Intensity, color, and pattern discrimination deficits after lesions of the core and belt regions of the ectostriatum

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Abstract
Pigeons were trained to discriminate visual stimuli that differed in intensity, color, or pattern, after which lesions were made in the ectostriatum, either the core region (EC), the belt region (EB), or both (EC + EB). Control lesions were made in the lateral neostriatum. After surgery, the birds were again trained to discriminate the stimuli. On the basis of a quantitative analysis of the lesion reconstructions, each pigeon was assigned to one of five groups: EC, EB, moderate (EC + EB), slight (EC + EB), or control. Postoperative savings scores, based on the number of preoperative and postoperative sessions required to discriminate the stimuli, were calculated. An analysis of variance indicated a significant effect of lesion location on the extent of postoperative savings or loss. Only the moderate (EC + EB) group was significantly different from the neostriatum controls. A multiple regression analysis of performance on the individual discrimination tasks indicated that the extent of damage to EC predicted the initial performance deficit on the intensity and one of the two pattern discrimination tasks (vertical versus horizontal bar). The color discrimination deficit, which was modest in extent and of short duration, was predicted only by the damage to (EC + EB) that was at least moderate in extent (20–40% of the volume of (EC + EB)).