Reinforcement of least-frequent sequences of choices

When a pigeon's choices between two keys are probabilistically reinforced, as in discrete trial probability learning procedures and in concurrent variable-interval schedules, the bird tends to maximize, or to choose the alternative with the higher probability of reinforcement. In concurrent variable-interval schedules, steady-state matching, which is an approximate equality between the relative frequency of a response and the relative frequency of reinforcement of that response, has previously been obtained only as a consequence of maximizing. In the present experiment, maximizing was impossible. A choice of one of two keys was reinforced only if it formed, together with the three preceding choices, the sequence of four successive choices that had occurred least often. This sequence was determined by a Bernoulli-trials process with parameter p. Each of three pigeons matched when p was ½ or ¼. Therefore, steady-state matching by individual birds is not always a consequence of maximizing. Choice probability varied between successive reinforcements, and sequential statistics revealed dependencies which were adequately described by a Bernoulli-trials process with p depending on the time since the preceding reinforcement.     

The reinforcement of short interresponse times

Five contingencies were superimposed successively on a variable-interval schedule of reinforcement. In each of the resulting conditions, a different short, interresponse time was reinforced and an interresponse-time distribution was obtained from each of three pigeons. The lower bound of the reinforced interresponse times ranged from 0.3 to 2.4 sec. The resulting distributions were combined, according to a rationale based upon concurrent operants, induction, and a property of variable-interval schedules, to describe the interresponse-time distributions from a variable-interval schedule.     

Book reviews

The Journal of Value Inquiry -     

Two types of phenomenal instructions for size and distance judgments of objects presented on a two-dimensional plane

Demand characteristics were studied in a simple situation in which observers made size and distance estimates of stimuli presented on a two-dimensional linear perspective drawing. Half the Ss were asked questions stressing phenomenal report: The other half were asked the same questions preceded by instructions stressing the objective nature of the stimulus configuration but requesting, nonetheless, phenomenal report. Instructions resulted in a significantly greater perspective size illusion but did not affect the distance estimates. No meaningful correlations between size and distance estimates were found.