Modification of depth judgment following exposures to magnification of uniocular image: Are changes in perceived absolute distance and registered direction of gaze involved?

Two studies were designed to determine whether the perceptual learning that has been demonstrated to occur during exposure to uniocular image magnification can be explained by either a modification in the perception of egocentric distance or the direction of gaze. Experiment 1 was designed to determine whether exposure to uniocular image magnification produces changes in perceived absolute distance. Experiment 2 tested the possibility that exposure to uniocular image magnification modifies the registration of direction of gaze. The results showed that, despite the occurrence of adaptive shifts in perceived depth, no significant changes in perceived absolute distance or in registered direction of gaze occur. These findings bolster confidence in the hypothesis that adaptation to uniocular image magnification is the result of a recalibration of retinal disparity.     

Interaction of Tremor and Magnification in a Motor Performance Task With Visual Feedback

In this study, the interaction between increased gain in the visual feedback loop and motor control of the periphery was investigated. Participants (N = 15) were asked to maintain a constant finger position while they used magnified visual feedback. The measure of the accuracy of each trial was the standard deviation (trial error) of the finger position. Trials performed under magnification had lower trial errors than trials without magnification. The change in trial error between trials with and without magnification proved greater than the difference between trials at any 2 magnifications. In contrast, the differences between individual subjects were often greater than the differences between performances at individual magnifications. At higher magnifications, performance seemed to be limited by the tremor; the ratio of trial error to tremor intensity was constant. When applied to microsurgery, the present results accord with those found in earlier research, including investigations that have found that the level of magnification used in microsurgery is not the most significant factor in achieving good results and that tremor is the limiting factor in microsurgical tasks.     

The effect of visual magnification and reduction on perceived hand size

The aim of the present study was to clarify the mechanisms underlying body understanding by examining the impact of visual experience (magnification and reduction) on perception of hand size and neutral external objects (squares). Independent groups of participants were asked to look through a 2× magnification lens, a ½-× reduction lens, or a control UV filter and to make visual size judgments about square stimuli and their hands. In Experiment 1, participants used a measuring device with unmarked wooden slats orientated in horizontal and radial/vertical space for their visual judgments. In Experiment 2, participants used an upright frontal slat for visual length judgments of their hands to eliminate any potential foreshortening in viewing the measurement apparatus. The results from the two experiments demonstrate that participants significantly underestimated both the square stimuli and their hands when they viewed them under a reduction lens. While overestimation and underestimation of squares was found for females in Experiment 2, males generally underestimated the squares. However, overestimation was not seen when the participants viewed their hands under a magnification lens. Implications of these findings are discussed.     

Magnification rate of objects in a perspective image to fit to our perception

Abstract: A landscape photograph may give a different impression from that formed at the real scene, with respect to the size and distance of objects. Researchers have reported that the perceived sizes and distances of objects in a photograph are not identical to those in a real space. In order to develop a method to create a graphic image that is close to our visual impression as seen in the real space, two experiments were conducted. In Experiment 1, we examined how the magnification rate of the perceived size to the object size on the retina varied with the viewing distance (range was from 1 m to 10 m). In Experiment 2, we examined whether transformation based on the magnification rate is effective for creating an image that matches the perceived size of the object at the scene. Our results indicate that the magnification rate is useful for transforming the perspective image to match our perception of the objects regardless of the viewing distance.     

Parallel,exhaustive processing underlies logarithmic search functions: Visual search with cortical magnification

Our lab recently found evidence that efficient visual search (with a fixed target) is characterized by logarithmic Reaction Time (RT) × Set Size functions whose steepness is modulated by the similarity between target and distractors. To determine whether this pattern of results was based on low-level visual factors uncontrolled by previous experiments, we minimized the possibility of crowding effects in the display, compensated for the cortical magnification factor by magnifying search items based on their eccentricity, and compared search performance on such displays to performance on displays without magnification compensation. In both cases, the RT × Set Size functions were found to be logarithmic, and the modulation of the log slopes by target–distractor similarity was replicated. Consistent with previous results in the literature, cortical magnification compensation eliminated most target eccentricity effects. We conclude that the log functions and their modulation by target–distractor similarity relations reflect a parallel exhaustive processing architecture for early vision.     

Steering toward a goal by equalizing taus

Steering toward a target can be controlled by equalizing the time-to-closure of the angle between the target and the direction of locomotion and the time-to-passage of the observer by the target. Two experiments required observers to steer through a computer-simulated environment toward a target depicted as either a floating cross that did not optically expand, a floating sphere that optically expanded or a grounded post that optically expanded. Experiment 1 revealed better performance in the post and sphere conditions, suggesting that steering is influenced by local optical expansion but not by perceived spatial target location or distance. Experiment 2 revealed differences in steering behavior between target types that suggested observers attempted to equalize time-to-closure and time-to-passage.     

The time course of response inhibition in masked priming

In two experiments, we studied the temporal dynamics of the response time effects of masked visual prime stimuli, as a function of stimulus eccentricity and size. Experiment 1 factorially varied prime-target congruency, eccentricity, and mask-target stimulus onset asynchrony. Early facilitative and late inhibitory effects of congruency were observed at all eccentricities, with temporal dynamics modulated by eccentricity. To test whether this dependence on eccentricity is due to cortical magnification, Experiment 2 varied stimulus size as well. Response inhibition time courses were influenced by size and eccentricity jointly, with no discernible difference when stimuli were matched for cortical magnification. Analysis of the individual time course data revealed that the timescale of inhibition changes with the strength of the cortical representation of the prime stimulus. This imposes constraints on possible models.     

Contrast thresholds for identification of numeric characters in direct and eccentric view

Aubert and Foerster (1857) are frequently cited for having shown that the lower visual acuity of peripheral vision can be compensated for by increasing stimulus size. This result is seemingly consistent with the concept of cortical magnification, and it has been confirmed by many subsequent authors. Yet it is rarely noted that Aubert and Foerster also observed a loss of the "quality of form." We have studied the recognition of numeric characters in foveal and eccentric vision by determining the contrast required for 67% correct identification. At each eccentricity, the lowest contrast threshold is achieved with a specific stimulus size. But the contrast thresholds for these optimal stimuli are not independent of retinal eccentricity as cortical magnification scaling would predict. With high-contrast targets, however, threshold target sizes were consistent with cortical magnification out to 6 degrees eccentricity. Beyond 6 degrees, threshold target sizes were larger than cortical magnification predicted. We also investigated recognition performance in the presence of neighboring characters (crowding phenomenon). Target character size, distance of flanking characters, and precision of focusing of attention all affect recognition. The influence of these parameters is different in the fovea and in the periphery. Our findings confirm Aubert and Foester's original observation of a qualitative difference between foveal and peripheral vision.     

Wilde's dot-row phenomenon as a special case of aniseikonia

Summary In this investigation on Wilde's dot-row phenomenon vertical lines were used instead of dots. If was found that within the conditions of these experiments the apparent rotation of the patterns increased with increasing difference between the width of the monocular patterns (magnification between 5% and 10%), and decreased with increasing distance between the lines of the patterns. This distance varied from 4 arcmin to 10 arcmin. The apparent rotation of the patterns could be expressed by the regression equation R=a–b₁+b₂M, in which is the distance between the lines of the patterns and M is the percentage of magnification of one of the patterns in relation to the other one. From this regression equation the apparent rotation in aniseikonic random-dot patterns could be predicted. It was concluded that Wilde's phenomenon can be considered as an aniseikonic depth effect inhibited by the equal distance between the lines of the pattern.     

Vertical disparity can alter perceived direction

It has been well established that vertical disparity is involved in perception of the three-dimensional layout of a visual scene. The goal of this paper was to examine whether vertical disparities can alter perceived direction. We dissociated the common relationship between vertical disparity and the stimulus direction by applying a vertical magnification to the image presented to one eye. We used a staircase paradigm to measure whether perceived straight-ahead depended on the amount of vertical magnification in the stimulus. Subjects judged whether a test dot was flashed to either the left or the right side of straight-ahead. We found that perceived straight-ahead did indeed depend on the amount of vertical magnification but only after subjects adapted (for 5 min) to vertical scale (and only in five out of nine subjects). We argue that vertical disparity is a factor in the calibration of the relationship between eye-position signals and perceived direction.     

Is prism adaptation "for" growth?

The assumption that prism adaptation mechanisms evolved for developmental plasticity was questioned by analyzing natural transformations (magnification, rotation, displacement) of the arm and shoulder. Accommodating ordinary movement was found to be a closer match to prisms than transformations caused by growth. In addition, overlap between equations of movement and growth may point to a distal function of adaptation that is very general.     

First-trial adaptation to prism exposure: artifact of visual capture

Terminal target-pointing error on the 1st trial of exposure to optical displacement is usually less than is expected from the optical displacement magnitude. The authors confirmed 1st-trial adaptation in the task of pointing toward optically displaced targets while visual feedback was delayed until movement completion. Measurement of head-shoulder posture while participants (N = 24) viewed the optically displaced field revealed that their shoulders felt turned in the direction opposite to the displacement (visual capture), accounting for all but about 4% to 10% of 1st-trial adaptation. First-trial adaptation was unrelated to realignment aftereffects. First-trial adaptation is largely an artifact of the asymmetry of the structured visual field produced by optical displacement, which induces a felt body rotation, thereby reducing the effective optical displacement.     

Estimator reliability and distance scaling in stereoscopic slant perception

When a horizontal or vertical magnifier is placed before one eye, a frontoparallel surface appears slanted. It appears slanted away from the eye with horizontal magnification (geometric effect) and toward the eye with vertical magnification (induced effect). According to current theory, the apparent slant in the geometric and induced effects should increase with viewing distance. The geometric effect does scale with distance, but there are conflicting reports as to whether the induced effect does. Ogle (1938 Archives of Ophthalmology 20 604-623) reported that settings in slant-nulling tasks increase systematically with viewing distance, but Gillam et al (1988 Perception & Psychophysics 44 473-483) and Rogers et al (1995 Perception 24 Supplement, 33) reported that settings in slant-estimation tasks do not. We re-examined this apparent contradiction. First, we conducted two experiments whose results are consistent with the literature and thus replicate the apparent contradiction. Next, we analyzed the signals available for stereoscopic slant perception and developed a general model of perceived slant. The model is based on the assumption that the visual system knows the reliability of various slant-estimation methods for the viewing situation under consideration. The model's behavior explains the contradiction in the literature. The model also predicts that, by manipulating eye position, apparent slant can be made to increase with distance for vertical, but not for horizontal, magnification. This prediction was confirmed experimentally.     

Age and individual differences in visuospatial processing speed: Testing the magnification hypothesis

Forty young adults and 40 older adults performed seven visuospatial information processing tasks. Factor analyses of the response times (RTs) yielded a single principal component with a similar composition in both age samples. For both samples, regressing the mean RTs of fast and slow subgroups for the seven tasks (18 conditions) on the corresponding mean RTs for their age group accounted for 99% of the variance. Taken together, these findings suggest that individual differences in processing time were largely task independent. The magnification hypothesis, a simple mathematical model of the interaction between age and ability, is presented. This model correctly predicts the finding that in both the young and the older adult groups, individual differences increased systematically with task difficulty. The magnification hypothesis also explains the regression parameters describing individual differences among young adults and predicts correctly that equivalent parameters describe individual differences among older adults. According to the magnification hypothesis, the RTs of slower individuals are more affected by aging than those of faster individuals, and slower individuals may be more at risk with respect to other biological insults (e.g., changes in health status) as well.     

Fractal-Scaling Properties as Aesthetic Primitives in Vision and Touch

Axiomathes - Natural forms, often characterized by irregularity and roughness, have a unique complexity that exhibit self-similarity across different spatial scales or levels of magnification. Our...     

Some consequences of stereoscopic depth constancy

Retinal disparity decreases in proportion to the square of the distance of the corresponding objective depth interval from the eyes. Up to a distance of 2 m, stereoscopic depth perception compensates well for this decrease in disparity with observation distance; for a given disparity, experienced depth increases approximately in proportion to the square of the observation distance. When disparities are artificially produced, by anaglyphs or vectograms, or by spectacles, they decrease only in proportion to the first power of the observation distance. The same is true when the Pulfrich effect gives rise to equivalents of disparity. Depth perception, however, compensates for the normal disparity loss. As a result, there should be a net gain in perceived depth approximately in proportion to the first power of observation distance. When perceived depth caused by horizontal magnification in one eye or by the Pulfrich effect was measured, it was found to increase approximately in proportion to observation distance.     

Planar motion permits perception of metric structure in stereopsis

A fundamental problem in the study of spatial perception concerns whether and how vision might acquire information about the metric structure of surfaces in three-dimensional space from motion and from stereopsis. Theoretical analyses have indicated that stereoscopic perceptions of metric relations in depth require additional information about egocentric viewing distance; and recent experiments by James Todd and his colleagues have indicated that vision acquires only affine but not metric structure from motion—that is, spatial relations ambiguous with regard to scale in depth. The purpose of the present study was to determine whether the metric shape of planar stereoscopic forms might be perceived from congruence under planar rotation. In Experiment 1, observers discriminated between similar planar shapes (ellipses) rotating in a plane with varying slant from the frontal-parallel plane. Experimental conditions varied the presence versus absence of binocular disparities, magnification of the disparity scale, and moving versus stationary patterns. Shape discriminations were accurate in all conditions with moving patterns and were near chance in conditions with stationary patterns; neither the presence nor the magnification of binocular disparities had any reliable effect. In Experiment 2, accuracy decreased as the range of rotation decreased from 80° to 10°. In Experiment 3, small deviations from planarity of the motion produced large decrements in accuracy. In contrast with the critical role of motion in shape discrimination, motion hindered discriminations of the binocular disparity scale in Experiment 4. In general, planar motion provides an intrinsic metric scale that is independent of slant in depth and of the scale of binocular disparities. Vision is sensitive to this intrinsic optical metric.     

Planar motion permits perception of metric structure in stereopsis.

A fundamental problem in the study of spatial perception concerns whether and how vision might acquire information about the metric structure of surfaces in three-dimensional space from motion and from stereopsis. Theoretical analyses have indicated that stereoscopic perceptions of metric relations in depth require additional information about egocentric viewing distance; and recent experiments by James Todd and his colleagues have indicated that vision acquires only affine but not metric structure from motion--that is, spatial relations ambiguous with regard to scale in depth. The purpose of the present study was to determine whether the metric shape of planar stereoscopic forms might be perceived from congruence under planar rotation. In Experiment 1, observers discriminated between similar planar shapes (ellipses) rotating in a plane with varying slant from the frontal-parallel plane. Experimental conditions varied the presence versus absence of binocular disparities, magnification of the disparity scale, and moving versus stationary patterns. Shape discriminations were accurate in all conditions with moving patterns and were near chance in conditions with stationary patterns; neither the presence nor the magnification of binocular disparities had any reliable effect. In Experiment 2, accuracy decreased as the range of rotation decreased from 80 degrees to 10 degrees. In Experiment 3, small deviations from planarity of the motion produced large decrements in accuracy. In contrast with the critical role of motion in shape discrimination, motion hindered discriminations of the binocular disparity scale in Experiment 4. In general, planar motion provides an intrinsic metric scale that is independent of slant in depth and of the scale of binocular disparities. Vision is sensitive to this intrinsic optical metric.     

The extent of Panum's area and the human cortical magnification factor

The horizontal extent of Panum's fusional area was measured by means of a single-vertical-line stimulus placed at thirty-two locations throughout the peripheral visual field. These results were transformed by using known values of the human cortical magnification factor (CMF), and the hypothesis that variations in the magnitude of Panum's area may be accounted for by variations in the CMF was tested. It was found that the increase in Panum's area with increasing stimulus eccentricity correlates well with the CMF, but that variations in the extent of Panum's area as a function of angular position around the line of sight do not correspond well with the CMF.