Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)




Amy L Odum


Memory-trace theories of remembering suggest that performance in delayed matching-to-sample (DMTS) procedures depends on a memory trace that degrades with time. By contrast, the theory of direct remembering suggests that increasing the delay between sample and comparison stimuli in DMTS procedures is functionally equivalent to decreasing the disparity between sample stimuli. The present dissertation tested this assumption by assessing the degree to which changes in the frequency of reinforcement for correct choices biased the distribution of choice responses in a conditional-discrimination procedure. Seven pigeons responded under a temporal-discrimination procedure in which temporal sample-stimuli were categorized as being of either short or long duration by a response to a corresponding comparison key. In the sample-stimulus disparity condition, the disparity between the sample stimuli (difference between the short and long samples) was manipulated. In the retention-interval condition, the delay between sample offset and presentation of the comparison stimuli was manipulated. Importantly, the same general procedure was used across conditions, facilitating conclusions regarding functional equivalence of the two manipulations. The theory of direct remembering suggests that the relation between sensitivity of behavior to changes in reinforcer frequency and discriminability (accuracy) should be similar in the sample-stimulus disparity and retention-interval condition. The results showed that discriminability decreased with both the sample-stimulus disparity and retention-interval manipulations. Overall estimates of sensitivity were similar to those obtained previously. There was, however, no difference in the estimates of sensitivity as a function of discriminability during either the sample-stimulus disparity or retention-interval conditions; sensitivity was independent of discriminability. These results are in contrast to most previous reports, and are interpreted in terms of the use of temporal-sample stimuli in the current experiment. Further analyses of the choice-response data showed that the effects of variation in reinforcer ratios differed across conditions as a function of trial type and trial difficulty. These results suggest the need for careful consideration of behavioral outcomes at several levels of analysis when assessing functional equivalence of experimental manipulations. The potential benefits and hindrances of characterization of behavioral outcomes in terms of functional equivalence are discussed.

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