Ullman proposes that subjective contc,.us consist of two circles which meet smoothly and which arc tangential to the contrast boundaries from which they originate. The foim of the solution derives from a number of premises, one of which Ullman calls “the locality hypothesis”. ‘Ihis is “based in part on cxpcrimcntal obscrvntions, and partly on a theoretical consideration” ([I 51 ~2). ‘I’hc “cxpc...