Tadasu Oyama

Perceived size and perceived distance in stereoscopic vision and an analysis of their causal relations

Effects of visual angle and convergence upon the perceived sizes and perceived distances of a familiar object (playing card) and a nonrepresentational object (blank white card) were investigated by means of a projector stereoscope with polarizing filters. The results obtained with six Ss indicated that size estimates increased nearly proportionally as the visual angle increased and decreased nearly linearly as the convergence increased. Distance estimates decreased nearly linearly as either the visual angle or the convergence increased. The ratio of the size estimate to the distance estimate for a given visual angle was almost constant irrespective of convergence. In this sense, the size-distance invariance hypothesis held. No clear effect of familiarity was found. Partial correlations were used to discriminate direct and indirect causal relationships between the stimulus variables and perceptual estimates. Both perceived size and perceived distance were found to be determined directly by the two stimulus variables, but to be mutually related only indirectly.

Determinants of the Zöllner illusion

SummaryEffects of various stimulus variables on the Zöllner illusion were investigated. 1) The illusion was maximal when both the stimulus figure and the comparison stimulus were oriented 45 degrees to the vertical. 2) It decreased as the gap between the oblique lines and the parallel lines increased, reaching zero at a gap of 24 to 48 min. 3) It increased as the length of the oblique lines increased and reached an asymptote when the perpendicular distance from the end of the oblique lines to the parallel lines was about 45 min. 4) It always varied systematically with the intersect angle, but the optimal angle varied from 15 to 30 degrees according to the conditions of the gap and the length of oblique lines. 5) Considerable illusions were obtained even when the stimulus figure was reduced to a single line intersected by oblique lines. 6) Negative illusions were obtained with the intersect angle of 10 degrees. 7) These results supported a view that the Zöllner illusion is caused by neural interactions among direction analyzers in the cortex.

Feature Analysers, Optical Illusions, and Figural Aftereffects

Simple displacement models cannot explain some aspects of optical illusions and figural aftereffects. The orientation-detector interaction model proposed by Blakemore and others is more suitable to explain many aspects of the Zöllner illusion, positive and negative illusions, the effect of gap between the inducing and test lines, and the anisotropy of illusions. If we hypothesize size detectors whose tuning width and distribution steps are proportional to logarithmic size, interactions between them explain well the fact that the Delboeuf illusion and figural aftereffects of circles are determined by the size ratio of the inducing to test circle, not by the absolute distance between the contours of these circles.

A behavioral study of color mixture in the carp

Abstract Twelve carp were trained to discriminate yellow lights from red and green lights, each obtained with an interference filter of narrow band. In this training, the intensity of yellow light was randomly varied among three levels to avoid the possibility that brightness rather than hue was the response cue. The carps responded to some red-green mixtures in the same way as they did to yellow. The distribution curve of response frequency to red-green mixtures of various ratios had a peak approximately at the same ratio obtained by human subjects matching to the yellow light. It is concluded that the present experiment gives us clear evidence of color mixture in the carp, but the coincidence of the peak of their response frequency with the results of human hue matches was probably fortuitous.

Perceptual grouping between successively presented stimuli and its relation to visual simultaneity and masking.

SummaryA 4×4 matrix of dots was presented by a tachistoscope. The first and the third columns of the stimulus pattern were presented first for 20 ms and then the second and the fourth columns were presented for 20 ms with SOAs of 0 to 170 ms. Luminous dots on a dark background, black dots on a white background, and black dots and small outline circles on a white background were used in Experiments I, II, and III, respectively. In each experiment, 5 Ss were asked to report whether the stimulus dots were seen as 4 horizontal rows or 4 vertical columns, and whether they were seen simultaneously or successively. The experimental results showed that the time range of successive grouping was nearly the same as that of perceptual simultaneity in Experiments I and II, but was much greater than the latter in Experiment III where the similarity factor favored successive grouping. Successive grouping generally occurred in the same time range with visual masking of dot patterns by random dots, temporal organization of patterns from successive stimulus elements. But the time range was generally wider than those of contrast reduction caused by temporal luminance summation, metacontrast, and apparent movement.

Role of convergence and binocular disparity in size constancy

SummaryThe effect of convergence on the perceived size of a light disk presented against a dark background was investigated by means of a projector stereoscope with polarizing filters. The results obtained with four subjects indicate that the logarithm of matched size decreases linearly as the convergence angle increases. The effect of binocular disparity was also examined by presenting a vertical bar beside the disk, but this did not add to the convergence effect. The results of a previous study on binocular disparity were reinterpreted as an effect of convergence difference between two objects. Implications of the present findings to the phenomenon of size constancy were discussed.ZusammenfassungDer Effekt der Konvergenz auf die wahrgenommene Größe einer gegen einen dunklen Hintergrund dargebotenen Lichtscheibe ist durch ein Projektorstereoskop anhand Polarisationsfiltern untersucht worden. Die Ergebnisse, die mit vier Versuchspersonen erworben wurden, zeigen, daß der Logarithmus der subjektiv gleichgestellten Größe sich linear mit zunehmendem Konvergenzwinkel verkleinert. Außerdem wurde der Effekt der Querdisparation durch das Darbieten eines vertikalen Lichtbalkens neben der Lichtscheibe untersucht; aber dieser war ohne Effekt. Die Ergebnisse einer vorhergehenden Untersuchung über die Querdisparation wurde neu interpretiert als ein Effekt der Konvergenzdifferenz zwischen zwei Objekten. Die Bedeutung des Versuches für das Phänomen der Größenkonstanz wurde erläutert.

Wavelength-specific brightness contrast as a function of surround luminance.

Abstract We studied the effect of a monochromatic surround of varying wavelength on the brightness of five monochromatic test fields using a binocular matching technique. The results showed that brightness reduction of the test field was greatest when the wavelength of the surround was similar to that of the test field, particularly within the three wavelength regions of red, green and blue. In addition, the slope of brightness reduction with increase in surround luminance was found to vary as a function of surround wavelength: also, the wavelength-selective brightness reduction was much more prominent for the higher luminance surrounds. A two-factor model with channel-specific and channel-nonspecific lateral inhibition is proposed.

A behavioristic analysis of Stevens magnitude estimation method

A procedure independently proposed by Oyama and Lewis for treating the data of magnitude estimation is discussed in relation to the Graham-Stevens controversy on the psychophysical methods. In this procedure, the critical value of the stimulus needed to make the subject report numbers equal to or greater than each integral number is sought, instead of the median or geometrical mean of numbers reported for each level of stimulus intensity. Stevens’ magnitude estimation method has no special advantage over the other cross-modality matching methods, and the subjective magnitude of number should be estimated if one wants to know real relations between stimulus intensities and sensory magnitudes in various modalities.