IN MATLAB:

Optical illusions are fascinating visual phenomena for which our perception of the stimulus differs from reality. Often these are seen as failures of our visual system that gets fooled but they happened to be a wonderful tool for vision scientists to unravel some of the machinery underlying visual perception. Here, you will re-create the Hermann grid illusion, named after the psychologist Ludimar Hermann (1838 - 1914).

The stimulus is constructed by painting white grids on a black background. We can build such a display by creating a 100x100 binary matrix the_mat2 (i.e., consisting of 0s and 1s).

the_mat2 =

To see the illusion for yourself you may display the matrix on the screen as an image using the imagesc and colormap gray commands. You will notice black dots appearing at the intersections of the vertical and the horizontal bars. A widely held assumption is that the illusion arises because of the center-surround organization of receptive fields in the early stages of visual processing.

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