Distortions in length perception: visual field anisotropy and geometrical illusions

Brightness Perception in World-Centered Coordinates Assessed by Pupillometry

Subjective brightness perception reportedly differs among the peripheral visual fields owing to lower- and higher-order cognition. However, there is still a lack of information associated with subjective brightness perception in the world-centered coordinates, not in the visual fields. In this study, we aimed to investigate the anisotropy of subjective brightness perception in the world-centered coordinates based on pupillary responses to the stimuli in five locations by manipulating the world-centered coordinates through active (requiring head movement) and passive scenes (without head movement) in a virtual reality environment. Specifically, this study aimed to elucidate if there is an ecological advantage in the five different locations in the world-centered coordinates. The pupillary responses to glare and halo stimuli indicated that the brightness perception differed among the five locations in the world-centered coordinates. Furthermore, we found that the pupillary response to stimuli at the top location might be influenced by ecological factors (such as from the bright sky and the sun's existence). Thus, we have contributed to the understanding of the extraretinal information influence on subjective brightness perception in the world-centered coordinates, demonstrating that the pupillary response is independent of head movement.

Anisotropy in the peripheral visual field based on pupil response to the glare illusion

Visual-field (VF) anisotropy has been investigated in terms of spatial resolution of attention, spatial frequency, and semantic processing. Brightness perception has also been reported to vary between VFs. However, the influence of VF anisotropy on brightness perception using pupillometry has not been investigated. The present study measured participants' pupil size during glare illusion, in which converging luminance gradients evoke brightness enhancement and a glowing impression on the central white area of the stimulus, and halo stimuli, in which the same physical brightness of the glare illusion is used with a diverging luminance pattern. The results revealed greater stimulus-evoked pupillary dilation and glare-related dilated pupil reduction in the upper VF (UVF) compared with other VFs and halo-related pupillary changes, respectively. The stimulus-evoked pupillary dilation was affected by poor contrast sensitivity. However, owing to the superior cognitive bias formed by statistical regularity in natural scene processing of the glare illusion in the UVF, we found reduced pupillary dilation compared with the response to halo stimuli and the response from other VFs. These findings offer valuable insight into a method to reduce the potential glare effect of any VF anisotropy induced by the glare effect experienced in daily vision. An important practical implication of our study may be in informing the design of applications aimed at improving nighttime driving behavior. We also believe that our study makes a significant contribution to the literature because it offers valuable insights on VF anisotropy using evidence from pupillometry and the glare illusion.

Bimanual thumb-index finger indications of noncorresponding extents

Two experiments tested a prediction derived from the recent finding that the Oppel-Kundt illusion - the overestimation of a filled extent relative to an empty one - was much attenuated when the empty part of a bipartite row of dots was vertical and the filled part horizontal, suggesting that the Horizontal-vertical illusion - the overestimation of vertical extents relative to horizontal ones - only acted on the empty part of an Oppel-Kundt figure. Observers had to bimanually indicate the sizes of the two parts of an Oppel-Kundt figure, which were arranged one above the other with one part vertical and the other part tilted -45°, 0°, or 45°. Results conformed to the prediction but response bias was greater when observers had been instructed to point to the extents' endpoints than when instructed to estimate the extents' lengths, suggesting that different concepts and motor programs had been activated.

The Oppel-Kundt Illusion and Its Relation to Horizontal-Vertical and Oblique Effects

The Oppel-Kundt illusion consists in the overestimation of the length of filled versus empty extents. Two experiments explored its relation to the horizontal-vertical illusion, which consists in the overestimation of the length of vertical versus horizontal extents, and to the oblique effect, which consists in poorer discriminative sensitivity for obliquely as opposed to horizontally or vertically oriented stimuli. For Experiment 1, Kundt's (1863) original stimulus was rotated in steps of 45° full circle around 360°. For Experiment 2, one part of the stimulus remained at a horizontal or vertical orientation, whereas the other part was tilted 45° or 90°. The Oppel-Kundt illusion was at its maximum at a horizontal orientation of the stimulus. The illusion was strongly attenuated with L-type figures when the vertical part was empty, but not enhanced when this part was filled, suggesting that the horizontal-vertical illusion only acts on nontextured extents. There was no oblique effect.

Spatial dynamics of the eggs illusion: Visual field anisotropy and peripheral vision

The eggs illusion is a visual phenomenon in which bright circular patches located at the midpoints between the intersections of a dark grid are perceived as being elongated along the direction orthogonal to the grid line. In the four experiments we report here, we explored the spatial properties of the eggs illusion by manipulating retinal eccentricity and the location of the stimulus in the visual field. In Experiment 1, we examined whether central and peripheral configurations affected the illusory magnitude. In Experiment 2, we varied the spatial location of grid patterns and found that the eggs illusion was intensified when the pattern was presented in the horizontal, not vertical or diagonal position, relative to the fixation. In Experiment 3, we varied the retinal eccentricity of the pattern along the horizontal meridian and found that the illusion was enhanced in the retinal periphery. In Experiment 4, we manipulated the size of the stimulus and found that peripheral enhancement of the eggs illusion was more apparent for a larger pattern. The visual field anisotropy and the peripheral enhancement of the eggs illusion are discussed in relation to mechanisms underlying grid-induced illusions.