Effects Of Trial Spacing Research Articles

Response Competition and the Trial-Spacing Effect in Autoshaping with Rats

Two experiments studied the relationship between contextual conditioning, reinforcer quality (food pellets, sugar solution), and the trial-spacing (TS) effect. In a contextual conditioning situation, Experiment 1 showed that Feeder responses (nose inserted into the feeder) were more frequent after training with pellets than with the sugar solution, but Rearing responses (standing on hind legs with front legs on the air or on a wall) were more frequent with the sugar solution than with pellets. In an autoshaping situation, Experiment 2 showed that when the solution is used as the reinforcer, a robust TS effect emerges in lever pressing as a result of very low levels of lever-pressing responses in the massed condition. When food pellets are used as the reinforcer, no evidence was found of a TS effect. The results of Experiment 2 were analyzed in relation to the levels of Feeder and Rearing responses, which were shown to be, respectively, noncompetitive and competitive in relation to lever-pressing. A hypothesis based on response competition can account for most aspects of the present results, which are also discussed in relation to models stressing the processing of conditioned and unconditioned stimuli and a mediating role for contextual conditioning.

Trial spacing and trial distribution effects in Pavlovian conditioning: contributions of a comparator mechanism.

A potential basis for trial spacing and trial distribution effects was investigated in rats. In Experiment 1, a conditioned stimulus (e.g., CS A) was trained with either massed (e.g., A---->A---->A) or spaced (e.g., A-->A-->A) trials. When trials were massed, brief exposure to the training context (a condition typical of massed training) impaired responding, whereas more extensive exposure to the context during or after training reduced this apparent massed trials deficit. In Experiment 2, different CSs were trained in either a massed (e.g., A-->A-->A--> B-->B-->B-->C-->C-->C) or a distributed (e.g., A-->B-->C-->A-->B-->C, etc.) manner. Trials massed in this sense resulted in impaired responding to the CS, and this impairment was attenuated by posttraining extinction of the context cues. Thus, trial distribution and apparent trial spacing effects are at least in part reversible deficits in performance rather than failures of learning.

Trial-spacing effects in Hermissenda suggest contributions of associative and nonassociative cellular mechanisms.

In behaving Hermissenda, a preparatory conditioned response developed across repeated pairings of light (conditioned stimulus; CS) and rotation (unconditioned stimulus; US) with intertrial intervals (ITIs) of 60 and 120 s, but not 30 s. Likewise, contiguous in vitro stimulation of the visual and vestibular receptors, an analog of behavioral conditioning, resulted in an increase in the input resistance (i.e., excitability, a correlate of conditioning) of the B photoreceptors of the Hermissenda's eye, but only with ITIs greater than 60 s. Calcium signaling in the B cell, critical to the induction of this neuronal plasticity, was attenuated with shorter ITIs owing to (a) a reduction of the light-induced generator potential and hence voltage-dependent Ca2+ influx during the light CS, (b) a depression of the Ca2+ current that persisted throughout shorter ITIs, and (c) a steady-state inactivation of the Ca2+ current as a result of a sustained depolarization persisting from the previous trial. These results are consistent with a 2-process theory of associative learning in which a primary process (Ca2+ influx) may be opposed by a secondary process (depression of the Ca2+ current) during short ITIs.

Trace conditioning of the rabbit's nictitating membrane response as a function of CS-US interstimulus interval and trials per session

The present experiment examined modification of URs and acquisition of CRs in the rabbit's nictitating membrane preparation as a function of the CS-US interstimulus interval (ISIs = 400, 800, 1600, and 3200 ms) and trials per session (1, 5, and 25). In both paired CS-US groups and corresponding unpaired groups ( n = 12), UR amplitude was greater under 1 and 5 trials per session than under 25 trials per session. In early CR acquisition, ISI interacted with trials per session such that CRs emerged rapidly for all ISIs under 1 and 5 trials per session but emerged more slowly as an inverse function under 25 trials per session. Later in training, CR frequency tended to be inversely related to ISI under 1, 5, and 25 trials, but training under 1 and 5 trials per session differentially raised the asymptotic CR frequency at the longer ISIs, especially the 3200-ms value. The results are discussed in terms of their implications for accounts of trial spacing effects and the time course of CS representations in trace conditioning.

The role of local context in autoshaping

Three experiments used an autoshaping procedure with pigeons to examine the effects of nonreinforced, nontarget stimuli (ITI-fillers) during the intertrial interval on responding to a reinforced target CS. Experiment 1 replicated a previous demonstration that an ITI-filler that occupied a substantial portion of the ITI attenuated responding to the target CS relative to a group trained with a similar ITI but lacking the ITI-filler. Experiment 2 found that the superiority of responding typically found with a long ITI relative to a short ITI, that is, the trial-spacing effect, can be reversed by imposing a filler stimulus during the ITI in the former condition. Experiment 3, using a within-subject design, found that when one background stimulus condition occupied a majority of the interreinforcement interval, pairings of one target CS with reinforcement that were embedded within this background condition, that is, a long duration local context occurred for this CS, yielded better performance that a second, reinforced, target CS paired with reinforcement in the shorter duration background condition. These results confirmed predictions derived from a local context view of cycle time. Comparator theories of classical conditioning require incorporation of this notion into their conceptualization of effective cycle time in order to explain the present findings.

Distributed familiarization and test delay as predictors of infant preferences for familiarity and novelty

We investigated the time course of spatial-memory decay in rats using an eight-arm radial maze. It is well established that performance remains high with retention intervals as long as 4 h, but declines to chance with a 24-h retention interval (Beatty, W. W., & Shavalia, D. A. (1980b). Spatial memory in rats: time course of working memory and effect of anesthetics. Behavioral & Neural Biology, 28, 454–462). It is possible that 24 h reflects a genuine retention limitation of rat spatial memory. Alternatively, it may be possible to identify factors that might support memory performance even after very long delays. The current experiment was conducted to test the above two hypotheses. We evaluated performance using two intertrial intervals (24 and 48 h) and two retention intervals (1 and 25 h). Increasing the intertrial interval produced an approximately constant increase in performance for both retention intervals. This improvement is consistent with a trial-spacing effect (i.e., the superiority of spaced over massed trials). Rat spatial memory apparently lasts at least 25 h.

Reinforcement expectancy and trial spacing effects in delayed matching-to-sample by pigeons

Four experiments assessed the role of reinforcement expectancies in the trial spacing effect obtained in delayed matching-to-sample by pigeons. In Experiment 1, a differential outcome (DO) group received reinforcement with a probability of 1.0 for correct comparison responses following one sample stimulus and a probability of 0.2 for correct comparison responses following the other sample stimulus. The nondifferential outcome (NDO) group received reinforcement with a probability of 0.6 for correct responses to either stimulus. While matching accuracy was higher for the DO group than for the NDO group, both groups showed an equivalent decline in accuracy as the intertriai interval (ITI) duration was decreased. However, within the DO group, ITI duration affected performance on low-probability-of-reinforcement trials but not on high-probability-of-reinforcement trials. In Experiment 2, delay interval (DI) duration was 5, 10, or 15 sec and accuracy was higher for the DO group than for the NDO group at all DI durations. In addition, accuracy decreased similarly on high- and low-probability-of-reinforcement trials for the DO group as DI was increased. In Experiment 3, all birds were studied under DO conditions and ITI duration was manipulated along with DI duration. At the short DI duration, decreasing ITI duration had a detrimental effect on low-probability-of-reinforcement trials but no effect on high-probability-of-reinforcement trials. At the long DI duration, decreasing ITI duration had detrimental effects on both types of trials. In Experiment 4, unsignaled ITI reinforcers disrupted accuracy when the DI was long and when the ITI was short. The applicability of scalar expectancy theory to these data is discussed.

The trial spacing effect in delayed matching-to-sample by pigeons is dependent upon the illumination condition during the intertrial interval.

The trial spacing effect in delayed matching-to-sample by pigeons is dependent upon the illumination condition during the intertrial interval.

Sequential effects in pigeon delayed matching-to-sample performance.

Pigeons were tested in a three-alternative delayed matching-to-sample task in which second-choices were permitted following first-choice errors. Sequences of responses both within and between trials were examined in three experiments. The first experiment demonstrates that the sample information contained in first-choice errors is not sufficient to account for the observed pattern of second choices. This result implies that second-choices following first-choice errors are based on a second examination of the contents of working memory. Proactive interference was found in the second experiment in the form of a dependency, beyond that expected on the basis of trial independent response bias, of first-choices from one trial on the first-choice emitted on the previous trial. Samples from the previous trial were not found to exert a significant influence on later trials. The magnitude of the intertrial association (Experiment 3) did not depend on the duration of the intertrial interval. In contrast, longer intertrial intervals and longer sample durations did facilitate choice accuracy, by strengthening the association between current samples and choices. These results are incompatible with a trace-decay and competition model; they suggest strongly that multiple influences act simultaneously and independently to control delayed matching-to-sample responding. These multiple influences include memory for the choice occurring on the previous trial, memory for the sample, and general effects of trial spacing.

US duration and local trial spacing affect autoshaped responding

The acquisition and maintenance of signal-directed pecking was examined in week-old Leg-Horn chicks responding to a keylight stimulus paired with heat. In contrast with previous studies using pigeons with food as the US, both speed of acquisition and asymptotic level of keypecking were a direct function of US duration. Experiment 2 examined responding using a within-subject design to isolate the effects of trial spacing on performance during the immediate trial from the effects on performance during a following trial of fixed length. These comparisons revealed a significant effect of intertriai interval (ITI), with less responding after shorter intervals. The effect of different temporal spacing was apparent in responding on the immediate trial, but not on the following trial. These local ITI effects were better predicted by a recent autoshaping model based on relative waiting time (Jenkins, Barnes, & Barrera, 1981) than by a model based on relative US expectancy (Gibbons & Balsam, 1981). However, neither model predicted the effect of US duration. A reexamination of the US-duration literature suggested that the diversity of previous findings is consistent with the assumption that conditioned responding is an inverted U-shaped function of US duration.

Intracranial stimulation and natural reward: Differential effects of trial spacing

Rats rewarded with intracranial stimulation (ICS) in a runway ran faster after a decrease in intertrial interval and slower after an increase. The effect was not found in rats rewarded with water under highly similar conditions. The effect appears on the first trial. Therefore, it must be attributed to the decay of a drive-like process, and not to a change in the incentive value of ICS.

Trial Spacing in Instrumental Running

Trial spacing was studied over 120 acquisition trials and 20 each of extinction, reacquisition, and re-extinction, using five intertrial intervals from 40 sec. to 120 min. in between four daily trials. Throughout acquisition, performance of the 120-min. group increased throughout the course of a daily block, while the others first increased, then decreased. Spontaneous regression persisted throughout acquisition. Extinction performance was not systematically related to trial spacing, and no evidence for spontaneous recovery was found. Changes in measured spatial variability in the alley indexed learning but did not differentiate trial spacing effects. The results generally failed to confirm qualitative hypotheses about trial spacing derived from statistical learning theory.