The effect of reinforcement probability on time discrimination in the midsession reversal task
Unequal reinforcement within a session pulls learners off a clock-based rule, so keep payoff rates matched when teaching mid-session switches.
01Research in Context
What this study did
Santos et al. (2019) worked with pigeons in a timing game. The birds pecked one key for the first half of the session, then had to switch to a second key for the second half.
The twist: one half of the session paid off twice as often as the other half. The team watched to see if the richer side pulled more errors—either jumping the gun early or staying too long.
What they found
When the first half was rich, birds anticipated too soon and pecked the wrong key early. When the second half was rich, birds stuck with the first key too long after the switch.
In short, the side that paid more often dragged both timing mistakes—early starts and late hangs-on.
How this fits with other research
Landon et al. (2003) saw the same pull from rich sides, but they tracked long strings of wins and breaks. Their birds followed local streaks; Santos shows the same tug can warp a clock-based rule.
Dougherty et al. (1994) used bigger snacks, not more snacks, and got cleaner timing. Their payoff-size cue helped birds stay accurate, while Santos shows payoff-rate shifts hurt accuracy—two levers for the same goal.
Parrott (1984) found preference flips when sessions ended differently. Santos keeps session length fixed, proving you can still flip choice just by tilting the payoff rate inside the session.
Why it matters
If you run conditional-discrimination drills that swap rules mid-session—like receptive labels that flip from one set to another—keep reinforcement rates even on both sides. A lopsided payoff can lure learners into early guesses or stubborn perseveration, even if they know the timing rule. Balance the goodies and you balance the timing.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Count reinforcers delivered in each half of your reversal drill and rebalance if one side is pulling ahead.
02At a glance
03Original abstract
We examined how biasing time perception affects choice in a midsession reversal task. Given a simultaneous discrimination between stimuli S1 and S2, with choices of S1 reinforced during the first, but not the second half of the trials, and choices of S2 reinforced during the second, but not the first half of the trials, pigeons show anticipation errors (premature choices of S2) and perseveration errors (belated choices of S1). This suggests that choice depends on timing processes, on predicting when the contingency reverses based on session duration. We exposed 7 pigeons to a midsession reversal task and manipulated the reinforcement rate on each half of the session. Compared to equal reinforcement rates on both halves of the session, when the reinforcement rate on the first half was lower than on the second half, performance showed more anticipation and less perseveration errors, and when the reinforcement rate on the first half was higher than on the second half, performance showed a remarkable reduction of both types of errors. These results suggest that choice depends on both time into the session and the outcome of previous trials. They also challenge current models of timing to integrate local effects.
Journal of the Experimental Analysis of Behavior, 2019 · doi:10.1002/jeab.513