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. In three experiments, observers judged whether the changes in two successive visual sequences followed the same or different rhythms. We assessed temporal representations by measuring the extent to which both task-irrelevant auditory information and task-irrelevant visual information interfered with rhythm discrimination. Incongruent auditory information significantly disrupted task performance, particularly when presented during encoding; by contrast, varying the nature of the rhythm-depicting visual changes had minimal impact on performance. Evidently, the perceptual system automatically and obligatorily abstracts temporal structure from its visual form and represents this structure using an auditory code, resulting in the experience of "hearing visual rhythms."

Contour interpolation mechanisms allow perception of bounded objects despite incomplete edge information. Here, we introduce a paradigm that maps interpolated contours as they unfold over time. Observers localize dots relative to perceived boundaries of illusory, partly occluded, or control stimuli. Variations in performance with dot position and processing time reveal the location and precision of emerging contour representations. Illusory and occluded contours yielded more proficient dot localization than control stimuli containing only spatial cues, suggesting performance based on low-level representations. Further, illusory contours exhibited a distinct developmental time course, emerging over the first 120 ms of processing. These experiments establish the effectiveness of the dot localization paradigm for examining interpolated edge representations, contour microgenesis, and the underlying processing mechanisms.

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The completion of partly occluded objects appears instantaneous and effortless, but empirically takes measurable time. The current study investigates how amount of occlusion affects the time course and mechanisms of visual completion. Experiment 1 used a primed-matching paradigm to determine completion times for objects occluded by various amounts. Experiments 2 and 3 used a dot-localization paradigm to probe completed contour representations for a qualitative shift above some spatial limit. The results demonstrate that time to completion rises with amount of occlusion. Nonetheless, the visual system can complete highly occluded objects, even when the occlusion renders visible contours nonrelatable. Furthermore, prolonged completion times for highly occluded objects do not result from a breakdown of low-level interpolation processes: The same contour completion mechanism operates on objects occluded by different spatial extents.

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. That is, human vision groups elements that change according to the same global pattern, even if the changes themselves are not synchronous. This finding prompts an important, testable prediction concerning the neural mechanisms of binding: Patterns of neural spiking over time may be more important than absolute spike synchrony.