To bind or not to bind: addressing the question of object representation in visual short-term memory

J Vis. 2012 Jan 1;12(8):14. doi: 10.1167/12.8.14.

Abstract

Visual short-term memory (VSTM) is a capacity limited resource, which is consistently estimated to hold about four visual items at a time. There is, however, debate in the literature about what constitutes an "item" and how resources are allocated within VSTM. Some research suggests information is stored in VSTM as discrete objects; however, there is also evidence suggesting that within-object features alter VSTM performance. The present study addresses the question of whether VSTM load effects reflect the number of discrete objects and/or the number of within-object features. An electrophysiological correlate of VSTM--the contralateral delay activity (CDA)--was measured while participants performed a lateralized change-detection task, in which to-be-remembered items varied in the number of features and locations. Each trial contained either a solitary simple feature (shape, color, or orientation) or one of two multifeature arrays: three features presented at three separate locations or three features bound at one location. While presenting multiple features--regardless of whether they are at discrete locations or bound within a single object--resulted in greater CDA amplitude relative to a solitary feature, there was a dissociation in the distribution of activity between the two multifeature conditions, such that the CDA at site P1/P2 was sensitive to the number of discrete objects, while activity at P7/P8 was most enhanced when multiple features were bound in one object. The findings demonstrate the inhomogeneity of the CDA and suggest this electrophysiological marker may reflect both discrete object individuation/separation and flexible feature-feature binding in VSTM.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Attention / physiology*
  • Color Perception / physiology*
  • Female
  • Form Perception / physiology*
  • Humans
  • Male
  • Memory, Short-Term / physiology*
  • Photic Stimulation / methods
  • Young Adult