Association for Behavior Analysis International

Every event occurs in the context of time, but time is more relevant for some events than for others. When events occur regularly at a particular time after a marker event, behavior comes under control by time elapsed since the marker event. Yet even when the correlation between time and events is perfect, control by time is imperfect. This symposium explores factors that influence the strength of temporal control, including the duration to be discriminated, the reinforcers associated with particular times, and the time-based contingency itself. We discuss procedures where time is a discriminative stimulus for when to begin responding, to stop responding, to withhold responding, or to change between different responses, as well as procedures in which time signals the non-contingent occurrence of a reinforcer. We assess similarities between control by time and by other stimuli that are exteroceptive, discretely different, or intermittently present, across a range of subjects including pigeons, rats, and dogs.

Domestic dogs completed a temporal bisection procedure that required them to respond to one lever following a short-light-signal duration and to another lever following a longer light-signal duration. The durations of short and long stimuli were varied across four conditions (0.5 2.0 s, 1.0 4.0 s, 2.0 8.0 s and 4.0 16.0 s). Intermediate durations, along with the original training stimuli, were presented during generalization tests. The dogs bisected the intervals near the geometric mean of the short and long stimulus pair. Weber fractions were not constant, instead they were well described by a U-shaped function. These results replicate the findings of Church and Deluty (1977) where the points of subjective equality also close to the geometric mean, as well as Bizo et al. (2006) and Zeiler (1991) who also demonstrated departures from Weber's Law.

How do reinforcers affect control by time-based contingencies? Four pigeons worked on a two-key concurrent schedule where the reinforcer ratio reversed once a fixed amount of time had elapsed since the most recent reinforcer. Thus, one response was more likely to produce a reinforcer before the reversal, while the other response was more likely to produce a reinforcer after the reversal. Across conditions, the percentage of reinforcers arranged before the reversal was manipulated from 5 to 95%. The magnitude of the change in choice around the reversal was greater when reinforcers were more equally distributed before and after the reversal, but the speed with which choice changed, and the time at which it reversed, was much less affected by the reinforcers. Thus, numbers of reinforcers appeared to influence discrimination of the contingency before and after the change, rather than the time of the reversal.These findings are not consistent with theories that assume that reinforcers alter discrimination of time itself, but can be understood in terms of discrimination of the relation between responses and reinforcers in time and space.

Organisms exposed to intermittent reinforcement schedules display behaviors that consistently occur throughout the inter-reinforcement intervals, even when no overt contingency has been arranged between those behaviors (adjunctive) and reinforcer occurrence. The most studied example of adjunctive behavior is schedule-induced drinking, characterized by an elevated licking to a waterspout when food is intermittently delivered. Under different experimental protocols we have been examining if adjunctive drinking serves time estimation, by means of performance under fixed interval schedules and peak probes, the bi-peak or bisection procedures. Results are generally consistent with a role of chaining of adjunctive behavior that serves organization of behavior in time rather than actual time estimation. A further role of adjunctive behavior that needs to receive some consideration is the subjective shortening of the pass of time while awaiting for the reinforcer.

In two experiments, male and female C57 mice were trained to withhold a response for either 3 or 6 s under a differential reinforcement of low rates (DRL) schedule of reinforcement, or under a fixed minimum interval (FMI) schedule. In DRL, reinforcement (sucrose pellet in Experiment 1; diluted sweetened condensed milk in Experiment 2) was contingent on the interval between two consecutive lever presses (LP mice) or two consecutive nose-pokes (NP mice). In FMI, reinforcement was contingent on similar intervals, but terminated with a head entry into the feeder. In DRL, but not in FMI, performance varied between LP and NP mice, between levels of deprivation, and between types of reinforcers. These results are consistent with previous data from rats, suggesting that FMI provides measures of response-inhibition capacity and timing that are more robust to motivational and sensorimotor variables than DRL. We suggest these difference between FMI and DRL are likely due to the differential discriminability and function of responses between DRL and FMI.