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Fig. 7.9. Cortical response during adaptation and during direct and indirect tilt aftereffect. Using the same plotting conventions as in Figure 7.4, each row shows (a) an example input, (b) the initial response of the central 64 × 64 region of V1 to that input (before the lateral connections), (c) the response of that region settled through the lateral connections but before adaptation to a vertical input line (SB), (d) the histogram of SB (SBH), (e) the corresponding settled response after a very long period of adaptation (SA), and (f) the histogram of SA (SAH). The top row (labeled "Adaptation") shows these responses to the same input as used for adaptation. After adaptation, the settled response is weaker, broader, and includes a wider range of orientations, but the perceived orientation stays approximately the same (compare the black lines in each histogram). For an input with a slightly different orientation (row "Direct effect"), more units encode orientations greater than 10^o (green areas), and fewer encode those less than 10^o (blue areas) in the settled response after adaptation than before. The net effect is a direct TAE, with the perceived orientation shifting away from the adaptation orientation, from 8.8^o to 21.1^o (compare the black lines in each histogram). For an input with an orientation very different from the adaptation pattern, the changes are more subtle (row "Indirect effect"). Only the neurons around 0^o were activated during adaptation. Their inhibition from other vertical-preferring neurons increased, but decreased from those not active during adaptation. As a result, the green-colored neurons nearest 0^o are now less inhibited by the rest of the neurons responding than before adaptation, and so they respond more strongly. The net effect is an indirect TAE, with the perceived orientation shifting toward the adaptation orientation, from 57.4^o to 54.2^o (compare the black lines in each histogram). Animated demos of these examples can be seen at ...