Figure 3.2 The wiring of the rods (left) and the cones (right). The spot and arrow above each receptor represents light that stimulates the receptor. The numbers represent the number of response units generated by the rods and the cones in response to a spot of intensity of 2.0.
Figure 3.7 How lateral inhibition can explain the dark “ghosts” at the intersections. (a) View of four squares of the grid showing the position of receptor A, at the intersection, and the surrounding receptors in the “corridors.” (b) Perspective view of the squares and receptors in (a), showing that each receptor connects to a bipolar cell, and that the bipolar cells that surround A all send a large amount of lateral inhibition to A’s bipolar cell (indicated by the thick arrows). (c) and (d) Same as (a) above but focusing on receptor B, which is located in the corridor of the grid.
Figure 3.8 (a) Mach bands at a contour. Just to the left of the contour, near B, a faint light band can be perceived, and just to the right at C, a faint dark band can be perceived. (b) The physical intensity distribution of the light, as measured with a light meter. (c) A plot showing the perceptual effect described in (a). The bump in the curve at B indicates the light Mach band, and the dip in the curve at C indicates the dark Mach band. The bumps that represent our perception of the bands are not present in the physical intensity distribution.
Figure 3.10 Circuit to explain the Mach band effect based on lateral inhibition. The circuit works like the one for the Hermann grid in Figure 3.6, with each bipolar cell sending inhibition to its neighbors. If we know the initial output of each receptor and the amount of lateral inhibition, we can calculate the final output of the receptors. (See text for a description of the calculation.)
Figure 3.18 Circuit with convergence and inhibition. Because stimulation of the receptors on the side (1, 2, 6, and 7) sends inhibition to neuron B, neuron B responds best when just the center (3 - 5) are stimulated.
Figure 3.20 (a) Response of a ganglion cell in the cat’s retina to stimulation: outside the cell’s receptive field (area A on the screen); inside the excitatory area of the cell’s receptive field (area B); and inside the inhibitory area of the cell’s receptive field (area C). (b) The neuron’s receptive field is shown without the screen.
Figure 3.22 (a) Side view of the visual system, showing the three major sites along the primary visual pathway where processing takes place: the retina, the lateral geniculate nucleus, and the visual receiving area of the cortex. (b) Visual system seen from underneath the brain showing how some of the nerve fibers from the retina cross over to the opposite side of the brain at the optic chiasm.
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Figure 3.27 (a) Results of a psychophysical selective adaptation experiment. This graph shows that the participant’s adaptation to the vertical grating causes a large decrease in her ability to detect the vertical grating when it is presented again, but has less effect on gratings that are tilted to either side of the vertical. (b) Orientation tuning curve of the simple cortical neuron from Figure 3.23b.
Figure 3.30 How neurons that respond best to narrow (N), medium (M), and wide (W) bars respond to the medium-bar grating on the right of Figure 3.28. (a-b): Response before adaptation. (c) Response after adaptation to the wide-bar grating at the top left. (d) Response after adaptation to the narrow-bar grating on the bottom left.
Figure 3.31 (a) Striped tube used in Blakemore and Cooper’s (1970) selective rearing experiments. (b) Distribution of optimal orientations for 52 cells from a cat reared in an environment of horizontal stripes, on the left, and for 72 cells from a cat reared in an environment of vertical stripes, on the right. (Blakemore & Cooper, 1970).