The perception and prehension of objects oriented in the depth plane. II. Dissociated orientation functions in normal subjects

Normal human subjects were tested for their ability to discriminate the orientation of a square plaque tilted in depth, using two different tasks: a grasping task and a perceptual matching task. Both tasks were given under separate monocular and binocular conditions. Accuracy of performance was measured by use of an opto-electronic motion analysis system, which computed the hand orientation (specifically, a line joining the tips of the thumb and index finger) as the hand either approached the target during grasping or was used to match the target. In all cases there was a very strong statistical coupling between hand orientation and target orientation, irrespective of viewing conditions. However, the matching data differed from the grasping data in showing a consistent curvature in the hand-target relationship, whereby the rate of change of hand orientation as a function of object orientation was smaller for oblique orientations than for those near the horizontal or vertical. The results are interpreted as reflecting the operation of two different mechanisms for analysing orientation in depth: a visuomotor system (assumed to be located primarily in the dorsal cortical visual stream) and a perceptual system (assumed to be located in the ventral stream). It may be that the requirements of visuomotor control dictate a primary need for absolute orientation coding, whereas those of perception dictate a need for more categorical coding.

A possible role for the Hering-Breuer deflation reflex in apnea of prematurity

BACKGROUND

The vagally mediated Hering-Breuer deflation reflex terminates expiration and initiates inspiration when lung volume is reduced to less than functional residual capacity. The effects of prematurity on this reflex are not known.

STUDY DESIGN

Fifteen term and 20 preterm nonventilated infants were studied. Lung deflation was achieved by chest compression using an inflatable jacket. Relative changes in expiratory time and inspiratory time on chest compression were calculated from airflow recordings. Esophageal pressure changes in the term infants and chest wall movements in the preterm infants were also measured.

RESULTS

The term infants had a mean prolongation of inspiratory time on squeezing of 15% versus a 24% shortening in the preterm infants (p < 0.001). The term infants had a mean shortening of expiratory time on squeezing of 35% versus 18% in the preterm infants (p < 0.001). Fifteen of the 20 preterm infants demonstrated a tendency to have short apneas (2 to 5 seconds) on squeezing, 88% of which were central in origin. In these infants shortening of inspiratory time was greater than that seen in the preterm infants not having apneas (p < 0.05).

CONCLUSIONS

Preterm infants responded to a rapid reduction in lung volume with a shortened inspiratory effort and a tendency to have central apneas. This may be due to an immaturity in part of the reflex arc responsible for transmitting the Hering-Breuer deflation reflex.

Vision without knowledge

A brain-damaged patient (D.F.) with visual form agnosia is described and discussed. D.F. has a profound inability to recognize objects, places and people, in large part because of her inability to make perceptual discriminations of size, shape or orientation, despite having good visual acuity. Yet she is able to perform skilled actions that depend on that very same size, shape and orientation information that is missing from her perceptual awareness. It is suggested that her intact vision can best be understood within the framework of a dual processing model, according to which there are two cortical processing streams operating on different coding principles, for perception and for action, respectively. These may be expected to have different degrees of dependence on top-down information. One possibility is that D.F.'s lack of explicit awareness of the visual cues that guide her behaviour may result from her having to rely on a processing system which is not knowledge-based in a broad sense. Conversely, it may be that the perceptual system can provide conscious awareness of its products in normal individuals by virtue of the fact that it does interact with a stored base of visual knowledge.

Adrenal function and high dose inhaled corticosteroids for asthma

OBJECTIVE

To investigate effects on adrenal function of fluticasone, a recently released inhaled steroid preparation with lower systemic bioavailability than beclomethasone dipropionate.

METHODS

34 children on high doses (400-909 micrograms/m2/d) of inhaled beclomethasone dipropionate or budesonide were recruited into a double blind, crossover study investigating the effects on adrenal function of beclomethasone and fluticasone propionate, given using a standard spacer (Volumatic). The 24 hour excretion rates of total cortisol and cortisol metabolites were determined at baseline (after a two week run in), after six weeks treatment with an equal dose of beclomethasone, and after six weeks of treatment with half the dose of fluticasone, both given through a spacer device.

RESULTS

The comparison of effects between fluticasone and beclomethasone during treatment periods, although favouring fluticasone in all measured variables, reached significance only after correction for urinary creatinine excretion (tetrahydrocortisol and 5 alpha-tetrahydrocortisol geometric means: 424 v 341 micrograms/m2/d). The baseline data showed adrenal suppression in the children taking beclomethasone (total cortisol geometric means: 975 v 1542 micrograms/d) and a dose related suppression in the children taking budesonide. Suppressed adrenal function in the children who were taking beclomethasone at baseline subsequently improved with fluticasone and beclomethasone during treatment periods.

CONCLUSIONS

Fluticasone is less likely to suppress adrenal function than beclomethasone at therapeutically equivalent doses. The baseline data also support the claim that spacer devices should be used for the administration of high doses of inhaled topical steroids.

Respiratory status and allergy nine to 10 years after acute bronchiolitis

In order to evaluate further the relationship between acute bronchiolitis in infancy and subsequent respiratory problems, children prospectively followed up from the time of their admission to hospital were reviewed along with a group of matched controls recruited at the previous five and a half year assessment. Sixty one index children and 47 controls took part. The groups were well matched for age, height, parental smoking, and social class. Although the prevalence of respiratory symptoms had fallen when related to the previous review, there remained an excess of coughing (48 and 17% in index and control children respectively; odds ratio 4.02) and wheezing (34 and 13% in index and control children respectively; odds ratio 3.59). Bronchodilator therapy was used by 33% of index children compared with 3% of controls. Lung function tests revealed no significant differences in the measurements of lung growth-for example, forced vital capacity, functional residual capacity, and total lung capacity-but the index children had significant reductions in measurements of airways obstruction-for example, forced expiratory volume in one second, maximum expiratory flow at 75, 50 and 25% of vital capacity, and airways resistance. Family history and personal skin tests showed no excess of atopy in the index group. This study supports the claim that the excess respiratory symptoms after acute bronchiolitis are not due to familial or personal susceptibility to atopy.

Determination of gas-trapping during high frequency oscillatory ventilation

OBJECTIVE

To determine the effect of frequency and percent inspiratory time on tidal volume and gas-trapping during high-frequency oscillatory ventilation (HFOV).

SUBJECTS

Nine preterm infants with respiratory distress syndrome tested in the first 48 h of life.

METHODS

Tidal volumes and the presence of gas-trapping were measured by respiratory jacket plethysmography at frequencies of 10, 14, and 17.8 Hz and at inspiratory times of 30%, 50% and 70%, using a commercially available high frequency oscillator.74

RESULTS

Mean (SD) tidal volumes were 2.40 (1.06) ml/kg at 10 Hz, 2.52 (1.07) ml/kg at 14 Hz and fell significantly to 1.96 (0.92) at 17.8 Hz (p < 0.05). Tidal volumes at 50% inspiratory time were significantly greater than at 30% inspiratory time [2.81 (1.42) ml/kg and 2.32 (1.18) ml/kg, respectively] but fell to baseline levels at 70% inspiratory time. There was no significant gas-trapping with increases in either frequency or percent inspiratory time.

CONCLUSIONS

Gas-trapping is not a significant problem during HFOV in premature infants. Changes in tidal volume with increases in frequency and percent inspiratory time are similar to that seen in animal models.

Copying without perceiving: motor imagery in visual form agnosia

Patient DF has severely impaired visual contour perception, despite being able to use that same visual information to guide her motor actions. We report that DF has developed a strategy to overcome some of her perceptual deficits. DF was first asked to copy single lines set at different orientations. She performed surprisingly accurately, although her responses were slow. When questioned, DF reported imagining tracing the line with her finger before copying the line on paper, although she was still unable to discriminate perceptually between different line orientations. We found that time restraints, or the requirement to perform secondary concurrent tasks, severely disrupted DF's orientation copying ability. We conclude that DF can use pure motor imagery to compensate for some of her perceptual difficulties.

The influence of sleeping position on functional residual capacity and effective pulmonary blood flow in healthy neonates

Variation in body position has been shown to affect respiratory function in adults and neonates with and without respiratory illness. At present it remains unclear why respiratory function should be affected by different body positions. We hypothesized that the effect of body weight on the relatively compliant chest wall of the newborn infant in the prone position would cause a reduction in functional residual capacity (FRC) and a compensatory improvement in ventilation/perfusion matching as measured by effective pulmonary blood flow. To evaluate this, a paired crossover study was performed on 12 normal newborn infants. The inert gas (argon) rebreathing method adapted for neonates was used to measure FRC. Simultaneously effective pulmonary blood flow (Qpeff) was determined using Freon 22 and a mass spectrometer with computerized analysis. The babies were studied in three different positions in random order: prone, supine and right lateral decubitus. The means (95% confidence intervals) of the three groups of FRC were 23.8 (19.2 to 28.4), 23.8 (20.2 to 27.5), and 24.3 (19.5 to 29.2) ml/kg, respectively (P = 0.59) and for Qpeff were 104 (91 to 116), 108 (95 to 122), 109 (97 to 122) ml/ kg-min, respectively (P = 0.11). Thus no significant differences were demonstrated. In nine of the babies, a repeat supine measurement was taken at the end of the study to assess repeatability of the method. In these nine babies alone the results were 22.7 (19.1 to 26.3) and 22.1 (18.6 to 25.6) ml/kg for FRC, and 102 (89 to 116) and 98 (90 to 107) ml/kg-min for Qpeff. The coefficients of repeatability were 4.7 ml/kg for FRC (21%) and 30 ml/kg-min for Qpeff (30%).

The perception and prehension of objects oriented in the depth plane. I. Effects of visual form agnosia

Previous studies have reported that the visual form agnosic D.F. is able to use information about visual targets for the control of motor acts, but has great difficulty in using the same visual information for perceptual report. This intact visuomotor performance may be mediated by relatively intact parieto-frontal cortical mechanisms. The present study investigated the ability of D.F. to use binocular and monocular information about the orientation of an object in the depth plane for perceptual and visuomotor purposes. A square plaque was presented at seven different orientations in depth to D.F. and to three age- and sex-matched control subjects. Subjects were required to reach out and grasp the plaque using a precision grip (index finger and thumb) under binocular and monocular viewing conditions, and in separate trials to match the orientation of a hand-held plaque to the perceived orientation of the target object, also under both binocular and monocular conditions. D.F.'s performance in grasping trials was found to be normal under binocular conditions, but was substantially worsened by removal of binocular vision. She was severely impaired at matching the orientation of the test square, although under binocular conditions her performance rose clearly above chance. The data suggest that the separation of cortical processing for visuomotor and visual perceptual purposes also applies, at least in part, to information about the orientation in depth of an object. The impaired performance under monocular viewing conditions on the visuomotor task is in agreement with recent physiological data and suggests that posterior parietal systems depend critically on binocular input for the processing of orientation in depth when ventral-stream information is unavailable.

Estimation of fetal lung volume using enhanced 3-dimensional ultrasound: a new method and first result

OBJECTIVE

To measure fetal lung volume using a computer based, enhanced, 3-dimensional ultrasound imaging system.

DESIGN

An observational study.

SETTING

The Fetal Medicine Unit at Guys Hospital, London.

PARTICIPANTS

Twenty healthy women with a singleton pregnancy between 24 and 36 weeks of gestation were scanned on one occasion during pregnancy using an ultrasound based 3-dimensional imaging system. All delivered at term with weights above the 10th centile for gestation.

RESULTS

Total lung volume increased exponentially with gestational age. Right lung volume measured consistently greater than left lung volume.

CONCLUSIONS

The use of this new enhanced 3-dimensional imaging system allows for estimations of fetal lung volume. Preliminary data confirm that fetal lung volume, measured by a computerised 3-dimensional ultrasound imaging system increased exponentially with gestational age. The use of this system has obvious application in the further study of lung growth in utero and possible clinical application in disease states where fetal lung growth may be impaired.

Treatment of recurrent acute wheezing episodes in infancy with oral salbutamol and prednisolone

The aim of this study was to investigate the role of oral salbutamol and prednisolone in the treatment of acute episodes of wheezing in infants under 15 months of age. Sixty-two acute episodes of wheezing were studied in 59 babies (age range 3-14 months; mean 7 months), who had all suffered at least one previous wheezy episode. Patients were randomised to receive either salbutamol and prednisolone, salbutamol and placebo or double placebo. Parents were requested to keep a diary card record of twice daily scoring of their baby's symptoms over the next 14 days. A significantly greater number of treatment failures occurred in the placebo group compared to babies treated with oral salbutamol (relative risk 2.51; 95% confidence intervals for relative risk 1.09-5.79). There was no difference in the number of treatment failures between babies treated with a combination of salbutamol and placebo and those treated with salbutamol and prednisolone (relative risk 0.71; 95% confidence intervals for relative risk 0.18-2.80).

CONCLUSION

This study demonstrates that oral salbutamol is beneficial in the treatment of acute episodes of wheezing in infancy. A combination of oral salbutamol and oral prednisolone appeared to have no additional benefit over treatment with oral salbutamol alone.

Visuomotor sensitivity for shape and orientation in a patient with visual form agnosia

We have previously demonstrated that a patient with visual form agnosia (DF), who is unable to report the orientation or size of visual targets, can nevertheless use these same visual attributes to control motor acts. In the first of three new experiments, we found that DF is able to grasp everyday tools and utensils proficiently (i.e. with a well-formed hand posture) but has difficulty in visually selecting the correct part of the object to grasp (e.g. the handle) for subsequent use of that object. A second experiment revealed that DF's visuomotor system is able to adjust concurrently to variations in both the size and orientation of target objects; when these visual attributes were both varied, she adjusted both her grip aperture and the orientation of her hand well in advance of target contact. These spared visuomotor abilities do not seem to extend to shape processing per se, however. In the final experiment we found that DF was insensitive to changes in the orientation of a cross-shaped object, where no single principal axis could be extracted to control orientation of the grasp. These observations extend our knowledge of DF's residual visuomotor abilities, and suggest limitations on the visual processing capacities of the human dorsal stream.

Surfactant and respiratory distress syndrome

Since the late 1950s it has been known that the cause of respiratory distress syndrome (RDS) is surfactant deficiency, especially in preterm infants. But surfactant protein B deficiency may cause RDS in term infants as well. Administration of natural surfactant produce is well known to a rapid improvement in oxygenation within 15 to 20 minutes. The effect of synthetic surfactant is less dramatic. Although randomized controlled trials have been done, the majority have been relatively small. Studies on the role of natural surfactant given to infants with established RDS (rescue therapy) have shown a reduction in the incidence of neonatal death and pneumothorax of 40% and 65%, respectively, compared to untreated infants. However, natural surfactant provides no apparent benefits in terms of the incidence of intraventricular hemorrhage (IVH), patent ductus arteriosus (PDA) or bronchopulmonary dysplasia (BPD). The results of synthetic surfactant given as rescue therapy have shown a similar effect with a 40% reduction in mortality and a 48% reduction in pneumothorax. However, synthetic surfactant also led to a 23% reduction in IVH, 27% in PDA, and 32% in BPD. When natural surfactant is given as prophylaxis (i.e. at or soon after birth, before the development of RDS), the reduction in mortality is 45% and the reduction in pneumothorax is 69%, but as with rescue therapy, there is no effect on the incidence of IVH or BPD. The effect on the incidence of PDA is an increase of 27%. When synthetic surfactants are given prophylactically, there is a similar reduction in mortality of 44% and a reduction in pneumothorax of 36%. The incidence of IVH and BPD is unchanged, but as with the natural surfactant, there is a small increase in the incidence of PDA of 27%. The main side effect is pulmonary hemorrhage that has been reported to occur in 4-7% of infants given surfactant. Although the administration of surfactant has had a dramatic effect on neonatal practice, it is likely that further studies will lead to more appropriate use of surfactant.

Differential effects of line length on bisection judgements in hemispatial neglect

Recent studies have shown that certain symptoms of spatial neglect are co-determined by two major factors: one whose general nature is perceptual, the other whose nature is directional and/or motor. In the present study, patients whose neglect was classified as predominantly 'perceptual' or 'directional' through use of the Landmark task (Milner, Brechmann and Pagliarini, 1992) were asked to bisect lines ranging in length from 20 to only 2.5 cm. It was found that the one patient with predominantly directional neglect showed large rightward errors at all line lengths. In contrast, those with perceptual neglect made very small (usually leftward) errors on short lines. It is argued that it is essential to separate these different subtypes of neglect patient if we are to understand the causation of their behaviour in tasks such as line bisection.

Cerebral correlates of visual awareness

While it may be a long time before we can specify the mechanisms through which a brain process achieves awareness, it may be possible to determine as a first step whether awareness is limited to the products of certain kinds of processing. In the domain of vision, for example, perceptual awareness might only be attainable in association with object-centred coding, configural representations of space, and other such forms of abstracted (non-retinocentric) coding. It appears that these forms of visual coding are anatomically restricted to telencephalic structures, and indeed it has been argued that they may be peculiar to, or at least visually dependent upon, the 'ventral stream' of visual areas with the cortex. It is suggested here that such a brain process would still not be able to enter visual awareness unless it was selectively amplified through neuronal gating of the kind that has been shown to be correlated with selective spatial attention. The present paper explores the extent to which this putative dual requirement for visual consciousness might form a basis for understanding the various phenomena of "covert vision" seen in patients suffering from hemianopia, apperceptive agnosia, and unilateral spatial neglect.

Lung sounds in neonates with and without an added dead space

Previous studies have reported great difficulty in recording lung sounds from neonates and have found conflicting results. We studied lung sounds in neonates during the inspiratory phase of the respiratory cycle as monitored by inductive plethysmography (A) and by a pneumotachograph and a face mask (B) which added a dead space of 12 mL. Sixteen term babies were tested 12 hr to 6 days (median 45 hours) after birth. Lung sounds were recorded and then analysed using overlapping and non-overlapping fast Fourier transforms. The two methods of analysis showed a difference in intensity but not in frequency. Fourteen babies provided enough breaths for comparison; a total of 596 inspirations were analysed. The intensity of lung sounds on occasion B was higher in all but two babies with a mean B/A ratio of 2.4. The mean (SD) power on occasions A and B was 13.9 (8.5) mW and 26.9 (21.0) mW, P = 0.02, respectively. In all but 4 babies the B/A ratios of the median (f50) and 90th centile (f90) frequencies were scattered randomly within 20% of unity. The mean (SD) f50 on occasions A and B was 205.5 (51.1) Hz and 225.8 (32.3) Hz, P = 0.10, respectively; the mean f90 was 370.3 (91.0) Hz and 396.1 (67.8) Hz, P = 0.25, respectively. Linear regression showed that there is a third-order polynomial relationship between sound intensity and air flow at the mouth. A weaker positive association exists between frequency and air flow, showing that the median and 90th centile frequencies approach an asymptote as flow increases.(ABSTRACT TRUNCATED AT 250 WORDS)

Lung volume and pulmonary blood flow measurements following exogenous surfactant

Lung function in eight infants with clinical and radiological features of surfactant deficiency treated with exogenous porcine surfactant was studied before and at 15 min, 2h and 6h after the intratracheal administration of porcine surfactant. We measured alveolar-arterial oxygen tension difference, dynamic lung compliance, lung volume and effective pulmonary blood flow in all infants. The alveolar-arterial oxygen tension difference fell from a mean (SD) 43.3 (14.5) kPa before treatment to 8.8 (8.8) kPa at 1 h and 12.2 (6.8) kPa 6h after treatment (P < 0.001). There was no change in mean (SD) dynamic compliance (0.39 [0.10] ml/cmH2O/kg pre dose; 0.36 [0.13] ml/cmH2O/kg 6h post treatment). Accessible functional residual capacity and effective pulmonary blood flow were measured using an adaptation of the argon/freon rebreathing method and showed an increase in mean (SD) functional residual capacity from 7.5 (1.4) ml/kg predose to 10.8 (3.3) ml/kg within 15 min of treatment, 11.4 (3.4) ml/kg 2h later and 12.7 (3.1) ml/kg 6h after treatment (P = 0.009). Mean (SD) effective pulmonary blood flow values did not differ significantly, changing from 78.2 (20.9) ml/kg per min predose to 88.7 (24.1) ml/kg per min 15 min post dose, 87.6 (21.7) ml/kg per min 2h post dose and 90.0 (22.7) ml/kg per min 6h post dose (P = 0.711).

CONCLUSION

The improvement in oxygenation after surfactant treatment is associated with an increase in lung volume but is not related to an improvement in dynamic lung compliance or effective pulmonary blood flow. The change in lung volume is detectable within 15 min of administration of the surfactant.

An investigation of hemispatial neglect using the Landmark Task

The "Landmark Task" is designed to tease apart two major factors in determining line bisection errors in spatial neglect: one whose general nature is perceptual, the other whose nature is motor. On critical test trials, the subject is required to point to whichever end of a mid-transected line is judged as nearer to the transection. Seven out of eight neglect patients pointed consistently to the left end of such lines. Thus their misjudgments were made in the direction opposite to any putative "directional hypokinesia." One patient, however, pointed predominantly rightward on these test trials. Normal controls and unilateral stroke patients were also tested on the Landmark Task. Cueing of one end of a line led to a relative perceptual overestimation of that half of the line in all of these groups.

How does exogenous surfactant really work?

The finding of a lag of up to 24 h between the response to exogenous surfactant in infants with respiratory disease syndrome as assessed by blood gases and improvements in respiratory system compliance has generated considerable interest. Studies have shown that there is rapid increase in functional residual capacity after natural surfactant and a less dramatic rise in effective pulmonary blood flow. These changes in blood flow are not associated with a sustained fall in pulmonary artery flow or pressure indicating that the main improvement in oxygenation results from a reduction in intrapulmonary shunting. Recent studies have shown that natural surfactant does produce rapid increases in lung compliance but only if the expired gases are vented to ambient rather than to positive end expiratory pressures. Thus the mechanical effects of natural surfactant are initially largely limited to the part of the tidal volume which is close to the functional residual capacity.

Distortion of size perception in visuospatial neglect

BACKGROUND

A number of studies have shown that most patients with symptoms of unilateral (left-sided) visuospatial neglect make consistently rightward errors when attempting to bisect a horizontal line at its midpoint. One possible interpretation of this impairment is that such patients misperceive the left half of the line: that is, that they underestimate its extent relative to the right half.

RESULTS

We have carried out direct tests for such a perceptual distortion in three neglect patients by asking them to make matching judgements on pairs of horizontal rectangles, vertical rectangles or nonsense shapes, of varying relative size, presented on a computer screen. We report here that all of the patients tested showed a significant and substantial relative underestimation of the horizontal extent or area of stimuli presented on the left side of their egocentric space. There was no such misperception of vertical extent.

CONCLUSIONS

It is suggested that size perception may be partially determined by a representational system that is anatomically centred in the parieto-temporal region of the brain. The results are interpreted in terms of damage to this system in neglect patients.

Effective argon-FRC with a rebreathing technique in children with acute asthma

In children with asthma the measurement of functional residual capacity (FRC) with standard dilution techniques requires long rebreathing times of the inert gas, i.e., helium, to reach alveolar units with long time constants. A modification of the argon-freon-22 rebreathing technique enables argon to dilute in the readily accessible lung volume and potentially can give a measurement of FRC. However, the rebreathing tests cannot be prolonged for more than 1 min thus allowing argon to reach only the rapidly accessible lung units which are grossly useful in gas exchange (effective FRC, EFRC). The aim of this study was to measure the EFRC and standard lung function in children with acute severe asthma, assess their response to nebulized salbutamol, and evaluate the relations of the EFRC response to baseline spirometric measurements. Twenty-four asthmatic children who were admitted to the hospital with an acute asthma attack had spirometry and triplicate EFRC measurements before and after treatment with nebulized salbutamol. Eighteen patients had repeated the respiratory tests 50 days later when they had fully recovered. A significant proportion (28.9%) of the argon traces obtained at baseline before treatment did not equilibrate. However, in the great majority of these tests the oscillation of the argon traces over the last 3 breaths of the test was < 5% of the simultaneous argon concentration. The EFRC values derived from the argon traces with minimal oscillation (< 5%) were reduced during the acute asthma attack when compared with the paired values obtained after recovery (P = 0.03). The administration of salbutamol caused a fall from the baseline EFRC (P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)