TITLE:
Visual Working Memory in Human Cortex
AUTHORS:
Brian Barton, Alyssa A. Brewer
KEYWORDS:
Visual Working Memory; Visual Field Maps; EEG; fMRI
JOURNAL NAME:
Psychology,
Vol.4 No.8,
August
12,
2013
ABSTRACT: Visual working memory (VWM) is the ability to
maintain visual information in a readily available and easily updated state.
Converging evidence has revealed that VWM capacity is limited by the number of
maintained objects, which is about 3 - 4 for the average human. Recent work
suggests that VWM capacity is also limited by the resolution required to
maintain objects, which is tied to the objects’ inherent complexity.
Electroencephalogram (EEG) studies using the Contralateral Delay Activity (CDA)
paradigm have revealed that cortical representations of VWM are at a minimum
loosely organized like the primary visual system, such that the left side of
space is represented in the right hemisphere, and vice versa. Recent functional
magnetic resonance imaging (fMRI) work shows that the number of objects is
maintained by representations in the inferior intraparietal sulcus (IPS) along
dorsal parietal cortex, whereas the resolution of these maintained objects is
subserved by the superior IPS and the lateral occipital complex (LOC). These
areas overlap with recently-discovered, retinotopically-organized visual field
maps (VFMs) spanning the IPS (IPS-0/1/2/3/4/5), and potentially maps in lateral
occipital cortex, such as LO-1/2, and/or TO-1/2 (hMT+). Other fMRI studies have
implicated early VFMs in posterior occipital cortex, suggesting that visual
areas V1-hV4 are recruited to represent information in VWM. Insight into
whether and how these VFMs subserve VWM may illuminate the nature of VWM. In
addition, understanding the nature of these maps may allow a greater
investigation into individual differences among subjects and even between
hemispheres within subjects.