| |
Abstract:
Abstract: Event-related potentials (ERPs) of the brain were
recorded in healthy volunteers with an high-density electrode
montage. The same set of stimuli (equiluminant sinusoidal gratings
of different spatial frequency presented in the two upper
hemifields of the visual space) were administered in two different
conditions. In Experiment 1 participants attended and selectively
responded to stimulus spatial frequency (object selection)
independent of its location; in Experiment 2 they selected stimulus
location (space selection) independent of its spatial frequency. In
the space selection task, attention modulated Pl amplitude as early
as 100 ms at lateral occipital sites, as shown by scalp current
density (SCD) maps, whereas in the object selection task, attention
modulation started as early as 60-80 msec at both mesial and
lateral occipital sites. Reaction times (RTs) were about 100 ms
faster in the location than the frequency selection task. ERPs for
space selection were characterized by a prominent Pl peaking at
about 140 ms, followed by a tiny N1 and a very early P300
component. Conversely, ERPs for object selection showed an early
PN80 deflection followed by a prominent selection negativity (SN)
and a delayed late positive component (LPC). Spatio-temporal SCD
mapping of ERP data showed two anatomically and functionally
distinct neural mechanisms for space and object selection.
Submission
|
