Bernal S D_2010.pdf - University of Plymouth

2.2. HIGH-LEVEL FEEDBACK
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Figure 2.9: a) Rapid high-level ohjecl cai;;gi'rizatiii[i. The scrambled face rapidly pops i>ul,
whereas ihe noseless face requires a serial search, h) High-level implicit prot:essin^.
The irit^omplete square rapidly pops iiul whereas an idenlical shape is
interpreled as an occluded square (Hothstein and Ahissar 2002J.
live field approach accounts for feedback originating in high levels with large receptive tields
which targets specific low-level features. An example is shown in Figure 2.9a where, although
the non-facial object pops out immediately, a slower serial search mechanism is required to
identify the noseless face. A similar tinding reported thai subjects require less time to identify
target orientation than to accurately localize il. This is consistent with explicit perception later
accessing low-level detailed represcntalions, such as those encoding spatial localization.
The Reverse Hierarchy Theory also points out the initial coherence and feature binding prop­
erties of visual perception. liven for images containing ambiguous interpretations, such as
illusions or bistable images, the initial explicit perception is typically of a complex coherent
scene, and not of an unlinked collection of lines and coloured regions. This phenomenon can be
considered a direct outcome of hierarchical perceptual organization (Ahis.'iar el al. 2009) and the
resulting receptive field of high-level object-related neurons. Il is coherent with the template
matching-like operation which assigns images to categories, implemented in the feedforward
object recognition models described in Section 2.1.2.
The temporal evolution of activity in low-level regions is also predicted by this theory. Initial
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