Response rates track the history of reinforcement times.

Abstract

When conditioning involves a consistent temporal relationship between the conditioned stimulus (CS) and unconditioned stimulus (US), the expression of conditioned responses within a trial peaks at the usual time of the US relative to the CS. Here we examine the temporal profile of responses during conditioning with variable CS-US intervals. We conditioned stimuli with either uniformly distributed or exponentially distributed random CS-US intervals. In the former case, the frequency of each CS-US interval within a specified range is uniform but the momentary probability of the US (the hazard function) increases as time elapses during the trial; with the latter distribution, short CS-US intervals are more frequent than longer intervals, but the momentary probability of the US is constant across time within the trial. We report that, in a magazine approach paradigm, rats' response rates remained stable as time elapses during the CS when the CS-US intervals were uniformly distributed, whereas their response rates declined when the CS-US intervals were exponentially distributed. In other words, the profile of responding during the CS matched the frequency distribution of the US times, not the momentary probability of the US during the CS. These results are inconsistent with real-time associative models, which predict that associative strength tracks the momentary probability of the US, but may provide support for timing models of conditioning in which conditioned responding is tied to remembered times of reinforcement.

Adjunctive behaviors are operants

“…This seems to be the case (Millenson, Allen, & Pinker, 1977;Plonsky, Driscoll, Warren, & Rosellini, 1984). Consistent with this inference, Harris, Gharaei and Pincham (2011) demonstrated that response rates during a CS track the relative frequencies, not the marginal probabilities, of reinforcement. Gaps in irregular distribution are likely to be filled with adjunctive responses.…”

Interval, blocking, and marking effects during the development of schedule-induced drinking in rats.

“…In all of these studies, pretraining involving intermittent pellet delivery took place immediately prior to an SID stage in the same chamber and with the same mean rate of pellet delivery. In the present experiment, rats gained prior exposure to intermittent pellet delivery some weeks before the experiment started, in somewhat different conditioning chambers, and at lower rates of pellet delivery, which were variable, with a mean interval of 150 s between pellets (Harris et al, 2011), as opposed to the fixed interpellet interval of 30 s used here. It should be noted that there was, however, no indication in the present experiment that a rat's experimental history affected classical conditioning in the pretraining stage (Stage 1) when the house light was paired with pellet delivery in the blocking condition.…”

“…Twenty-four male hooded Wistar rats from the same source as in previous experiments had previously served in fiavor learning experiments involving maltodextrin, 16 of which also had prior experience in a classical conditioning experiment in which food pellets served as the unconditioned stimulus signaled by auditory and visual conditioned stimuli (Harris, Gharaei, & Pincham, 2011). This prior history was essentially the same as that of the rats used in Experiment 1.…”

Changes in the distribution of response rates across the CS-US interval: Evidence that responding switches between two distinct states.

“…Rats in Group FT30 should show a systematic change in their response rate, rising across the first 30-s of the CS and then declining again beyond that time (Church et al, 1994). An interpretation of this pattern in terms of timing of the CR to the US would be confirmed by comparing Group FT30 to Group VT30, because rats in the latter group should maintain a relatively steady level of responding across the 60-s CS presentation (Harris & Carpenter, 2011;Harris, Gharaei, & Pincham, 2011). The rats in both groups were trained for 40 days, and their response rates were analyzed from the last 20 days.…”