CNH Roundtable Talk by Dr Erin Goddard

Talk Title: Using MEG to measure the dynamics of visual perception

Talk Abstract: Visual perception depends not only on stimulus-driven input, but also on ‘top-down’ factors such as attention, task, and prior experience. In this talk I will present a few recent projects where we measured the interaction between stimulus-driven and top-down factors using magnetoencephalography (MEG) combined with measures of stimulus-related information exchange between regions. Most recently, we used this approach to investigate binocular rivalry (BR), where conflicting images presented to each eye cannot be fused into a stable percept, and perception spontaneously oscillates between the two images. While BR has been studied extensively, the role of attention in the neural dynamics of BR remains unclear. We used MEG to compare the neural information about a dominant BR percept and the associated suppressed stimulus, and how attention modulates this relationship. Participants (N = 20) viewed a stimulus with a rivalrous and non-rivalrous component, alternating whether their attention was directed to the rivalrous or non-rivalrous component. We used classification analyses to quantify the amount of information about each stimulus component contained in the MEG signal over time. As expected, classifier accuracy is greater for the attended than the unattended non-rivalrous stimulus, from ~200ms post stimulus presentation. For the BR stimulus, we decoded the image content of both dominant and suppressed stimuli, finding that information about the suppressed stimulus was surprisingly robust. Information about the suppressed stimulus was lower than the dominant stimulus, but was less attenuated than the unattended non-rivalrous stimulus. Overall, the decoding dynamics are consistent with the onset of BR involving similar processes to engaging covert spatial attention.