[Within-session changes in responding to water reinforcement: effects of variability in the duration of...

This study tested the hypothesis (McSweeney & Swindell, 1999) that habituation contributes to within-session decreases in drinking. Six rats' lever-pressing was reinforced by water under a continuous reinforcement (CRF) schedule. During the fixed amount sessions, duration of reinforcement was fixed at 3 seconds. Reinforcement duration varied from 1 to 5 seconds, with a mean of 3 seconds, during variable amount sessions. Experimental phase lasted 10 successive days and consisted of 5 fixed amount and 5 variable amount sessions, alternating day by day. Within-session decreases in responding were steeper during fixed amount than variable amount sessions. In addition, response rates were well described as linear functions of cumulative number of reinforcements. The regression line for the fixed amount sessions had steeper slope and smaller x-axis intercept than those for the variable amount sessions. These results support the habituation hypothesis and are not explained by post-ingestive factors.