Comparing Neural Correlates of Foveally and Peripherally Encoded Memories

Current consensus ascribes visual working memory to the maintenance of the incoming sensory signal through top-down feedback mechanisms, when the stimulus is no longer available. Crucially, we know from perception research that both feedforward and feedback mechanisms favor central over peripheral vision. Yet, it is currently unknown whether and how these biases impact visual working memory processes, such as encoding and maintenance. We, therefore, compared the neural correlates of foveally and peripherally encoded memories of oriented Gabor stimuli presented either at the centre of fixation or left/right-lateralized at 15° eccentricity. Behavioral, EEG and eye data were recorded from 30 participants who completed the task. Multivariate decoding analyses of the EEG data revealed clear dissociations across presentation location (foveal, peripheral) and time window (encoding, early maintenance, late maintenance period). During stimulus encoding, decoding was strong for foveal items, yet untraceable for peripheral items. Orientation information of peripheral items emerged only after stimulus offset, was location-specific, but of comparable strength as for foveal items, suggesting an equivalent involvement of feedback-based maintenance mechanisms for both central and peripheral items. Later during maintenance, the memory signal disappeared from the voltage data, and orientation information gradually emerged in alpha power instead. This transformation also included a conversion from spatially specific neural codes to a spatially generalized format. Moreover, transformed representations were accessible through impulse-driven perturbations, further unveiling the underlying memory state. We conclude that feedback mechanisms do not necessarily suffer from eccentricity. Furthermore, the eccentricity-driven dissociation between disparate sensory and common maintenance representations indicates that storage activity patterns as measured by EEG must reflect signals beyond the primary visual cortex.