Mobility of normal observers under conditions of reduced visual input.

The importance in mobility performance of the rate of presentation of visual information, binocular versus monocular vision, the use of multiple rather than single reference points, and local motion parallax was investigated in two experiments. In each experiment ten subjects walked a triangular mobility course in a totally darkened room; the only visible targets were light emitting diodes (LEDs), mounted on poles, at the apices of the triangle. The LEDs were mounted so that one or two could be used in a trial; if two were used the distance between them was varied horizontally (in experiment 1) and vertically (in experiment 2). The subjects walked around the course under a range of conditions, including two 'optimal trials' in full light. The LEDs were flashed for 1 ms at frequencies of 0.5, 1 and 5 Hz in experiment 1 and at 1 and 5 Hz in experiment 2. Mobility was measured with the use of an ultrasonic locator system which measured the subject's position on the course 10 times per second. The mean velocity of the subject in traversing the course was significantly reduced when the flash rate was slower, when the subject had one eye occluded, or when there was only one LED on the pole; when the spacing between the LEDs was varied, either vertically or horizontally performance was unaffected. These results imply that the frequency of updating of visual information is important in determining mobility performance, as are binocular cues, but that local motion parallax is not important. The number of LEDs on each pole had a significant effect on mobility performance an 'object' (two lights) gave more information than a point reference.     

Monocular deprivation in adult mice alters visual acuity and single-unit activity

It has been discovered recently that monocular deprivation in young adult mice induces ocular dominance plasticity (ODP). This contradicts the traditional belief that ODP is restricted to a juvenile critical period. However, questions remain. ODP of young adults has been observed only using methods that are indirectly related to vision, and the plasticity of young adults appears diminished in comparison with juveniles. Therefore, we asked whether the newly discovered adult ODP broadly reflects plasticity of visual cortical function and whether it persists into full maturity. Single-unit activity is the standard physiological marker of visual cortical function. Using a more optimized protocol for recording single-units, we find evidence of adult ODP of single-units and show that it is most pronounced in deep cortical layers. Furthermore, using visual evoked potentials (VEP), we find that ODP is equally robust in young adults and mature adults and is observable after just one day of monocular deprivation. Finally, we find that monocular deprivation in adults changes spatial frequency thresholds of the VEP, decreasing the acuity of the deprived pathway and improving the acuity of the non-deprived pathway. Thus, in mice, the primary visual cortex is capable of remarkable adaptation throughout life.     

Monocular occlusion impairs stereoscopic acuity,but total visual deprivation does not

Wallach and Karsh (1963) reported that 24 h of monocular occlusion leads to a significant deterioration of stereoscopic depth estimates and attributed this phenomenon to “disuse.” We designed an apparatus for testing stereoscopic accuracy which eliminated all cues to depth save binocular disparity. With it, we tested the relative effect of 8 h of monocular—;as opposed to binocular—;occlusion on subsequent stereoscopic performance. Monocular patching led to significant increases in mean standard deviation and in mean absolute error as compared to baseline testing. Binocular patching led to no such impairment. Thus, truedisuse (such as occurs during binocular deprivation) did not impair stereopsis, whereas monocular occlusion, which may involve temporarymisuse of the stereoscopic system, did.     

A visual acuity test for infants under six months of age

The Psychological Record -     

Effect of static visual acuity on dynamic visual acuity: a pilot study

The aim of this pilot study was to evaluate whether dynamic visual acuity changes with or without refractive correction. 42 healthy enrolled subjects with normal vision were divided into two age-matched groups. In Group A, dynamic visual acuity was measured first with the refractive error fully corrected and then without. In Group B, dynamic visual acuity measurements were taken in the reverse order of that performed by Group A. The measurements were binocularly performed five times using free-head viewing after dynamic visual acuity values were stable. Significant changes in dynamic visual acuity (static visual acuity 20/20 vs 12/20) were observed in both Group A (171.6 +/- 36.0 deg./sec. vs 151.8 +/- 39.6 deg./sec., Wilcoxon test, p < .001) and Group B (169.8 +/- 30.0 deg./sec. vs 151.2 +/- 36.0 deg./sec., Wilcoxon test, p < .001). The interaction was significant (F1.20 = 8.12, p = .009). These results indicated that refractive correction affected dynamic visual acuity.     

Incentive properties of sucrose and saccharin under different deprivation conditions

In Expt 1 it was found that hungry rats developed a 100% preference for 8% sucrose over water in a maze-choice situation, whereas thirsty rats developed no preference. When deprivation conditions for the two groups were reversed the pattern of preference relations also reversed. In a 2nd experiment nondeprived rats developed a preference for either 8% sucrose or 0.2% saccharin over water while thirsty Ss did not develop a preference for either of these over water. The results are discussed in terms of incentive theory.     

Large-scale visual frontoparallels under full-cue conditions

We determined the curvature of apparent frontoparallels in a natural scene (a large lawn in broad daylight). Data on frontoparallels in these conditions are very sparse and reveal idiosyncratic curvatures of frontoparallels and irregular variation with distance. We used a method of bisection of linear segments indicated through pairs of stakes at angular separations (from the vantage point) of up to 120 deg. Distances of 2 m and 10 m (in the forward direction) were used. The bisection was carried out by the observer through maneuvering a radio-controlled vehicle carrying a third stake. Four observers participated in the experiment; they had no problems with the task and yielded mutually consistent results. We found that the frontoparallels are significantly curved and are concave towards the observer. Surprisingly, the sign of the curvature is opposite to that found when the frontoparallels are defined through an exocentric pointing task. Available theory (Luneburg's) does not predict this, but the theory is hardly applicable to the case of vision in natural scenes. This interesting discrepancy has not been reported before.     

Infant visual attention under response-contingent and response-independent conditions

The visual attention behavior of 2- to 3-month-old infants was monitored as part of their participation in an operant conditioning study. Attention was monitored under three conditions: a baseline condition where a visual target remained stationary; a baseline conditioning where the target was made to move on an aperiodic, response-independent schedule; and a conditioning phase where the target was operantly under the control of the subjects. Fixation time differed significantly as a function of experimental condition, with the response-contingent condition producing the greatest amount of fixation and the stabile, baseline condition producing the least amount of fixation. The implications of the findings for intervention purposes are discussed.     

Influence of differences of visual acuity in various visual field conditions on spectral characteristics of the center of pressure sway

This study examined the influence of visual acuity and visual field on the spectral characteristics of the center of pressure during standing. 17 men and 20 women participated in High and Low visual acuity groups. Both groups underwent center of pressure measurements under three visual field conditions: No vision: subjects were given no visual information, Central vision: they were given only central visual field information, and Full vision: they were given full visual information. To assess the spectral characteristics of center of pressure, mean power frequency and frequency of maximal power were calculated from medial-lateral and anterior-posterior center of pressure directions. The Friedman test and Scheffé pairwise comparison tests showed that frequency of maximal power was higher in the No vision than in the Central and Full vision conditions in the High visual acuity group. In conclusion, people with high visual acuity are more susceptible to visual field conditions than those with low visual acuity. It is suggested that postural control characteristics differ with visual acuity or resolution in the central visual field.     

The structure of mood: A comparison between sleep deprivation and normal wakefulness conditions

The stability of the factor structure of mood was examined under two different experimental conditions, sleep deprivation and normal wakefulness In the first phase of the study, two different forms of a mood scale were administered to several college classes, and the ratings for each scale were intercorrelated and factored Eight interpretable factors emerged from each analysis, and the two sets of factors were highly congruent. In the second phase of the study subjects completed the mood ratings after staying awake all night or after getting a good night's rest Comparisons between the means for the two groups showed significant differences on 26 of the 44 variables included in the scale The scores for the sleep-deprived group were then intercorrelated and factored, and the factor structure was compared with the relevant factor structure obtained in the first phase of the study The results of the comparison showed that six of the eight factors appeared under both conditions of sleep deprivation and normal wakefulness Additional analysis indicated that a seventh factor appeared, but in the guise of different variables The only factor which failed to appear under sleep deprivation was elation. It was concluded that although variable ratings showed high sensitivity to the experimental operations, the basic structure of the underlying mood states remained remarkably stable The results indicate that the search for a list of basic mood states may be quite fruitful An important methodological implication was that a variable may be selected to measure a mood under various experimental operations with the assurance that the nature of the mood to be measured does not change as a result of those operations