Incentive learning and the motivational control of instrumental performance

Hungry rats were trained to press a lever and pull a chain concurrently, with one action being reinforced with a sucrose solution and the other with food pellets. In addition, in the first two experiments all animals experienced non-contingent presentations of the two incentives in the absence of the operant manipulanda while either thirsty or hungry and either before (Experiment 1A) or after (Experiment 1B) the instrumental training. When lever pressing was assessed subsequently in extinction under thirst, the animals pressed at a relatively high rate only if (1) this action had been reinforced with the sucrose solution rather than the food pellets during training and (2) they had received the non-contingent presentations of the sucrose solution and food pellets on days on which they were thirsty rather than hungry. A third experiment demonstrated that non-contingent exposure to the sucrose solution alone, but not to water under thirst was sufficient to bring about this type of motivational control of instrumental performance.     

A re-examination of one-trial blocking in conditioned suppression

Three experiments on the conditioned suppression of licking in rats examined the amount of conditioning produced by a single conditioning trial to a clicker-light compound and the effect of prior conditioning to the light on the level of conditioning to the clicker. In Experiment I, prior conditioning to the light, far from blocking conditioning to the clicker, actually enhanced it, whether the clicker was presented in a simultaneous compound with the light or in a serial compound preceding the light. Experiment II, however, showed that this potentiation effect could be abolished if a trace interval was inserted between the clicker and light in the serial compound arrangement. Moreover, Experiment III demonstrated a significant blocking effect when a trace interval separated the clicker and light on the single compound trial. These results establish that one-trial blocking of conditioned suppression is possible, and suggest that in some earlier studies blocking may have been masked by higher-order conditioning to the target stimulus.     

Associative learning and representation: Introduction

The papers published in this Special Issue are based upon presentations at a workshop on “Associative Learning and Representation”, which was sponsored by the Experimental Psychology Society and hosted by Emmanuel College, Cambridge. The workshop celebrated the contribution of Professor Nicholas Mackintosh to animal learning and conditioning in particular and experimental psychology in general in the year of his retirement from the Chair of Psychology at the University of Cambridge after 21 years in post. The date of the workshop, 9 July 2002, was particularly auspicious as it was the day of Professor Mackintosh's birth 67 years ago. Moreover, it is particularly fitting that this tribute is published in the Comparative and Physiological Psychology Section (B) of Quarterly Journal of Experimental Psychology, which he founded in 1981 during his editorship of the Journal between 1977 and 1984.