Contingency and stimulus change in chained schedules of reinforcement

Higher rates of pecking were maintained by pigeons in the middle component of three-component chained fixed-interval schedules than in that component of corresponding multiple schedules (two extinction components followed by a fixed-interval component). This rate difference did not occur in equivalent tandem and mixed schedules, in which a single stimulus was correlated with the three components. The higher rates in components of chained schedules demonstrate a reinforcing effect of the stimulus correlated with the next component; the acquired functions of this stimulus make the vocabulary of conditioned reinforcement appropriate. Problems in defining conditioned reinforcement arise not from difficulties in demonstrating reinforcing effects but from disagreements about which experimental operations allow such reinforcing effects to be called conditioned.     

Preference for free choice over forced choice in pigeons

Eight severely retarded young men learned color and line-tilt discrimination. After 95% accuracy was achieved for both dimensions, they were combined to form "conflict-compound" stimuli in which prior reinforcement history was reversed for one element of the compound and unchanged for the other. When responding to the compound was 95% accurate, control exerted by each element was measured. The unchanged element consistently exercised control in agreement with the reinforcement contingencies associated with the compound, regardless of whether it was color or line orientation. The reversed element, which had a conflicting prior history or reinforcement, most often exerted control associated wtih original training, or no control, suggesting that it had been "ignored" during the compound. Conflict compounds produced selective attention. When elements were combined to form "compatible-compound" stimuli, both exercised control in agreement with the compound in post-tests. Selective attention was not produced by compatible compounds.     

Major stimulus dimensions determining detection of simulated breast lesions

Five adult humans palpated silicone breast models in a lump-detection task. The effects on detection of several lump and model characteristics were studied in three phases, using both discrete trial (restricted search procedure) and “free response” (free search procedure) psychophysical methods. Size and depth of fixed steel lumps were varied in Phase 1. Depth and hardness of uniformly sized, fixed lumps were varied in Phase 2. The presence and depth of simulated breast nodularity were also studied in Phases 1 and 2. In Phase 3, all breast models were uniformly nodular and lumps varied along dimensions of size, depth, hardness, and fixation. In Phase 1, lump detection was greatest with maximum lump size and minimum depth within the model. Neither lump hardness nor depth differentially influenced detection of the fixed lumps in Phase 2. When breast lumps were mobile, in Phase 3, size and hardness were major stimulus dimensions determining detection. These results suggest physical parameters for realistic breast models and lumps to be used in training effective breast self-examination and breast lump detection.     

Concurrent fixed-ratio and avoidance responding in the squirrel monkey

Squirrel monkeys maintained concurrent performances appropriate to a fixed-ratio schedule of food reinforcement on one lever and an avoidance schedule on a second lever. The overall rate of responding maintained by either schedule was not systematically affected when the other schedule was discontinued and its lever removed.