Fig. 1. A partial reinforcement (PR) schedule does not result in learning. Three separate groups of snails were used. (A) A control group of snails (N=15) received three continuous reinforcement 30 min training sessions each separated by a 1 h interval. Learning occurred (ANOVA, F_14,2=32.07, P<0.001; session 3 significantly less than session 1, P<0.01), and a long-term memory was formed [the memory test session, 24 h after session 3, was not significantly different from session 3 (P>0.05) but was significantly different (P<0.01) from session 1]. Two other cohorts, each of 20 snails, received three 30 min PR sessions each separated by a 1 h interval. One cohort was administered a tactile stimulus on odd-numbered (B) pokes, while the other was administered a tactile stimulus on even-numbered (C) pokes. In neither group was there learning (i.e. there was no significant difference between session 1 and sessions 2 and 3). Values are means + S.E.M.