THE ORGANIZATION OF MULTIDIMENSIONAL SELECTION ON THE BASIS OF COLOR AND SHAPE - AN EVENT-RELATED BRAIN POTENTIAL STUDY

In this paper, we examine whether color and shape, tied to a single ob ject in space, (1) are identified and selected in series or in paralle l, (2) are identified and selected in a dependent, self-terminating ma nner or in an independent and exhaustive manner, and (3) are conjoined by a feature integration process before or only after an initial stag e of separate attribute analyses has finished. We measured response ti me and the selection negativity (SN) derived from event-related brain potentials when participants responded to a unique conjunction of colo r and shape in a go/no-go target detection task. The discriminability of the color and the shape of the conjunction was manipulated in three conditions. When color and shape were easy to discriminate, the SNs t o color and shape started at the same time. When one attribute was les s discriminable, the SN to that attribute started later, but not the S N to the complementary attribute. This suggests that color and shape a re identified and selected in parallel. In all three discriminability conditions, the SNs to color and shape were initially independent but later interacted. This suggests that color and shape are initially sel ected independently and exhaustively, after which their conjunction is analyzed. The SN to local shape features started later than that to t he conjunction of color and global shape features, which suggests that feature integration can start before the analyses of the separate att ributes have finished.