Bernal S D_2010.pdf - University of Plymouth

Chapter 5
Results
5.1 Feedforward processing
5.1.1 Layer by layer response
This section provides details of the internal representation of ihe image maintained hy each
of the layers. It serve.s to illustrate how the probahili.slic representation compares with the
claiisical HMAX model representation and facilitates understanding of the Feedback results. All
theresuUsin this section are for the first input image of the training data.set, namely the letter/I.
Figure 5.1 shows the response of the battery of Gabor filters at four different orientations and
If) different sizes (bands) applied to the input image. The bottom-up messages from Ihe layer
of dummy nodes, A^ummvl^l), are made up of the responses to the four orientations at each
location and scale band.
Figure 5.2 shows the likelihtKxi response of the SI nodes. A(.^l), obtained by sum-normalizing
the input Xdummy{S]) messages. The grey colour over the blank input regions indicates thai all
four orientations are equally probable at that location, thus each one has a value of I /4.
Figure 5.3 shows the likelihood response of the CI nodes. A (CI). The 2D maps represent the
sum of the features in each CI group at each location. Figure 5.4 shows the response of the
CI units in the original HMAX model, in other words, calculating the max over the SI afferent
units, for the same parameter set. This allows one to compare the response between the CI
nodes in the model proposed and die CI nodes in the original HMAX model.
Figure 5.5 shows the likelihood response of the S2 nodes, X{S2). at all locations of a specific
band and RF size. The figure also includes a reconstruction of the S2 interna! representation
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