No evidence for early modulation of evoked responses in primary visual cortex to irrelevant probe stimuli presented...

During rapid serial visual presentation (RSVP), observers often miss the second of two targets if it appears within 500 ms of the first. This phenomenon, called the attentional blink (AB), is widely held to reflect a bottleneck in the processing of rapidly sequential stimuli that arises after initial sensory registration is complete (i.e., at a relatively late, post-perceptual stage of processing). Contrary to this view, recent fMRI studies have found that activity in the primary visual area (V1), which represents the earliest cortical stage of visual processing, is attenuated during the AB. Here we asked whether such changes in V1 activity during the AB arise in the initial feedforward sweep of stimulus input, or instead reflect the influence of feedback signals from higher cortical areas.

EEG signals were recorded while participants monitored a sequential stream of distractor letters for two target digits (T1 and T2). Neural responses associated with an irrelevant probe stimulus presented simultaneously with T2 were measured using an ERP marker--the C1 component--that reflects initial perceptual processing of visual information in V1. As expected, T2 accuracy was compromised when the inter-target interval was brief, reflecting an AB deficit. Critically, however, the magnitude of the early C1 component evoked by the probe was not reduced during the AB.

Our finding that early sensory processing of irrelevant probe stimuli is not suppressed during the AB is consistent with theoretical models that assume that the bottleneck underlying the AB arises at a post-perceptual stage of processing. This suggests that reduced neural activity in V1 during the AB is driven by re-entrant signals from extrastriate areas that regulate early cortical activity via feedback connections with V1.