Feature selection in the human brain: electrophysiological correlates of sensory enhancement and feature integration

This study examined the latency and amplitude of cortical processes associated with feature-based visual selective attention, using frequency-domain and time-domain measures derived from dense-array electroencephalography. Participants were asked to identify targets based on conjunctions of three types of object features (color, size, and completeness). This procedure aimed to examine (1) the modulation of sensory responses to one or more stimulus features characterizing an object and (2) the facilitation and reduction effects associated with competing features, attended and unattended, in the same object. The selection negativity, an event-related potential measure of sensory amplification for attended features, showed a parametric increase of amplitude as a function of the number of attended features. Late oscillations in the gamma band range were also smaller for stimuli with one or more non-attended visual features but were enhanced for stimuli sharing the overall gestalt with the target. The latency of this late gamma modulation was delayed when two target features were combined, compared to one single discriminative feature. Latency analyses also showed that late bursts of induced high-frequency oscillatory activity peaked around 60 ms later than the selection negativity. Oscillatory activity reflected both selective amplification and competition between object features. These results suggest that sensory amplification of selected features is followed by integrative processing in more widespread networks. Oscillatory activity in these networks is reduced by distraction and is enhanced when attended features can be mapped to specific action.