Attentional Scanning in Macaque Area V4

Abstract

Sensitivity to perception varies on a moment-to-moment basis. It has been shown to be dependent on the phase of spontaneous ongoing oscillations in the low frequency (alpha and theta) bands. When inputs arrive at this optimal phase, the representation of the stimulus is stronger which leads to beneficial processing. Studies have also revealed the existence of traveling waves in the monkey visual cortex and that covert visual attention samples stimuli in a theta-rhythmic way. We hypothesized that attention can scan different locations of an attended object which could lead to beneficial processing of different locations over time. This means the ‘optimal phase’ of neighboring neuronal populations will be systematically shifted in cortical space. In this project, we focused on looking at whether an optimal phase for processing exists by analyzing correlations between the amplitude of the evoked response and the prestimulus phase. We observed that, indeed, perception is associated with the prestimulus phase. We also developed and tested a method for phase estimation in the process. Developing this method was crucial in order to be able to estimate the phase reasonably well while dealing with the group delay problem. The role of traveling waves in attentional scanning can be explored in future analysis. It will help us understand the possible mechanisms by which attention scans different attended items (locations or objects or features).