Learning to See Complex Random-Dot Stereograms

Many observers of complex random-dot stereograms find that the depth effect takes several seconds, or even minutes, to develop. Julesz (1971) has noted that giving a priori information to such observers about the nature of the ‘hidden’ cyclopean object appears to facilitate their stereopsis. An experiment is reported which investigated this possible facilitation. Naive subjects were shown a complex stereogram following various kinds of preliminary assistance, ranging from simply telling them about the amount of depth they could expect to see to showing them a full-scale model of the cyclopean object. Surprisingly, no benefit from such assistance could be demonstrated. All observers improved their stereopsis perception times with repeated presentations of the stereogram, showing that they could, in principle, benefit from assistance. A follow-up study three weeks later revealed that a substantial part of this improvement was maintained, indicating that the perceptual learning involved can last for a considerable period of time.