The effect of the discriminability of the stimuli associated with the probability reversal is evident in the differences in the speed with which response rates on each key changed (Fig. 4). In Continuous conditions, response rates on the H→ L key decreased gradually across time, while response rates on the L →H key increased gradually. These changes appeared more gradual when the reversal occurred later (after 30 s rather than 10 s), suggesting that discrimination was weaker in conditions arranging a later schedule reversal. In Discrete conditions, the change in response rates on both keys was abrupt, regardless of the reversal time. Thus, discrimination appeared slightly better under conditions arranging a shorter reversal time, and substantially better under conditions arranging a discrete stimulus change at the reversal.