The spatial memory of senescent (29 mo) and middle-aged (14 mo) Long Evans rats was investigated using three tasks. In the first, rats were required to move from the brightly lit surface of a circular platform into a dark tunnel under one of 18 holes lining its circumference. The second task dissociated the strategy of preference (i.e., cue, response place) of these rats in a two-choice (T-maze) discrimination problem. The third task involved memory for specific places in the environment, with the use of water reward to induce running on a radial 8-arm maze. The senescent rats exhibited poorer memory for rewarded places, and evidence is presented that this may be a result of using less efficient performance strategies because of a deficit in spatial memory.
This paper is a selective review of the methods, problems, and findings in the area of operant stimulus generalization over the 25 years since the publication of the original paper by Guttman and Kalish (1956) on discriminability and spectral generalization in the pigeon. The paper falls into five main sections, which encompass the main themes and problems stemming from the Guttman and Kalish work and its immediate successors. The first section addresses the relationship between stimulus generalization and stimulus control, as well as the variety of testing procedures and dependent variables used to measure generalization. The next section reviews the limited literature on the effects of early rearing on the generalization gradient. The relationship between discriminability among test stimuli and the slope of the spectral gradient is discussed in the third section, with emphasis upon recent reassessments of the pigeon's hue discriminability function. The fourth section reviews the topic of inhibitory stimulus control, one which developed with the discovery of the peak shift following intradimensional discrimination training. Problems of definition and measurement are discussed in conjunction with the gradient forms used to index inhibitory control. The last section is devoted to attentional effects and the two principal theories postulated to account for them. A survey of different attentional paradigms is provided and the possible role of constant irrelevant stimuli as a source of control is examined. A brief conclusion summarizes the contribution of the generalization technique toward an understanding of the nature and acquisition of stimulus control.
When sample-specific responding is occasioned by sample stimuli in matching and oddity tasks with pigeons, such responding controls the choices between comparison stimuli. This control was investigated in four experiments. In Experiments 1 and 2, differential responding to the samples in line-line matching and line-line oddity was reversed following acquisition of these problems. The reversal interfered with reacquisition of the same conditional discrimination but facilitated acquisition of the opposite discrimination. In Experiment 3, pigeons initially trained on line-line matching were shifted to hue-line matching. Positive transfer occurred when correct choices in both tasks were paired with the same sample-response patterns. Conversely, negative transfer occurred when correct choices were paired with opposite patterns. In Experiment 4, two concurrent conditional discriminations were designed so that sample-response patterns were paired with specific sample stimuli, but not with correct choices. Faster acquisition occurred when response patterns differed within rather than between sample dimensions. Furthermore, sample-specific responding controlled choices when the dimensional stimuli were difficult to discriminate but not when they were easy to discriminate. The combined results are interpreted in terms of overshadowing. Visual stimuli that control choice can be overshadowed by sample-specific responding if the latter facilitates conditional discrimination acquisition.
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