Abstract
In Motion-induced-blindness (MIB; Bonneh et. al., Nature 2001), a salient static or slowly moving pattern (target) may disappear and reappear spontaneously in the presence of a global moving pattern (mask). The effect which varies in magnitude across the visual field, involves, at least in part, high level processing as disappearance depends on Gestalt properties of the target, on the 3D relations of target and mask, and on some residual processing of the invisible patterns (adaptation, grouping). Here we report that practice across several weeks may show gradual increase of the amount of disappearance. Six naïve observers reported the disappearance of a single target in an optimal position at 2.5 deg. of eccentricity, which was embedded in a dynamic mask of two types: the standard rotating dot sphere and a new mask constructed from an inner small sphere and a larger rotating dot ring around fixation that surrounded the target from the outside. During the course of 12 sessions along 3 weeks, four of the observers reported progressively more disappearance, reaching a two-fold increase in the accumulated duration of invisibility (up to 80% invisibility). The increase of disappearance was mainly expressed as lengthening of the invisibility periods and shortening of the visibility periods rather than changing the rate of disappearance events. The effect was partially specific to the position of the target (quadrant, eccentricity) as well as to the type of mask. We interpret the results in terms of “learning to ignore” in which the system learns to adapt and ignore more rapidly and for longer durations a trained stimulus in a trained context as part of a novelty-seeking process. The lengthening of the invisibility periods indicates altered processing of the invisible target, and/or enhanced processing of the visible mask, possibly by learning to better objectify it in a competitive process that occurs in the absence of a coherent stimulus interpretation.
Supported by the National Institute for Psychobiology in Israel founded byThe Charles E. Smith Family.