What Are Lightness Illusions and Why Do We See Them?
Figure 4
White's Stimuli and ANN Responses
(A) Three White's stimuli of varying spatial frequency and (B) three White's stimuli with different target patch heights. In all cases, the left-hand target patch has the same intensity as the right-hand patch, but generally appears darker to humans. The stimuli seen by the ANNs are 20 × 20 pixels.
(C) Mean ANN responses to White's stimuli of varying frequencies with varying test patch heights. Each value is the difference in predicted reflectance for the two test patches. A positive difference means that the test patch on the light bar appears darker than the test patch on the dark bar; a negative difference means the test patch on the light bar appears lighter than the patch on the dark bar. The former is consistent with White's illusion, the latter with brightness contrast. The results show i) that decreasing the frequency of the background stripes (i.e., making them wider) also decreases the strength of White's illusion; and also ii) that increasing the height of the test patch decreases the strength of White's illusion. Both results correspond to human psychophysical responses [5].