Simultaneity and sequence in the perception of apparent motion.

Motion perception usually is accompanied by the phenomenological impression of sequence as objects move through successions of locations. Nonetheless, there is accumulating evidence that sequential information is neither necessary nor sufficient for perceiving motion. It is shown here that apparent motion is specified by counterchange rather than sequence-that is, by co-occurring toward- and away-from-background changes at two spatial locations, regardless of whether the changes are simultaneous or sequential.

Depth of interocular suppression associated with continuous flash suppression, flash suppression, and binocular rivalry.

When conflicting images are presented to the corresponding regions of the two eyes, only one image may be consciously perceived. In binocular rivalry (BR), two images alternate in phenomenal visibility; even a salient image is eventually suppressed by an image of low saliency. Recently, N.

Spatial grouping in human vision: temporal structure trumps temporal synchrony.

Temporal information promotes visual grouping of local image features into global spatial form. However, experiments demonstrating time-based grouping typically confound two potential sources of information: temporal synchrony (precise timing of changes) and temporal structure (pattern of changes over time). Here, we show that observers prefer temporal structure for determining perceptual organization.

The interaction between binocular rivalry and negative afterimages.

Afterimage formation, historically attributed to retinal mechanisms, may also involve postretinal process. Consistent with this notion are results from experiments, reported here, investigating the interaction between binocular rivalry and negative afterimages (AIs). In Experiment 1, one eye was exposed to a grating never consciously experienced by the observer because this grating remained suppressed in rivalry throughout induction (the exclusively dominant stimulus was designed to preclude formation of an AI).

Hearing what the eyes see: auditory encoding of visual temporal sequences.

When the senses deliver conflicting information, vision dominates spatial processing, and audition dominates temporal processing. We asked whether this sensory specialization results in cross-modal encoding of unisensory input into the task-appropriate modality. Specifically, we investigated whether visually portrayed temporal structure receives automatic, obligatory encoding in the auditory domain.

Mixed messengers, unified message: spatial grouping from temporal structure.

In dynamic visual environments, objects can differ from their backgrounds in terms of their associated temporal structure--the time course of changes in some stimulus property defining object and background. In a series of experiments, we investigated whether different "messengers" of temporal structure group into coherent spatial forms. Observers viewed arrays of Gabor patches in which different temporal structures designated figure and ground regions; extracting the figure required grouping across synchronized orientation, spatial frequency, phase, and/or contrast changes.

A common mechanism for the perception of first-order and second-order apparent motion.

A common mechanism for perceiving first-order, luminance-defined, and second-order, texture-contrast defined apparent motion between two element locations is indicated by: (1) transitivity--whether or not motion is perceived is inter-changeably affected by activationally equivalent luminance and contrast changes at each location, (2) local integration--whether or not motion is perceived depends on the net activation change resulting from simultaneous background-relative luminance and background-relative contrast changes at the same element location, and (3) inseparability--apparent motion is not perceived through independent first- or second-order mechanisms when luminance and contrast co-vary at the same location. These results, which are predicted by the response characteristics of directionally selective cells in areas V1, MT, and MST, are not instead attributable to changes in the location of the most salient element (third-order motion), attentive feature tracking, or artifactual first-order motion. Their inconsistency with Lu and Sperling's [Lu, Z.

Physics embedded in visual perception of three-dimensional shape from motion.

Visual perception, and by implication underlying neural events, can become unstable when optical information specifying objects is ambiguous. Here we report that one striking form of instability-perceived three-dimensional structure-from-motion (SFM)-can be stabilized when an otherwise ambiguous object appears within a context implying frictional interactions with another rotating object; violations of physical conditions specifying friction disrupt stabilization. Evidently, information about frictional interaction is embedded within neural mechanisms specifying SFM.

Multiplicative nonlinearity in the perception of apparent motion.

Evidence is reported indicating that the perception of apparent motion is better predicted by the multiplicative combination of luminance changes at two element locations than by the sum or squared-sum of the luminance changes, or by the motion energy in the stimulus. Because the results were obtained with a stimulus for which motion was specified by simultaneous luminance changes, they support a Reichardt-style motion detector model, but without the asymmetrical delay specified by current versions. Motion direction in the modified model relies on asymmetrical stimulus information rather than asymmetrical delay.

Detection of counter-changing contrast: second-order apparent motion without postrectification motion-energy analysis or salience mapping/feature tracking.

The perception of 2nd-order, texture-contrast-defined motion was studied for apparent-motion stimuli composed of a pair of spatially displaced, simultaneously visible checkerboards. It was found that background-relative, counter-changing contrast provided the informational basis for the perception of 2nd-order apparent motion; motion began where contrast changed toward the contrast value of the background checkerboard and ended where contrast changed away from the background value. The perceived apparent motion was not attributable to either postrectification motion-energy analysis or salience-mapping/feature-tracking mechanisms.

Visual motion retards alternations between conflicting perceptual interpretations.

When the visual system is faced with conflicting or ambiguous stimulus information, visual perception fluctuates over time. We found that perceptual alternations are slowed when inducing stimuli move within the visual field, constantly engaging fresh, unadapted neural tissue. During binocular rivalry, dominance durations were longer when rival figures moved compared to when they were stationary, yielding lower alternation rates.

Perceptual consequences of centre-surround antagonism in visual motion processing.

Centre-surround receptive field organization is a ubiquitous property in mammalian visual systems, presumably tailored for extracting image features that are differentially distributed over space. In visual motion, this is evident as antagonistic interactions between centre and surround regions of the receptive fields of many direction-selective neurons in visual cortex. In a series of psychophysical experiments we make the counterintuitive observation that increasing the size of a high-contrast moving pattern renders its direction of motion more difficult to perceive and reduces its effectiveness as an adaptation stimulus.