Perception of reversible figures after brain injury.

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Reversible figures are drawings in which figure and ground appear to alternate on continued inspection (e. g., the Rubin vase, Fig. 1 A ), or in which perspective appears to shift (e. g., the Necker cube, Fig. 1 B ); in yet a third type, a moving pattern, such as the vanes of a windmill, seems to reverse the direction of its movement. The neural mechanisms underlying these apparent fluctuations remain obscure, despite numerous investigations involving such aspects of the patterns as size (Washburn, Mallay, and Naylor 34 ; Cohen 5 ), complexity (Donahue and Griffitts 7 ; Washburn, Reagan, and Thurston 35 ), or brightness (Mull, Ord, and Locke 19 ). That retrochiasmal processes are involved, however, is suggested by two facts: ( a ) In figures with reversible perspective or movement, rate of apparent change (RAC) increases with continued fixation (Kohler 15 ; Brown 3 ; Cohen 5 ), and ( b ) inspection of a reversible figure with one eye causes an