INTERTRIAL INTERVAL DURATION AND LEARNING IN AUTISTIC CHILDREN

This study investigated the influence of intertrial interval duration on the performance of autistic children during teaching situations. The children were taught under the same conditions existing in their regular programs, except that the length of time between trials was systematically manipulated. With both multiple baseline and repeated reversal designs, two lengths of intertrial interval were employed: short intervals with the S^D for any given trial presented approximately one second following the reinforcer for the previous trial versus long intervals with the S^D presented four or more seconds following the reinforcer for the previous trial. The results showed that: (1) the short intertrial intervals always produced higher levels of correct responding than the long intervals; and (2) there were improving trends in performance and rapid acquisition with the short intertrial intervals, in contrast to minimal or no change with the long intervals. The results are discussed in terms of utilizing information about child and task characteristics in terms of selecting optimal intervals. The data suggest that manipulations made between trials have a large influence on autistic children's learning.     

Intertrial-interval effects on sensitivity (A') and response bias (B") in a temporal discrimination by rats.

Killeen and Fetterman's (1988) behavioral theory of animal timing predicts that decreases in the rate of reinforcement should produce decreases in the sensitivity (A') of temporal discriminations and a decrease in miss and correct rejection rates (decrease in bias toward "long" responses). Eight rats were trained on a 10- versus 0.1-s temporal discrimination with an intertrial interval of 5 s and were subsequently tested on probe days on the same discrimination with intertrial intervals of 1, 2.5, 5, 10, or 20 s. The rate of reinforcement declined for all animals as intertrial interval increased. Although sensitivity (A') decreased with increasing intertrial interval, all rats showed an increase in bias to make long responses.     

Choice as a function of local versus molar reinforcement contingencies.

Rats were trained on a discrete-trial probability learning task. In Experiment 1, the molar reinforcement probabilities for the two response alternatives were equal, and the local contingencies of reinforcement differentially reinforced a win-stay, lose-shift response pattern. The win-stay portion was learned substantially more easily and appeared from the outset of training, suggesting that its occurrence did not depend upon discrimination of the local contingencies but rather only upon simple strengthening effects of individual reinforcements. Control by both types of local contingencies decreased with increases in the intertrial interval, although some control remained with intertrial intervals as long as 30 s. In Experiment 2, the local contingencies always favored win-shift and lose-shift response patterns but were asymmetrical for the two responses, causing the molar reinforcement rates for the two responses to differ. Some learning of the alternation pattern occurred with short intertrial intervals, although win-stay behavior occurred for some subjects. The local reinforcement contingencies were discriminated poorly with longer intertrial intervals. In the absence of control by the local contingencies, choice proportion was determined by the molar contingencies, as indicated by high exponent values for the generalized matching law with long intertrial intervals, and lower values with short intertrial intervals. The results show that when molar contingencies of reinforcement and local contingencies are in opposition, both may have independent roles. Control by molar contingencies cannot generally be explained by local contingencies.     

Role of intertrial interval following an escape or avoidance response in bar-press avoidance

In three experiments, rats learned bar-press avoidance as a function of the intertrial interval following an escape or an avoidance. The general hypothesis is that the length of these intervals affects bar-press avoidance differentially, depending on whether an avoidance follows an escape (avoidance/escape) or an avoidance (avoidance/avoidance) on the previous trial. Specifically, it is proposed that short escape ITIs will facilitate avoidance/escape and avoidance/avoidance, while avoidance ITIs will have no effect on avoidance responding. The results tend to support this hypothesis. The shorter the intertrial interval following an escape, the higher the probability of both measures: avoidance/escape and avoidance/avoidance. No effect of avoidance interval was found on avoidance/avoidance. Unpredictedly, however, it was found that in comparison to a very short intertrial interval following an avoidance (0.5 sec), relatively long intervals (5 and 45 sec) facilitate avoidance/escape. These results were interpreted as mainly reflecting nonassociative factors such as shock-produced activity.     

Interference effects on preschool children's learning sets

Four experiments investigated interference in 5-year-olds' learning sets. Experiment 1 manipulated intertrial and interproblem intervals, showing that increased intertrial intervals retarded performance. Long interproblem intervals interacted with short intertrial intervals to produce performance facilitation. Experiment 2 investigated interpolations within problems with either similar or dissimilar stimulus presentations. Similar stimuli caused greater performance decrements than dissimilar. Experiment 3 hypothesized that the within-subjects design of Experiment 1 masked interproblem interval effects. Testing between-subjects established that increased interproblem delays facilitate performance. In Experiment 4 interproblem delays were further tested in a series of shifts within and between dimensions. Increased delays more greatly benefited shifts within dimensions. It is concluded that intertrial and interproblem intervals affect learning set performance differentially. Intertrial delays result in performance deterioration due in part to interference. Interproblem delays facilitate performance at least in part by providing the opportunity for suppression of proactive interference, and perhaps in part by providing the opportunity for constructive cognitive processing.     

Response patterning in goldfish: single alternation in a Pavlovian aversive paradigm

Single alternation behavior was studied in a Pavlovian aversive shuttle-response situation using goldfish. Independent groups of fish were given either a fixed interval between alternating reinforced (R) and nonreinforced (N) trials or were given differential temporal information between trials. Although all groups exhibited higher response probabilities on reinforced than on nonreinforced trials, goldfish receiving a short interval (10 s) following R trials and a long interval (60 s) following N trials (R10N60) demonstrated significantly superior alternation performance compared with subjects receiving a fixed intertrial interval (R35N35) or a long interval following R trials and a short interval following N trials (R60N10). The alternation performance exhibited by the R10N60 group was shown to be equivalent to that of subjects receiving standard color discrimination training. However, the alternation performance in group R35N35 showed a great deal of within-subject variability and raises questions concerning the elusive nature of alternation using Pavlovian conditioning procedures.     

Support for a theory of memory for event duration must distinguish between test-trial ambiguity and actual memory loss

Staddon and Higa's (1999) trace-strength theory of timing and memory for event duration can account for pigeons' bias to "choose short" when retention intervals are introduced and to "choose long" when, following training with a fixed retention interval, retention intervals are shortened. However, it does not account for the failure of pigeons to choose short when the intertrial interval is distinct from the retention interval. That finding suggests that stimulus generalization (or ambiguity) between the intertrial interval and the retention interval may result in an effect that has been attributed to memory loss. Such artifacts must be eliminated before a theory of memory for event duration can be adequately tested.     

Temporal parameters of the feature positive effect

Trial duration and intertrial interval duration were parametrically varied between groups of pigeons exposed to a discrimination involving the presence vs. the absence of a dot. Half the groups received the dot as the positive stimulus (feature positive groups) and half the groups received the dot as the negative stimulus (feature negative groups). Faster learning by the feature positive birds (feature positive effect) was found when the trial duration was short (5 sec) regardless of whether the intertrial interval was short (5 sec) or long (30 sec). No evidence for a feature positive effect was found when the trial duration was long (30 sec) regardless of the length of the intertrial interval (30 sec or 180 sec). The results suggest that short trial duration is a necessary condition for the occurrence of the feature positive effect, and neither intertrial interval nor trial duration/intertrial interval ratio are important for its occurrence. The suggestion that mechanisms underlying the feature positive effect and autoshaping might be similar was not supported by the present experiment since the trial duration/intertrial interval ration parameter appears to play an important role in autoshaping but not the feature positive effect.     

Spatial memory in rats after 25 hours

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.     

Acquisition and reversal of a discriminated autoshaped response in male and female rats: Effects of long or short and fixed or variable intertrial interval durations

Groups of male and female Wistar rats were exposed to autoshaping procedures in which the duration (50 vs 20 s) and the variablity (fixed vs variable) of the intertrial interval were manipulated. Pellet delivery occurred after one of the levers (CS+) had been presented for 10 s. Presentation of the other lever (CS−) was not associated with pellet delivery. CS+ contacts occurred more frequently and at higher rates when the intertrial interval was 50 s than when it was 20 s, while intertrial interval variability did not play an important role. Males contacted CS+ and CS− more frequently and at a higher rate than did females. Goal-directed activity (nose pokes in feeder tray) occurred more often when the intertrial interval was short than when it was long. Females showed higher goal-directed activity than did males, both during CS presentation and during the intertrial interval. When experimental contingencies were reversed, CS+ contacts decreased and CS− contacts increased for males and females, but the decrease in CS+ contacts occurred more slowly for males than for females. The results of these experiments add to a growing body of literature suggesting the existence of fundamental behavioral differences between the sexes. These differences are partly attributable to the influence of gonadal hormones during development and maturation and partly attributable to the behavioral requirements of the experimental procedures.     

Effects of discrete-trial and free-operant procedures on the acquisition and maintenance of successive discrimination in rats.

Rats were trained on a successive discrete-trial discrimination between two tonal stimuli to examine the effects of availability of a lever during intertrial intervals. In the discrete-trial condition, in which a lever was removed from the chamber during intertrial intervals, 10-s trials were initiated by the presentation of both discriminative stimulus and lever. In the free-operant condition, in which a lever was present during both trials and intertrial intervals, 10-s trials were initiated only by the presentation of a discriminative stimulus. Experiment 1 employed 50-s intertrial intervals and demonstrated that discriminative performances were acquired faster and maintained better in the free-operant conditions than in the discrete-trial conditions. Experiment 2 employed 5-s intertrial intervals and showed that poor discriminative performances in the discrete-trial conditions were improved. These results indicate that the presentation of a lever to start a trial can overshadow or mask the control by a discriminative stimulus and thereby obstruct the acquisition and maintenance of discriminative performances. Furthermore, the overshadowing or masking effects are strengthened as a function of the duration of intertrial intervals.     

The sex difference in rotary pursuit performance: aptitude or inhibition?

This study examined the hypothesis that male dominance in the acquisition and performance of rotary pursuit skill reflects a lower male proclivity for the generation and accumulation of reactive inhibition rather than some innately superior ability to profit from practice. On this hypothesis, the magnitude of male dominance should decline as the length of the intertrial interval increases. The experimental sample consisted of 120 Caucasian subjects (60 of each sex) who were given sixty 30-sec trials on rotary pursuit with intertrial intervals ranging from 0 to 40 sec. The principal finding was that the magnitude of the sex difference depended significantly upon the length of the intertrial interval, as hypothesized. When the interval was 10 sec or longer, performance levels of the sexes were essentially equal. The sex variance was reduced to insignificance even on the first trial when allowance was made for the inhibitory effect of practice. Thus, male dominance in rotary pursuit skill appears to be a procedural effect mediated by and inhibitory mechanism rather than a consequence of differential endowments of learning ability.     

The Sex Difference in Rotary Pursuit Performance

This study examined the hypothesis that male dominance in the acquisition and performance of rotary pursuit skill reflects a lower male proclivity for the generation and accumulation of reactive inhibition rather than some innately superior ability to profit from practice. On this hypothesis, the magnitude of male dominance should decline as the length of the intertrial interval increases. The experimental sample consisted of 120 Caucasian subjects (60 of each sex) who were given sixty 30-sec trials on rotary pursuit with intertrial intervals ranging from 0 to 40 sec. The principal finding was that the magnitude of the sex difference depended significantly upon the length of the intertrial interval, as hypothesized. When the interval was 10 sec or longer, performance levels of the sexes were essentially equal. The sex variance was reduced to insignificance even on the first trial when allowance was made for the inhibitory effect of practice. Thus, male dominance in rotary pursuit skill appears to be a procedural effect mediated by an inhibitory mechanism rather than a consequence of differential endowments of learning ability.     

Rats' lever-press durations as psychophysical judgments of time

Hungry rats received food following lever-press durations exceeding a minimum value, which ranged from 0 to 6.4 sec. When no intertrial intervals separated successive presses, modal press durations remained at very short values as the minimum value required for food was increased. This was particularly true immediately after a food presentation. When an 8-sec intertrial interval followed each lever release, modal press durations were always at or beyond the minimum value required for food, and outcome of the preceding press had no effect on press duration. Possible reasons for the effects of intertrial intervals included punishment of short presses, increased delay of reinforcement of short presses, and reduced density of reinforcement. In addition, functions relating discrete-trials lever-press duration to minimum duration required for food were found to be qualitatively and quantitatively similar to the power functions recently proposed by Catania (1970) for interresponse time and response latency. This similarity was taken as support for a general psychophysical law of temporal judgments.     

The effects of variation of intertrial interval on exploration of elevatd and enclosed mazes

The interval between exploratory trials was varied in experiments using simple elevated or enclosed mazes. Activity on the second trial was depressed for short intertrial intervals but had recovered after about 10 min.; the degree of recovery was different in the two types of maze. A second decrease in second trial activity was found with inter-trial intervals of more than 20 min., but a further experiment suggested this was due to the effects of delay itself, rather than to previous experience of the environment.     

Vertical jumping and signaled avoidance

This paper reports an experiment intended to demonstrate that the vertical jumping response can be learned using a signaled-avoidance technique. A photoelectric cell system was used to record the response. Twenty female rats, divided equally into two groups, were exposed to intertrial intervals of either 15 or 40 s. Subjects had to achieve three successive criteria of acquisition: 3, 5, and 10 consecutive avoidance responses. Results showed that both groups learned the avoidance response, requiring increasingly larger numbers of trials as the acquisition criteria increased. No significant effect of intertrial interval was observed.     

Determinants of serial discrimination learning by squirrel monkeys

Squirrel monkeys were presented multiple serial discriminations 1, 2, 4, and 8 problems long. They were then presented problems designed to separate the effects of within-list associative interference from the effects of within-problem intertrial interval as list length was increased. The Ss committed consistently fewer errors after Trial 1 reward than after Trial 1 nonreward and showed strong stimulus perseveration. An increase in within-problem intertrial interval from 30 sec to 4 min had no effect whereas the associative interference resulting from increased problem length caused a small but significant performance decrement. Old and new problems had about equal effects on serial discrimination. The findings indicated that squirrel monkeys are relatively insensitive to within-problem associative interference.     

Optimal Stimulus Parameters In Avoidance Conditioning Of Inbred Strains Of Mice

Highly inbred mice of fast and slow conditioning strains (N = 228) were trained in avoidance conditioning and 180 were continued to extinction. The principal goal was to determine optimal stimulus conditions for fast learning, small variances, and maximal strain differences. Conclusions are: a) the major effect of change in CS-US and intertrial intervals occurs, respectively, for intervals less than 3 sec. and 60 sec.; b) change in amperage (150-400 pa) or voltage (250-400 v.) caused no significant differences; c) strain differences in extinction occurred after nearly optimal conditioning, and d) strain differences were altered considerably as stimulus conditions became optimal. Optimal levels of parameters are: 3 sec. CS-US interval, 120-sec. intertrial interval, and 400 v. (220 K ohm impedance circuit).     

A stochastic model for rote serial learning

A model for the acquisition of responses in an anticipatory rote serial learning situation is presented. The model is developed in detail for the case of a long intertrial interval and employed to fit data where the list length is varied from 8 to 18 words. Application of the model to the case of a short intertrial interval is considered; some predictions are derived and checked against experimental data.The author wishes to thank Professors C. J. Burke and W. K. Estes for advice and assistance in carrying out this research.     

The effects of interval duration on temporal tracking and alternation learning

On cyclic-interval reinforcement schedules, animals typically show a postreinforcement pause that is a function of the immediately preceding time interval (temporal tracking). Animals, however, do not track single-alternation schedules-when two different intervals are presented in strict alternation on successive trials. In this experiment, pigeons were first trained with a cyclic schedule consisting of alternating blocks of 12 short intervals (5 s or 30 s) and 12 long intervals (180 s), followed by three different single-alternation interval schedules: (a) 30 s and 180 s, (b) 5 s and 180 s, and (c) 5 s and 30 s. Pigeons tracked both schedules with alternating blocks of 12 intervals. With the single-alternation schedules, when the short interval duration was 5 s, regardless of the duration of the longer interval, pigeons learned the alternation pattern, and their pause anticipated the upcoming interval. When the shorter interval was 30 s, even when the ratio of short to long intervals was kept at 6:1, pigeons did not initially show anticipatory pausing-a violation of the principle of timescale invariance.