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Graham, & Nyberg, 2002; Fletcher & Henson, 2001; Petrides,
1994; Thompson-Schill, D’Esposito, Aguirre, & Farah, 1997). The
perceptual-motor modules’ buffers are based on Byrne and Anderson’s
(2001) ACT–R/perceptual-motor (ACT–R/PM), which in
turn is based on Meyer and Kieras’s (1997) EPIC. The manual
buffer is responsible for control of the hands and is associated with
the adjacent motor and somatosensory cortical areas devoted to
controlling and monitoring hand movement. One of the visual
buffers, associated with the dorsal “where” path of the visual
system, keeps track of locations, while the other, associated with
the ventral “what” system, keeps track of visual objects and their
identity. The visual and manual systems are particularly important
in many tasks to which ACT–R has applied, in which participants
scan a computer screen, type, and use a mouse at a keyboard.
There also are rudimentary vocal and aural systems. The contents
of these buffers can be determined by rather elaborate systems
within the modules. For instance, the contents of the visual buffers
represent the products of complex processes of the visual perception
and attention systems. Similarly, the contents of the retrieval
buffer are determined by complex memory processes, as we describe
below.
ACT–R 5.0 includes a theory of how these buffers interact to
determine cognition. The basal ganglia and associated connections
are thought to implement production rules in ACT–R. The cortical
areas corresponding to these buffers project to the striatum, part of
the basal ganglia, which we hypothesize performs a patternrecognition
function (in line with other proposals; e.g., Amos,
2000; Frank, Loughry, & O’Reilly 2000; Houk & Wise, 1995;
Wise, Murray, & Gerfen, 1996). This portion of the basal ganglia
projects to a number of small regions known collectively as the
pallidum. The projections to the pallidum are substantially inhibitory,
and these regions in turn inhibit cells in the thalamus, which
projects to select actions in the cortex. Graybiel and Kimura (1995)
have suggested that this arrangement creates a “winner-lose-all”
system such that active striatal projections strongly inhibit only the
pallidum neurons representing the selected action (which then no
longer inhibit the thalamus from producing the action). This is a
mechanism by which the winning production comes to dominate.
According to Middleton and Strick (2000), at least five regions of
the frontal cortex receive projections from the thalamus and are
controlled by this basal ganglia loop. These regions play a major
role in controlling behavior.
Thus, the basal ganglia implement production rules in ACT–R
by the striatum serving a pattern-recognition function, the pallidum
serving a conflict-resolution function, and the thalamus controlling
the execution of production actions. Because production rules
represent ACT–R’s procedural memory, this also corresponds to