How long does it take for the human visual system to recognize objects? This
issue is important for understanding visual cortical function as it places
constraints on models of the information processing underlying recognition.
We designed a series of event-related potential (ERP) experiments to measure
the timecourse of electrophysiological correlates of object recognition. We
find two distinct types of components in the ERP recorded during categorization
of natural images. One is an early presentation-locked signal arising around
135 ms that is present when there are low-level feature differences between
images. The other is a later, recognition-related component arising between
150-300 ms. Unlike the early component, the latency of the later component
covaries with the subsequent reaction time. In contrast to previous studies
suggesting that the early, presentation-locked component of neural activity
is correlated to recognition, these results imply that the neural signatures
of recognition have a substantially later and variable time of onset.