The positional-specificity effect reveals a passive-trace contribution to visual short-term memory

PLoS One. 2013 Dec 26;8(12):e83483. doi: 10.1371/journal.pone.0083483. eCollection 2013.

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Brain / physiology
  • Humans
  • Magnetic Resonance Imaging
  • Memory, Short-Term*
  • Photic Stimulation
  • Reaction Time
  • Visual Perception*