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Abstract:
Event-related brain potentials (ERPs) were recorded to
fragmented pictures of objects that were named correctly or
unidentified for the purpose of studying stages of visual object
identification. The moment when ERPs to identified and unidentified
pictures first differ provides an upper limit on the time by when
human brain regions have at least begun to activate long-term
memory representations that specify the identity of a visual
object. ERPs recorded from 15 young people show that this time
varied with the extent to which object parts were recoverable from
the visual input. When object parts were readily recoverable,
successful identification was evident relatively early by around
300 ms. However, when object parts were difficult to recover or
nonrecoverable (i.e., poorly specified and hard to recover from the
available contours), successful identification was not evident
until relatively late, around 550 ms. In both cases, successful
identification was associated with greater positivity. In addition,
unidentified nonrecoverable pictures elicited an enhanced frontal
negativity that was not seen for recoverable pictures. Taken
together, these results implicate at least two distinct critical
processing stages in the successful identification of visual
objects.
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