Bernal S D_2010.pdf - University of Plymouth

1.1. HIGH-LEVEL FEEDBACK
context of motion. Two different sets of stimuli were used, one moving coherently and one
incoherently. In each case ihe stimulus inter-element distance wa.s ai least 3" apart, so from
a local perspective they were all identical. We define local as being wiUiin ihe range of the
proximal surround lield, which is about 2.3". Nevertheless, VI responses were sensitive to
the global context of motion, implying Iheir receptive held comprises not only the proximal
surround field, but a further region which is known as the extra-classical receptive lield. Another
remarkable .'cludy in support of this concept showed thai the feedback-mediated response in the
foveal relinotopic corlex contains information about objects presented in the periphery, faraway
Irom the fovea, even in the absence of foveal stimulation (Williams el al, 2008).
This shift in (he traditional view of receptive field was reinforced by Ihe study comparing hori­
zontal to feedback connections (Angelucci and Bullicr 2003, Angelucci ei al. 2002). described
in Section 2.2.]. Anatomical and physiological dala indicated that the spaliolemporal proper­
ties of feedback connections from higher levels provided a plau,siblc substrate for all observed
extra-classical receptive field effects. Horizontal connections could also be involved, but only
in center-surround interactions within the proximal surround range.
2.2.2.2 Integrated model of visual processing.
One main implication that can he derived from the existence of high-level feedback is that
information doesn't necessarily have to be processed serially through successive cortical areas.
Instead, multiple areas can carry out simultaneous computations, which evolve over time as
successively higher cortical regions become involved in the process (Ixe 2(K)3.1.-ee et al. 1998).
For example, evidence shows thai the early pari of VI neuronal response is correlated with the
orientation of local features, while the later response is correlated with higher order contextual
processing. It has been suggested that VI could potentially lake an active part in all the different
processing stages usually attributed to higher levels, such as the representation of surface shapes
or object saliency (Hochstein and Ahissar 2002, Lee 2003. Builier 2001, Lee el al. 1998).
This idea is consistent with conccpluaUzing VI as an active blackboard (Builier 2001) or high-
resoiufion buffer (Lee 2003). Higher cortical areas feed back global and contextual information
10 complete or update the high-resolution detailed representation maintained at the lower levels,
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