Journal of experimental psychology: human perception and performance

We examined the nonveridicality of visual direction produced by monocular viewing. In Experiment 1, 19 subjects pointed to a small light and moved a small light to their subjective median plane. The extent of constant error under monocular and binocular viewing conditions differed in both tasks (p less than .001). The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm (p less than .01). Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of Hering's .001). The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm (p less than .01). Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of Hering's .001). The monocular-binocular difference was larger when the viewing distance was 25 cm than when it was 50 cm (p less than .01). Also, correlations between phoria and monocular-binocular differences ranged from .58 to .77, depending on viewing distances and tasks. The effects of phoria within the context of Hering's principle of visual direction can account for these results. In Experiment 2, the same subjects adapted to phoria-induced error by placing a finger over a monocularly viewed target. The difference in their pointing responses before and after the task were reliable (p less than .005), and the correlations between phoria and the pre- to posttest differences were .45 and .77, depending on the number of adaptation trials. We argue that all monocular experiments dealing with visual direction should control for these effects.     

Subjective staircase: a multiple wallpaper illusion

When observers binocularly fixate on an inclined sheet of paper with equally spaced dots, an apparent "staircase" is seen. We varied the inclination of the sheet, the spacing among the dots, and the viewing distance. The results indicate that (1) as the space and the inclination decreased, the number of apparent steps increased and the height of apparent steps decreased, and (2) as the distance and the inclination increased, the number of apparent steps decreased, and eventually the illusion disappeared. The nearest-neighbor rule and the extent of the vertical horopter inclination explain the characteristics of the illusion.     

Motion parallax judgements of depth as a function of the direction and type of head movement

We compared the relative effectiveness of rotating or translating the head, either horizontally or vertically, on the perception of depth resulting from motion parallax. Using Rogers and Graham's (1979) paradigm, we yoked the movement of random dots on a screen to movements of the head, simulating a corrugated surface. In two experiments, subjects nulled the apparent depth or motion seen in the display. Horizontal head movements yielded the most precise depth judgements, irrespective of whether the head translated or rotated. Motion thresholds were higher than those for depth and were independent of direction of head movement. In a third experiment, suprathreshold stimuli that simulated differing amounts of depth were used, and the subjects' perception of depth was virtually the same for all types and directions of head movement. In our stimulus situation, rotating or translating the head either vertically or horizontally produced motion parallax cues for depth that were equally effective. Our results also showed that, within a range, retinal image motion from head movement is converted into a depth signal and that above that range location constancy breaks down and motion is seen.     

The contraction rule and decision problems for logics without structural rules

This paper shows a role of the contraction rule in decision problems for the logics weaker than the intuitionistic logic that are obtained by deleting some or all of structural rules. It is well-known that for such a predicate logic L, if L does not have the contraction rule then it is decidable. In this paper, it will be shown first that the predicate logic FL_ec with the contraction and exchange rules, but without the weakening rule, is undecidable while the propositional fragment of FL_ec is decidable. On the other hand, it will be remarked that logics without the contraction rule are still decidable, if our language contains function symbols.     

Size-distance paradox with accommodative micropsia

Two experiments tested the hypothesis that the paradoxical relative distance judgment associated with the size-distance paradox is due to the visual system’s assuming equal linear size and perceiving a smaller angular size for the closer stimulus equal in visual angle. In Experiment I, two different sized coins were presented successively, and 16 Ss were asked to give ordinal judgments of apparent distance and apparent size. When the two coins depicted the same figures, the closer stimulus was judged to be farther and smaller, more frequently, than when two coins depicted different figures. In Experiment II, 48 Ss were asked to give ratio judgments of apparent distance, apparent linear size, and apparent angular size for two stimuli which were presented successively. When the stimuli were of equal shape, the mean ratios of the far stimulus to the near stimulus were smaller for the apparent distance but larger for the apparent linear size and angular size than when the stimuli were of different shape. The obtained distance judgments were consistent with the hypothesis but the obtained judgments of linear size and angular size were not.     

Apparent movement and change in perceived location of a simulus produced by a change in accommodative vergence

Using a psychophysical method of adjustment, 175 Ss, ranging in age from 3 to 20 years, made four adjustments each of a luminous line to subjective vertical, horizontal, and 45-deg tilts in the dark. There were no significant differences in mean errors of adjustment to the vertical and horizontal over the ages tested. There were significant differences in intra-S variability of adjustment to the horizontal and vertical, with the greatest improvement occurring before age 10. Older children and adults produced significantly larger mean errors of adjustment to the 45-deg tilt than did the younger children; but the variability of settings by younger children was very high, indicating that they did not discriminate the 45-deg tilt more accurately than the older groups. The intra-S variability at all ages showed that adjustment was more accurate to the horizontal and vertical than to the 45-deg tilt.     

Depth perception as a function of motion parallax and absolute-distance information

The results of three experiments demonstrated that the visual system calibrates motion parallax according to absolute-distance information in processing depth. The parallax was created by yoking the relative movement of random dots displayed on a cathode-ray tube to the movements of the head. In Experiment 1, at viewing distances of 40 cm and 80 cm, observers reported the apparent depth produced by motion parallax equivalent to a binocular disparity of 0.47 degree. The mean apparent depth at 80 cm was 2.6 times larger than at 40 cm. In Experiment 2, again at viewing distances of 40 cm and 80 cm, observers adjusted the extent of parallax so that the apparent depth was 7.0 cm. The mean extent of parallax at 80 cm was 31% of that at 40 cm. In Experiment 3, distances ranged from 40 cm to 320 cm, and a wide range of parallax was used. As distance and parallax increased, the perception of a rigid three-dimensional surface was accompanied by rocking motion; perception of depth was replaced by perception of motion in some trials at 320 cm. Moreover, the mean apparent depths were proportional to the viewing distance at 40 cm and 80 cm but not at 160 cm and 320 cm.     

The lost direction in binocular vision: the neglected signs posted by Wells, Towne, and LeConte

Studies of vision have informed theories first in philosophy and then in psychology. Over the centuries, an increasing number of phenomena have been enlisted to refute or reinforce particular theories. Nowhere has this been more evident than in binocular vision. How we see a single world with two eyes is one of the oldest and most consistently studied topics in vision research. It has been discussed at least since the time of Aristotle and it has been examined experimentally since the second century, when Ptolemy defined lines of visual correspondence for the two eyes. Prior to Wheatstone's invention of the stereoscope in the 1830s, binocular vision had been studied in terms of visual directions. The stereoscope established distance (or depth) as well as direction as dimensions of binocular vision. Subsequently, depth rather than direction has been the principal concern of students of vision, and texts in English devoted to analyses of direction rather than depth have been neglected. We examine the experiments on binocular visual direction conducted by Wells before Wheatstone, and by Towne and LeConte after him, and discuss the reasons for their neglect.     

Kanizsa's shrinkage illusion produced by a misapplied 3-D corrective mechanism

In order to include the monocular areas from the left and the right eye in the cyclopean view, the visual system displaces the occluded elements which would result in a horizontal elongation of the shape but does not occur thanks to a correction mechanism which preserves the shape. We hypothesised that this mechanism causes Kanizsa's amodal shrinkage illusion (the apparent elongation of a partially occluded square) when it is incorrectly applied by the visual system to a two-dimensional stimulus. Four experiments tested this hypothesis: (i) one-eyed observers were less susceptible to the illusion than people with normal binocular vision because, for them, the correction for shape is unnecessary; (ii) the illusion was stronger with binocular than with monocular vision since binocularity induces the visual system to correct for the shape distortion; (iii) the illusion diminished when the stimulus was rotated 90 degrees given that displacement and compression are not required for vertical occlusion; (iv) the magnitude of the illusion was a function of the width of the occluder because, as previous research has shown, the edges of a partially occluded square are less displaced the farther they are from the edges of the occluder. The data from the four experiments support our hypothesis even though no condition was able to eliminate the illusion; other possible causes are discussed.     

The stereoscopic views of Wheatstone and Brewster

Summary The study of stereopsis, made possible by the invention of the stereoscope, freed binocular vision from the yoke of monocular phenomena. Wheatstone used this freedom to determine the factors involved in the perception of size and distance, and interpreted them within a cognitive framework. He devised an adjustable stereoscope which allowed him to apply the systematic experimental procedures of physics to the phenomena of depth perception. Brewster, by contrast, tried to force the newly discovered binocular phenomena back into the mould of monocular vision, using the lever of visible direction. His interpretations of visual phenomena, be they monocular or binocular, could be reduced to the two fundamental laws of visible direction and distinct vision. While Wheatstone's cognitive approach influenced Helmholtz, and thereby modern cognitive theorists. Brewster's interpretations, based as they were in analyses of the retinal projection, find an echo in modern direct theorists.