Analysis of ambiguity in visual pattern completion.

It is possible to construct an ambiguous line drawing representing several objects partly hidden behind another object. This article deals with two problems: (a) What are the necessary and sufficient conditions for ambiguity to occur? (b) How can the response frequencies of the completions of ambiguous drawings be explained? Whether completions occur or not, the predictions based on the coding theory, better termed the structural information theory, have been discussed in a previous article (Buffart, Leeuwenberg, & Restle, 1981). It is shown here that the theory also specifies the conditions for ambiguity to occur. The theory describes all possible interpretations of a drawing and selects those interpretations or completions to which subjects will respond. A direct relation between the response frequencies and the possible theoretical descriptions of each response is shown to exist. Two one-parameter models describing the behavior of subjects each fit the response frequencies measured in two experiments with 25 drawings. It is argued that the type of ambiguity that is studied in both experiments generally appears during the perceptual process. The character of the theoretical descriptions indicates that guidance of perceptual behavior by interpretations might occur.