A novel speed illusion involving expansion and rotation patterns

Using random dot stimuli well controlled for dot speed, we found that the moving features in expanding patterns appear to move faster than those in rotating patterns. The illusion is well correlated with the strength of the global motion signal. For example, in displays where the number of motion directions defining the patterns is reduced, the magnitude of the illusion decreases. Similarly, the strength of the effect diminishes as dot density is reduced. In patterns where only wedge-shaped segments of the stimuli are left exposed, the difference in perceived speed increases with the angular size of the wedge. Stimulus placement relative to the fixation point has little effect on the persistence of this phenomenon-expansion patterns appear to contain elements of greater speed, independent of stimulus eccentricity. These results argue against a local explanation for this perceptual illusion, suggesting that the global motion pattern of the stimulus, per se, is responsible.     

The motion analogue of the Café Wall illusion

Detecting visual motion is computationally equivalent to detecting spatiotemporally oriented contours. The question addressed in this study is whether the illusory oriented contour in the space-space domain induces corresponding illusory motion perception. Two experiments were conducted. In experiment 1, the Café Wall pattern, which elicits a strong illusion of orientation (Café Wall illusion), was found to induce an illusion of motion when this pattern was converted to the space-time domain. The strength of the motion illusion depends on the mortar luminance and width, as for the Café Wall illusion. In experiment 2, the adaptation to this illusion of motion was found to induce a motion aftereffect in a static test, which indicates that a first-order-motion system contributes to the induction of the motion illusion. In fact, the motion-energy model was able to predict the strength of this motion aftereffect.     

The line–motion illusion: Attention or impletion?

When a brief lateral cue precedes an instantaneously presented horizontal line, observers report a sensation of motion in the line propagating from the cued end toward the uncued end. This illusion has been described as a measure of the facilitatory effects of a visual attention gradient (O. Hikosaka, S. Miyauchi, & S. Shimojo, 1993a). Evidence in the present study favors, instead, an account in which the illusion is the result of an impletion process that fills in interpolated events after the cue and the line are linked as successive states of a single object in apparent motion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceived location of two-dimensional patterns

The study attempted to test the possibility that the center of gravity of two-dimensional patterns is the cue used by a human observer for their localization. Four experiments were carried out. The first, using a matching procedure, required the localization of the center of irregular dot patterns, contour and filled polygons which varied in size and orientation. In the other three experiments the subjects had to point to briefly exposed dot patterns in which overall shape (convex and concave in Expts 2 and 3) and dot density (Expt 4) were manipulated. The performance of these direct localization tasks was found to be as accurate as the performance in previous studies of indirect localization or regular patterns. The results consistently supported the claim that information about position of the center of gravity is used for the localization of visual objects.     

Global induced motion and visual stability in an optic flow illusion

When an expansion flow field of moving dots is overlapped by planar motion, observers perceive an illusory displacement of the focus of expansion (FOE) in the direction of the planar motion (Duffy and Wurtz, Vision Research, 1993;33:1481-1490). The illusion may be a consequence of induced motion, wherein an induced component of motion relative to planar dots is added to the motions of expansion dots to produce the FOE shift. While such a process could be mediated by local 'center-surround' receptive fields, the effect could also be due to a higher level process which detects and subtracts large-field planar motion from the flow field. We probed the mechanisms underlying this illusion by adding varying amounts of rotation to the expansion stimulus, and by varying the speed and size of the planar motion field. The introduction of rotation into the stimulus produces an illusory shift in a direction perpendicular to the planar motion. Larger FOE shifts were perceived for greater speeds and sizes of planar motion fields, although the speed effect saturated at high speeds. While the illusion appears to share a common mechanism with center-surround induced motion, our results also point to involvement of a more global mechanism that subtracts coherent planar motion from the flow field. Such a process might help to maintain visual stability during eye movements.     

Reducing two-dimensional rearfoot motion variability during walking

Although three-dimensional movement analysis is the preferred method of assessing rearfoot motion during gait, the high cost of equipment and the time required to use it often make it unreasonable or impractical in a clinical setting. The authors discuss a method of minimizing the variability of rearfoot motion measurements during walking, using two-dimensional analysis when three-dimensional is not available to the clinician.     

A halo visual illusion

A visual illusion consisting of transparent halos extending beyond the boundaries of rotating discs is reported. The effect can be obtained by rotating a variety of black-and-white discs at moderate speeds. It is not due solely to rods, as opposed to cones, and does not appear to be explainable in terms of intermittent stimulation of portions of visual fields of fixed visual angle.     

Perceptual organization of two-dimensional patterns.

The perceptual organization of image patterns is considered from 2 standpoints. First, a theoretical framework is presented from which computational models of perceptual organization can be constructed and tested. Second, a specific computational model for perceptual organization of line images is described. In this model, input images are first processed by a dense array of neurons that have properties consistent with recent analyses of single-neuron responses in primary visual cortex. Then, complex image structure is discovered by interleaved pattern-matching and grouping processes constrained by a generalized uniqueness principle. A series of 3-pattern grouping experiments was performed to test a restricted version of the model and to estimate critical parameters. Using the estimated parameters, an extended version of the model was tested by generating predictions for a series of textbook perceptual organization demonstrations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Constraints on the processing of rolling motion: The curtate cycloid illusion.

When a wheel rolls along a flat surface, a point on its perimeter traces a cycloid trajectory, forming a sequence of adjacent semicircle-like scallops. However, when mentally visualizing this point's trajectory, participants erroneously describe the point's path as looping back on itself between each scallop or phase of the cycloid, a phenomenon called the curtate cycloid illusion. The studies supported the hypothesis that the curtate cycloid illusion occurs because the cognitive system sometimes does not have sufficient resources for simultaneously processing 2 components of the motion: its translation and its rotation about its current instant center. Four experiments using computer-animated rolling wheels found that participants who were high in spatial ability were less susceptible to the curtate cycloid illusion than were low-spatial participants, that high-spatial participants were not susceptible to the illusion if they could control the animated wheel display, and that the illusion was substantially decreased if the opportunity to compute instant centers was reduced. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Ames window illusion: Perception of illusory motion by human infants.

The sensitivity of human infants, 5?-9 months of age, to the illusory oscillation of the Ames window was assessed in three experiments that employed some variant of the habituation–dishabituation and forced-choice preferential looking paradigms. In Experiment 1, three groups—5?, 7?, and 9 months of age—were given a visual choice between rotating rectangular and Ames windows after exposure to a rotating circular form. The two older groups preferred the Ames window. The results of Experiment 2 showed that this preference is not based on structural differences between the two windows. In Experiment 3, familiarization with an Ames window produced a preference for rotary motion while familiarization with a rectangular window produced a preference for oscillatory motion. These results suggest that sensitivity to the illusion emerges around 7? months of age, an outcome consistent with the emergence, at this time, of sensitivity to pictorial cues to depth. (PsycINFO Database Record (c) 2010 APA, all rights reserved)