Object-Category Processing, Perceptual Awareness, and the Role of Attention during Motion-Induced Blindness

The extent of visual processing that occurs outside of awareness is an unresolved issue of broad importance to the field of cognitive neuroscience. Research examining this question is predicated on the notion that any information that is represented in the brain, whether an individual is aware of it or not, holds the potential to affect subsequent behavior in a relevant way. Identifying the information coded in the brain with or without explicit awareness therefore enhances our understanding of what determines or influences behavior. One method of identifying perceptual processes that occur in the absence of awareness is through the dissociation paradigm, which is comprised of several essential components (Reingold & Merikle, 1988). In vision, for example, once a visual perceptual process of interest is identified, two measures of this process are obtained as a viewer is presented with images invoking this process. An explicit measure is derived from the viewer's behavioral output or report regarding the content of the images, which serves as an index of their level of awareness. A second measure is typically implicit in nature and reflects the processing of the image content of which the viewer may not be aware, as in the case of behavioral priming or neural responses. Through any number of possible manipulations of the presentation parameters of relevant images (e.g., a manipulation using motioninduced blindness (MIB), for example, as described below), conditions are created in which images are present but not visible to the viewer, which is reflected in a marked decrease of the explicit measure (Kim & Blake, 2005). The implicit measure is then probed in these conditions of reduced awareness vs. those with full awareness. If the implicit measure of the perceptual process is shown to be intact, regardless of the viewer's ability to report relevant image content, then it is inferred that this process is occurring in the absence of awareness (Holender, 1986; Reingold & Merikle, 1988). Discrimination of object category by the visual system is evident through multiple measures, behavioral and neural, and thus provides explicit and implicit indices that can be used to examine its relationship with visual awareness. A particularly well-studied and readily measured process reflecting such categorical discrimination is face-specific processing. Neural reflections of this process have been most directly observed as enhancements of specific neural responses to face images relative to images of any other object category that are observed in functional modules of the ventral extrastriate and ventral temporal cortices in human and nonhuman primates (Allison et al., 1994; Harries & Perrett, 1991; Perrett, Hietanen, Oram, & Benson, 1992). In normal human observers, for example, face-specific responses have been localized to C H A P T E R