Illusory contours can arise in dot figures

Frisby and Clatworthy have suggested that subjective contours depend on special contrast effects acting at the tips of lines and at right angles to the lines. Their suggestion depends in part on the absence of such contours in dot figures. However, if the dots are grouped regularly and make a 'good figure', strong subjective contours appear, including a pattern comparable to Kaniza's triangle. The kind of contrast explanation required for these figures would be one in which individual dots create small contrast effects which are only manifest in perception when the effects are grouped together, by Gestalt form indicators, overlap cues, or the like.