Abstract
Recent work by Grill-Spector and Kanwisher (2005) examined the time course of visual object recognition, contrasting accuracy at object detection, basic-level categorization, and subordinate-level identification across a range of image presentation durations. One intriguing result was that the time-course of object detection and basic-level categorization was identical, prompting them to subtitle their paper “As soon as you know it is there, you know what it is.” This tight temporal coupling is consistent with a view that basic-level categorization may be an initial stage of object perception. An alternative view is that detection, categorization, and identification are perceptual decisions that can be made easier or harder, faster or slower, depending on a variety of task factors. Detection and categorization are both perceptual decisions dependent on a hierarchy of perceptual processing, but they are not associated with any particular stage of perceptual processing per se. In the present work, we decoupled the time course of detection and categorization through task manipulations. For example, inverted objects were categorized significantly less accurately than upright objects across a range of image presentation durations, but inversion had no significant effect on object detection performance. By contrast, upright objects were detected and categorized equally well across presentation durations, replicating Grill-Spector and Kanwisher. Object detection and categorization may be based on the same general mechanisms involved in perceptual decision making, but the difficulty of those perceptual decisions can be selectively manipulated. As soon as you know it is there, you may or may not know what it is.
This research was supported by a grant from the James S. McDonnell Foundation (NSF Grant HSD-DHBS05). The authors thank Dr. Kalanit Grill-Spector for use of her image database.