A Simon effect induced by induced motion and location: Evidence for a direct linkage of cognitive and motor maps

In the literature, a distinction has been made between two separate visual pathways: a (more or less) nonspatial “what” path and a spatial “where” path (e.g., Bridgeman, Peery, & Anand, 1997; Goodale & Milner, 1992). It has been assumed that these two pathways serve different functions: One is concerned with what is generally considered as “visual perception,” whereas the other feeds directly into action control. Two lines of evidence support this view. First, Goodale, Milner, Jakobson, and Carey (1991) tested a patient with lesions in the ventral stream of projections from the striate cortex to the inferotemporal cortex. Despite a pronounced disorder in the perception of object features, such as form, orientation, and size, this patient showed accurate guidance of hand and finger movements toward objects. According to the authors, this finding suggests that different neural substrates underlie visual object perception on the one hand and the use of object information for the control of manual movement on the other. Second, Bridgeman and colleagues (Bridgeman, Kirch, & Sperling, 1981; Bridgeman, Lewis, Heit, & Nagle, 1979; Bridgeman et al., 1997) obtained perceptual and motor measures of illusory (or real) target displacement from healthy subjects. Using either induced motion (Bridgeman et al., 1981; see Figure 1) or the Roelofs effect (Bridgeman et al., 1997; see Figure 4), the authors demonstrated a dissociation between these measures: Subjects’ performance was less affected by the visual illusion when they pointed toward the target than when they indicated the target’s position by means of a perceptual adjustment procedure. Bridgeman et al. (1997) argue that two distinct maps of visual space are formed: a cognitive map and a motor map. Whereas the former is susceptible to illusions, the latter is not supposed to be susceptible to illusions, but rather to represent the physical world in a more or less veridical fashion. The content of the cognitive map is accessed in the course of explicit retrieval of spatial information, as required in spatial judgments, whereas the content of the motor map is assumed not to enter awareness and to directly control spatial responses, such as pointing. A different view on dissociations between motor and perceptual tasks was proposed by Smeets and Brenner (1995). They pointed out that in the study of Bridgeman et al. (1981), the perception of an (apparently moving) object’s velocity was compared with a motor response to a The authors thank R. Proctor, G. J. Andersen, and an anonymous referee for their helpful comments on an earlier version of the manuscript, and S. Bauer for helping to collect the data. Correspondence should be addressed to D. Kerzel, Department of Cognition and Action, Max Planck Institute for Psychological Research, Amalienstr. 33, 80799 Munich, Germany (e-mail: [email protected]). A Simon effect induced by induced motion and location: Evidence for a direct linkage of cognitive and motor maps