Locus of dimension weighting: Preattentive or postselective?

In visual search for singleton feature targets, detection RTs are faster when the target-defining dimension is constant across trials rather than variable; in the latter case, RTs are faster when the target dimension on a trial is the same, rather than different, relative to preceding trial (with little effect of a feature change within a repeated dimension); and RTs are expedited when the target dimension is validly indicated by a symbolic precue on a given trial (e.g., Found & Müller, 1996; Müller, Heller, & Ziegler, 1995; Müller, Reimann, & Krummenacher, 2003). Müller and his colleagues have explained these effects in terms of a “dimension-weighting” account, according to which these effects arise at a preattentive, perceptual stage of saliency coding. In contrast, Cohen (e.g., Cohen & Magen, 1999) and Theeuwes (e.g., Theeuwes et al., 2006 this issue) have recently argued that these effects are postselective, response-related in nature. The present paper examines these challenges and puts forward counterarguments in support of the view that dimensional weighting operates at a preattentive stage of processing.