The effect of changes in criterion value on differential reinforcement of low rate schedule performance

Abstract

The differential reinforcement of low rate (DRL) schedule is commonly used to assess impulsivity, hyperactivity, and the cognitive effects of pharmacological treatments on performance. A DRL schedule requires subjects to wait a certain minimum amount of time between successive responses to receive reinforcement. The DRL criterion value, which specifies the minimum wait time between responses, is often shifted towards increasingly longer values over the course of training. However, the process invoked by shifting DRL values is poorly understood. Experiment 1 compared performance on a DRL 30-s schedule versus a DRL 15-s schedule that was later shifted to a DRL 30-s schedule. Dependent measures assessing interresponse time (IRT) production and reward-earning efficiency showed significant detrimental effects following a DRL schedule transition in comparison with the performance on a maintained DRL 30-s schedule. Experiments 2a and 2b assessed the effects of small incremental changes vs. a sudden large shift in the DRL criterion on performance. The incremental changes produced little to no disruption in performance compared to a sudden large shift. The results indicate that the common practice of incrementing the DRL criterion over sessions may be an inefficient means of training stable DRL performance.

Keywords: differential reinforcement of low rate schedule; interresponse time; rats; timing.

Fig 1

Mean lever press responses per reinforcer earned as a function of two-session blocks for groups S15 → 30 and M30 in Phases 1 and 2 of Experiment 1. The error bars indicate the SEM. A vertical line marks the transition to Phase 2, when all rats received DRL 30 s. The data from group M30 are double-plotted to allow comparisons as a function of total training as well as training on DRL 30 s.

Fig 2

Interresponse time (IRT) distributions obtained during the first, third, and final block of training in each phase. The different panels display functions for groups S15 → 30 (left column) and M30 (right column) during Phase 1 (top row) and Phase 2 (bottom row) of training in Experiment 1. Vertical lines denote the DRL criterion value.

Fig 3

IRT distributions for individual rats in groups S15 → 30 (left column) and M30 (right column) during the final block of Phases 1 and 2 in Experiment 1. Vertical lines denote the 15-s and 30-s DRL criterion values.

Fig 4

The proportion of IRTs that exceeded 30 s as a function of two-session blocks of training in Phase 1 of Experiment 1. The error bars indicate the SEM.

Fig 5

Mean lever press responses per reinforcer earned as a function of two-session blocks of training during Phases 1 and 2 of Experiment 2a. Error bars indicate the SEM. A vertical line marks the transition between phases. The data from group M30 are double-plotted to allow comparisons as a function of total training on DRL 30 s. The numbers near the data points in Phase 1 indicate the DRL criterion in effect in group P15 → 30.

Fig 6

Interresponse time (IRT) distributions obtained during the first, third, and final block of training in each phase. The different panels display functions for the groups P15 → 30 (left column) and M30 (right column) during Phase 1 (top row) and Phase 2 (bottom row) of training in Experiment 2a. Vertical lines denote the DRL criterion, except in Phase 1 for group P15 → 30 when these rats were exposed to the progressive DRL schedule. The first and third blocks of data are missing from group M30 in Phase 1 due to a computer error.

Fig 7

IRT distributions for individual rats in groups P15 → 30 (left column) and M30 (right column) during the final block of Phases 1 and 2 in Experiment 2a. Vertical lines denote the 30-s DRL criterion value.

Fig 8

The proportion of IRTs exceeding 60 s as a function of two-session blocks of training in Phases 1 and 2 of Experiment 2a. The error bars indicate the SEM. Missing data points for group M30 in Phase 1 were due to loss of IRT data (see Methods). The numbers that appear near the data points in Phase 1 indicate the DRL criterion in effect in group P15 → 30.

Fig 9

Mean lever press responses per reinforcer earned as a function of two-session blocks during Phases 1 and 2 of Experiment 2b. The error bars indicate the SEM. The numbers that appear near the data points in Phase 1 indicate the DRL criterion in effect in group P30 → 60. A vertical line marks the transition between phases. The data from group S30 → 60 are double-plotted to allow comparisons as a function of total training on DRL 60 s.

Fig 10

Interresponse time (IRT) distributions obtained during the first, third, and final block of training in each phase. The different panels display functions for the groups P30 → 60 (left column) and S30 → 60 (right column) during Phase 1 (top row) and Phase 2 (bottom row) of training in Experiment 2b. The vertical bars denote the DRL criterion, except in Phase 1 for group P30 → 60 when these rats were exposed to the progressive DRL schedule.

Fig 11

IRT distributions for individual rats in groups P30 → 60 (left column) and S30 → 60 (right column) during the final block of Phases 1 and 2 in Experiment 2b. The vertical bars denote the 60-s DRL criterion value.