Effect of imprinting on visually evoked intrinsic signals in the visual wulst. (a) Representative intrinsic optical signals in the right visual wulst obtained from chicks imprinted with the blue square (Imp with Blue), red square (Imp with Red) or trained without image (No Imp). The blue or red square was presented on the display. The blue and red squares were the same images as those used in training and evaluation. In the blue-imprinted chicks, the intrinsic signal to blue extends from anterior to posterior, while that to red is confined to the posterior portion. In contrast, in the red-imprinted chicks, the intrinsic signal to red extends and covers the blue-responding region. Finally, in the non-imprinted chicks, the intrinsic responses to blue and red are similar, with peaks in the middle or posterior regions. AM, experimental number that designates individual chicks. Scale bar, 1 mm. (b) Intensities of the signals in the defined loci (see Additional files 3 and 4) evoked by blue or red squares are plotted as a function of position. In the blue-imprinted group, the response peak to blue is detected in both the anterior and posterior, while the peak response to red is only detected in the posterior position. In the red-imprinted group, the response peak to blue is detected in the posterior, while that to red is detected in the anterior and posterior, although the former is less prominent. In the no imprinting group, the response peak is observed in the middle or posterior portion, irrespective of the color of the presenting image. A, anterior; M, middle; P, posterior. (c) The calculated slopes between the anterior and middle and between the posterior and middle are shown. Only those chicks that were imprinted with the blue square show positive anterior/middle slopes for blue-square presentation. Similarly, only the red-imprinted chicks exhibit positive anterior/middle slopes to red. The posterior/middle slope for blue is greater for the blue- or red-imprinted chicks than for the non-imprinted chicks.