Bernal S D_2010.pdf - University of Plymouth

6.1. ANALYSIS OF RESULTS
over lime. The fact the both the bottom and lop layers are clamped means that beliefs can
only evolve freely along Ihe intermediate layers, as the belief in peripheral layers will he
dominated by the clamped representations. The present results suggest that if only ihe
input image is clamped and beliefs allowed to evolve across [he whole network, these
show greater contextual modulation through lateral interactions. This is illustrated in
Figure 5.31 and discussed below in Section 6.1.2.5,
It is also possible that the structure and parameters of the network, derived from the HMAX
model and mimicking the venlral path, are not suflicient for the precise spalial refinement of
feedback. Indeed the dorsal path, which has been shown to be tightly interlinked with the ventral
path at many levels, may play a crucial role by providing spatial and motion related information
which could guide the feedback disambiguation process (Fa/,letal, 2009. Chikkeruretal, 2010.
Grossberg el al. 2007). In this sense even for static images, such as those employed in this
model, the continuous microsaccadic movements of the eye might be providing crucial infor­
mation for perceptual completion processes (?). In this same line, George and Hawkins (2009)
demonstrated that simulating saccadic movemenls in ihe input image improved the feedback
reconstruction performance of the model. A more complete model of visual perception could
therefore be accomplished by implementing a parallel interconnected Bayesian network thai
modelled the dorsal path and provided the additional information required.
Nonetheless, the results in Figure 5.28 demonstrate the ability of the model to feed back high-
level information to lower levels, even in the absence of boitom-up input, consistent with evi­
dence on mental imagery. Evidence has consistently shown ihat the regions and cortical repre­
sentations of mental imagery are surprisingly similar to those of visual perception, suggesting
boih modalities share a common substrate (Ishai 2010). Slotnick et al. (2005) showed that vi­
sual mental imagery can evoke relinolopic activations in early visual regions, in agreemeni with
generative modelling approaches. Recently. Reddy el al. (2010) obtained results suggesting
the same pauems on neural activity generated during visual perception get reaclivaled during
mental imagery, mediated by feedback connections from high-level object recognition layers.
The setup where feedback originates from ;r(52) was also used to explore the different belief
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