Recent Exposure to a Dangerous Context Impairs Extinction and Reinstates Lost Fear Reactions.

Rats were shocked in a context and then exposed to that context in the absence of shock. Shorter intervals between these extinction trials produced more long-term freezing than did longer ones, and shorter intervals between the final extinction trial and test produced more freezing than did longer ones. A short interval between a context extinction trial and test with an extinguished conditioned stimulus (CS) produced more freezing than did a longer one, and a short interval between a nonreinforced context exposure and an extinguished CS reinstated freezing when the CS was tested 24 hr later. The results suggest that recent fear acts to favor subsequent retrieval of the memory formed at conditioning rather than extinction and to render the retrieved memory more salient. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 SD for any given trial presented approximately one second following the reinforcer for the previous trial versus long intervals with the SD 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.     

Exploration of cerebellar-dependent associative learning in schizophrenia: Effects of varying and shifting interstimulus interval on eyeblink conditioning.

Eyeblink conditioning abnormalities have been reported in schizophrenia, but the extent to which these anomalies are evident across a range of delay intervals (i.e., interstimulus intervals; ISIs) is unknown. In addition, the effects of ISI shifts on learning are unknown, though such manipulations can be informative about the plasticity of cerebellar timing functions. Therefore, the primary purpose of the present study was to investigate the interactions between ISI manipulations and learning in schizophrenia. A standard delay eyeblink conditioning procedure with four different interstimulus intervals (ISIs; 250, 350, 550, 850 ms) was employed. Each eyeblink conditioning experiment was immediately followed by another with a different ISI, thus permitting the characterization of conditioned response (CR) learning at one ISI and the extent to which CRs could be generated at a different latency following an ISI shift. Collapsing across all conditions, the schizophrenia group (n = 55) had significantly fewer conditioned responses and longer onset latencies than age-matched controls (n = 55). Surprisingly, shifting to a new ISI had negligible effects on conditioned response rates in both groups. These findings contribute to evidence of robust eyeblink conditioning abnormalities in schizophrenia and suggest impaired cerebellar function, but underscore the need for more research to clarify the source of these abnormalities and their relationship to clinical manifestations of schizophrenia. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The temporal dynamics of a visual discrimination: The role of stimulus comparison and opponent processes.

The influence of trial spacing on simple conditioning is well established: When successive reinforced conditioned stimulus, CS+, trials are separated by a short interval (massed training), conditioned responding emerges less rapidly than when such trials are separated by longer intervals (spaced training). This study examined the influence of trial spacing on the acquisition of an appetitive visual discrimination in rats. Experiments 1 and 2 established that massed training facilitates the acquisition of such discriminations. The results of subsequent experiments demonstrated that this trial-spacing effect reflects the proximity of nonreinforced, CS-, trials to preceding (Experiment 3) and signaled (Experiment 4) presentations of the reinforcer. Experiment 5 showed that the facilitation of discrimination learning with massed training reflected an effect on learning rather than performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eyeblink conditioning during an interstimulus interval switch in rabbits (Oryctolagus cuniculus) using picrotoxin to disrupt cerebellar cortical input to the interpositus nucleus.

The role of the cerebellar cortex in eyeblink classical conditioning remains unclear. Experimental manipulations that disrupt the normal function impair learning to various degrees, and task parameters may be important factors in determining the severity of impairment. This study examined the role of cerebellar cortex in eyeblink conditioning under conditioned stimulus?unconditioned stimulus intervals known to be optimal or nonoptimal for learning. Using infusions of picrotoxin to the interpositus nucleus of the rabbit cerebellum, the authors pharmacologically disrupted input from the cerebellar cortex while training with an interstimulus interval (ISI)-switch procedure. One group of rabbits (Oryctolagus cuniculus) was 1st trained with a 250-ms ISI (optimal) and then switched to a 750-ms ISI (nonoptimal). A 2nd group was trained in the opposite order. The most striking effect was that picrotoxin-treated rabbits initially trained with a 250-ms ISI learned comparably to controls, but those initially trained with a 750-ms ISI were severely impaired. These results suggest that functional input from cerebellar cortex becomes increasingly important for the interpositus nucleus to learn delay eyeblink conditioning as the ISI departs from an optimal interval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term habituation to repeated loud noise is impaired by relatively short interstressor intervals in rats.

The phenomenon of spaced (longer intertrial interval) compared with massed (shorter intertrial interval) training leading to better long-term habituation and associative learning is well documented. However, the effects of intertrial intervals on response habituation to repeated stress exposures have not been previously examined. The present experiments found that massed (six 30-min exposures of 95 dB white noise in 6 hr) and spaced (one 30-min exposure daily for 6 days) noise exposures led to similar habituation of plasma corticosterone and ACTH responses, heart rate, and core body temperature after the 6th exposure in male Sprague-Dawley rats. However, these habituated responses were not retained in the massed group on a similar noise re-exposure 48 hr later, compared with the spaced group. The habituated responses found in the massed group after the 6 noise exposures were not due to differential hearing threshold shifts, as examined with modifications of the acoustic startle reflex. These data indicate that relatively short interstressor intervals impair long-term stress adaptation. This series of studies supports the idea of distinct short- and long-term habituation processes to stress responsiveness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dorsal hippocampus involvement in trace fear conditioning with long, but not short, trace intervals in mice.

Placing a "trace" interval between a warning signal and an aversive shock makes consolidation of the memory for trace conditioning hippocampus dependent. To determine the trace at which memory consolidation requires the hippocampus, mice were trained with 0-s, 1-s, 3-s, or 20-s trace intervals and tested for freezing to context and tone. Posttraining dorsal hippocampus (DH) lesions decreased context conditioning regardless of trace interval. However, DH lesions attenuated only the 20-s trace tone freezing. Like eyeblink conditioning, the DH is necessary for trace fear conditioning only at long trace intervals, but the time scale for the effective interval in fear conditioning is about 40 times longer. Manipulations that alter trace fear conditioning with short trace intervals probably do not reflect altered DH function. Given this difference in time scale along with the use of posttraining DH lesions, hippocampus dependency of trace conditioning is not related to a bridging function or response timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intertrial interval as a contextual stimulus: Further analysis of a novel asymmetry in temporal discrimination learning.

Four experiments investigated discrimination learning when the duration of the intertrial interval (ITI) signaled whether or not the next conditional stimulus (CS) would be paired with food pellets. Rats received presentations of a 10-s CS separated half the time by long ITIs and half the time by short ITIs. When the long ITI signaled that the CS would be reinforced and the short interval signaled that it would not be (Long+/Short?), rats learned the discrimination readily. However, when the short ITI signaled that the CS would be reinforced and the long interval signaled that it would not (Short+/Long?), discrimination learning was much slower. Experiment 1 compared Long+/Short? and Short+/Long? discrimination learning with 16-min/4-min or 4-min/1-min ITI combinations. Experiment 2 found no evidence that Short+/Long? learning is inferior because the temporal cue corresponding to the short interval is ambiguous. Experiment 3 found no evidence that Short+/Long? learning is poor because the end of a long ITI signals a substantial reduction in delay to the next reinforcer. Long+/Short? learning may be faster than Short+/Long?because elapsing time involves exposure to a sequence of hypothetical stimulus elements (e.g., A then B), and feature-positive discriminations (AB+/A?) are learned quicker than feature-negative discriminations (A+/AB?). Consistent with this view, Experiment 4 found a robust feature-positive effect when sequentially presented CSs played the role of elements A and B. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of CS-US interval on several different indices of learning in appetitive conditioning.

Four experiments examined the effects of varying the conditioned stimulus-unconditioned stimulus (CS-US) interval (and US density) on learning in an appetitive magazine approach task with rats. Learning was assessed with conditioned response (CR) measures, as well as measures of sensory-specific stimulus-outcome associations (Pavlovian-instrumental transfer, potentiated feeding, and US devaluation). The results from these studies indicate that there exists an inverse relation between CS-US interval and magazine approach CRs, but that sensory-specific stimulus-outcome associations are established over a wide range of relatively long, but not short, CS-US intervals. These data suggest that simple CR measures provide different information about what is learned than measures of the specific stimulus-outcome association, and that time is a more critical variable for the former than latter component of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contextual conditioning with massed versus distributed unconditional stimuli in the absence of explicit conditional stimuli.

Rats received unsignaled shocks in an observation chamber, with different groups varying with respect to time between shocks. Twenty-four hours later the rats were returned to the observation chamber for a test of conditioning to contextual stimuli. The freezing response served as the dependent variable. In Experiment 1 we found that distributed shock trials (60 s) resulted in more context conditioning than did massed trials (3 s or 6 s). Experiment 2 replicated this intertrial interval (ITI) effect when total time in the context was equated for the massed and distributed groups. The observed beneficial effect of distributed practice for conditioning to contextual stimuli runs counter to the predictions of Pavlovian conditioning models that posit that the benefit of distributed conditioning trials for discrete conditional stimuli arises because of decreased contextual conditioning with longer ITIs (e.g., Gibbon & Balsam, 1981; Rescorla & Wagner, 1972). Although the basic effect of enhanced performance with longer ITIs is consistent with Wagner's rehearsal model (e.g., 1978), three findings argue against such an account. First, posttrial stimulation did not reduce the benefit obtained from distributed trials (Experiment 3). Second, intertrial distractors did not improve performance of the animals subjected to massed trials (Experiment 4). And third, the ITI effect was not eliminated when conditioning was brought to its asymptote (Experiment 5). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of training intertrial interval on acquisition of trace and long-delay fear conditioning in rats.

Many factors govern conditioning effectiveness, including the intertrial interval (ITI) used during training. The present study systematically varied the training ITI during both trace and long-delay fear conditioning. Rats were trained using one of six different ITIs and subsequently tested for conditioning to the white noise conditioned stimulus (CS) and the training context. After trace conditioning, percent freezing to the CS was positively correlated with training ITI, whereas percent freezing to the context was negatively correlated with training ITI. In contrast, when rats were trained using a long-delay paradigm, freezing during the CS test session did not vary as a function of training ITI; rats exhibited robust freezing at all ITIs. The long-delay conditioned rats exhibited relatively low levels of freezing during the context test. Thus, trace is more sensitive than long-delay fear conditioning to variations in the training ITI. These data suggest that training ITI is an important variable to consider when evaluating age or treatment effects, where the optimal ITI may vary with advancing age or pharmacological treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Massed extinction trials produce better short-term but worse long-term loss of context conditioned fear responses than spaced trials.

A series of experiments studied the effects of the interval between extinction trials on the loss of context conditioned freezing responses. Rats were shocked in one context (A) but not in another (B) and subjected to extinction trials in context A. In Experiment 1, massed trials produced more rapid loss than spaced trials. A shift from spaced to massed trials maintained this loss, but the shift from massed to spaced trials restored lost responses. Experiments 2-5 examined this effect of massed trials on responding across spaced trials. They provided evidence that (a) a single trial was as effective as multiple daily massed trials, (b) learning occurred on the first of the massed trials but not on later ones, and (c) the first trial reduced the amount learned across subsequent massed trials. Finally, alternating extinction trials in A and B produced more response loss across spaced trials than blocks of trials in A and B. The results were discussed in terms of the role accorded to self-generated priming in the models developed by A. R. Wagner (1978, 1981). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Backward inhibitory conditioning with signaled and unsignaled unconditioned stimuli: Distribution of trials across days and intertrial interval.

Through summation tests in conditioned suppression with rats we assessed the effects of distribution of trials across days (Experiment 1) and intertrial interval (ITI) (Experiment 2) on the degree of backward conditioned inhibition established through signaled and unsignaled unconditioned stimuli (USs). Two backward conditioned inhibitory stimuli (CS-s) were established within subjects: One backward CS- followed signaled shocks; the other followed unsignaled shocks. After 12 daily sessions (Experiment 1), the signaled backward CS- was strongly inhibitory and significantly more inhibitory than the unsignaled backward CS-. When the same number of trials occurred in a single long session, performances to both CS-s converged at moderate levels. At the 90-s ITI, (Experiment 2) the signaled and unsignaled backward CS-s were nearly equivalent in effectiveness. When the ITI was 540 s, performances diverged, and signaled backward CS- was substantially more effective; the longer ITI facilitated inhibitory backward conditioning based upon signaled USs but prevented the development of inhibitory backward conditioning based upon unsignaled USs. These functionally opposite effects on backward conditioned inhibition, depending on whether the US was signaled or not, are anticipated by Wagner's "standard operating procedure" (SOP) model of short-term memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scopolamine affects response-to-change test involving 20-min retention interval after locomotor exploration in rats

The tendency to select the T-maze arm that has been changed in brightness between two successive trials (response-to-change) was investigated. Our previous findings indicated that scopolamine injections (1.0 mg/kg) impaired responding to change of brightness in a choice trial (trial II) following a 1-min retention interval, when in the first acquisition trial rats could only inspect the white-black T-maze arms through transparent partitions (the passive test). The drug was ineffective when rats were allowed locomotor exploration of the maze (the active test). The aim of the present experiment was to investigate the effect of the same dose of scopolamine on the active test involving a longer 20-min retention interval between the acquisition trial and the choice trial. The effect of cue salience also was examined by using grey-black arms. Rats injected with scopolamine (Scopo) 20 min before the acquisition trial performed in the white-black maze on the chance level, whereas saline-injected rats (Sal) showed significant preference for the changed arm. Decreasing the cue salience impaired response-to-change in Sal rats (50% of changed arm choices) but had no further effect on performance of Scopo rats, presumably because of a floor effect. The postacquisition injection had a somewhat stronger effect than the injections preceding acquisition, which most probably reflects the state dependency phenomenon. The deficient performance due to scopolamine treatment that appeared in the present study at a longer retention interval could be interpreted in terms of increased forgetting.     

Contextual influences on crossover in the reaction time performance of schizophrenics.

Conducted 3 investigations with a total of 55 female process schizophrenics and 54 normal controls to test the resilience of the crossover phenomenon observed in schizophrenic reaction time performance. The crossover effect portrays an interaction of the predictability (regularity) and the duration of the delay (preparatory interval) factors in the simple reaction time procedure. The effect, believed pathognomonic of schizophrenic reaction time performance, shows performance on regular trials to be faster than irregularly presented trials at short duration, but the regular presentation of trials is slower at longer duration preparatory intervals. The present studies tested an interpretation that the difference between the regular and irregular trials with long preparatory intervals might be dependent on the influence of certain contextual influences operating within the arrangement of trials. Findings show that the contextual factors studied did not account for this difference. Neither eliminating the presence of shorter trials preceding the irregular test trials nor loading the series with short duration trials substantially influenced the extent to which the long regular trials were slower than the long irregular trials. As observed before, the crossover characterized the process schizophrenic group and was not characteristic of the reactive schizophrenic or normal control groups. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Encoding specific associative memory: Evidence from behavioral and neural manipulations.

Within-subjects procedures with rats assessed the associative structures acquired during conditioning trials in which the interval between the stimuli and food was either short or long (i.e., A–10 s→food and B–40 s→food). In Experiments 1 and 2, after these conditioning trials, A and B served as second-order reinforcers for 2 further stimuli (i.e., X→A and Y→B); whereas Experiment 3 used a sensory preconditioning procedure in which X→A and Y→B trials occurred before the conditioning trials, and rats were finally tested with X and Y. In each experiment, Y elicited greater responding at test than did X. This finding supports the contention that the long-lived trace of B (associated with food on B–40 s→food trials) is more similar to the memory of B that was associatively provoked by Y, than is the short-lived trace of A (associated with food on A–10 s→food trials) to the memory of A that was associatively provoked by X. These conclusions were reinforced by the effects of a neural manipulation that disrupted discrimination learning involving the short traces of stimuli but not the long traces of the same stimuli. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effects of response strategy and retention interval on performance of Clark's nutcrackers in a radial maze analogue.

Two groups of Clark's nutcrackers (Nucifraga columbiana) were trained to use either a stay or shift response strategy in a radial maze analog. Each trial had a preretention stage, a retention interval, and a postretention test. In Exp 1, acquisition with a 5-min retention interval was studied. Response strategy did not affect the rate at which the task was learned. Performance following longer retention intervals was tested in Exps 2–4. Changes in retention intervals were presented in trial blocks of increasing duration in Exp 2 and were randomly presented between trials in Exp 3. Exp 4 extended the retention interval to 24 hrs. No difference in performance was found between the 2 groups in any of these experiments. These results suggest a flexible relationship between spatial memory and response requirement in food-hoarding birds for at least 1 spatial memory task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posttraining shifts in the overshadowing stimulus–unconditioned stimulus interval alleviates the overshadowing deficit.

Two conditioned lick suppression experiments explored the effects on overshadowing of a posttraining change in the temporal relationship between the overshadowing conditioned stimulus (CS) and the unconditioned stimulus (US). Rats received either trace (Experiment 1) or delay (Experiment 2) overshadowing training. Then pairings of the overshadowing CS and US were given with either a trace or delay temporal relationship. Overshadowing was alleviated by shifting the overshadowing CS–US temporal relationship so that it no longer matched the overshadowed CS–US temporal relationship. These outcomes are explicable in terms of an integration of the comparator hypothesis, which states that cue competition effects (e.g., overshadowing) will be maximal when the information potentially conveyed by competing CSs is equivalent, and the temporal coding hypothesis, which states that CS–US intervals are part of the information encoded during conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trace eyeblink conditioning in the freely moving rat: Optimizing the conditioning parameters.

Trace eyeblink conditioning (EBC) parameters, with an airpuff unconditioned stimulus, were examined in male Fischer 344?×?Brown Norway F1 rats. Integrated electromyographic activity from the upper eyelid was recorded. An 8-kHz tone was superior to white noise as a conditioning stimulus. Rats trained with 30 or 50 trials per session showed similar learning. Reversal of environmental lighting had no significant effect. Trace intervals of 0 and 250 ms yielded well-timed conditioned responses (CRs); intervals of 500 ms or more did not. These experiments provide parameters that reliably yield CRs and suggest limits on the temporal processing capabilities of the rat. EBC can thus be used as part of a comprehensive test battery for learning and memory in this species. Physiological recording and pharmacological manipulations may also be done easily. This combination of approaches should facilitate a more complete understanding of learning mechanisms and age-related memory impairments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception and production of brief durations: Beat-based versus interval-based timing.

Two experiments examined whether timing of short intervals is beat- or interval-based. In Experiment 1, subjects heard a sequence of standard tones followed by 2 test tones; they compared the interval between test tones to the interval between the standards. If optimal precision required beat-based timing, performance should be best in blocks in which the interval between standard and test reliably matched the standard interval. No such effect was observed. In Experiment 2, subjects heard 2 test tones and reproduced the intertone interval by producing 2 keypress responses. Entrainment to the beat was apparent: First-response latency clustered around the standard interval and was positively correlated with the produced interval. However, responses occurring on or near the beat showed no better temporal fidelity than off-beat responses. One plausible interpretation of these findings is that the brain always times brief intervals with an interval timer; however, this timer can be used in a cyclic fashion to trigger rhythmic responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)