Modulation of local and global motion responses by sustained visual attention

Abstract

Previous fMRI studies have shown that global motion responses in human MT+ depend on attention. Global motion responses in areas such as MT+ are fed by local motion detectors in first-tier visual areas. Here we used high-density EEG recording and dynamic optic flow stimuli to determine if attentional modulation has comparable effects at these two levels of processing. EEG recording allowed us to monitor directly both dot-related, local motion responses as well as global motion responses in several visual areas that were defined separately by functional MRI mapping.Responses were recorded when attention was directed to optic flow (during discrimination of changes in the coherence of the global motion: Motion task) or when it was diverted to a foveal letter discrimination task (during detection of a randomly oriented letter T in a matrix of randomly oriented L's: Letter task). The global-flow-related EEG response is about a factor of two smaller in the Letter task than in the Motion task. The local motion response was largest when flow was present and task relevant and was smallest when flow was absent and motion was task irrelevant. Attentional modulation of dot-related activity took two forms: a gain enhancement in hMT+ and a timing change in a range of areas extending from roughly the IPS to V1. The observation that attentional modulation of local motion responses is strongest in the presence of flow, suggests the presence of top-down influences of both flow and attention.

Supported by EY015790 and the Pacific Vision Foundation.

Footnotes

 Supported by EY015790 and the Pacific Vision Foundation