Individual differences in visual acuity and face matching ability

The visual acuity of the eyes varies outside the range of normal vision, requiring corrective lenses, but also within the normal range. This study investigated whether both types of variation relate to individual differences in face-identity matching, considering this applied task requires perception of detail. Across two experiments, face-matching accuracy correlated with variation in acuity when this fell outside the normal range of vision and was uncorrected with glasses or contact lenses. In contrast, variation in visual acuity within the normal range did not affect face-matching accuracy, whereas matching accuracy at a given level of acuity could vary substantially. These results indicate that visual acuity is only a problem for occupations performing face-identity matching when below-normal acuity is not diagnosed or adequately corrected. In turn, these findings suggest that variation in acuity within the normal range is not a contributing factor to individual differences in face matching accuracy.     

Competition-induced visual field differences in search

Do visual field effects point to differences in cortical representation, or do they reflect differences in the way these representations are used by other brain regions? This study explored three attributes of visual search that provide strong evidence in favor of differences in use. Competition refers to the finding that visual field differences in search efficiency are larger in whole- than in half-field displays (both left-right and upper-lower half-fields). Task specialization refers to the finding that some tasks favor one hemisphere whereas other tasks favor the other hemisphere, even though the same stimulus displays are used in both tasks. Anatomical alignment refers to the finding that competition effects are altered if the quadrants of the visual display are not aligned with the cortical quadrants of the observer. We propose that visual field specialization in search is the result of a competition involving limited access to cortical visual representations by the extended neural networks of attention.     

Power spectrum characteristics of sway position and velocity of the center of pressure during static upright posture for healthy people

This study assessed sex and individual differences in sway-position and velocity power spectra and reliability of power frequency with 30 health young people. The body sway for 1 min. was measured twice over a 1-min. rest. There were no significant sex differences in the spectra. Frequency bands with a large coefficient of variance over 10.0 appeared up to 0.6 Hz. 75% relative accumulated power frequency appeared at 1.10-1.23 Hz in the position and at 2.00-3.05 Hz in the velocity spectra. Most power was in the low frequency band (A and B frequency intervals) of the international standard. Relative accumulated power frequency of position and velocity power spectra was reasonably reliable. It may be necessary to establish a new evaluation frequency interval by direction of sway-position and velocity using relative accumulated power frequency for healthy people.     

Age differences in the relationship between visual movement imagery and performance on kinesthetic acuity tests

The Vividness of Movement Imagery Questionnaire was administered to 280 fourteen-year-olds and 186 ten-year-olds, who were then tested on measures of kinesthetic acuity. The relationship between visual movement imagery and kinesthetic acuity scores was significant in the older group: Those with high levels of visual movement imagery performed significantly better on measures of kinesthetic acuity than did those with low imagery. No such effect was found in the younger group. The results indicate that for adolescents, the confounding effect of visual imagery affects the researcher's ability to interpret kinesthetic acuity scores. The relationship between imagery and kinesthesis appears to develop over the period between 10 and 14 years, although such an interpretation may be premature because the measurement of visual movement imagery in the younger age group is problematic.     

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.     

Influence of foveal load on the functional visual field

Attention, Perception, & Psychophysics - The functional visual field defined in terms of a discrimination task of a target presented peripherally among ambiguous background patterns was...     

Limits of visual acuity in the frontal field of the rock pigeon (Columba livia)

The eye of the rock pigeon is typical of a granivorous lateral-eyed bird, in that it has both a laterally projecting central fovea and a second high-density cellular area in peripheral retina (area dorsalis) which projects to the binocular frontal field below the beak. Such a dual system is faced with potentially different optical restraints arising from central and peripheral vision. We asked whether the frontal axis can support high resolution vision from a refractive resting position (predicted to be 25-33 cm; Fitzke et al, 1985 Journal of Physiology 369 33-44) to some near point of accommodation. We measured the visual acuity on the frontal axis in five pigeons using an operant discrimination of high-contrast square-wave gratings at a series of distances from 7 to 80 cm from the eye. The peak average acuity was 11.04 cycles deg(-1), which occurred 10 cm from the eye. The average of the maximum acuity of each bird at 10 cm was 12.8 +/- 1.1 cycles deg(-1), a value equal to the Nyquist frequency calculated from the peak ganglion cell density of the area dorsalis. However, this maximum acuity was restricted to a narrow depth in space, located around 10 cm from the eye, and at greater distances fell exponentially such that acuity was 50% of its maximum at 35 cm and less than 1 cycle deg(-1) at 100 cm. We propose that the range of high-acuity vision is limited in the frontal field by either increased refractive power and/or inaccuracy in frontal accommodation, and is optimized for a preferred far point located 10 cm from the eye.     

On the visual acuity of the pigeon

Several lines of evidence suggest that the pigeon is near-sighted for stimuli located in front of its beak and far-sighted for stimuli located to the sides of its head.     

Power spectral density analysis of the standing sway of males

Application of power spectral density analysis to normal human standing sway showed that the power in sway was unevenly distributed among various frequencies below 1.0 Hz. Ss were divided, with regard to antero-posterior sway, into two types on the basis of the frequencies at which peaks of power occurred. The same Ss were divided into four types, with regard to lateral sway, using similar criteria. The different types appear to represent normal variations in the basic mechanism for standing upright.     

Age and visual field differences in computing visual-spatial relations.

Age and brain hemispheric differences in visual-spatial performance were investigated using 2 versions of categorical and coordinate (metric) spatial relations tasks. Thirty-two young adults (M = 19.2 years) and 32 older adults (M = 68.8 years) participated. An overall age-related decrement in computing visual-spatial relations was obtained for lateralized presentations and when items were presented centrally. In contrast to some previous findings, there was no evidence to suggest differential aging of the right hemisphere in computing visual-spatial relations.     

Assessment of visual acuity in preschool children

Abstract.— Problems in testing visual acuity of preschool children were discussed with regard to choice of optotype and test distance, illumination, instruction and response indicator, and the motivational aspect of the test situation. A test situation conforming to these requirements for measuring visual acuity was arranged for testing of preschool children, using a discrimination learning paradigm with simultaneous presentation of the cues. The test figures were two Landolt Cs of equal size but one with the gap filled in, thus forming a circle. Small toys were used as rewards for choosing the Landolt C. Of 27 children, 2–6 years of age, 25 achieved a visual acuity level corresponding to a Snellen value of 20/20. The results thus indicate a better visual acuity for preschool children than is commonly believed.     

Effect of pupil size on dynamic visual acuity

This study was conducted to assess the effect of pupil size on dynamic visual acuity (DVA). 60 young healthy men (M = 28.1 yr., SD = 3.9) with normal vision were divided into three age-matched groups by pupil size: dilated (n=20), unchanged (n=20), and constricted (n=20). DVA was measured binocularly with freehead viewing before and at 30 min. after each drop was instilled. Each of the three groups got a different amount. The sizes of the constricted, unchanged, and dilated pupils were 2.8 mm (SD = 0.5), 4.1 mm (SD = 0.3), and 7.8 mm (SD = 0.5), respectively. The pupil size x DVA interaction was significant (F(2,114)= 6.07). DVA in the constricted pupil decreased, but that in the dilated pupil increased (paired t test). DVA in the unchanged pupil did not change significantly (paired t test). Pupil size is possibly one of the factors which may affect DVA measurement.     

Effect of visual surrounding motion on body sway in a three-dimensional environment

Unidirectional motion of a uniplanar background induces a codirectional postural sway. It has been shown recently that fixation of a stationary foreground object induces a sway response in the opposite direction (Bronstein & Buckwell, 1997) when the background moves transiently. The present study investigated factors determining this contradirectional postural response. In the experiments presented, center of foot pressure and head displacements were recorded from normal subjects. The subjects faced a visual background of 2 x 3 m, at a distance of 1.5 m, which could be moved parallel to the interaural axis. Results showed that when the visual scene consisted solely of a moving background, the conventional codirectional postural response was elicited. When subjects were asked to fixate an earth-fixed foreground (window frame) placed between them and the moving background, a consistent postural response in the opposite direction to background motion was observed. In addition, we showed that this contradirectional postural response was not transient but was sustained for the 11 sec of background motion. We investigated whether this contradirectional postural response was the consequence of the induced movement of the foreground by background motion. Although induced movement was verbally reported by subjects when viewing an earth-fixed target projected onto the moving background, the contradirectional sway did not occur. These results indicate that foreground-background separation in depth was necessary for the contradirectional postural response to occur rather than induced movement. Another experiment showed that, when the fixated foreground was attached to the head of the observer, the contradirectional sway was not observed and was therefore unrelated to vergence. Finally, results showed that the contradirectional postural response was, in the main, monocularly mediated. We conclude that the direction of the postural sway produced by a moving background in a three-dimensional environment is determined primarily by motion parallax.     

Objective determination of human visual acuity from the visual evoked potential

The natural visual acuities of 11 subjects were predicted from their flashed pattern evoked potentials. An objective data analysis technique was employed, based on the slope of the high spatial frequency side of the function between pattern element size and the amplitude of the evoked potential.     

The effect of intermittent illumination on the visual acuity threshold

Senders (1949) reported that with intermittent illumination short flashes needed less energy than larger ones to make a visual acuity target visible. This apparent breakdown of the reciprocal relationship between time and intensity, which has been found almost universally by earlier workers under a very wide range of experimental conditions, raised a number of interesting theoretical issues such as the relationship between visual acuity and intensity discrimination thresholds, and the plausible importance of eye movements in each. Unfortunately we have been unable to repeat Senders' result in spite of the most determined efforts to reproduce her experimental conditions. We are unable to suggest why our results differ from hers, but feel that our experiments at least show that her data are very difficult to reproduce and hence no general theoretical argument can be based on them.

In view of this we felt at liberty to predict results on the basis of a model, we had tentatively constructed, which we regarded as integrating Bloch's and Talbot's laws. This enabled us to make predictions about the effect of frequency of repetitive stimulation on thresholds. Experiments were carried out to ascertain how far these predictions were substantiated. Agreement was remarkably good.     

Upper and lower visual field differences in categorical and coordinate judgments

Kosslyn (1987) theorized that the left and right hemispheres differ in processing categorical and coordinate spatial relationships, respectively. Previc (1990) hypothesized that the upper and lower visual fields are functionally specialized for visual search and visuomotor manipulations, respectively. Conceptual similarities between these two theories suggested possible upper visual field advantages for categorical judgments and lower visual field advantages for coordinate judgments. In the present two experiments, subjects made either categorical or coordinate judgments to stimuli in the upper left, upper right, lower left, or lower right visual fields. The first experiment manipulated categorical/coordinate judgments as a between-subjects variable. The second experiment manipulated categorical/coordinate judgments as a within-subjects variable. In the first experiment, reaction times (RTs) for categorical judgments were equal in all visual fields except the lower left, in which RTs were slower. For coordinate judgments, RTs were equal in all visual fields except the lower left, in which RTs were faster. In general, these effects were replicated in the second experiment. However, there appeared to be consequences associated with manipulating the categorical/coordinate variable in a within-subjects fashion. The requirements of visual search versus visuomotor processes appear to map onto the nature of categorical versus coordinate processing, respectively, suggesting possible upper-lower visual field differences in categorical versus coordinate processing.     

Age-stage differences in body sway during a static upright posture based on sway factors and relative accumulation of power frequency

This study was done to examine age-stage (preschool children, young adults, and elderly people) differences in the center-of-pressure sway using body-sway factors (unit-time sway, front-back sway, left-right sway, and high frequency-band power), power-spectrum distribution, and relative accumulation of power frequency (25%, 50%, and 75% RAPF) of the center-of-pressure spectrum. The center-of-pressure movement for 1 min. was measured twice using Anima's stabilometer. Data-sampling frequency was set at 20 Hz. Significant age-stage differences were found for 3 factors except for left-right sway, which was larger for preschool children and elderly than for young adults. The power spectrum of body sway in any age-stage was noted mainly in low frequency bands. A marked age-stage difference was found at 75% RAPF. Body-sway characteristics in each age-stage differ, and differences of postural-sway frequency are marked in the low frequency bands.