Stationary phantoms and grating induction with oblique inducing gratings: implications for different mechanisms underlying the two phenomena

The visibility of stationary visual phantoms and the grating induction (GI) effect were concurrently analyzed with both black and gray inspection areas (IA) using the same subjects with counterbalanced orders of measurements. Oblique inducing gratings were employed in order to compare the visibility of obliquely aligned and vertically misaligned appearances between the two phenomena. Aligned and misaligned phantom responses with a black IA were similar, whereas overall phantom visibility was severely suppressed when the IA was gray. In contrast, misaligned GI dominated with a gray IA, whereas aligned and misaligned GI responses were similar with a black IA. Phantoms appear to be related to visual mechanisms' selectively utilizing relative luminance information between the inducing grating and IA in a manner consistent with more global figural characteristics of the display (e.g., modal and amodal completion). On the other hand, GI may be predominantly due to locally operating brightness/contrast mechanisms.

Saccadic latency during perceptual processing and sequence learning

The difference between simple and choice manual reaction time (RT) has been taken to be a measure of the time necessary for various cognitive operations. In contrast, simple and choice saccadic latencies (SL - time elapsing from stimulus onset to saccade initiation) are quite similar, suggesting that such responses may be more automated. In the present investigation, SL and saccadic reaction times (SR - time elapsing from stimulus onset to saccade completion) were measured for targets appearing in the same and different locations, and to different ends of compound stimuli (big arrows) composed of small elements (little arrows) using either the global figure or the local elements as indicators of required saccade direction. In addition, measures of sequence learning were obtained behaviorally over iterative trials (decreases in response time) and with post-test interrogation. The results indicated that local response times were significantly slower than choice or global response times. Both global precedence and consistency effects were observed. Robust sequence learning was observed under the local condition, but only in the choice condition were all subjects able to recall the sequence correctly. These results are discussed in terms of proposed models of visual perception and saccade generation based on parallel processing.

Afterimages, grating induction and illusory phantoms

Under some conditions (dark or light inspection areas) illusory gratings often appear to be in-phase with the inducing gratings and under others (gray inspection area) illusory gratings often appear to be out-of-phase with the inducing gratings. McCourt reported that point-by-point brightness matches reveal only out-of-phase illusory gratings, no matter what the luminance of the inspection area (McCourt, M. E. (1994). Vision Research, 34, 1609-1617). Since the technique used might have led to afterimages which mimic out-of-phase illusory gratings, the present series of experiments was undertaken to determine how such afterimages might bias illusory grating judgments. Afterimages were induced during fixation with brief flashes of inducing gratings within the inspection area (Experiment 1), or by vertical shifts in the entire stimulus which exposed the retina to real gratings prior to judgments within the inspection area (Experiment 2). Experiment 2 was replicated with drifting inducing gratings (Experiment 3). The subjects were asked to indicate whether illusory gratings appeared in- or out-of-phase. The results of all three experiments reveal that out-of-phase illusory gratings predominate, and that afterimages can only bias judgments with stationary displays. It is suggested that grating induction is perceived when subjects attend to local contrast differences, while phantom visibility is facilitated when attention is captured by the more global aspects of the stimulus.

Change in the mode of inhibition of acetylcholinesterase by (4-nitrophenyl)sulfonoxyl derivatives of conformationally constrained choline analogues

A chiral, five-step synthesis of 2-(hydroxymethyl)-2,4-dimethylmorpholine (12) from (R)- and (S)-2-methylglycidols gives an overall yield of 63%. Morpholines (R)- and (S)-12 are converted into 2-(azidomethyl)-2,4-dimethylmorpholine (15) via 2,4-dimethyl-2-[[(4-nitrophenyl)sulfonoxy]methyl]morpholine (14). The tertiary morpholines 12, 14, and 15 are quaternarized to afford 2-(hydroxymethyl)-2,4,4-trimethylmorpholinum iodide (2), 2,4,4-trimethyl-2-[[(4-nitrophenyl)sulfonoxy]methyl]morpholinium iodide (3), and 2-(azidomethyl)-2,4,4-trimethylmorpholinium iodide (4), respectively, which all inhibit acetylcholinesterase (AChE). These morpholinium inhibitors are compared with conformationally constrained aryl hemicholinium AChE inhibitors. Enantiomers of 2 and 4 are reversible competitive inhibitors of AChE, with values of Ki = 360 +/- 30 microM for (S)-2, 650 +/- 90 microM for (R)-2, 450 +/- 70 microM for (S)-4, and 560 +/- 30 microM for (R)-4, respectively. Enantiomers of 3 are noncompetitive inhibitors of AChE with values of Ki = 19.0 +/- 0.9 microM for (S)-3 and 50 +/- 2 microM for (R)-3, respectively. AChE shows a 2-fold chiral discrimination in the case of inhibition by 2 and 3. Inhibition also changes from competitive to noncompetitive when (3-hydroxyphenyl)-N,N,N-trimethylammonium iodide (18) [Ki = 0.21 +/- 0.06 microM; Lee, B. H., Stelly, T. C., Colucci, W. J., Garcia, J. G., Gandour, R. D., and Quinn, D. M. (1992) Chem. Res. Toxicol. 5, 411-418] is converted into [3-[(4-nitrophenyl)sulfonoxy]phenyl]-N,N,N-trimethylammonium iodide (5), Ki = 6.0 +/- 0.5 microM. These results indicate that the 4-nitrobenzenesulfonyl group controls the mode of inhibition.

On a failure to replicate: methodologically close, but not close enough. A response to hogben et al

Williams, Brannan and Lartigue (1987) (Clinical Vision Science, 1, 367-371) reported that poor readers took significantly longer to search letter arrays for a target than did good readers. In addition, they reported that blurring the letter arrays leads to faster search times for poor readers and a loss of the significant differences between the groups seen with unblurred displays. In a recent attempt to replicate these findings, Hogben et al. (1996) (Vision Research, 36, 1503-1507) found no differences in search rates between good and poor readers using unblurred arrays, and no differences in search rate between the groups when blurred arrays were used. In the present article, we have compared these two research efforts, and a third paper on the same topic, with regard to methodological factors in an attempt to understand how these two different results could occur. It is our belief that the letter spacing employed in the two studies may account for the difference and should be the focus of future studies of the original effect.

The effectiveness of a motion sickness counselling programme

Unselected volunteers were offered a course of instruction in using the cognitive-behavioural approach to helping individuals tolerate the deleterious effects of different motion environments. In order to evaluate that programme, 11 of the participants volunteered to counsel independently individuals who were prone to motion sickness, using cognitive-behavioural training which included reinforcement by visually induced apparent motion. The subjects were pre- and post-tested by an independent observer using tolerance and motion response as the dependent variables. These test scores were compared to previous data obtained with subjects who had received counselling from an experienced counsellor, or had received no such counselling. The results indicated that the newly trained counsellors' subjects showed significant pre- to post-test tolerance to the motion stimulus, although they did not benefit as much as subjects trained by the experienced counsellor. However, in terms of post-test symptomatology and magnitude estimates of motion sickness, the trainees' subjects exhibited as much benefit as did those of the experienced counsellor. These data are taken as strong support for the feasibility of training counsellors to employ this method of alleviating motion sickness.

Reading-related wavelength and spatial frequency effects in visual spatial location

Specific deficits in the processing of transient visual stimuli have been identified in reading-disabled children, and it has been shown that the filtering out of some medium to high spatial frequencies and some visible wavelengths impacts on their performance in a number of visual tasks. To assess further how these light diffusing and colour filtering manipulations might mediate visual processing, this study compared the letter-naming accuracy and visual spatial location judgements of eighteen poor readers with those made by eighteen good readers of the same age. Naming and spatial discrepancy measures were recorded for briefly displayed target letters at varying eccentricities, for each child, under a normal (NI) condition and wearing blue (Be), yellow (Yw), diffusion (Dn), blue with diffusion (BeDn), and yellow with diffusion (YwDn) optical framed lenses. A preliminary analysis of the data detected larger spatial discrepancies for the poor readers, and this finding was consistent with the presence of a deficit in transient (or magnocellular) activity in these children. Both the naming accuracy data and the spatial location data showed filter-dependent differences in reading ability. The letter-naming data showed that the addition of the blue filter to the diffusion lens significantly depressed performance only for the good readers, and that the addition of the yellow filter to the diffusion lens significantly improved performance only for the poor readers. Comparison of the spatial discrepancies showed that the rate at which location accuracy declined with increasing target eccentricity was smaller for the blue and yellow lenses than for normal viewing in the case of the good readers but not in the case of the poor readers.(ABSTRACT TRUNCATED AT 250 WORDS)

The time-course of global precedence and consistency effects

The global precedence effect refers to the finding that global aspects of a scene are processed more rapidly than local detail in the scene. In experiments with large Hs and Ss (global stimuli) made up of small Hs and Ss (local stimuli), choice reaction time (RT) to the global letters is shorter than RT to the local letters (global precedence effect). In addition, RT for local letters is shorter when the local letters are the same as the global letter (consistency effect). We sought to determine the time course of the global precedence and consistency effects by delaying the global information relative to the local information. In Experiment I, the middle cross-bar of the global letter (S or H) was presented followed by the rest of the global letter at delays of 0, 48, 80, 160, 320 and 640 ms. The results indicated that the global precedence effect was obtained at delays < 48 ms and local precedence effects are obtained at delays > 80 ms. Consistency effects were found in the absence of global precedence effects, but only at delays of 48 and 80 ms. Experiment II was a replication with delays of 16, 32, 48, 64, 80, and 96 ms. The results of this experiment were in agreement with those of Experiment I. These findings offer support for the notion that the consistency effect is mediated by a higher level process than is the global precedence effect.

The effects of spatial filtering and contrast reduction on visual search times in good and poor readers

Recent experiments with reading disabled children have shown that image blurring (produced with frosted acetate overlays) results in an immediate benefit in search performance, eye movement pattern and reading comprehension. This suggests that the contrast and spatial frequency content of visual stimuli are important factors for these children. In the present experiment, spatial frequency filtering and contrast reduction were employed to determine whether either of these factors contributes to the beneficial effects observed. Letter arrays were spatially filtered to produce low pass (< 3.5 c/deg) and high pass (> 7.0 c/deg) images. In addition, a low contrast control image was generated to match the low contrast of the high pass image. Children classified as good reader controls (CON), specific reading disabled (SRD), attention deficit disordered (ADD) or comorbid SRD/ADD (COM) were asked to perform a visual search task with each type of image. With high contrast, unfiltered arrays, the search times for the CON and ADD groups were much shorter than those of the SRD and COM groups. While both high pass and low pass filter conditions improved the search speed for the COM group, improvement for the SRD group was only obtained with low contrast stimuli. These results support the notion that the beneficial results of image blurring with SRDs derives from the contrast reduction produced by such manipulations.

Cognitive-behavioral management of motion sickness

This monograph is intended to provide health professionals with information on a cognitive-behavioral technique which was developed to teach individuals who are prone to motion sickness to better cope with motion environments. It includes an overview of motion sickness, describing the signs and symptoms, etiology and incidence of this malady. Prevention and treatment are then reviewed, including both pharmacological and non-pharmacological therapies. The historical background on the cognitive-behavioral technique is then discussed. This is followed by a review of supporting experimental work, and an account of how such counselling should be carried out. Finally, a number of current military desensitization programs are compared and contrasted with cognitive-behavioral therapy.

Stimulus manipulations that reduce the square-wave illusion

When observers view a triangle-wave luminance profile, they often report a square-wave illusion with a depth component. Alternate bars appear to be in different depth planes and the surface appears corrugated; illuminated from either the right or the left. These perspectives alternate with continuous viewing. One explanation for this illusion stems from a local energy model of feature detection proposed by Morrone and Burr (Proc. Roy. Soc. Lond. B235, 221-245, 1988). This model assumes two phase-sensitive mechanisms that process lines and edges in the visual image. It is suggested that the square-wave illusion derives from rivalry between these two mechanisms. In experiment 1, the aim was to determine whether phase alternation of the triangle wave would lead to differences in the duration and number of perceptual reversals of the illusion. The results indicate a decline in illusion duration and frequency of reversal rate with increased alternation rate. With the addition of some assumptions about the temporal resolution of the line and edge detectors, the results support the proposed explanation. In Experiment 2, the effects of high spatial-frequency contrast increments and decrements were explored. Increments did not lead to significant increases in the duration of the square-wave illusion or reversal rate, but decrements resulted in a substantial reduction in the illusion duration and reversal rate. The results indicate that manipulations which alter the phase relationships of the triangle wave decrease the illusion, but manipulations which maintain them do not.

Effects of spatial filtering and lack of effects of visual imagery on pattern-contingent color aftereffects

Checkerboards contain fundamental two-dimensional Fourier components oriented 45 degrees from the edges of individual checks. Previous studies have shown that contingent color aftereffects following adaptation to chromatic checkerboard stimuli were associated with the fundamental components rather than the edges. In the present experiments, we measured contingent color aftereffects, using the method of constant stimuli, after subjects adapted to unfiltered checkerboards and checkerboards with the fundamental Fourier components removed. The adaptation stimuli were magenta (or green) squares and green (or magenta) diamonds; the test stimuli were vertical or oblique sine-wave gratings with different saturations. After adaptation to unfiltered checkerboards, aftereffects contingent on the fundamental components were obtained. In contrast, after adaptation to filtered stimuli, aftereffects of smaller magnitude were found to be aligned with the edges. The data support the previous findings of spatial-frequency-contingent color aftereffects with checkerboard adaptation stimuli and indicate that the aftereffects can be associated with edges if the fundamental components of adaptation stimuli are removed by spatial filtering. We reexamined the possibility of color aftereffects induced by imagery of checkerboards. Contrary to the previous reports, no significant aftereffects were obtained.

Immunohistochemical organization of the ventral lateral geniculate nucleus in the ground squirrel

The ventral lateral geniculate nucleus (vLGN) of the thirteen-lined ground squirrel (Citellus tridecemlineatus) is a highly differentiated nucleus that is divisible into five major subdivisions on the basis of retinal projections and cytoarchitecture. To pursue the likelihood that these subdivisions (the dorsal cap, intergeniculate leaflet, external magnocellular lamina, internal magnocellular lamina, and parvicellular segment) correlate with the functional diversity of this complex, the present study examined the neurochemical composition of the vLGN with regard to substances that have previously proved useful in distinguishing functionally distinct subregions within nuclei (i.e., neuropeptide Y (NPY), substance P (SP), leucine and methionine enkephalins, gamma-aminobutyric acid (GABA), cytochrome oxidase (CO), acetylcholinesterase (AChE), and NADPH-diaphorase). The results showed a clear differential neurochemical distribution within the nucleus. Neuropeptide Y immunoreactive perikarya were found predominantly in the intergeniculate leaflet and external magnocellular lamina, with only a few present in the internal magnocellular lamina and dorsal cap, and none observed in the parvicellular segment. NPY+ fibers, however, were present in all divisions except the parvicellular segment. The highest concentration of SP immunoreactive cells was observed in the internal magnocellular lamina, and substantial numbers also were scattered in the external magnocellular lamina and parvicellular segment. SP+ fibers were seen predominantly in the intergeniculate leaflet and the magnocellular laminae. The heaviest concentration of enkephalinergic fibers occurred in the internal magnocellular lamina and dorsal cap, but fibers were also observed in the external magnocellular lamina and intergeniculate leaflet. GABA reactivity was widespread throughout the vLGN, with the dorsal cap and external magnocellular lamina most heavily labeled, followed by the intergeniculate leaflet and the internal magnocellular lamina. Cytochrome oxidase, AChE, and NADPH-diaphorase histochemistry revealed rich reactivity within the dorsal cap, and external and internal magnocellular laminae and paler reactivity in the intergeniculate leaflet and parvicellular segment. The external magnocellular lamina was more reactive for CO and NADPH-diaphorase than AChE, while the internal magnocellular lamina showed the opposite pattern of reactivity. In addition, NADPH-diaphorase reactive cells were present in caudal intergeniculate leaflet and lateral external magnocellular lamina. These local differences in the neurochemical character of the vLGN support its parcellation into multiple subdivisions. Taken in conjunction with the differences in cytoarchitecture and retinal projections, these results suggest substantial functional diversity within the ventral lateral geniculate complex.

Immunohistochemical organization of the ventral lateral geniculate nucleus in the tree shrew

The ventral lateral geniculate nucleus (vLGN) of the tree shrew (Tupaia belangeri) was differentiated into multiple subdivisions (dorsal cap, intergeniculate leaflet, parvicellular segment, and internal and external magnocellular laminae, the latter being further divisible into a lateral and medial division) on the basis of retinal projections, immunochemistry, and histochemistry. Retinal projections traced with intravitreal injections of wheat germ agglutinin conjugated horseradish peroxidase revealed direct bilateral input to all subregions of the vLGN, except for the internal magnocellular lamina (which received only contralateral input) and the parvicellular segment (which was not retinorecipient). Furthermore, retinal inputs clearly distinguished the relatively heavily retinorecipient intergeniculate leaflet from the less prominently labeled dorsal cap. Immunohistochemical localization of Neuropeptide Y (NPY) perikarya revealed their prominence in the intergeniculate leaflet and the external magnocellular laminae with a concentration along the optic tract. NPY immunoreactive fibers were seen in all but the parvicellular subregion. Gamma amino butyric acid immunoreactivity was seen throughout the vLGN, but was most concentrated in the dorsal cap and the magnocellular laminae, followed by the intergeniculate leaflet. Histochemical studies of cytochrome oxidase and nicotinamide adenosine dinucleotide phosphate (NADPH)-diaphorase localization revealed similar patterns of dense reactivity within the external magnocellular lamina, intergeniculate leaflet and dorsal cap, and somewhat less dense, but substantial reactivity in the internal magnocellular lamina. Within the external magnocellular lamina, cells reactive for cytochrome oxidase were noted in the lateral portion bordering the optic tract, whereas those specific for NADPH-diaphorase were dispersed throughout the lamina. Poor reactivity for both histochemical markers was evident in the parvicellular segment. Overall, the markedly different patterns of retinal input and neurochemical organization between the subdivisions of the tree shrew vLGN suggest their involvement in diverse functions. Furthermore, the basic similarity of the organization of the tree shrew vLGN to that of the taxonomically unrelated ground squirrel may indicate a common mammalian scheme.

A posteriori digital filtering to reduce signal-averaging of steady-state evoked potentials

This paper describes a signal extraction technique that involves taking the time series representation of signals, transforming them into the frequency domain, determining the chance occurrence of power at each frequency, and filtering accordingly. An inverse Fourier transform is then used to recreate the new time domain representation, which has been appropriately filtered for extraneous noise. Thus, this technique involves a posteriori digital filtering based on a statistical criterion for component inclusion. Computer simulation indicated that, at poor signal-to-noise ratios and with fewer samples, this technique is 5 to 10 times better at signal extraction than conventional signal averaging. Examples of pattern-elicited electroretinograms (PERG's) are used to illustrate the efficacy of this method.

Phase shifts and the square-wave illusion

When observers view a vertical triangle-wave luminance profile, they often report a square-wave illusion with a depth component, resembling a corrugated surface. Alternate bars seem to be in front of or behind adjacent bars and the surface appears to be illuminated from the right or left. These perspectives alternate with continuous viewing. One explanation for this illusion stems from the notion of instability among phase-selective mechanisms. Two experiments (1 and 3) were designed to determine whether systematic phase shifts introduced between the fundamental and the odd harmonics of the waveform would lead to a systematic bias of the illusion. The results indicated that a significant bias occurred when a phase shift as small as 9 deg was introduced, and that the bias from the phase shifts was more powerful than previous reports of drift-induced bias. There was a highly significant effect of direction of phase shift and the corresponding perceived direction of illumination. Another experiment (2) was designed to determine if illusional cues within the phase-shifted profiles aided phase discrimination. The results indicated that experienced subjects, presumably using cues within the profiles, discriminated between the stimuli significantly better than did naive subjects. These data support the role of phase in the square-wave illusion, but they also raise questions about the role of contrast changes in local regions of the stimulus.

Visual search for simple volumetric shapes

Five experiments measured reaction time (RT) to detect the presence or absence of a simple volumetric shape (target) dependent on the number of display items (distractors) and their depicted three-dimensional (3-D) orientation. Experiments 1-4 examined every pairwise combination of two different simple volumetric shapes in two 3-D orientations. Conditions exhibiting "pop-out" could be predicted by differences in their two-dimensional (2-D) features. Conditions in which search was slower support previously found search asymmetries for particular 2-D features. When the distractors were a mixture of the other shapes in the same 3-D orientation, search was serial, except when the target had a curved principal axis (Experiment 5). The results suggest that these simple volumetric shapes are not processed preattentively.

The transfer of adaptation between actual and simulated rotary stimulation

It is well known that continued exposure to motion environments leads to adaptation, but it is not clear whether such changes are specific to the particular type of motion experienced. The present investigation sought to evaluate the extent of transfer between real motion and visually-induced apparent motion. In addition, the direction of motion was varied and these two factors, mode of exposure and direction of rotation, were examined in a cross-adaptational design. Thirty-two subjects were pre- and posttested on measures of disorientation after active bodily rotation and visually-induced self-vection. Two groups received ten consecutive trials of active bodily rotation (clockwise or counter-clockwise) for 4 consecutive days. Two other groups received ten consecutive trials of visually-induced self-vection (clockwise or counter-clockwise) in a rotating drum for 4 consecutive days. During the exposure phase, dizziness and self-vection increased over trials for the groups exposed to the drum, while dizziness remained unchanged over trials for the groups exposed to bodily rotation. Repeated exposure to bodily rotation resulted in improved walking performance over trials and days. Subjects exposed to bodily rotation exhibited increased tolerance to visually-induced self-vection; however, exposure to visually-induced self-vection did not result in greater tolerance to bodily rotation. No support for directional specificity was evident.

Eye movement indices of mental workload

Four investigations were carried out to assess the feasibility of using eye movement measures as indices of mental workload. In the first experiment, saccadic extent was measured during free viewing while subjects performed low, moderate and high complexity, auditory tone counting as the workload tasks. The range of saccadic extent decreased significantly as tone counting complexity (workload) was increased. In the second experiment the range of spontaneous saccades was measured under three levels of counting complexity with a visual task that did not require fixation or tracking. The results indicated that the extent of saccadic eye movements was significantly restricted as counting complexity increased. In the third experiment, the effects of practice were examined and decreased saccadic range under high tone counting complexity was observed even when significant increases in performance occurred with practice. Finally, in experiment 4, the first experiment was repeated with additional optokinetic stimulation and the saccadic range was again observed to decrease with tone counting complexity. The results indicated that the extent of spontaneous and elicited eye movements was significantly restricted as counting complexity increased. We conclude that this measure may provide a valuable index of mental workload.

Relaxation pretraining, pulse wave velocity and thermal biofeedback in the treatment of essential hypertension

Twelve white male subjects with a physician's diagnosis of essential hypertension participated in the study over a 3- to 4-month period (23-38 sessions). Subjects were assigned to one of four sequences of training in which the order of presentation of pulse wave velocity (PWV) or thermal feedback, and presence or absence of relaxation pretraining were varied. The overall effectiveness of the treatment program was demonstrated by average blood pressure decreases of 8.8 mm Hg/4.1 mm Hg from initial session measures to follow-up one month after completion of the program. Systolic pressures were significantly lower at follow-up but not diastolic. In addition, 3 subjects had ceased taking any blood pressure medication by follow-up, and maintained normal pressure. The effectiveness of relaxation pretraining was demonstrated by the fact that relaxation pretrained subjects attained significantly greater blood pressure decreases from baseline to the last 3 sessions of training, and by the fact that relaxation pretraining appeared critical in the acquisition of PWV feedback training.

Emotional processing and fear measurement synchrony as indicators of treatment outcome in fear of flying

Minimal-therapist-involvement stress inoculation training was used to treat flying phobics. Relative to no-treatment controls, treatment subjects reported more fear reduction, were more likely to participate in an exposure session, and flew more during a two-month follow-up period. Subjects who exhibited synchronous changes in heart rate and report of anxiety during exposure had greater fear reduction than subjects showing less synchrony. Subjects who voluntarily took plane flights in the two months following treatment showed greater indications of emotional processing during in vivo exposure. Relative to flight avoiders, fliers had higher mean heart rate in the plane, a greater reduction in heart rate from the beginning to the end of the flight, and greater reported fear reduction from pre- to post-flight.

Generalization of tolerance to motion environments

The aim of the present investigation was to determine to what extent training tolerance to one motion stimulus would generalize other motion experiences. Twenty subjects prone to motion sickness were selected and assigned to one of four groups after pretesting in a Dichgans and Brandt drum to determine their susceptibility to visually-induced apparent motion. They were also pretested with a VDT display of an expanding surface, and on a revolving/tilting chair. Subjects were assigned to one of the four groups by matching their mean tolerance to visually-induced motion. Subjects in the first group served as controls and received only cognitive counseling regarding their ability to tolerate motion environments. Subjects in the other groups received the same counseling coupled with incremental exposures to the drum, chair, or VDT, respectively. Posttests on each apparatus revealed that the treatments involving the chair and the drum provided specific increases in tolerance to the device used during treatment, and that the treatment involving the chair provided a generalized tolerance to visually-induced motion. These results support the notion that there are both specific and general components in learning to tolerate motion environments.

The acuity card procedure: longitudinal assessments

Traditional methods of visual assessment in preverbal pediatric patients rely on refined but subjective measurement techniques. A standard ophthalmologic examination includes evaluation of a child's fixation patterns, with performance ranked on the basis of ability to fix and follow an object (F & F) or maintain central, steady fixation (CSM). In the hands of a skilled clinician, these evaluations are important for diagnosis and treatment. Documentation of quantitative changes in visual abilities of preverbal patients, however, has only recently become feasible. We began using the acuity card procedure in our pediatric clinical practice more than 3 years ago. This assessment, a modified version of the standard Forced-Choice Preferential Looking paradigm (FPL), provides quantitative evaluation of visual functioning in preverbal patients. The total number of patients assessed on one or more occasions exceeds 900. Of this group, we followed 83 patients with at least four acuity card evaluations on separate visits. Thirty of these patients, all with different diseases, have been evaluated with acuity cards on six or more visits. We found the information provided by the acuity card assessments extremely helpful in quantifying the developmental and therapeutic changes in vision, previously monitored only qualitatively.

Visual persistence of spatially filtered images

Periodic stimuli such as sine-wave gratings and checkerboard patterns have been used in many studies of visual perception. It is well known that with such stimuli, visual persistence increases as spatial frequency increases and as contrast decreases. It is not clear, however, that similar relationships obtain for aperiodic stimuli such as natural images. Digitized images of objects (a face and a vase) were submitted to two-dimensional Fourier analysis. Four pairs of spatial frequency band-limited images were created for each image. Each pair consisted of a normal (NP) and a scrambled (SP) phase version, with the magnitude spectrum and space-averaged luminance the same within each pair. Filter bandwidths were one octave wide. Threshold persistence was measured for each spatially filtered image. Visual persistence for SP images increased significantly as spatial frequency increased, whereas no significant differences were found for NP images. This suggests that the temporal processing of complex, aperiodic visual images is influenced by the spatial frequency and contrast of local features within the image and cannot be predicted by space-averaged estimates of contrast and spatial frequency.

Response persistence of cat retinal ganglion cells to the temporally discrete presentation of sinewave gratings

The neural basis of visible persistence is not well understood. In the present study the initial onset responses of cat retinal ganglion cells to the abrupt onset and offset of sinewave gratings were examined to determine if ganglion cells display a degree of response persistence that might account for the phenomenon of visible persistence. The responses of X and Y ganglion cell axons were tested using single-unit extracellular recording techniques. Both cell types displayed some degree of response persistence and over a limited range of short stimulus durations response persistence was inversely related to stimulus duration. These data suggest that neural persistence at the ganglion cell level may be the initial physiological basis for some types of visible persistence.

Changes in ERG amplitude following laser induced damage to the primate retina

The flash evoked ERG is used extensively as a measure of retinal function. To understand better the relationship between extent of retinal damage and the ERG we created multistage laser lesions in one eye each of three Macaca fascicularis monkeys. An argon-dye laser was used to deliver 630 nm energy to cumulative quarter sectors of the temporal hemiretina and the foveal region at two week intervals. Latencies of the a- and b-waves and amplitude from the trough of the a-wave to peak of the b-wave were measured preoperatively and one week after each new lesion. Following the last recording session the eyes were removed and prepared for histological examination. In general, but depending on stimulus condition, the maximum decrease in ERG amplitude (50-70% of normal) occurred following the third or fourth sector lesions. These lesions accounted for a loss of the outer nuclear layer in 18-25% of the entire retinal surface area extending from the edge of the fovea into the anterior equatorial region. Surprisingly, subsequent lesions of the remaining sector and fovea did not result in further reduction of ERG amplitudes. Significant increases in amplitudes were even observed for some stimulus conditions following these final lesions. Latencies of the a- and b-waves were not affected. The fact that in the present study ERG amplitudes recovered, suggest that such values may be tenuous evidence of amount of functional retina in laser-lesioned eyes.

Visual motion response properties of neurons in dorsolateral pontine nucleus of alert monkey

1. In this study we sought to characterize the visual motion processing that exists in the dorsolateral pontine nucleus (DLPN) and make a comparison with the reported visual responses of the middle temporal (MT) and medial superior temporal (MST) areas of the monkey cerebral cortex. The DLPN is implicated as a component of the visuomotor interface involved with the regulation of smooth-pursuit eye movements, because it is a major terminus for afferents from MT and MST and also the source of efferents to cerebellar regions involved with eye-movement control. 2. Some DLPN cells were preferentially responsive to discrete (spot and bar) visual stimuli, or to large-field, random-dot pattern motion, or to both discrete and large-field visual motion. The results suggest differential input from localized regions of MT and MST. 3. The visual-motion responses of DLPN neurons were direction selective for 86% of the discrete visual responses and 95% of the large-field responses. Direction tuning bandwidths (full-width at 50% maximum response amplitude) averaged 107 degrees and 120 degrees for discrete and large-field visual motion responses, respectively. For the two visual response types, the direction index averaged 0.95 and 1.02, indicating that responses to stimuli moving in preferred directions were, on average, 20 and 50 times greater than responses to discrete or large-field stimulus movement in the opposite directions, respectively. 4. Most of the DLPN visual responses to movements of discrete visual stimuli exhibited increases in amplitude up to preferred retinal image speeds between 20 and 80 degrees/s, with an average preferred speed of 39 degrees/s. At higher speeds, the response amplitude of most units decreased, although a few units exhibited a broad saturation in response amplitude that was maintained up to at least 150 degrees/s before the response decreased. Over the range of speeds up to the preferred speeds, the sensitivity of DLPN neurons to discrete stimulus-related, retinal-image speed averaged 3.0 spikes/s per deg/s. The responses to large-field visual motion were less sensitive to retinal image speed and exhibited an average sensitivity of 1.4 spikes/s per deg/s before the visual response saturated. 5. DLPN and MT were quantitatively comparable with respect to degree of direction selectivity, retinal image speed tuning, and distribution of preferred speeds. Many DLPN receptive fields contained the fovea and were larger than those of MT and more like MST receptive fields in size.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of spatial phase on reaction time to spatially filtered images

Many studies of visual perception have used periodic stimuli such as sine-wave gratings and checkerboard patterns. It is well known that reaction time (RT) to such stimuli increases with increasing spatial frequency and decreasing contrast. While this is the case with periodic stimuli it is not clear that these relationships obtain for aperiodic stimuli such as natural scenes. A digitized image of an object (a vase) was submitted to two-dimensional Fourier analysis. Four pairs of spatial frequency band-limited images were created for each image. Each pair consisted of a normal-phase (NP) and a scrambled-phase (SP) version, with the magnitude spectrum and space-averaged luminance the same within each pair. Filter band-widths were 1 octave wide. Manual RT was measured for onset and offset of each spatially filtered image. Mean RT for SP images increased significantly with increasing spatial frequency, while no other significant differences were found with the NP images. This suggests that the temporal processing of complex, aperiodic images is influenced by the spatial frequency and contrast of local regions within the image, rather than by the space-averaged contrast of the entire image, and cannot be predicted by global estimates of contrast and spatial frequency.

Retinal projections in the ground squirrel (Citellus tridecemlineatus)

The retinal projections of the thirteen-lined ground squirrel were determined by tracing anterograde transport of intravitreally injected horseradish peroxidase (HRP) or wheat-germ conjugated horseradish peroxidase (WGA-HRP). Label was seen in the suprachiasmatic nucleus and adjacent anterior hypothalamic area, the accessory optic system (the medial, dorsal, and lateral terminal nuclei), the dorsal and ventral lateral geniculate nuclei, the intergeniculate leaflet, the pretectal nuclei (the anterior, posterior, and olivary pretectal nuclei and the nucleus of optic tract), and the superior colliculus. Most of these structures were labeled bilaterally, with dense contralateral label and sparse ipsilateral label, a pattern typical for animals with laterally placed eyes. However, the suprachiasmatic nucleus and the nucleus of the optic tract received input only from the contralateral eye. In contrast to previous degeneration studies, the sensitive HRP tracers (in conjunction with cytochrome-oxidase reactivity) revealed an elaborate organization within the lateral geniculate nucleus (dorsal LGN, ventral LGN, and intergeniculate leaflet) that is consistent with existing organizational schemes for other mammalian species.

Striped pattern of labeling in ground squirrel superior colliculus following intraocular HRP injections

In the 13-lined ground squirrel (Citellus tridecemlineatus), intravitreal injections of horseradish peroxidase (HRP) or wheat germ-agglutinated HRP (WGA-HRP) tracers produced a striped pattern of labeling in the contralateral superficial gray (SGS) of the superior colliculus in most, but not all, cases. The stripes extended dorsoventrally throughout the SGS in a rostral-medial to caudal-lateral orientation. In general, the striped labeling was more distinct and was observed more frequently with the HRP, rather than the WGA-HRP, tracer.

An evaluation of cognitive-behavioral therapy for training resistance to visually-induced motion sickness

This investigation examined the techniques for reducing visually-induced motion sickness. On the basis of their responses to a motion sickness history questionnaire, 32 subjects were selected and assigned to 1 of 4 groups such that the groups were matched on the basis of their ability to tolerate visually-induced apparent motion (VM). One group received 10 sessions of desensitization training only (DT); a second group received 10 sessions of cognitive therapy only (CT); a third group received 10 sessions of combined desensitization and cognitive therapy treatment (CG); and a fourth group received no treatment (C). (There are many speculations about why and how an individual's response changes with repeated stimulation. We have arbitrarily selected the term desensitization to connote the decrease in sensitivity over time with repeated exposures). The results indicated that only the groups which received cognitive therapy (i.e., CT and CG) exhibited significant increases in tolerance to VM when pretreatment measures were compared to posttreatment measures. No significant differences in pre- vs. posttreatment measures were observed in the desensitization only or control groups (i.e., DT and C). A similar pattern of results was obtained with the symptomatology data.

Clinical and serum lipid findings in a large family with autosomal dominant retinitis pigmentosa

Retinitis pigmentosa, of unknown cause, has recently been associated with decreased amounts of the polyunsaturated fatty acid, docosahexaenoic acid, in the plasma of affected as compared with unaffected relatives. It has been suggested that this finding may serve as a marker for the disease and might indicate alterations in photoreceptor cell metabolism. The authors studied 54 members of a family with dominantly inherited retinitis pigmentosa in five generations. In addition to the typical clinical findings of retinitis pigmentosa, eight persons also had a bull's eye maculopathy, and four persons had uni- or bilateral optic nerve drusen. When the authors determined the plasma fatty acid and lipid contents, they saw the expected age-related effect on cholesterol and triglycerides, but an unexpected, significant reduction in fatty acids in the unaffected controls as compared with persons with retinitis pigmentosa. The authors' results emphasize the heterogeneity of phenotypic expression of retinitis pigmentosa within a single family.

EEG biofeedback and relaxation training in the control of epileptic seizures

Research utilizing sensorimotor rhythm (SMR) biofeedback with epileptics suggests that it is useful in decreasing seizures. Subjects were 6 young adults with a diagnosis of epilepsy of at least two years who had been unable to control their seizures with different regimens of anticonvulsant medications. Subjects ranged from severely mentally handicapped to above average functioning. Seizure type, frequency, and duration were recorded by subjects and caretakers. Measures of operant learning were percent time in SMR. The experiment utilized a single subject multiple baseline design which consisted of 6 phases: baseline one, relaxation training; baseline two, biofeedback training one; baseline three, biofeedback treatment two and follow-up. The results of this study are in agreement with other studies using SMR biofeedback. All subjects were able to significantly increase percent time in SMR. Five out of the 6 subjects demonstrated decreases in seizure frequency during the treatment phase. Two of the 6 subjects benefited from relaxation training. Four subjects demonstrated significant negative correlations between percent SMR and seizure rats. Consistent with other studies utilizing multiple baseline designs, a majority of the subjects did not follow the design of the study.

The effects of spatial frequency and temporal waveform on three measures of temporal processing

The effects of spatial frequency and temporal transition of sine-wave grating onset and offset were assessed using measures of reaction time, visual persistence, and temporal order judgements. The stimuli were lateralized fields, separated by 1 degree of visual angle. Slow temporal transition resulted in significantly poorer performance than did abrupt onset and offset, but spatial frequency had a minimal effect. Thus, the latency, temporal resolution, and temporal ordering of events are mediated by a mechanism that is sensitive to abrupt temporal transients. The stimulus conditions employed did not result in a shift in the point of subjective simultaneity.

Teller acuity cards versus clinical judgment in the diagnosis of amblyopia with strabismus

Teller acuity card testing, which is a form of the preferential-looking procedure, is a popular way of assessing visual acuity in preverbal patients. The authors suspected that the clinical judgment of a pediatric ophthalmologist is superior to the Teller acuity cards in diagnosing amblyopia when strabismus is present. Acuity card and fixation preference measurements on each eye were compared at the same clinical visit in a group of 108 strabismic patients. The authors found that the acuity cards could be used to detect amblyopia. However, the pediatric ophthalmologist was more sensitive in diagnosing amblyopia than the Teller acuity cards in the presence of strabismus.

Reaction time measures of backward masking

We employed both simple and choice reaction time (RT) paradigms in which the subjects were required to respond to 3.0 cycles per degree (c/d) square-wave gratings presented to one eye, while checkerboard masks were presented at various stimulus-onset asynchronies to the other eye. No masking was evident using the simple RT paradigm, but with the choice RT task, checkerboard masks presented to the contralateral eye of three subjects resulted in substantial decreases in response speed when the test preceded the mask by stimulus-onset asynchronies of 25 to 75 ms. Masks that contained lower fundamental spatial frequencies (1.0 c/d) than the target were more effective than masks containing fundamental spatial frequencies (6.0 c/d) higher than the target, while masks that contained fundamental components identical to those in the target (3.0 c/d) produced maximum masking. The results offer support for the sustained-transient theory of visual processing and validate RT as a technique for examining spatio-temporal factors in masking.

Smooth-pursuit eye movement deficits with chemical lesions in the dorsolateral pontine nucleus of the monkey

1. Anatomical and single-unit recording studies suggest that the dorsolateral pontine nucleus (DLPN) in monkey is a major link in the projection of descending visual motion information to the cerebellum. Such studies coupled with cortical and cerebellar lesion results suggest a major role for this basilar pontine region in the mediation of smooth-pursuit eye movements. 2. To provide more direct evidence that this pontine region is involved in the control of smooth-pursuit eye movements, focal chemical lesions were made in DLPN in the vicinity of previously recorded visual motion and pursuit-related neurons. Eye movement responses were subsequently recorded in these lesioned animals under several behavioral paradigms. 3. A major deficit in smooth-pursuit performance was produced after unilateral DLPN lesions generated either reversibly with lidocaine or more permanently with ibotenic acid. Pursuit impairments were observed during steady-state tracking of sinusoidal target motion as well as during the initiation of pursuit tracking to sudden ramp target motion. Through the use of the latter technique, initial eye acceleration was reduced to less than one-half of normal for animals with large lesions of the dorsolateral and lateral pontine nuclei. 4. The pursuit deficit in all animals was directional in nature and was not dependent on the visual hemifield in which the motion stimulus occurred. The largest effect for horizontal tracking occurred in all animals for pursuit directed ipsilateral to the lesion. Animals also showed major deficits in one or both directions of vertical pursuit, although the primary direction of the vertical impairment was variable from animal to animal. 5. Chemical lesions in the DLPN also produced comparable deficits in the initiation of optokinetic-induced smooth eye movements in the ipsilateral direction. In contrast to this effect on the initial optokinetic response, in the one lesioned animal studied during prolonged constant velocity optokinetic drum rotation, smooth eye speed increased slowly over a 10- to 15-s period to reach a level that closely matched drum speed. These results suggest that pathways outside the DLPN can generate the steady-state optokinetic response. 6. Saccades to stationary targets were normal after DLPN lesions, but corrective saccades made to targets moving in the direction ipsilateral to the lesion were much more hypometric than similar prelesion control saccades. 7. The pursuit deficits produced by lidocaine injections recovered within 30 min. The ibotenic acid deficits were maximal approximately 1 day after the injection and recovered rapidly thereafter over a time period of 3-7 days.(ABSTRACT TRUNCATED AT 400 WORDS)

Temporal order judgements in good and poor readers

The amount of time required to make accurate (75% correct) temporal order judgements was measured in groups of 3rd and 4th grade children who were selected on the basis of reading ability. The stimuli, two words (Box and Fox), were tachistoscopically presented to the left and right or above and below a fixation point. Subjects were asked to say which word came first under one condition, or which position contained the stimulus that occurred first under another condition. The stimulus onset asynchrony (SOA) was varied in half octave steps until threshold was determined. The results indicate that good readers required significantly longer SOAs to achieve 75% correct than adults, but significantly shorter SOAs than poor readers. There was not a significant difference in thresholds for the word and position conditions for adults or good readers, but poor readers required significantly more time to achieve criterion for the word condition. The word thresholds were highly correlated (-0.77) with reading level, but the correlation between position threshold and reading level was not significant. The implications of a temporal order deficit are discussed.

A comparison of two methods of training resistance to visually-induced motion sickness

This report concerns the use of two methods of training subjects to tolerate visually-induced motion sickness (VMS). Sixteen subjects were selected on the basis of their response to a motion sickness history questionnaire and assigned to one of four groups on the basis of their ability to tolerate visually-induced motion (VM). One group received 10 sessions of confidence building and desensitization training (BT); a second group received 10 sessions of EMG and temperature biofeedback (FB); a third group received 10 sessions of BT and 10 sessions of FB (BTFB); and a fourth group received no treatment (C). The results indicated that the BT and BTFB groups exhibited significant increases in tolerance to VM when pretreatment measures were compared to posttreatment measures, while no significant differences in pre-post measures were observed in the FB or C groups. A similar pattern emerged from the symptomatology data.

Measures of auditory evoked potentials during optokinetic stimulation

In this investigation auditory brainstem responses (ABR) elicited by click stimuli were recorded before, during, and after optokinetic stimulation in subjects that were (N = 10) or were not (N = 10) prone to visually induced motion sickness. The latency of Wave I, and the I-III and I-V interwave intervals were measured. A significant increase in the I-III interwave interval occurred only during optokinetic stimulation. Neither the Wave I latency nor the interwave interval differed with respect to subject groups and this factor did not interact with any other variables. These results suggest that optokinetic stimulation may alter neural activity in the region of the superior olivary complex, a structure known to be important in sound-source localization.

The effects of grating complexity on transient evoked potentials

In the present investigation, the effects of spatial frequency (1.0, 3.0 and 9.0 c/deg), grating complexity (1 + 3 or 3 + 9), and relative phase relationships (peaks-add or peaks-subtract) on the amplitude and latency of VEP components were examined with a pattern appearance (50 msec, 1.9 Hz) technique. The effects of temporally modulating one spatial component of a complex grating while the other component was continuously viewed were also investigated. Two components of the response obtained with pattern appearance were differentially affected by these stimulus manipulations. In general, most conditions that involved spatial complexity resulted in a loss of information that could be obtained when simple sine-waves were used.