Retinotopy and its modulation by attention in higher cortical areas studied with structured motion stimuli

Abstract

Using action videos as stimuli in fMRI experiments, we have recently found retinotopic responses in parietal, temporal and even frontal cortex in the human brain. We are now interested in the nature of these responses — e.g., whether the activity is driven primarily by the stimuli, and whether attention is necessary. We developed novel stimuli which are complex enough to drive maps in these high-level areas, but are manipulable in terms of low-level visual features and are amenable to attentional manipulation. We use moving objects defined by point-lights (primarily point-light biological motion, but also non-biologically moving, translating objects composed of point-lights) in phase-encoded polar angle mapping paradigms. These stimuli are almost as effective as video stimuli in activating multiple maps outside of visual cortex. Here we ran an experiment in which the stimuli rotated in a polar angle wedge and the background was filled either with control stimuli (scrambled motion) or identical stimuli, such that the whole visual field was stimulated at all times. Subjects either attended to the stimuli (performed a task on the polar angle stimuli) or ignored the stimuli (performed an unrelated attentionally demanding task at fovea). With control stimuli in the background, well-defined maps were found in parietal, lateral and ventral temporal cortex, and in some subjects in frontal cortex under the attend condition. Attention appears necessary for the activation of these maps, except in the vicinity of area MT/MST, where attention increased the response but strong retinotopy was seen even when the stimuli were completely ignored. Finally, even when the background contained identical stimuli as the wedge, significant retinotopy was observed in temporal, parietal and frontal cortex in the attend condition. Thus retinotopic responses are affected both by the complexity of stimuli and by attention, with attention seemingly as important as visual stimuli in evoking activity in some areas.

Footnotes

 This research was supported by NSF BCS 0224321 to Sereno.