Effects of discrimination training on stimulus generalization in pigeons: Role of resistance to extinction and response-produced stimuli

Abstract

In Experiment 1, two groups (n = 10) of pigeons received 17 sessions of TD (true discrimination) or ND (nondifferential) training with line angles. Seventeen sessions of SS (single stimulus) training with a wavelength preceded this training and two followed it. Subsequent wavelength generalization testing in extinction revealed a sharper TD than ND gradient. This slope difference was evident from the very first test stimulus presentation and remained stable throughout testing. As a consequence of substantial overtraining, there was no reduction of response strength and no sharpening of generalization during testing for either group. In Experiment 2, two groups (n = 16) of pigeons received 10 sessions of TD or PD (pseudodiscrimination] training with line angles, followed by four sessions of SS training with a single wavelength. During this training and in subsequent wavelength generalization testing in extinction, brief blackouts separated stimulus presentations. Again, the TD group yielded the sharper gradient. Although responding weakened and the gradients sharpened during the test, these effects were comparable in the two groups. Furthermore, gradients based on the percentage of trials with at least one response showed the same TD-PD slope difference. This finding indicates that differential control over responding by responseproduced feedback is inadequate to account for the TD-PD difference in generalization slope. Both experiments indicate that a purported difference in resistance to extinction is also an inadequate explanation.301 Honig (1969) was the first to demonstrate that "extradimensional" discrimination training with one pair of stimuli may enhance the control gained subsequently by an entirely different stimulus. Honig trained one group of pigeons on a discrimination between different key colors (Group TD, for true discrimination), A second group (Group PD, for pseudodiscrimination) received the same sequence of stimuli, uncorrelated with reinforcement. Both groups were then reinforced for pecking at a set of vertical lines on the response key and finally received a generalization test, in extinction, along the dimension of line orientation. The TD group showed a significantly steeper angularity generalization gradient. Similar findings have been reported by many other investigators (e.g., Bresnahan, 1970; Mackintosh & Honig, 1970;Thomas, Freeman, Svinicki, Burr, & Lyons, 1970.) This research was supported by research grants from NICHD (HD-03486) and NSF (BNS78-01407) to David R. Thomas. C. F. Hickis is now at Weber State College, Ogden, Utah. Requests for reprints should be addressed to: Dr. David R. Thomas, Department of Psychology, University of Colorado, Boulder, Colorado 80309.Copyright 1979 Psychonomic Society, Inc. interpreted the TD-PD generalization slope difference as evidence for a process of "general attentiveness." They proposed that discrimination training in which one stimulus dimension is predictive of reinforcement will enhance attention to other stimulus dimensions which are not...

Remembering Another Aspect of Forgetting

“…An indirect demonstration of forgetting of attributes comes from a study using a variation of the Kamin blocking effect. Substituting a generalized stimulus for the training CS shortly after conditioning did not block learning to the added element, but substituting the same stimulus did produce blocking after 3 weeks (Thomas and Riccio, 1979). Thus, the generalized stimulus came to function like the original CS.…”