Effects of percentage occurrence of response members and its method of presentation on verbal discrimination learning and transfer

Each of 144 Ss learned two verbal discrimination (VD) lists for six trials. Two levels of percentage occurrence of response members (100% or 50%) were combined factorially with two methods of presentation and three transfer paradigms (C₁-I₂, C₂-I₁, C₂-I₂). In first-list learning, with one method of presentation in the 50,% ORM entire list was presented with only half the correct (C) items designated on each study trial, while in the second method only half the list was presented with all C items underlined. There were no differences between the two methods in the 100% ORM condition. The results indicated that % ORM was a significant variable in first-list learning, supporting the findings of Newby and Young (1972). No effect was found for method of presentation. Also, no real significant effect of these two variables was found in VD transfer. All results were interpreted in terms of the frequency theory of VD learning.     

Schedule-induced drinking as a function of percentage reinforcement

Drinking was recorded in rats while lever pressing was maintained on a series of percentage reinforcement schedules in which the per cent of 1-min fixed intervals terminating with food was 100, 90, 30, 70, 10, 50, and 100%. Intervals in which a pellet was omitted were terminated by brief light flash and click stimuli that were also correlated with food presentations. Drinking failed to develop in five of six subjects following intervals in which the brief stimuli were presented regardless of percentage reinforcement. Postpellet drinking, which followed intervals terminated with pellet delivery, however, increased in both duration and amount ingested per interval as percentage reinforcement was systematically decreased. The increase in postpellet drinking above that produced by 100% reinforcement was interpreted as an analogue of the positive-contrast effect observed with food-reinforced operants.