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Abstract:
The present experiment tested predictions of a
perceptual-mnemonic/feature conjunction (PMFC) model of perirhinal
cortex function. The model predicts that lesions of perirhinal
cortex should disrupt complex visual discriminations with a high
degree of feature ambiguity, a situation that can occur when
features of an object are rewarded when part of one object, but not
when part of another. The idea was evaluated by testing control
monkeys and monkeys with aspiration lesions of perirhinal cortex on
a series of concurrent discriminations in which the number of
object pairs was held constant, but the degree of feature ambiguity
was varied systematically. Monkeys were tested in three conditions:
High Feature Ambiguity, in which all four features were explicitly
ambiguous (AB+, CD+, BC-, AD-; the biconditional problem); Minimum
Feature Ambiguity, in which no features were explicitly ambiguous
(AB+, CD+, EF-, GH-); and Intermediate Feature Ambiguity, in which
two features were explicitly ambiguous (AB+, CD+, CE-, AF-). The
pattern of results closely matched that predicted by simulations
using a connectionist network: monkeys with perirhinal cortex
lesions were unimpaired in the Minimum Feature Ambiguity condition,
mildly impaired in the Intermediate condition, and severely
impaired in the High Feature Ambiguity condition. These results
confirm the predictions of the PMFC model. In contrast to the
prevailing view, perception and memory are unlikely to be neatly
organized into anatomically segregated modules in the brain.
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