Tracking of the expected time to reinforcement in temporal conditioning procedures

Abstract

In one experiment, the rate and pattern of responding (head entry into the food cup) under different distributions of intervals between food deliveries were examined. Separate groups of rats received fixed-time (45, 90, 180, or 360 sec), random-time (45, 90, 180, or 360 sec), or tandem fixed-time (45 or 90 sec) random-time (45 or 90 sec) schedules of reinforcement. Schedule type affected the pattern of responding as a function of time, whereas mean interval duration affectedthe mean rate of responding. Responses occurred in bouts with characteristics that were invariant across conditions. Packet theory, which assumes that the momentary probability of bout occurrence is negatively related to the conditional expected time remaining until the next reinforcer, accurately predicted global and local measures of responding. The success of the model advances the prediction of multiple measures of responding across different types of time-based schedules. KIRKPATRICK AND CHURCHgiven that food, has not yet occurred (Catania & Reynolds, 1968). (See Anger, 1956, for the application of the hazard function to interresponse time [IRT] distributionsin DRL schedules.) As is shown in Figure 1, the hazard function for a random interval is constant over time and, therefore, could explain the relatively constant rate of responding that is observed. However, a different distribution form is required for fixed-interval performance, because the hazard function does not map onto response rate. One could use the hazard function with added variability to explain both fixed-and random-interval performance, but this would lead to a departure from constancy in the random-interval case and, therefore, would not accurately fit the data.A third proposal has been to assume that temporal control over behavior decreases as variability increases, so that fixed intervals exhibit strong control but (exponential) random intervals exhibit no control over behavior (Lund, 1976).All three approaches propose different processes in random and fixed intervals. This leads to the unparsimonious conclusion that there may be multiple timing systems, each tuned to a different distribution form. A simpler alternative would be to assume that temporal performance is controlled by some common aspect of different distribution forms.In addition to an examination of the effects of variability on responding, the present experiment provided an as- EXPECTED TIME TO REINFORCEMENT 5 sessment of the role of mean interval duration. Interval duration usually is negatively related to measures of response rate or strength (Bitterman, 1964;Black, 1963;de Villiers & Herrnstein, 1976;Gibbon, Baldock, Locurto, Gold, & Terrace, 1977;Herrnstein, 1970;Salafia, Terry, & Daston, 1975;Schneiderman & Gormezano, 1964). This relationship is often reported to be nonlinear in form (e.g., Herrnstein, 1970). Predictions of the rate of responding have traditionally required a separate explanation from predictions of the pattern of responding in interval-based procedures. For example, Herrnstein's ...

Response rates track the history of reinforcement times.

“…These experiments confirmed that rats' response rates are sensitive to reinforcement rates: the rats responded more to CSs with higher mean reinforcement rates than to CSs with lower reinforcement rates (Kirkpatrick & Church, 2003). The more important observation concerns how response rates across the duration of a CS were affected by the distribution of the CS's reinforcement times.…”

“…The common observation has been that response rates increase as time elapses during uniformly distributed VIs (Catania & Reynolds, 1968;Church, Lacourse, & Crystal, 1998;Harzem, Lowe, & Priddle-Higson, 1978;Lund, 1976), and remain at a constant level as time elapses during exponentially distributed VIs (Catania & Reynolds, 1968;Harzem et al, 1978;Kirkpatrick & Church, 2003). Most of these studies measured instrumental responses for food (bar pressing in rats, key pecking in pigeons) during VI schedules.…”

“…Random schedules of reinforcement produce relatively uniform patterns of responding over time (Catania & Reynolds, 1968;Kirkpatrick & Church, 2003). Here, we are interested in comparing two different types of randomly varying schedule in delay conditioning.…”

“…Some theorists have argued that subjects explicitly keep track of time during each trial, and conditioned responding is governed by a memory for the precise time at which the US occurred (e.g., Balsam & Gallistel, 2009;Gallistel & Gibbon, 2000;Gibbon, 1977;Kirkpatrick & Church, 2003). An alternative approach maintains the central features of associative processes, but attributes the evidence for response timing to a representation of the CS that is distributed across time.…”

Temporal Uncertainty During Overshadowing

“…When the target was a fixed 30-s there was a gradually increasing rate of responding which reached a peak at about the time of US delivery ( Figure 2a) and a slope that differed significantly from zero; when it was of variable duration, on the other hand, responding was relatively stable and the slope did not differ from zero (Figure 2b). Although the different patterns of responding during stimuli of fixed and variable duration have been demonstrated before (Kirkpatrick & Church, 2003), one further marked feature of the present results was that this pattern was unaffected by whether the target stimulus had suffered overshadowing or not. Whether or not this is a general feature of response form during cue competition will require further investigation; however, these results are consistent with previous reports that demonstrate that stimuli of differing fixed durations were tracked accurately by rat subjects during both blocking and overshadowing (Jennings & Kirkpatrick 2006;Jennings et al, 2007).…”