| |
Abstract:
It has been reported that the majority of the inputs to even
primary visual cortex come, not from bottom-up sensory input, but
from other cortical areas. This anatomical finding highlights the
crucial role that "top-down" information must play in visual
processing. Using event-related potentials (ERPs), we explored the
role of variables such as stimulus familiarity and context-based
expectancy on picture processing, both in central vision and with
hemifield presentation. Participants viewed line drawings, some of
which they had seen previously and some of which were novel,
embedded in congruent or incongruent sentences of varying
constraint. Familiarity, congruency, sentential constraint, and
hemifield of presentation all influenced the amplitude of early ERP
components linked to visual processing and the allocation of
visuo-spatial attention. For example, the amplitudes of the
posterior P1 and P2 and the anterior N1 were reduced by
familiarity. Equal N1 reductions, however, were also observed for
novel pictures when these were in constraining, congruent contexts.
P2 amplitudes were affected by congruency and constraint, but only
for presentation in central vision or to the right visual field
(left hemisphere). In sum, "top-down" expectancy-based information,
as well as prior exposure, can affect visual processing by ~50 ms.
The two cerebral hemispheres seem to differ, however, in the extent
to which some types of top-down information are used.
|
