non-existent contours are sometimes constructed by the brain to compensate for the missing sensory information. Check the four wheels in the second
image – the “missing” parts can easily be mistaken as contours of the square, right? See what happens if we fill the missing segments with pink colored lines
– the color seems to transparently spread throughout the inside of the contours. In same manner contour of a circle appears, right inside the center of the lines
diagram to the right.
However, contours or surfaces don’t appear if we only see the colored segments. Curved line above is made of nothing but short blue lines and demonstrates this perfectly! Now,
if we add longer black lines next to each side of blue bar, curved blue band with subjective contours appears! How amazing was that?