title: The positional-specificity effect reveals a passive-trace contribution to visual short-term memory.
abstract: The positional-specificity effect refers to enhanced performance in visual short-term memory (VSTM) when the recognition probe is presented at the same location as had been the sample, even though location is irrelevant to the match/nonmatch decision. We investigated the mechanisms underlying this effect with behavioral and fMRI studies of object change-detection performance. To test whether the positional-specificity effect is a direct consequence of active storage in VSTM, we varied memory load, reasoning that it should be observed for all objects presented in a sub-span array of items. The results, however, indicated that although robust with a memory load of 1, the positional-specificity effect was restricted to the second of two sequentially presented sample stimuli in a load-of-2 experiment. An additional behavioral experiment showed that this disruption wasn't due to the increased load per se, because actively processing a second object--in the absence of a storage requirement--also eliminated the effect. These behavioral findings suggest that, during tests of object memory, position-related information is not actively stored in VSTM, but may be retained in a passive tag that marks the most recent site of selection. The fMRI data were consistent with this interpretation, failing to find location-specific bias in sustained delay-period activity, but revealing an enhanced response to recognition probes that matched the location of that trial's sample stimulus.
authors.affiliation: Departments of Psychology and Psychiatry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: Bradley R
authors.initials: BR
authors.lastname: Postle
authors.affiliation: Department of Psychology, University of Oregon, Eugene, Oregon, United States of America.
authors.forename: Edward
authors.initials: E
authors.lastname: Awh
authors.affiliation: Department of Psychology, University of California San Diego, San Diego, California, United States of America.
authors.forename: John T
authors.initials: JT
authors.lastname: Serences
authors.affiliation: Departments of Psychology and Psychiatry, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors.forename: David W
authors.initials: DW
authors.lastname: Sutterer
authors.affiliation: Wills Neuroscience Institute and Department of Psychology, University of California, Berkeley, California, United States of America.
authors.forename: Mark
authors.initials: M
authors.lastname: D'Esposito
mesh_terms: D001921:Brain / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008570:Memory, Short-Term; D010775:Photic Stimulation; D011930:Reaction Time; D014796:Visual Perception