| |
Abstract:
Abstract: Patient with hemispatial neglect may not perceive
stimuli contralateral to a brain lesion (most often of the parietal
lobe) when a competing stimulus is simultaneously presented in the
ipsilesional field - a phenomenon called visual extinction.
However, neuropsychological studies have shown that extinguished
stimuli may still be unconsciously processed. To identify the
cortical regions involved in processing faces in the absence of
awareness, we used event-related fMRI to compare the neural
activity evoked a by left-side face when it is perceived with that
evoked by an extinguished face in a task where faces or shapes were
briefly shown in the right, left, or both fields. We studied a
patient with right parietal damage and intact visual fields who
perceived 98% of left faces in unilateral trials but extinguished
54% in bilateral trials. Preliminary results show that perceived
stimuli in the LVF activated striate and extrastriate regions,
while extinguished faces activated only weakly a subset of these
areas in the medial temporal lobe. Physically identical bilateral
stimuli produced greater activity in right-side occipital and
temporal areas, as well as left-side parietal areas when faces in
the LVF were consciously perceived as compared to extinguished
trials. These findings were also extended by a study using ERPs in
the same task.
|
