and dynamic range. Although the device is quite linear with good isolation between channels, a computer-based linearization/calibration routine is described which further increases linearity and reduces crosstalk. The device is unobtrusive, inexpensive, and has proven reliable and easy to use.

Identification of peripheral visual images in a laterally restricted gaze field

When the peripheral visual field is restricted or distorted, as occurs with certain spectacle lenses, the identification of objects in the periphery requires a coordinated head and eye movement. Initial experiments on the identification of peripheral images under such restrictions show that the degradation in performance is defined by a consistent additional delay in the time required to identify the image correctly. An analysis of the motor movements shows that performance is solely determined by movements of the head; eye movements are sufficiently precise and fast so they do not limit performance. A quantitative model of the identification task was developed and model simulations confirmed the experimental findings that head movement variables, specifically response latency and movement duration, uniquely determine identification performance. Hence, improved performance under these conditions must come from modifications in head-movement control either through training or adaptive processes.

Mechanisms of short-term saccadic adaptation

A number of processes have been identified that adaptively modify oculomotor control components. The adaptive process studied here can be reliably produced over a short period of time by a visual stimulus that forces postsaccadic error. This short-term adaptive process, usually termed parametric adaptation, consists of a change in response amplitude that develops progressively over 50 to 100 training stimuli. The resulting compensation is proportional to, but substantially less than, the error induced by the training stimuli. Both increases and decreases in response amplitude can be evoked by an appropriately timed and directed movement of the stimulus target, which forces postsaccadic error. Results show that a single type of training stimulus can influence movements over a broad spatial region, provided these movements are in the same direction as the training stimulus. Experiments that map the range of modification suggest that the increasing adaptive modification operates by remapping final position, whereas the decreasing adaptive modification is achieved through an overall reduction of gain. Training stimuli that attempt to evoke both increases and decreases in the same region show a net modification equivalent to the algebraic addition of individual adaptive processes.

Mechanisms of short-term saccadic adaptation

A number of processes have been identified that adaptively modify oculomotor control components. The adaptive process studied here can be reliably produced over a short period of time by a visual stimulus that forces postsaccadic error. This short-term adaptive process, usually termed parametric adaptation, consists of a change in response amplitude that develops progressively over 50 to 100 training stimuli. The resulting compensation is proportional to, but substantially less than, the error induced by the training stimuli. Both increases and decreases in response amplitude can be evoked by an appropriately timed and directed movement of the stimulus target, which forces postsaccadic error. Results show that a single type of training stimulus can influence movements over a broad spatial region, provided these movements are in the same direction as the training stimulus. Experiments that map the range of modification suggest that the increasing adaptive modification operates by remapping final position, whereas the decreasing adaptive modification is achieved through an overall reduction of gain. Training stimuli that attempt to evoke both increases and decreases in the same region show a net modification equivalent to the algebraic addition of individual adaptive processes.

Oculo-manual tracking of visual targets: control learning, coordination control and coordination model

The processes which develop to coordinate eye and hand movements in response to motion of a visual target were studied in young children and adults. We have shown that functional maturation of the coordination control between eye and hand takes place as a result of training. We observed, in the trained child and in the adult, that when the hand is used either as a target or to track a visual target, the dynamic characteristics of the smooth pursuit system are markedly improved: the eye to target delay is decreased from 150 ms in eye alone tracking to 30 ms, and smooth pursuit maximum velocity is increased by 100%. Coordination signals between arm and eye motor systems may be responsible for smooth pursuit eye movements which occur during self-tracking of hand or finger in darkness. These signals may also account for the higher velocity smooth pursuit eye movements and the shortened tracking delay when the hand is used as a target, as well as for the synkinetic eye-arm motions observed at the early stage of oculo-manual tracking training in children. We propose a model to describe the interaction which develops between two systems involved in the execution of a common sensorimotor task. The model applies to the visuo-oculo-manual tracking system, but it may be generalized to other coordinated systems. According to our definition, coordination control results from the reciprocal transfer of sensory and motor information between two or more systems involved in the execution of single, goal-directed or conjugate actions. This control, originating in one or more highly specialized structures of the central nervous system, combines with the control processes normally operating in each system. Our model relies on two essential notions which describe the dynamic and static aspects of coordination control: timing and mutual coupling.

Oculo-manual tracking of visual targets in monkey: role of the arm afferent information in the control of arm and eye movements

The study was aimed at defining the role of hand (and arm) kinaesthetic information in coordination control of the visuo-oculo-manual tracking system. Baboons were trained to follow slow-moving and stepping visual targets either with the eyes alone or with the eyes and a lever moved by the forelimb about the vertical axis. A LED was attached to the lever extremity. Four oculo-manual tracking conditions were tested and compared to eye-alone tracking: Eye and hand tracking of a visual target presented on a screen, eye tracking of the hand, and eye tracking of an imaginary target actively moved by the arm. The performance of the animals evaluated in terms of latency, and velocity and position precision for both eye and hand movements was seen to be equivalent to that of humans in similar situations. After dorsal root rhizotomy (C1-T2) the animals were unable to produce slow arm motion in response to slow-moving targets. Instead, they produced successions of ballistic-like motions whose amplitude decreased as retraining proceeded. In addition, the animals could no longer respond with smooth pursuit eye movements to an imaginary target actively displaced by the animal's forelimb. It was concluded that the absence of ocular smooth pursuit after lesion results from the disruption of a signal derived from arm kinaesthetic information and addresses to the oculomotor system. This signal is likely to be used in the control of coordination between arm and eye movements during visuo-oculo-manual tracking tasks. One cause of the animal's inability to achieve slow arm movement in response to slow target motion is thought to be due to a lesion-induced alteration of the spinal common pathway dynamics which normally integrate the velocity signal descending from the arm movement command system.

Cerebellar involvement in the coordination control of the oculo-manual tracking system: effects of cerebellar dentate nucleus lesion

When the hand of the observer is used as a visual target, oculomotor performance evaluated in terms of tracking accuracy, delay and maximal ocular velocity is higher than when the subject tracks a visual target presented on a screen. The coordination control exerted by the motor system of the arm on the oculomotor system has two sources: the transfer of kinaesthetic information originating in the arm which increases the mutual coupling between the arm and the eyes and information from the arm movement efferent copy which synchronizes the motor activities of both subsystems (Gauthier et al. 1988; Gauthier and Mussa-Ivaldi 1988). We investigated the involvement of the cerebellum in coordination control during a visuo-oculo-manual tracking task. Experiments were conducted on baboons trained to track visual targets with the eyes and/or the hand. The role of the cerebellum was determined by comparing tracking performance defined in terms of delay, accuracy (position or velocity tracking errors) and maximal velocity, before and after lesioning the cerebellar dentate nucleus. Results showed that in the intact animal, ocular tracking was more saccadic when the monkey followed an external target than when it moved the target with its hand. After lesioning, eye-alone tracking of a visual target as well as eye-and-hand-tracking with the hand contralateral to the lesion was little if at all affected. Conversely, ocular tracking of the hand ipsilateral to the lesion side became more saccadic and the correlation between eye and hand movement decreased considerably while the delay between target and eyes increased. In normal animals, the delay between the eyes and the hand was close to zero, and maximal smooth pursuit velocity was around 100 degrees per second with close to unity gain; in eye-alone tracking the delay and maximal smooth pursuit velocity were 200 ms and 50 deg per second, respectively. After lesioning, delay and maximum velocity were respectively around 210 ms and 40 deg per second, that is close to the values measured in eye-alone tracking. Thus, after dentate lesioning, the oculomotor system was unable to use information from the motor system of the arm to enhance its performance. We conclude that the cerebellum is involved in the "coordination control" between the oculomotor and manual motor systems in visuo-oculo-manual tracking tasks.

Comparative effects of whole-body vibration on sensorimotor performance achieved with a mini-stick and a macro-stick in force and position control modes

The aim of this investigation was to assess the performance of subjects in a target recentering task, performed under both normal and vibration conditions. A conventional helicopter stick and an arm-side controller were used in both position and force control modes. The task was designed to simulate instrument flying. The results showed that in the no-vibration situation, the highest performance was achieved in the force control mode and little difference was observed between the two sticks. They also showed that vibration impaired the velocity control of the performance. It is suggested that the subject might be switching over from a visual and arm afferent and efferent control in the no-vibration situation, to a visual control only under vibration condition. From this study, it appears that the more efficient stick to execute the designed task is the mini-stick operating in the force control mode.

Inhibitory effects of combined agonist and antagonist muscle vibration on H-reflex in man

Vibration alters human sensory motor performance. Changes in the excitability of spinal reflex mechanisms may be responsible for the majority of the observed alterations. We studied the differential effects of vibration locally applied to gastrocnemius soleus and tibialis anterior muscles separately and to both muscles simultaneously. From the results, it is deduced that combined agonist and antagonist muscle vibration may lead to summative interaction between pre- and postsynaptic inhibition at motoneuronal level. Whole-body vibration is taken to mean a combination of synchronous vibrations applied locally and simultaneously to several muscles. The results also demonstrate that the level of inhibition of the H-reflex resulting from the vibration is directly related to the displacement amplitude of the vibration, regardless of the frequency.

Visually and acoustically augmented performance feedback as an aid in motor control learning: a study of selected components of the rowing action

The present work compares the efficiency of two training techniques as aids to learning selected aspects of a sequentially ordered action such as that of rowing. Subjects in one group were trained with a conventional learning technique (CLT) while those in a second group were trained by an augmented feedback technique referred to as external feedback (EFB). Progress was recorded on learning curves. Rowing athletes with limited experience and psychophysiology students were used for the study. The tasks consisted of learning movement timing (rhythmicity of action and coordination of body parts) and movement intensity (force and electromyogram development), in four separate experiments. The learning curves for EFB subjects were found to have significantly and consistently higher slopes than those for CLT subjects. Optimal criteria were reached by EBF subjects, after a continuous increase in performance levels and a concomitant decrease in standard deviations evaluated from periodicity, movement accuracy and force. Subjects, who after 8 to 10 sessions of CLT learning had not reached optimal level, were exposed to EFB. Their performances then showed a marked improvement and attained the required criterion in 2 to 4 sessions. This further demonstrates the efficacy of EFB as compared with CLT, as an aid to learning a complex sensorimotor action. The efficacy of EFB as a learning technique is discussed in relation to the internal model of the task to be executed and to sensory motor control and motor programmes.

Origin of eye movements induced by high frequency rotation of the head

Perception of stability of the visual world and control of ocular fixation and tracking are altered in subjects submitted to high frequency vibration. Studies of the eye movements induced in man by passively rotating the head sinusoidally around a vertical axis show that beyond 8 Hz, the amplitude of the eye movements increases and reaches 2.5 times the amplitude of head movement at 30 hz. The high amplitude eye oscillation may, at least in part, explain the perception of visual world instability and the decrease of visuo-oculomotor system performance in man submitted to high frequency vibration. Two interpretations of this phenomenon have been proposed (9). High amplitude eye movements induced at high frequency may be due to either a non-linearity of the vestibulo-ocular reflex (VOR) or mechanical resonance oscillations of the orbital apparatus. To test these hypotheses, baboons were trained to fixate visual targets. Each animal's head was rigidly attached to a rotating frame through a block of dental cement bolted to the skull. Head rotation was produced by a servo-controlled vibrator. Rotations in the frequency range 1 to 20 Hz were successively applied with the animal in darkness or fixating a stationary target. The results showed that gain curves obtained with baboons are similar to those obtained with man. Paralysis of the muscles of one eye by injection of lidocaine disclosed a behavioral asymmetry of the two eyes at low frequency. The paralysed eye showed no movement below 8 Hz, while the normal eye behaved as in the normal situation. Beyond 8 Hz, the gain of the treated eye increased gradually so that beyond 12 Hz, the two eyes responded.(ABSTRACT TRUNCATED AT 250 WORDS)

Spinal reflex alterations as a function of intensity and frequency of vibration applied to the feet of seated subjects

Sensorimotor system performance is known to be altered by vibration applied locally to tendons and muscles or to the whole body. The present study is an attempt to determine the influence of vibration amplitude, acceleration, and frequency on the excitability of the motoneurons as evaluated by the amplitude of electrically induced spinal reflex response in man. The results show that a vibration applied to the legs of a seated subject (S) decreased the reflex response. The effect is directly related to the vibration intensity. The reflex amplitude is minimal in the 10-30 Hz range. At constant acceleration, the depressive effect decreased beyond 20-30 Hz while, at constant displacement amplitude, the reflex inhibition was almost constant throughout the frequency range of 20-60 Hz. These observations suggest that the diminution of the reflex response is mainly related to the amplitude of the vibration, regardless of the frequency. The results are interpreted in light of current knowledge of the effect of locally applied vibration on muscle tendons. The marked inhibition observed in the 10-30 Hz range, even with moderate intensity, suggests that particular attention should be devoted to avoid vibration in that frequency range in vehicles in order to prevent alteration of the performance of sensorimotor systems.