Bernal S D_2010.pdf - University of Plymouth

5.2. FEEDBACK-MEDIATED ILLUSORY CONTOUR COMPLETION
5.2 Feedback-mediated Illusory contour completion
This section describes the model responses after feedback modulation has taken effect. This
illustrates the interaclion between the feedforward and feedback infonnation in the network,
reflected in the evolution over time of the l>elief at the dilTerenl layers. The scenario chosen to
illustrate these results consists of using the Kani/sa square as the inpul image and feeding back
the representation of a square from higher layers. This section is structured lo show the effects
of feedback arising from progressively higher layers. In other words, the first set of results
illustrates the simplest case, when feedback originates in the CI layer, while (he final set shows
results for feedback originating in the lop layer, S3, and iiu^geiing all inferior layers, including
SI. All ihe results in this section were obtained using the alternative 3-level architecture, as this
provided the best feedforward recognition results.
5.2.1 Feedback from C1 to S1
Figure 5.18 shows the SI model response to a Kanizsa square inpul image while the CI layer
is clamped to a square representalion. Thus, the resuhs illustrate how the bniiom-up evidence
from the inpul image, A(51), is combined with top-down infonnalion from the CI layer, ;r(51).
5.2.2 Feedback rrom S2 to SI
Figure 5.19 shows the SI and CI model responses to a Kanizsa square input image while the
S2 layer is clamped lo a square representation. Thus, the results illustrate how the bottom-up
evidence from the input image, A(6"l), is combined with top-down infonnalion from ihe S2
layer, Bel{S2), and how the representation at the SI and C1 layers evolves over time.
Figure 5.20 shows the temporal response of the S1 and C1 belief for the region corresponding
to Uie top horizontal illusory contour of the Kanizsa figure for the setup depicted in Figure 5.19.
Figure 5.21 compares the C1 belief responses as a function of the S2 RF size and the scale band
for the setup shown in Figure 5.19.
Figure 5.22 compares the SI and CI model responses lo the occluded Kanizsa and blurred
Kanizsa input images ai limes i-l and 1=4, for ihe setup depicted in I'igure 5.19.
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