The Effect of Stimulus Preexposure on Responding during a Compound Stimulus

In two experiments with rats, three stimuli, A, B, and X, were used for an AX+ BX+ Xo discrimination in which food was presented after the simultaneous presentation of A and X, or B and X, but never after X by itself. For one group in each experiment, X was repeatedly presented by itself before the start of discrimination training. This manipulation weakened responding on test trials in which the three stimuli were presented together. The results are interpreted in terms of a configural theory of conditioning that assumes that preexposure to a stimulus will reduce its capacity to promote generalization among different configurations to which it belongs.     

Absence of overshadowing and blocking between landmarks and the geometric cues provided by the shape of a test arena

In three experiments rats were required to escape from a pool of water by swimming to a submerged platform. The position of the platform was determined by the shape of the pool, which was either rectangular or triangular. A landmark that was located on the surface of the pool near the platform failed to overshadow (Experiment 1) or block (Experiment 2) learning about the position of the platform with reference to the shape of the pool. Experiment 3 revealed a similar outcome with cues outside the pool, which could be used, in addition to the shape of the pool, to identify the location of the platform. These findings imply that theories of learning that assume that stimuli must compete with each other for the control that they acquire may not apply to spatial learning based on the shape of the environment.     

Summation in Autoshaping with Short- and Long-duration Stimuli

Five autoshaping experiments with pigeons examined the effects of presenting in compound two stimuli that had individually been paired with food. The rate of responding during the compound was the same as for the individual stimuli when the stimulus duration was 10 sec. When the duration of the stimuli was 30 sec, the compound elicited a higher response rate than its components. This enhanced rate of responding during the compound was evident only for the initial portion of each trial. Moreover, the enhanced rate of responding was no greater than for a compound composed of an excitatory and a neutral element. These results present difficulties for both elemental and configural theories of conditioning.