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Stephen G. Lomber; Learning to see the trees before the forest: Reversible deactivation of the superior colliculus during learning of local and global visual features. Journal of Vision 2002;2(7):69. doi: 10.1167/2.7.69.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have established that the superior colliculus (SC) is critical for the rapid learning of pattern discriminations. This raises the question of whether pattern discrimination learning deficits during SC deactivation are related to an impairment in learning local or global pattern features. To answer this question, the ability of cats to learn three compound image discriminations was studied during bilateral reversible deactivation of the superficial layers of the SC. The animals concurrently learned to discriminate three pairs of visual patterns: 1) The congruent pair — a large T formed by small Ts versus a large 7 formed by small 7s. 2) The incongruent pair — a large T formed by small 7s versus a large 7 formed by small Ts. 3) The random pair — scattered small Ts versus scattered small 7s. The cats were trained to respond to the large T's in the congruent and incongruent pairs and the small T's in the random pair. In intact cats, learning of the random pair was slower than the rapid learning of the congruent and incongruent pairs. This finding demonstrated the theory of global precedence because the cats learned the global features of the congruent and incongruent pairs much more quickly than the local features of the random pair. In contrast, during bilateral deactivation of the superficial layers of the SC, the learning of the incongruent pair was significantly retarded and took longer than learning the random pair. Congruent and random pair learning rates were unchanged. The specific deficit in learning the incongruent pair indicates that the learning of global, but not local, elements of the visual pattern is impaired during deactivation of the SC. The unimpaired use of local features permitted the animals to learn the congruent and random pairs at normal rates. Therefore, deactivation of the superficial layers of the SC during pattern discrimination learning reverses the precedence for global visual features that is typical of normal learning.
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