Multiple levels of stimulus representation in visual working memory.

Full Abstract

Object recognition presumably involves activation of multiple levels of representation. Here we use the encoding-related lateralization (ERL) method [Gratton, G. The contralateral organization of visual memory:
A theoretical concept and a research tool. Psychophysiology, 35, 638-647, 1998] to describe the sequential activation of several of these levels. The ERL uses divided-field encoding to generate contralaterally biased representations in the brain. The presence and nature of these representations can be demonstrated by examining the event-related potentials (ERPs) elicited by centrally presented test probes for lateralized activity corresponding to the encoding side. We recorded ERPs during a memory-search task. Memory sets were composed of two or four uppercase letters displayed half to the left and half to the right of fixation. Probe stimuli were composed of one letter presented foveally in either upper- or lowercase. Letter case was manipulated to differentiate the time course of physical and symbolic levels of letter representation. Memory set size was manipulated to examine a relational level of letter representation. We found multiple ERLs in response to the probes:
(1) An early (peak=170 msec) case-dependent (but set size independent) ERL, most evident at P7/P8, indexing the availability of a physical level of letter representation; (2) a later (200-400 msec) more diffusedly distributed ERL, independent of both letter case and set size, indexing a symbolic level of letter representation; (3) a long-latency (400-600 msec) ERL occurring at posterior sites, larger for the case match, Set Size 2 condition, indexing competition for neural representation across multiple letters. By assuming that these ERL activities track the progression of letter representation over time, we propose a model of letter processing in the context of visual working memory.

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Author information

Author/s: Shin, Eunsam (E); Fabiani, Monica (M); Gratton, Gabriele (G);

Affiliation: Beckman Institute, University of Illinois at Urbana, IL 61801, USA.

Grants: EB002011 (Agency:NIBIB NIH HHS)

Journal and publication information

Publication Type: Comparative Study; Journal Article; Research Support, N.I.H., Extramural

Journal: Journal of cognitive neuroscience (J Cogn Neurosci), published in United States. (Language: eng)

Reference: 2006-May; vol 18 (issue 5) : pp 844-58

Dates: Created 2006/06/13; Completed 2006/09/14; Revised 2007/11/14;

PMID: 16768382, status: MEDLINE (last retrieval date: 12/26/2008)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Adolescent
Adult
Brain - physiology
Brain Mapping
Electroencephalography - methods
Evoked Potentials - physiology
Female
Functional Laterality - physiology

Functional Laterality - physiology
Humans
Male
Memory, Short-Term - physiology
Models, Psychological
Pattern Recognition, Visual - physiology
Photic Stimulation - methods
Reaction Time - physiology

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