H. R. Schiffman

Role of vibrissae for depth perception in the rat (Rattus norvegicus)

Summary The role of the vibrissae in the visual cliff performance of rats was investigated. With a moderately low centre-board height, rats with their vibrissae removed show a marked preference for the optically shallow side of the apparatus. In contrast, intact rats do not exhibit a preference for either side. The results indicate that tactual cues are prepotent over visual ones for the rat when conflicting information from both sensory modalities is present.

The Role of Number and Familiarity of Stimuli in the Perception of Brief Temporal Intervals.

The influence of stimulus number and familiarity on judged duration were investigated. The stimuli were slides with different numbers of stimulus elements of a familiar or unfamiliar nature. The task was to reproduce the durations of the slides, each shown for four intervals: 5, 9, 13, and 17 sec. The results show that the number of stimulus elements presented within a given interval affected its perceived duration, although the familiarity of those elements (as defined herein) did not. Finally, the shorter intervals sampled here were overestimated and the longer intervals were underestimated, thereby supporting Vierordts law.

Contextual effects in duration experience

The role of contextual factors on duration estimates was investigated, employing 6 time intervals ranging from 15 to 35 sec (demarcated by the onset and termination of a display panel of lights). When compared with earlier research, the results suggest that duration estimates are affected by the context of the stimulus intervals with regard to other stimuli in the series. Specifically, those stimuli that were overestimated when they were the shortest members of the series were underestimated when they were the longest intervals of the stimulus series. In addition, a lengthening effect was observed: duration estimates increased over blocks of trials for all stimulus intervals.

The Poggendorff illusion: an illusion of linear extent?

In the standard version of the Poggendorff figure a transversal intersects two parallel verticals and the segment of the transversal between the two intersection points, A and B, is not shown. The two portions of the transversal outside the parallels then seem to be misaligned. Besides this illusion of direction, there is also an illusion of size, the distance AB being underestimated in the standard figure. The influence of configural components in determining this spatial distortion of the Poggendorff figure was examined by having subjects reproduce the inner oblique (at 45°) extent AB in variations of the figure. This distance was found to be underestimated in Poggendorff variations which contained parallel (vertical) components that formed an acute angle with AB; and the underestimation increased as the number of these components present in the figure increased. The distance AB was found not to be significantly distorted in figures which contained only those parallel (vertical) components that formed an obtuse angle with AB, yet their presence in the figure tended to counteract the underestimation. When the transversals were omitted, the underestimation was found to increase. The findings are interpreted in support of an explanation that reduces the Poggendorff effect to those factors which mediate the Müller-Lyer illusion.

The role of structural components in the Mueller-Lyer illusion

In order to assess the role of the structural components of the Mueller-Lyer illusion, subjects reproduced the central extent of standard Mueller-Lyer figures and configural variations. Illusory magnitude of the underestimated wings-in and overestimated wings-out figures was examined with selective amputations of the oblique wings and central line segment (shaft). Variations were presented at 0, 45, 90, and 135 deg from vertical. Orientation had no reliable effect on illusory magnitude. Elimination of the shaft effected a decrease in the apparent extent for all variations, presumably due to the addition of the filled-unfilled space illusory effect to the standard Mueller-Lyer effect. A second study corroborated this finding The decrease in apparent extent consequent to shaft removal occurred independently of any response factor. Selective wing removal differentially decreased the illusory magnitude of the standard Mueller-Lyer figures; this was discussed with regard to a dual-illusion hypothesis. Finally, variations that contained no intersecting lines produced a significant illusion in the direction of the standard Mueller-Lyer figures, suggesting the involvement of higher level, nonperipheral distortion mechanisms.

Temporal experience as a function of organization in memory

The relationship between memory organization and perceived duration was investigated in two experiments. Degree of organization of the memory representation for an interval was assumed to be inversely related to the complexity of the interval’s content. Organization was manipulated by presenting an ambiguous stimulus during the interval either with or without the aid of a code that simplified the stimulus. Subjects judged the duration of a 60-sec interval by the method of magnitude estimation and then recalled the interval’s contents. In both experiments, facilitating memory organization by presenting the simplifying code before the interval was found to shorten apparent duration. In the second experiment, presenting the code after the stimulus interval also significantly shortened apparent duration when compared with the “no-code” condition. In general, the results were consistent with Ornstein’s (1969) storage size notion of the experience of duration. Some limitations of the storage size hypothesis are discussed.

The perception of brief temporal intervals: power functions for auditory and visual stimulus intervals.

Two experiments were performed to examine the role of method of estimation and the employment of a standard stimulus on the judged duration of auditory and visual stimuli presented for brief temporal intervals (0.25 to 5.0 s). The results indicate that the relationship between judged and physical duration is nearly direct and linear. Psychophysical methodology and stimulus modality exerted little influence on the obtained power functions.

Poggendorff and Müller-Lyer Illusions: Common Effects

Previous investigations have shown that the magnitude of the Müller-Lyer illusion is a function of the linear and angular dimensions of the figure. If the Müller-Lyer and Poggendorff illusions share a common basis, then the magnitude of the Poggendorff illusion should similarly be a function of the analogous configural dimensions. A study is reported in which changes were made in the dimensions of the Poggendorff figure that are analogous to the dimensions of the Müller-Lyer figure: (i) the length of the parallel components (analogous to the wings of the Müller-Lyer figure); (ii) the length of the intertransversal extent (analogous to Müller-Lyer shaft length); and (iii) the angle formed between the parallel components and the intertransversal extent (analogous to the angle of wing attachment in the Müller-Lyer figure). The relationship between the magnitude of the illusion and the dimensions of the Poggendorff figure was found to be generally in line with previous findings relating to the Müller-Lyer illusion. Adaptation-level theory and the positive-context model accommodate the major findings of the present study.

The Many Illusions of the Müller-Lyer: Comparisons of the Wings-in and Wings-out Illusions and Manipulations of Standard and Dot Forms

The assumed role of peripheral distortion mechanisms in both wings-in and wings-out Müller-Lyer illusions was investigated by requiring subjects to reproduce the central extent of standard Müller-Lyer figures and dot variations. Illusory magnitude of the line and dot variations was also examined with increasing wing length and wing angle. A reduction in the overestimation for the wings-out illusion occurred with the removal of intersecting lines; the dot variations evidenced a significant overestimation effect. In contrast, no reliable decrease in underestimation was found with the removal of intersecting lines in the wings-in illusion, and both standard and dot variations were significantly underestimated. These results support a conclusion that the wings-in and wings-out Müller-Lyer illusions are two distinct illusions, and may be differentially determined at the loci of distortion within the visual system. Parallel changes in illusory magnitude were noted with configural manipulations of standard and dot wings-out illusions. However, standard and dot forms of the wings-in illusion were not equivalently affected by equivalent configural manipulations, which suggests that they are different illusions. Thus, the use of the wings-in dot variation to separate empirically peripheral from nonperipheral distortion mechanisms may be ill-advised.

The effect on the magnitude of the horizontal-vertical illusion of horizontal retinal eccentricity

Abstract An experiment was performed to examine the effect of horizontal eccentricity of the target stimulus on the magnitude of the horizontal-vertical illusion. The result was that the magnitude of the illusion increased from foveal to near peripheral locus of stimulation. The findings were discussed in relation to two structural explanations of the illusion, one involving dioptrics and the other the neuroanatomy of the eye.