Bernal S D_2010.pdf - University of Plymouth

2.2. HIGH-LEVEL FEEDBACK
2.2.3 Functional models of feedback
The previous sections review some of the experimental evidence which indicates feedback con­
nections act to modulate lower levels' response. This yields several theoretical conclusions
which shift the traditional bottom-up serial processing ideas towards a more integrative and dy­
namic approach to visual perception. Ii has become clear thai inl'orniation from different visual
cortical regions needs to be combined lo achieve perception, but how this happens and the ex­
act function of feedback conneclions in llii.s process is siill unknown. This section describes
different approaches that provide a functional interpretation of the rnle of feedback, including
attention, biased competition, adaptive resonance, predictive c(xling and generative models. Il
is important lo note that the different interpretalions are not mutually exclusive and commonly
have overlapping features, which means computational models often fall into more than one
category. Likewise, each functional interpretation described below is likely lo be consistent
withasigniticant subset of the theoretical considerations described in the previous section.
2.2.3.1 Feedback as attention.
The visual system receives vast amounts of input information every second from Hght entering
the retina. Attention is aimed at reducing the associated computational cost by prioritizing and
consequently processing only a subset of the visual information. This subset would typically
correspond to Ihai of highest relevance in achieving the organism's goals (Summerlield and
Egner 200y). The function of feedback connections would be to mixlulate the visual input, by
enhancing or suppressing feedforward signals, in accordance with the attentional state. Alten-
tion can arise from high-level cognitive areas associated with task or motor-planning and be
directed towards specific objects or locations. On the other hand, attention can also be attracted
intrinsically by stimuli with strong visual salience, such as a sudden motion, which might lie an
indicator of immineni danger.
Another distinction which is usually made relates to the way of deploying attention. It can be
broadly categorized into spatial aiteniion. which acts as a kind of spotlight thai enhances the
processing at a specific location of the visual iield; and feature-based attention, whereby the
processing of specific features is biased in a lop-down fashion in order lo achieve a specific
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