When participants make part-whole proportion judgments, systematic bias is commonly observed. In some studies, small proportions are overestimated and large proportions underestimated; in other studies, the reverse pattern occurs. Sometimes the bias pattern repeats cyclically with a higher frequency (e.g., overestimation of proportions less than .25 and between .5 and .75; underestimation otherwise). To account for the various bias patterns, a cyclical power model was derived from Stevens' power law. The model proposes that the amplitude of the bias pattern is determined by the Stevens exponent, beta (i.e., the stimulus continuum being judged), and that the frequency of the pattern is determined by a choice of intermediate reference points in the stimulus. When beta < 1, an over-then-under pattern is predicted; when beta > 1, the under-then-over pattern is predicted. Two experiments confirming the model's assumptions are described. A mixed-cycle version of the model is also proposed that predicts observed asymmetries in bias patterns when the set of reference points varies across trials.

Previous research has shown that stimulation of the central visual field with radial flow patterns (produced by forward motion) can induce perceived self-motion, but has failed to demonstrate effects on postural stability ofeither radial flow patterns or lamellar flow patterns (produced by horizontal translation) in the central visual field. The present study examined the effects of lamellar and radial flow on postural stability when stimulation was restricted to the central visual field. Displays simulating observer motion through a volume of randomly positioned points were observed binocularly through a window that limited the field of view to 15 0 • The velocity of each display varied according to the sum of four sine functions of prime frequencies. Changes in posture were used to measure changes in perceived spatial orientation. A frequency analysis of postural sway indicated that increased sway occurred at the frequencies of motion simulated in the display for both lamellar and radial flow. These results suggest that both radial and lamellar optic flow are effective for determining spatial orientation when stimulation is limited to the central visual field.The importance of optical information for determining spatial orientation of the observer has been investigated using a variety of measures. Some studies have used subjective measures, such as the latency and duration of induced self-motion, the angle of induced tilt of a vertical line, and magnitude estimates of the speed of induced motion. Other studies have used more objective measures, such as postural adjustment or sway.Brandt, Dichgans, and Koenig (1973) examined the effects of the area and location of visual stimulation and angular velocity on the perception of self-motion about a vertical axis (circular vection). Subjects were required to make magnitude estimates of the speed of perceived self-motion while seated inside a large vertical drum with vertical lines painted on the inner walls. An increase in drum velocity resulted in an increase in the estimated speed of self-rotation. When stimulation was limited to the central visual field and the area of stimulation was less than 30°in diameter, subjects reported little or no induced rotation. These results suggest that a wide field of view is necessary for the perception of self-motion to occur from visual stimulation.A second study that found evidence indicating the dominance of peripheral stimulation examined induced rotation about the line of sight. Held, Dichgans, and Bauer (1975) a large rotating disk covered with a random pattern of texture elements. The retinal eccentricity measured from the point of fixation to the center of the sector varied from 18°to 63 0. Angular velocity of the disk and the area of stimulation were also varied. The subjects' task was to adjust the tilt of a line so that it always appeared vertical. Deviations of the line from true vertical were measured. The magnitude of perceived tilt increased with increasing angular velocity for velocities of 40 0 /sec and less. Pe...

A metric representation of shape is preserved by a Fourier analysis of the cumulative angular bend of a shape's contour. Three experiments examined the relationship between variation in Fourier descriptors and judgments of perceptual shape similarity. Multidimensional scaling of similarity judgments resulted in highly ordered solutions for matrices of shapes generated by a Fourier synthesis of a few frequencies. Multiple regression analyses indicated that particular Fourier components best accounted for the recovered dimensions. In addition, variations in the amplitude and the phase of a given frequency, as well as the amplitudes of 2 different frequencies, produced independent effects on perceptual similarity. These results suggest that a Fourier representation is consistent with the perceptual similarity of shapes, at least for the relatively low-dimensional Fourier shapes considered.

When tasks are performed, other tasks are postponed, at least implicitly. Little is known about how task sequencing is determined. We examined task sequencing in object transfer tasks for which either task could easily or logically come before the other. The task was to transfer ping pong balls from two buckets into a bowl. To perform the task, participants walked down a corridor, picked up one of two buckets (their choice), carried it to the end of the corridor, transferred the balls from the bucket into a bowl, carried the bucket back to the start position, and then did the same with the other remaining bucket. As in an earlier study where just one of two buckets had to be carried to the end of a corridor (Rosenbaum et al. Psychol Sci 25(7):1487-1496, 2014), participants showed a marked tendency to start with the near bucket. The near-bucket preference was modulated only to a small extent by the number of balls that could be emptied into the bowl. The relative lack of importance of the number of balls to be transferred (to finish the first task more quickly or to get closer to the end goal of transferring all balls into the bowl) was further demonstrated by the fact that the effect of the number of balls to be transferred did not depend on how the emptying was supposed to occur (by pouring the balls or placing the balls one at a time into the bowl), or by whether the instruction focused on filling the bowl or emptying the buckets. The results suggest that the near-bucket preference reflects a strong inclination to start the task (sub-goal) as soon as possible rather than complete the task (sub-goal) as soon as possible. Starting the task as soon as possible may be related to the affordance triggered by the sight of the near object or by the freedom to perform without having to inhibit a reach for a bucket when the performer is empty-handed. Starting a task sooner may free up cognitive resources for subsequent decision-making.

The Stevens exponent (beta) can be obtained from proportion estimation judgments using the power model. In this article, the authors extend that model to proportion production, in which the relative magnitudes of 2 stimuli are adjusted to correspond to a numeric proportion (e.g., 1/4 or .25). The model predicts that when beta < 1, small proportions are underproduced, and large proportions are overproduced, but it predicts the reverse when beta > 1, which is the opposite of the predicted patterns for estimation. Eight participants estimated and produced magnitudes and proportions with spatial volume (beta < 1; Experiment 1) and color saturation (beta > 1; Experiment 2). The model's predictions were generally supported. An extension of the model using reference points can account for multicycle patterns shown by some participants.

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Most theoretical approaches to perception of heading rely on the directions of image velocity vectors as the primary source of heading information. The research described in this article examined an additional source of information for determining heading: distributions of image velocity magnitudes. Displays simulated observer motion relative to rigid three-dimensional environments. Depth was distributed nonuniformly such that image velocity magnitudes provided, for some display conditions, conflicting heading information relative to the radial directions of the flow field. Results indicated that image velocity magnitudes influenced heading performance, suggesting that the perception of heading is not based solely on the radial structure of the directions of image flow.

Owen, Wolpert, and Warren (1984) proposed that egospeed may be perceived from global optical flow rate, discontinuity rate, or both. Previous psychophysical research found that both sources of information influence judgments of acceleration and control of egospeed, but that discontinuity rate dominated. However, the validity of these results is questionable due to problems with the visual stimuli used, such as confounding of discontinuity rate with proximal flow rate and low frame rates. The current study examined the relative contributions of global optical flow rate and discontinuity rate to perception of accelerating self-motion with stimuli that lacked these problems. I found that global optical flow rate accounted for 60% of the variability in acceleration judgments, compared with 0.86% for discontinuity rate. This result indicates that discontinuity rate exerts only a minor influence, and global optical flow rate is the primary basis for perception of accelerating self-motion, and hence, egospeed.