Nature and Dynamics of Reference Frames in Visual Search for Orientation: Implications for Early Visual Processing

Visual detection of a line target differing in orientation from a background of lines is assumed to occur early in vision and to involve filter mechanisms acting in parallel over the visual field in retinotopic maps (Foster & Ward, 1991; Treisman, 1985; Wolfe, 1994). But retinotopicality does not imply that early vision takes place in a retinal reference frame. This article briefly reviews experiments on this issue and analyzes their implications regarding early visual processing. The review shows that the spatial frame of reference used in visual search for orientation is dynamically determined by various sensory cues to orientation (Marendaz, Stivalet, Barraclough, & Walkowiac, 1993; Stivalet, Marendaz, Barraclough, & Mourareau, 1995). These findings suggest that intersensory integration and perceptual organization are involved at a processing level preceding visual search. This functional viewpoint is discussed in relation to data from neuroscience and psychology (visual search, microgravity).