Bernal S D_2010.pdf - University of Plymouth

2.2. HIGH-LEVEL FEEDBACK
sizes that perceptual grouping results from collinear facilitation, and demonstrates this using a
detailed physiological model of the interaction between horizontal and feedback connections.
These interactions are proposed to occur in the dendritic trees of pyramidal cells (De Meyer and
Sprat ling 2009).
Nonetlieless, as Suggested by a recent study (Summerfield and Egncr 2009). predictive cod­
ing mighi be more related to the effects of expectation, which facilitates visual perception by
constraining the interpretation space based on prior infonnation, than to attention. Although be-
haviounilty bolh attention and expectation can have similar effects, ihey might exert opposing
induenccs on the responses of Ihe neural populations involved, i.e. expectation might reduce
the response while attention might enhance ii. However, this distinction at the neural level is
only hypothetical and remains to be substantiated by further experimenlal and modelling work
on this research topic, which is still at a very early stage.
Independently of its relalionship with other theoretical approaches, predictive ctxling has been
outstandingly successful in explaining feedback experimental results. It is also consistent with
the growing collection of evidence showing thai lower level responses are inversely correlaled
to stimulus predictability (Alink el al. 20K), Murray et al. 2004, Sterzer et al. 2006, Harrison
et al. 2007. Rao and Ballard 1999), Furthermore, existing computational models can account for
several well-known phenomena, such as repetition suppression (Friston el al. 2006), biphasic
responses in LGN (Jehee and Ballard 2009}. objcci segmentation (Rao and Ballard 1997. 2005);
and a wide range of classical and extra-classical receptive field effects, including receptive
field luning properties, surround suppression and facilitation (Spratling 2010). and end-slopping
effects (Rao and Ballard 1997, Rao 1999).
Note that predictive coding might appear incompaiihic with the observation that feedback acts
to enhance activity consistent with the high-level percept, supported by evidence showing the
response in VI is reduced when higher areas are inactivated (e.g. by freezing MT) (Hupe et al.
2001. Huang el al. 2007, Galuske el al. 2002, Angelucci and Bullier 2003). However, as pre­
viously mentioned, this might be the result of over-emphasizing the error-detecling population
over the prediction population (Spratling 2008b, Friston 2005),
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