| |
Abstract:
Evidence from fMRI, ERPs, and intracranial recordings
suggests the existence of face-specific mechanisms in human
occipitotemporal cortex. Magnetoencephalography (MEG) offers the
possibility of studying focal neural activity in the normal brain
with high temporal resolution. The present study used a 64-channel
MEG system to monitor neural activity while normal subjects
passively viewed a sequence of grayscale photographs of unfamiliar
faces (upright and inverted) and a variety of non-face stimuli
including scenes, animals, human hands and tools. Stimuli were
randomly interleaved in each block. There were 200 trials per
stimulus category, stimulus duration 200msec, ISI 800msec. In four
out of six subjects, human faces evoked a larger response than
non-face stimuli at a latency of 160msec after stimulus onset at
occipitotemporal sensors (see also Sams et al, 1997). These data
are consistent with previous ERP studies of face processing
(Bentin, 1996; Jefferys, 1996). Furthermore, these face-specific
responses are negative in the left hemisphere and positive in the
right, which implies a hemispheric asymmetry of face dipoles.
Inverted face stimuli elicited responses that were smaller in
amplitude and about 20msec later in latency than the upright faces.
These data suggest that MEG may provide a powerful technique for
studying the time course of face recognition.
|
