LOCAL AND GLOBAL VISUAL MECHANISMS UNDERLYING INDIVIDUAL-DIFFERENCES IN THE ROD-AND-FRAME ILLUSION

The role of local and global visual mechanisms in individual differenc es in the rod-acid-frame (RF) effect was investigated. Field-dependent and field-independent observers, selected on the basis of Witkin and Asch's (1948) classical procedure, were submitted to the small RF test (Coren & Hoy, 1986). Four frame tilts and two gap sizes were used. As expected, direct effects (i.e., rod settings in the direction of fram e tilt) were observed at small degrees of frame tilt, while indirect e ffects (i.e., rod settings in the direction opposite that of frame til t) were observed at larger frame tilts. Field-dependent observers show ed larger direct effects in the case of the small gap. Indirect effect s were comparable in both field-dependent and field-independent subjec ts, regardless of gap size. Following the model proposed by Wenderoth and Johnstone (1987), these findings indicate that low-level visual me chanisms, responsible for local orientation interactions, have a diffe rent gain in field-dependent and field-independent individuals. In con trast, global visual mechanisms, presumably acting by means of long-ra nge mechanisms, do not distinguish between these two subgroups.