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Abstract:
128-channel ERP recordings were used to investigate the
timing and distribution of brain areas involved in shifting and
sustaining attention. A spatial cueing paradigm used a cue (S1) in
either the left or right lower visual quadrant to indicate that
covert attention be directed to that location for a subsequent (S2)
match-to-sample (S1) discrimination. Five size-variants of a
checkerboard wedge, served as both S1 and S2. Subjects were
required to determine if the S2 presented at the attended location
(50% of trials), was the same size (20% of trials) as the S1 that
cued them to that location. The use of identical stimuli as both S1
and S2 meant that they were viewed in a number of attention states
(passively; attended S1-cue; attended non-target S2; target S2;
ignored S2) allowing for differentiation of attentional processes.
The initial sensory responses (75 msec) were the same for all
stimulus classes (ruling out general arousal differences), but
later activity diverged greatly in accordance with the function of
the stimulus (passive, S1-cue, S2 attended and ignored). The S1-cue
revealed a sustained parietal negativity preceding the impending S2
(absent during passive viewing). Selective processing of attended
versus ignored S2 stimuli was mediated by enhanced contralateral
extrastriate activity and callosal transfer to the ispilateral
hemisphere which was absent for ignored S2s. Independent of
callosal transfer and selective attention type, all S2s elicited a
late sustained central-parietal positivity in preparation for the
next cue. (NS27900-GVS; MH11431-JJF; Human Frontier Science
Program).
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