Shull, R. L., & Grimes, J. A. (2003).
Bouts of responding from variable-interval reinforcement of lever pressing by rats.
Journal of the Experimental Analysis of Behavior,
80, 159-171.
Four rats obtained food pellets by lever pressing. A
variable-interval reinforcement schedule assigned reinforcers on
average every 2 min during one block of 20 sessions and on
average every 8 min during another block. Also, at each
variable-interval duration, a block of sessions was conducted
with a schedule that imposed a variable-ratio 4 response
requirement after each variable interval (i.e., a tandem
variable-time variable-ratio 4 schedule). The total rate of lever
pressing increased as a function of the rate of reinforcement and
as a result of imposing the variable-ratio requirement. Analysis
of log survivor plots of interresponse times indicated that lever
pressing occurred in bouts that were separated by pauses.
Increasing the rate of reinforcement increased total response
rate by increasing the rate of initiating bouts and, less
reliably, by lengthening bouts. Imposing the variable-ratio
component increased response rate mainly by lengthening bouts.
This pattern of results is similar to that reported previously
with key poking as the response. Also, response rates within
bouts were relatively insensitive to either variable.
Key words: response rate, log survival plot, variable-interval schedule, lever press, rats