Neuronal unit activity in the abducens nucleus during classical conditioning of the nictitating membrane response in the rabbit (Oryctolagus cuniculus).

Neuronal unit activity was recorded from the abducens (6th nerve) nucleus, the "final common path," during classical conditioning of the nictitating membrane (NM) response in the rabbit, with the use of a tone conditioned stimulus, an air puff unconditioned stimulus (UCS), 250-msec interstimulus interval, and 60-sec intertrial interval. Animals were given 2 days of conditioning training (104 trials in eight blocks per day) and 1 day of extinction. Control animals were given comparable periods of stimulus presentations, explicitly unpaired. Activity of small clusters of units--"multiple unit" recording--was compared with the amplitude-time course of the NM response. Between-blocks comparisons of neural and behavioral responses indicated an essentially perfect correlation during acquisition of the conditioned response (Day 1, r = .99; Day 2, r = .98) and a slightly lower correlation during extinction (r = .93) for the conditioning animals. Within-blocks comparisons indicated a close correspondence between the histograms of unit activity and the amplitude-time course of the NM response for the conditioning animals in all phase of training and for the control animals in the UCS trial blocks.     

Classical conditioning and retention of the infant's eyelid response: effects of age and interstimulus interval

Independent groups of 10-,20-, and 30-day-old infants were subjected to a classical eyelid conditioning procedure involving either a 500- or a 1500-msec interstimulus interval (ISI). Ten days later, all received a second conditioning session. A reliable increase in conditioned responding was observed at all ages but only by infants receiving the 1500-msec ISI. Although age was not a significant factor in any conditioning measure except final performance level, which was greater for the oldest than for the youngest group, it did influence long-term retention. A reliable memory component was observed in the Session 2 performance of infants initially trained at 20 and 30 days but not at 10 days. These data demonstrate the importance of temporal parameters in the formation of conditioned associations very early in infancy and provide evidence for the long-term behavioral consequences of those associations.     

Purkinje cell activity in the cerebellar anterior lobe after rabbit eyeblink conditioning

The cerebellar anterior lobe may play a critical role in the execution and proper timing of learned responses. The current study was designed to monitor Purkinje cell activity in the rabbit cerebellar anterior lobe after eyeblink conditioning, and to assess whether Purkinje cells in recording locations may project to the interpositus nucleus. Rabbits were trained in an interstimulus interval discrimination procedure in which one tone signaled a 250-msec conditioned stimulus-unconditioned stimulus (CS-US) interval and a second tone signaled a 750-msec CS-US interval. All rabbits showed conditioned responses to each CS with mean onset and peak latencies that coincided with the CS-US interval. Many anterior lobe Purkinje cells showed significant learning-related activity after eyeblink conditioning to one or both of the CSs. More Purkinje cells responded with inhibition than with excitation to CS presentation. In addition, when the firing patterns of all conditioning-related Purkinje cells were pooled, it appeared that the population showed a pattern of excitation followed by inhibition during the CS-US interval. Using cholera toxin-conjugated horseradish peroxidase, Purkinje cells in recording areas were found to project to the interpositus nucleus. These data support previous studies that have suggested a role for the anterior cerebellar cortex in eyeblink conditioning as well as models of cerebellar-mediated CR timing that postulate that Purkinje cell activity inhibits conditioned response (CR) generation during the early portion of a trial by inhibiting the deep cerebellar nuclei and permits CR generation during the later portion of a trial through disinhibition of the cerebellar nuclei.     

Intertrial interval effects on internal stimulus control of behavior in brightness differential conditioning

In Experiment 1, groups were given a trial sequence in differential conditioning in which all S+ trials preceded all S? trials (+? schedule) or one in which some S+ trials followed S? trials (+?+ schedule) and either a 1- or a 30-min intertrial interval (ITI). ITI affected discrimination learning only in the +? schedule condition; schedule affected discrimination only at massed trials. In Experiment.2, all groups received a +?+ schedule. In two groups, given a 1- or 15-min ITI between all trials, discrimination learning was independent of ITI. Discrimination learning was facilitated in two other groups given a 1-min ITI between all trials except between S? and the subsequent S+ trial, when the ITI was either 15 or 60 min. The results were discussed in terms of their implications for internal reward-related stimulus control of behavior in differential conditioning.     

Context-specific conditioning in the conditioned-emotional-response procedure

In 3 experiments, rats were used to investigate the conditions that influence the transfer of a conditioned emotional response from 1 context to another. The subjects experienced training in 2 contexts on each day. In Experiment 1, subjects received a single conditioning trial with a different target stimulus in each of the 2 contexts. Conditioned responding was found to be more vigorous when the target was presented subsequently in the context in which conditioning had taken place than when it was presented in the other context. Experiments 2 and 3 confirmed these results and also showed that neither the unconditioned response evoked by the target stimulus nor the conditioned response acquired after multiple training trials showed evidence of context specificity. Possible reasons for the difference in outcome between single-trial and multitrial conditioning procedures are discussed.     

Effects of paradigm and inter-stimulus interval on age differences in eyeblink classical conditioning in rabbits

The aim of this study was to examine parameters affecting age differences in eyeblink classical conditioning in a large sample of young and middle-aged rabbits. A total of 122 rabbits of mean ages of 4 or 26 mo were tested at inter-stimulus intervals (ISIs) of 600 or 750 msec in the delay or trace paradigms. Paradigm affected both age groups dramatically, with superior performance in the delay paradigm. ISI was salient as middle-aged rabbits were significantly impaired in 750-msec compared with 600-msec delays, and young rabbits were significantly less impaired in 600-msec than in 750-msec trace. Young rabbits performed equally well at both delay ISIs, and consequently, there were significant age differences in 750-msec but not in 600-msec delays. Middle-aged rabbits performed poorly at both 600- and 750-msec trace, resulting in significant age differences in 600-msec but not in 750-msec trace. Timing of the conditioned response has been associated with cerebellar cortical function. Normal aging of the cerebellar cortex likely contributed to the magnitude of the effect of ISI in delay conditioning in middle-aged rabbits. Results demonstrate that the magnitude of age differences in eyeblink conditioning can be enlarged or eliminated by ISI and paradigm.     

Semantic priming and identification of near threshold primes in a lexical decision task

Three experiments examined both the impact of semantic analysis of 50-msec, masked visual primes on a target response and the impact of semantic analysis of the target on a prime response. The first two experiments used a prime-target interval of 1000 msec. In Experiment 1, subjects reported the identity of each prime: (a) after a lexical decision about the target, (b) both before and after a lexical decision, or (c) after a target detection response. Prime report after both types of target response showed retroactive priming in which report was facilitated by related targets and inhibited by unrelated targets. Analyses of lexical decision latency and accuracy conditionalized on prime report showed that semantic priming was restricted to reported related primes. In Experiment 2, subjects made no overt response to the primes. Priming was conditionalized on recognition of the primes on a subsequent test. The pattern was the same as Experiment 1: There was priming only for recognized primes; recognition memory showed a pattern consistent with retroactive priming. Experiment 3 also conditionalized priming on recognition performance but used a prime-target interval of only 250 msec. Again, semantic priming was found only for recognized primes, and recognition memory revealed retroactive priming. Retroactive priming indicates an interdependency between prime and target processing that needs to be incorporated into models of semantic priming.     

Temporal organization of pattern structure

Two pattern reproduction experiments examined the relations among the figural goodness of a pattern, the organization of two parts within the pattern, and the interpart interval (ISI), which ranged from 40 to 200 msec. If the parts contained connected line segments, performance was slightly better (3%-5% gain in accuracy) at a 40-msec ISI than at a 200-msec ISI. If the parts contained unconnected line segments, reproduction accuracy of the first part declined sharply between 40 and 200 msec. These results were interpreted by assuming that the parts were perceived as a single whole pattern at a 40-msec ISI but as two separate patterns at a 200-msec ISI. One surprising finding, the lack of an interaction between figural goodness and ISI, was explained in terms of a response bias in favor of figural good patterns. A secondary manipulation revealed that a part was more accurately reproduced in a good figure context than in a poor figure context but was most accurately reproduced when it appeared alone.     

An anxiety-related bias in semantic activation when processing threat/neutral homographs

Three experiments are reported comparing high and low-trait anxious subjects in terms of their patterns of semantic activation in response to ambiguous primes, with one threat-related and one neutral meaning. Such primes were followed by targets related to either their threat or neutral meaning, or by unrelated targets, in a lexical decision task. Experiments 1 to 3 employed stimulus onset asynchronies (SOAs) of 750 msec, 500 msec, and 1250 msec, respectively. At 500-msec SOA all subjects showed facilitation for both meanings. At 750-msec SOA the only significant priming effect was that for the threat-related meaning in the high-anxiety group, and a similar trend was found at 1250-msec SOA. Consideration of the patterns of priming for targets following ambiguous threat/neutral primes suggest that at the longer SOAs, high-anxiety subjects consciously “lock on” to a threatening interpretation if one has been made available by earlier automatic spreading activation.     

Short-term memory for time intervals

The effect of intertrial interval, preset interval, and retention interval on the performance of rats in a time estimation task was described. On each trial a signal was presented for a duration of 2 to 8 sec. Eighteen rats were trained to press one lever (the short response) if the signal was shorter than 4 sec, and another lever (the long response) if the signal was longer than 4 sec. When trials were massed (Experiment 1), the percentage long response was affected by the classification of the previous signal, but not by its actual duration. This suggests that the animals remembered the response made on the previous trial, but not the signal duration. If a response was not permitted on the previous trial (Experiment 2), the duration or classification of the previous signal had no effect on performance. This supports the conclusion from the first experiment and suggests that an animal can reset its internal clock in less than 2 sec. In Experiment 3, the difference limen of the psychophysical function increased with the duration of the retention interval, but the point of subjective equality did not change. This suggests that resetting of the internal clock occurs on a non-time dimension.     

汉语双音节同音词词汇歧义消解过程的研究

使用跨通道词汇判断任务和语义启动技术,两个实验分别考察了孤立状态下和句子语境中汉语双音节同音词意义通达的情况,结果发现(1)在孤立状态下,无论ISI为0毫秒还是-150毫秒,与同音词主要或次要意义有关的探测词都受到了促进;(2)当ISI为0毫秒时,在语境一致的条件下,与同音词主要或次要意义有关的探测词均受到了促进,在语境不一致的条件下,则未发现任何促进效应;(3)当ISI为-150毫秒时,只是在语境一致并且探测词与同音词的主要意义有关的条件下才观察到促进效应。     

Second-order conditioning of the rabbit's nictitating membrane response. Interstimulus interval and frequency of CS-CS pairings.

Second-order conditioning of the rabbit's nictitating membrane response (NMR) was investigated when second-order trials (CS1-CS2) were intermixed with first-order trials (CS2-US) from the outset of training. Experiment 1 showed that CR acquisition to CS1 was inversely related to the CS1-CS2 interval but nevertheless extended to an interval of 8,400 ms. Experiment 2 revealed that CR acquisition of CS1 was an inverted-U function of the number of CS1-CS2 trials relative to a fixed number of CS2-US trials. Experiment 3 directly contrasted second-order conditioning with a reinforced serial compound procedure (CS1-CS2-US) and a mixed procedure in which second-order trials were intermixed with the reinforced serial compound. Second-order conditioning was about half the strength of either the reinforced serial compound or the mixed procedure, which were similar. The present results are discussed with respect to the relative strength of excitatory and inhibitory processes in second-order conditioning.     

Trace fear conditioning is reduced in the aging rat

Auditory trace fear conditioning is a hippocampus-dependent learning task that requires animals to associate an auditory conditioned stimulus (CS) and a fear-producing shock-unconditioned stimulus (US) that are separated by an empty 20-s trace interval. Previous studies have shown that aging impairs learning performance on hippocampus-dependent tasks. This study measured heart rate (HR) and freezing fear responses to determine if aging impairs hippocampus-dependent auditory trace fear conditioning in freely moving rats. Aging and Young rats received one long-trace fear conditioning session (10 trials). Each trial consisted of a tone-CS (5 s) and a shock-US separated by an empty 20-s trace interval. The next day rats received CS-alone retention trials. Young rats showed significantly larger HR and freezing responses on the initial CS-alone retention trials compared to the Aging rats. A control group of aging rats received fear conditioning trials with a short 1-s trace interval separating the CS and US. The Aging Short-Trace Group showed HR and freezing responses on the initial CS alone retention trials that were similar to the Young Long-Trace Group, but greater than the Aging Long-Trace Group. A second aging control group received unpaired CSs and USs, and showed no HR or freezing responses on CS-alone retention trials. These data show that HR and freezing are effective measures for detecting aging-related deficits in trace fear conditioning.     

Effects of Prime Type and Delay on Multiplication Priming: Evidence for a Dual-process Model

Two experiments investigated effects of numerical primes on production of simple multiplication facts (e.g. 4 × 8 = ?). In Experiment 1, a correct (32), related (24), unrelated (27), or neutral (##) prime appeared for 200 msec and was followed by a target problem at an ISI of 0, 750, or 1500 msec. Relative to neutral primes, correct primes produced constant RT and accuracy benefits across ISIs, and unrelated primes produced constant RT costs. Related primes produced costs compared to unrelated primes at the 0-msec ISI only. In Experiment 2, eliminating correct-answer primes from the stimulus set eliminated all the false-prime effects except the costs of related primes at the 0-msec ISI. We propose a dual-process account incorporating a familiarity-based name-the-prime strategy that produces benefits and costs insensitive to ISI and an automatic retrieval-priming process that is measurable only at short ISIs.     

Intertrial inhibition of focused attention in pop-out search

When a visual search for a color oddball is performed, responses to target-present trials are affected by the color of items in immediately preceding target-absent trials, a phenomenon known as the distractor-previewing effect (DPE). Specifically, the color of the items in the target-absent trial suppresses responses to a target of that color in the subsequent trial, even though participants report a target feature uncorrelated with color. We believe that this suppression reflects a transient inhibitory effect on focused attention that biases attention away from items that are of the same color as the items in the target-absent trial. Experiments 1-3 show that the DPE is present only in tasks that require focused attention. Experiments 4A and 4B show that the DPE persists even when target-absent displays are masked. Last, Experiment 5 shows that the DPE emerges as early as within the first 100 msec of a target-present trial and is fully in place by the 250-msec mark.     

Partial reinforcement effects in classical aversive conditioning in rabbits and human beings.

The partial reinforcement extinction effect (the PREE) in classical aversive conditioning was investigated in 2 experiments. In the first, the nictitating membrane responses of 120 rabbits were conditioned at a 250-msec. interstimulus interval (ISI) under continuous reinforcement, partial reinforcement with the unconditioned stimulus (US) omitted (Group PO), or partial reinforcement with the US delayed to 1,500 msec. (Group PD). These 3 groups were factorially extinguished under US-Omitted, US-Unpaired, or US-Delayed extinction regimens. A significant PREE was obtained, but only for PO training and US-Omitted extinction. The second experiment, employing human subjects in a masked eye blink conditioning task, produced parallel results. A general discrimination view of the classical PREE seems applicable, but one in which neither cognitive factors nor intertrial conditioning of reinforcement aftereffects play a significant role.     

Refractoriness in same-different judgments

Subjects judged as “same” or “different” pairs of visual stimuli, each either an X or an O, whose onsets were separated by intervals of 50, 100, 150 or 200 ms. When the interstimulus interval (ISI) was held constant within a block of 40 trials (Experiment I), decision time was independent of ISI. But when ISI was varied unpredictably from trial to trial (Experiments II and III), decision times increased the shorter the ISI. This effect was more marked for “same” than for “different” decisions. These results fail to support a single-channel interpretation, but suggest that variations in decision time depend on the subject's expectancy as to when the second stimulus will follow the first.     

Recall and recognition processes in motor memory: effects of feedback and knowledge of results delay

In linear movement tasks of 200 msec (Experiment 1 -ballistic movement) and 500 msec (Experiment 2 - nonballistic movement), motor recall strength was assessed by absolute, constant, and variable error; recognition strength was assessed by Z'-transformed actual-estimate correlations and absolute actual-estimate difference scores. Contrary to predictions, neither increased KR delay (45 vs. 5 sec) nor limited visual-auditory-tactile feedback caused decrements in recognition processes over KR-training or KR-withdrawal trial blocks for the 200-msec task. In the 500-msec task, the independent variables impaired recognition through training and transfer trials but impaired recall only in the training trials. Results generally did not support the hypothesized independence between recall and recognition processes. Several methodological issues related to recall, and recognition research were discussed.     

Pigeons' spatial memory: III. Effect of distractors on delayed matching of key location.

The effect of distractors on pigeons' delayed matching of key location was investigated. Baseline trials began with a "ready" stimulus (brief operation of the grain feeder). Then one (randomly chosen) key from a three-by-three matrix was lit briefly as the sample. After a short delay (retention interval) the sample key was lit again along with one of the other eight keys. A peck at the key that had served as the sample (correct comparison) produced grain reinforcement, whereas a peck to the other key (incorrect comparison) produced only the intertrial interval. In Experiment 1, a houselight distractor, presented during either the sample, retention interval, or choice phases of the trial, had little if any effect on accuracy of matching key location. In Experiment 2, one of three types of spatial stimuli was interpolated during the retention interval, or the interval was blank as during baseline trials. The three stimuli were: the sample (correct comparison) location for that trial, the incorrect comparison location for that trial, or one of the seven unused locations for that trial. Relative to blank trials, accuracy improved slightly on sample-interpolated trials, decreased slightly on unused location-interpolated trials, and decreased considerably on incorrect comparison-interpolated trials. In Experiment 3, retention intervals were blank or had one of six types of interpolation: the sample, the incorrect comparison, two presentations of the sample, two presentations of the incorrect comparison, the sample followed by the incorrect comparison, or the incorrect comparison followed by the sample.(ABSTRACT TRUNCATED AT 250 WORDS)     

Choice in the repeated-gambles experiment

Humans chose 10 times between two roulette wheels projected on a monitor. During the first trial, the left wheel provided a hypothetical $100 with p = .94, and the right wheel provided $250 with p = .39. A titration procedure adjusted the probability of a $250 win across trials to permit estimation of an indifference point between alternatives. In Experiment 1, intertrial-interval duration (25 vs. 90 s) and whether sessions began with an intertrial interval or a trial were varied in a 2 × 2 design in this risky-choice procedure. Risk aversion (preference for the $100 wheel) increased with intertrial interval but was unaffected by whether sessions began with a trial or an intertrial interval. In Experiment 2, all sessions began with a trial, and subjects were informed that the experiment ended after 10 trials. Intertrial-interval duration had no effect on choice. In Experiment 3, intertrial-interval duration and whether subjects were given $10 or $10,000 before beginning were varied among four groups in a 2 × 2 design. In all other ways, the procedure was unchanged from Experiment 2. Intertrial interval had no effect on choice, but the $10,000 groups showed less risk aversion than the $10 groups. These results can be explained more readily in terms of Kahneman and Tversky's (1984) notion of “framing of the prospect” than in terms of Rachlin, Logue, Gibbon, and Frankel's (1986) behavioral account of risky choice.