The representation of location in visual images

By definition, visual image representations are organized around spatial properties. However, we know very little about how these representations use information about location, one of the most important spatial properties. Three experiments explored how location information is incorporated into image representations. All of these experiments used a mental rotation task in which the location of the stimulus varied from trial to trial. If images are location-specific, these changes should affect the way images are used. The effects from image representations were separated from those of general spatial attention mechanisms by comparing performance with and without advance knowledge of the stimulus shape. With shape information, subjects could use an image as a template, and they recognized the stimulus more quickly when it was at the same location as the image. Experiment 1 demonstrated that subjects were able to use visual image representations effectively without knowing where the stimulus would appear, but left open the possibility that image location must be adjusted before use. In Experiment 2, distance between the stimulus location and the image location was varied systematically, and response time increased with distance. Therefore image representations appear to be location-specific, though the represented location can be adjusted easily. In Experiment 3, a saccade was introduced between the image cue and the test stimulus, in order to test whether subjects responded more quickly when the test stimulus appeared at the same retinotopic location or same spatiotopic location as the cue. The results suggest that location is coded retinotopically in image representations. This finding has implications not only for visual imagery but also for visual processing in general, because it suggests that there is no spatiotopic transform in the early stages of visual processing.