Showing papers by "Russell M. Church published in 2000"

Independent effects of stimulus and cycle duration in conditioning: The role of timing processes

Abstract: Rats received delay conditioning procedures with a white-noise conditioned stimulus (CS), a food unconditioned stimulus (US), and head entries into the food cup as the conditioned response. The stimulus duration (S) and the interval between food deliveries (C) were varied between groups:S=15, 30, 60, and 120 sec;C=90, 180, and 360 sec. The stimulus/cycle duration ratio was negatively related to the asymptotic level of conditioning but had no effect on the rate of acquisition. Conditioning and timing of responses emerged together in training. Timing occurred during the CS-US interval (ISI) and the US-US interval (ITI), as evidenced by increasing response rate gradients that were steeper for shorter intervals. The effects of the stimulus/cycle ratio on conditioning were attributed to independent timing of theS andC durations. Serial-, parallel-, and single-process accounts of conditioning and timing are compared.

Stimulus and temporal cues in classical conditioning.

Abstract: In 2 experiments, separate groups of rats were given stimulus conditioning, temporalconditioning, untreated control and (in Experiment 2) learned irrelevance control procedures,followed by a compound with both stimulus and temporal cues. Stimulus conditioningconsisted of a random 15-s duration conditioned stimulus (CS) followed by food; temporalconditioning consisted of food-food intervals of fixed 90 s (Experiment 1) or fixed 75 +random 15 s (Experiment 2). The stimulus group abruptly increased responding after CSonset, and the temporal group gradually increased responding over the food-food interval.When the food-food interval was fixed 90 s, the temporal cue exerted stronger control in thecompound, whereas when the food-food interval was fixed 75 + random 15 s, the stimuluscue exerted stronger control. The strength of conditioning, temporal gradients of responding,and cue competition effects appear to reflect simultaneous timing of multiple intervals.A common view of classical conditioning is that anassociation is formed between the conditioned stimulus (CS)and the unconditioned stimulus (US). In associative theoriesof conditioning (e.g., Mackintosh, 1975; Pearce & Hall,1980; Rescorla & Wagner, 1972), strength accrues to stimulithat are present at the time of US occurrence, and it accruesuniformly over the duration of a stimulus. Although associa-tive theories can account for many of the phenomena ofconditioning such as acquisition, extinction, blocking, andovershadowing, they do not assign any role of temporalcontent in conditioning, nor do they attempt to account forany changes in response strength over the duration of thestimulus.There are a number of well-established facts of condition-ing that indicate that temporal variables are importantcontributors to the conditioning process; (a) CS-US interval,trace interval, and intertrial interval durations all affect theacquisition of conditioned responses; and (b) a fixed timebetween the CS onset and US occurrence produces responsetiming relative to CS onset (inhibition of delay), and a fixedtime between successive USs produces response timingrelative to the time of the occurrence of the last US(temporal conditioning). To accommodate these phenom-ena, theories of conditioning need to include a representa-tion of time since an event, such as CS onset or the prior USdelivery.Real-time models of conditioning (e.g., Blazis, Desmond,Moore, & Berthier, 1986; Sutton & Barto, 1981, 1990) haveintegrated a representation of time with an associativemechanism. In these models, the perception of the CSchanges over its time-course so that it is possible todiscriminate different times within the CS. As a result of theKimberly Kirkpatrick and Russell M. Church, Department ofPsychology, Brown University.Correspondence concerning this article should be addressed toKimberly Kirkpatrick, Department of Psychology, Box 1853,Brown University, Providence, Rhode Island 02912. Electronicmail may be sent to Kim_Kirkpatrick@brown.edu.incorporation of a timing mechanism, the real-time modelsare able to account for the increasing likelihood of respond-ing as a function of time since CS onset. They can alsoaccuratel y reproduc e man of th effects temporalvariables on conditioning, such as differences in perfor-mance due to the CS-US interval or trace interval.Despite the recent growth of interest in the role oftemporal intervals in conditioning (Cooper, 1991; Gallistel& Gibbon, 2000; Holder & Roberts, 1985; Holland, 1998;Kehoe, Graham-Clarke, & Schreurs, 1989; Savastano M Gibbon B or, perhaps conditioning occurs through a singleprocess that encodes the strength of association of aparticular stimulus, with differential weighting over thetime-course of the stimulus, as in the real-time models.The purpose of the present study was to assess the role ofstimulus and temporal factors in the conditioning process. Inan initial phase, different distributions of time intervalsbetween events were used to produce either stimulus condi-tioning to the CS or temporal conditioning to the food-foodinterval. Acquisition to the stimulus and temporal cues wasexamined when the two cues were delivered separately toassess differences in learning. Then, in order to determinethe relative contribution of stimulus and temporal cues to theconditioning process, the two groups of rats were transferredto a compound conditioning procedure in which both the CSand the time since the prior food delivery were related to thetime of the upcoming food delivery.The design of the present study is similar to an earlierreport by Williams and LoLordo (1995). They discovered206