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Unformatted text preview: rly visual or subcortical areas directly to the orbitofrontal
-This coarse representation activates in the OFC expectations about the most likely
interpretations of the input image, which are then back-projected as an ‘‘initial
guess’’ to the inferior temporal cortex to be integrated with the bottom-up analysis.
-Bottom-up analysis is processed through the ventral visual route.
-Both pathways integrate in IT.
The top-down process (OFC) facilitates recognition by substantially limiting the
number of object representations that need to be considered and speeds up time
when a quick response is necessary. Attention and awareness
of visual percepts Attentional networks are found in the fronto-parietal regions. • It is widely agreed that the ventral pathway, interacting with areas
of prefrontal, parietal and temporal cortex, forms the basic circuit.
e.g. vision Within this parieto-frontal network, it is likely that visual target selection involving attention
to a salient target is associated first with firing of neurons in the lateral intraparietal area.
In contrast, top-down selection, involving volitional acts of attention, is associated first with
firing of neurons in the frontal eye fields.
Australian and New Zealand Journal of Psychiatry, 2008,42:11,915-31 17 Attention and awareness
of visual percepts (a) In the absence of attention, percepts evoke only slight activity in the visual extrastriate cortex.
(b) If the visual percepts are salient, networks in lateral intraparietal cortex are activated that
increase the extrastriate visual pathway activity;
slightly later, the frontal eyefield attentional area of the brain is active, also contributing to
activity in the extrastriate pathway.
(c) If attention is held, activity in the superior parietal and DLPFC is enhanced. This is graded
with an increase in extrastriate visual cortex activity, until a threshold is reached. At that time
there is a sudden non-graded large increase in activity in DLPFC as well as in superior
parietal cortex, which drives a very large late increase in extrastriate visual cortex.
The increase in the extent of recruitmen...
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