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1.
Rats received a single 4-sec 1-mA grid-shock US either preceded or followed by a 4-sec tone or light CS. Conditioning was later assessed by comparing the amount of lick suppression evoked by the forward- or backward-paired CS versus an explicitly unpaired CS. The backward-paired CS produced more suppression than the unpaired CS only when both were tone; the light evoked strong suppression whether paired or not. In the forward procedure, tone produced more suppression when paired and less when unpaired than did light; conditioning thus appeared stronger with the tone. In one experiment, observations showed that rats froze during the forward-paired tone but not during the light. Increasing CS duration from 4 to 12 sec had no effect for the forward-paired light but increased freezing to the forward-paired tone. Another experiment showed similar unconditioned suppression to tone and light but faster habituation to tone. Problems that these results create for interpreting evidence for excitatory backward conditioning in the conditioned suppression procedure are discussed. 相似文献
2.
Three experiments with rat subjects sought to enhance one-trial excitatory simultaneous and backward fear conditioning by using a two-element compound conditioned stimulus (CS) instead of only a single element. During conditioning, experimental groups received a 4-sec CS either coextensively with a 1-mA grid-shock unconditioned stimulus (US) or immediately after US termination. In subsequent tests, CSs evoked more lick suppression and freezing in these groups than in various controls. Compound CSs evoked more lick suppression and freezing than did CS elements, but did so equally for experimental and control groups. Therefore, the use of compounds did not enhance conditioning. Unexpectedly, an explicitly unpaired control in which CS followed US termination by 3 min tended to show more CS-evoked suppression and freezing than did a control in which CS preceded US onset by 3 min. This result raises the possibility that associations between the CS and the training context might engender responding to backward-paired CSs. 相似文献
3.
Lynn J. Hammond 《Learning & behavior》1995,23(3):349-356
Three experiments were conducted to demonstrate that the place where an organism has been, before the organism is moved to a place with aversive consequences, can also become aversive through classical conditioning. In Experiment 1, two groups of 8 mice were exposed to three different contexts in succession, with a single shock occurring in the third context. The distal context was a putative 3-min conditioned stimulus (CS) for freezing; the second context was a delay manipulation; and the unconditioned stimulus (US) occurred in the proximal context. The group delayed for 15 sec showed significantly more freezing to the distal CS context than did the group delayed for 3 h. In a second experiment, conditioning to the distal context was demonstrated with a discrimination procedure for 8 more mice by using two different distal contexts as CS+ and CS? for the proximal context with shock. On CS+ days, 3 min of exposure to the distal context was followed within 5 sec by placement in the proximal box where shock occurred, whereas on CS? days, exposure to a second distal context was followed immediately by return to the home cage. Very strong differences in freezing between the CS+ and CS? distal contexts were found in all 8 mice after 14 days of conditioning. In a third experiment, the discriminative procedure was repeated for 9 more mice, with two changes. More objective stabilometertype activity measures were substituted for observed freezing, and, in addition to the CS+ and CS? distal context trials, each mouse was also exposed to a third discriminative distal context, which was followed by 15 min in a delay chamber followed by shock in the proximal context. This discrimination procedure with the activity suppression measure again resulted in significant differences between the contexts. The CS+ context and the context followed by a 15-min delay did not differ, but both of them differed from the CS? context. 相似文献
4.
Twenty-eight male albino rats were given a single 4-sec 1-mA electric-grid-shock unconditioned stimulus (US). In the same session they received two 12-sec conditioned stimuli (CSs). One CS (explicitly unpaired) terminated 180 sec before the US began; the other (backward paired) began immediately after the US terminated. The CSs used were a 1000-Hz 85-dB tone and an 84-dB click; their roles were counterbalanced. Over the next 2 days, each CS was presented for 2 min while the rats drank from a water bottle. The backward-paired CS was found to suppress licking more than the explicitly unpaired CS. This suppression was accompanied by an increase in defensive behavior (freezing and freeze/nod) and by a decrease in other activity. The suppression did not seem to be due to a maintained or enhanced CS-orienting response reflex, nor could it be attributed to an adventitiously reinforced interfering operant. The results support the presumption made in previous reports that the lick suppression evoked by a backward CS reflected one-trial backward excitatory fear conditioning. 相似文献
5.
John J. B. Ayres Howard Axelrod Elizabeth Mercker Fran Muchnik Michael Vigorito 《Learning & behavior》1985,13(1):44-50
In a conditioned suppression study with rats, CS modality (light vs. noise) and type of conditioning (on-line vs. off-line training) were manipulated. All rats were then tested on-line with only half the test trials reinforced. Some results and conclusions were as follows: (1) During initial training, suppression following reinforced noise trials was moderately strong at first but weakened over days; for the light, it was weak from the start. It was suggested that this strong influence of CS modality might complicate interpretations of posttrial suppression as a measure of US effectiveness. (2) During testing, posttrial suppression and freezing were greater following non-reinforced trials than following reinforced trials (US-omission effect), and this effect was stronger for noise than for light. Since noise also produced more freezing than light, this result favors the hypothesis that the US-omission effect is due to persistent CS-elicited freezing that is un-disrupted by a shock US. (3) Although noise produced more freezing, both noise and light produced similar barpress suppression. This result is consistent with the suggestion that noise and light acquire equal associative strength but elicit different defensive behaviors. 相似文献
6.
Conditioned suppression in rats is often unaffected when the context (or set of background stimuli) is changed following conditioning. This suggests that responding to the conditioned stimulus (CS) can be relatively insensitive to the context in which the CS is presented. In two experiments, we examined whether sensitivity to contextual stimuli is affected by preexposure to the CS. In Experiment 1, when the CS was novel at the outset of conditioning, conditioned suppression was not affected when the context was changed following conditioning. However, when the CS had been preexposed, responding was weaker when extinction occurred outside of the conditioning context. In Experiment 2, responding was again sensitive to the test context, regardless of whether preexposure occurred in the conditioning context or in an alternate context. These results suggest that the extent to which responding is sensitive to context can depend on the conditioning history of the CS. 相似文献
7.
Two studies used a one-trial-a-day aversive conditioning procedure with rats as subjects to investigate the effects of a noise versus a light CS on conditioned freezing. Experiment 1 demonstrated that less conditioned freezing was elicited by the light, although the two CSs led to similar levels of freezing to the contextual cues of the conditioning chamber. Experiment 2 replicated these outcomes and showed that the manipulation of CS intensity produced results similar to those of modality, with the more intense CSs eliciting less freezing. The second experiment also determined that freezing to contextual cues resulted from context conditioning. According to the Rescorla-Wagner model, CSs that condition poorly should generate little competition with context conditioning. Since neither the modality nor intensity factor reliably influenced context conditioning, as measured by context-evoked freezing, the studies provide no support for the view that the effects on CS-evoked freezing represent differences in the strength of conditioning to the various stimuli. This finding raises the possibility that all of the CSs conditioned well but varied in their abilities to elicit freezing because they differed in terms of the form of defensive behavior under their control. 相似文献
8.
In three experiments, groups of albino rats received one strictly simultaneous pairing of a 4-sec auditory conditioned stimulus (CS) and a 4-sec 1-mA shock unconditioned stimulus (US). Other groups received a backward pairing, in which the US began before the CS, or a forward pairing, in which the CS began before the US. Control groups received only the US or received both the CS and the US but widely separated in time. Later, the CS was presented while the rats licked a drinking tube for water, and CS-elicited suppression of licking was taken as an index of the Pavlovian conditioned response (CR). It was found that groups receiving a single forward or a single simultaneous pairing suppressed more than groups that had received a backward pairing; and the backward groups, in turn, suppressed more than the control groups. It appears, then, that excitatory fear conditioning, as reflected in conditioned suppression of licking in rats, can be produced in a single trial by both backward and simultaneous conditioning procedures. 相似文献
9.
In two experiments with rat subjects, we examined the effects of a retention interval on performance in two conditioning paradigms in which a conditioned stimulus (CS) was associated with different unconditioned stimuli (USs) in successive phases of the experiment- Experiment 1 was designed to examine aversive-appetitive transfer, in which the CS is associated with shock and then food; Experiment 2 was designed to examine appetitive-aversive transfer, in which the CS is associated with food and then shock. Aversive and appetitive conditioned responses (freezing and head-jerk responding, respectively) were scored from videotape. In both experiments, a 28-day retention interval following the end of Phase 2 caused a recovery of the Phase 1 response and a resuppression of the Phase 2 response. The results suggest that the original association is not destroyed when the CS is associated with a new US in Phase 2. They also suggest that both retroactive and proactive interference effects may result-from interference with performance output rather than a disruption or loss of what is learned during or stored from the target phase. 相似文献
10.
In three experiments, rats received a single presentation of an auditory conditioned stimulus (CS) beginning simultaneously with an electric grid-shock unconditioned stimulus (US). Later, the CS was presented while the rats licked a drinking tube for water, and CS-elicited suppression of licking was taken as an index of the excitation conditioned to the CS. It was found that conditioning increased as a joint function of the duration of CS-US overlap and US duration. The evidence suggested that weak conditioning due to a brief CS-US overlap could be increased by extending the US beyond CS termination. Extending CS duration beyond US termination, however, did not strengthen conditioning; indeed, extending the CS 60 sec beyond US termination weakened conditioning significantly. It is suggested that these results shed light on a discrepancy in the recent literature on simultaneous conditioning. 相似文献
11.
Five experiments tested the effects of experience with a white compartment not paired with footshock (CS?) on conditioning of an aversion to a black compartment paired with footshock. As previously found with odors as CSs, a single pairing of the CS+ with footshock yielded significant conditioning only if the animal was also exposed to CS?, with greater conditioning when the CS? exposure preceded the CS+ than when the CS+ preceded the CS?. If, however, the CS? preceded CS+ by a 24-h interval, it was ineffective and no CS+ conditioning occurred. For adult rats, the effectiveness of the CS?/CS+ “integration” progressively decreased with increasing length of the interval separating their occurrence, although it was still significant (i.e., some CS+ conditioning occurred) with a 12-h CS? to CS+ delay. For preweanlings (16 days postnatal), no conditioning to CS+ occurred if the interval between CS? and CS+ was 1 h or longer, although significant conditioning to CS+ did occur with a CS? to CS+ interval as long as 40 min. It was as if active memory for the CS? at the time of CS+ exposure was necessary for CS+ conditioning, and forgetting of the CS? memory proceeded more rapidly for preweanling than for adult rats. Collectively, these experiments extend results previously indicating that (1) the CS+ contiguous to the US may or may not be “selected” for conditioning, depending on the rat’s exposure to, or memory for, a CS?, and (2) this stimulus selection might differ for immature and mature rats. 相似文献
12.
Lick suppression experiments with rats revealed that the magnitude of both second-order conditioning (Experiment 1) and sensory preconditioning (Experiment 2) was superior when that conditioning was based on backward (US→CS) relative to forward (CS→US) first-order pairings of a CS and US. The superiority of backward relative to forward first-order conditioning on suppression to the higher order cues can be understood by assuming that the magnitude of higher order conditioning was determined by a memory representation of the higher order cues that provided information about the expected temporal location of the US. The results suggest that temporal information such as order between paired CSs and USs was encoded, preserved, and integrated with memory for the higher order stimuli. The relevance of these findings to memory integration in Pavlovian learning, the temporal coding hypothesis (Barnet, Arnold, & Miller, 1991; Matzel, Held, & Miller, 1988), backward excitatory conditioning, and the associative structure that underlies second-order Pavlovian fear conditioning are discussed. 相似文献
13.
John Karpicke 《Learning & behavior》1978,6(2):216-224
Three experiments evaluated an alternative to accounts of positive conditioned suppression that stress central (i.e., motivational or emotional) states. This “competing-response” interpretation was tested by analyzing directed movements that develop in rats during a visual or an auditory stimulus (CS) that signals an appetitive reinforcer (US) in a situation where the subject is also emitting an instrumental response for food. In each experiment, positive conditioned suppression (i.e., a reduction in the rate of such instrumental responding during CS presentations) was accompanied by responses directed toward the CS source and/or the US-delivery site. In Experiment 1, a diffuse (auditory) CS signaled a US delivered at some specific place in the chamber and rats approached the US-delivery site during CS. In Experiments 2 and 3, the spatial proximity of a localized visual CS and US-delivery site determined whether CS-directed or US-directed behavior predominated during the CS. The results suggest that the topographies of conditioned responses on any positive conditioned suppression procedure depend upon the spatial arrangements of features that elicit and support these behaviors. They further suggest that the identification of these features and their spatial arrangements is necessary for the analysis of appetitive classical-instrumental interactions. 相似文献
14.
In two experiments, we examined the conditions under which signaling an unconditioned stimulus (US) with a nominal conditioned stimulus (CS) interferes with the conditioning of situational cues in defensive freezing in the rat. Subjects received footshock USs that were (1) either signaled or unsignaled and (2) either varied or fixed in their temporal location within the conditioning session. Experiment 1, with only one trial per session, yielded no evidence that signaling affected pretrial freezing using either a fixed or variable interval between placement in the context and shock onset. In a test in which no CSs or footshocks were presented, groups that previously had received footshock at a fixed temporal location showed greatest freezing at around that same time. For groups that had received footshocks at various times, freezing declined across the test session. Experiment 2 showed overshadowing of pretrial freezing after more extensive conditioning with many trials per session, but only if the intershock intervals were variable rather than fixed. 相似文献
15.
Two strains of rats (albino Wistar and hooded PVG/c) were exposed to a conditioned defensive burying paradigm that consisted of placing rats in a test chamber with bedding material on the floor, shocking them with a shock prod, and recording the time each rat spent in burying responses toward the prod. Various behaviors other than burying (freezing, grooming/paw licking) were observed by a time-sampling procedure during the control, conditioning, and extinction sessions, each of which was 15 min in duration. Wistar rats generally showed behavioral inhibition, as evidenced by less burying, lower exploratory and ambulatory behavior, and higher freezing behavior. PVG/c rats spent significantly more time engaged in burying and accumulated more bedding material in the conditioning session than did the Wistar rats. No significant differences between the two strains of rats were observed during the extinction session in terms of these measurements. The results indicate that Wistar rats have a greater tendency to freeze when coping with the noxious stimulus in a conditioned defensive burying paradigm, whereas the dominant coping style for PVG/c rats is defensive burying. 相似文献
16.
In two experiments with rats, we examined the developmental emergence of conditioned freezing following trace and short-delay
conditioning and also included a long-delay comparison group. In the short-delay and trace groups, a 10-sec conditioned stimulus
(CS) was paired with shock; for the trace rats, a 10-sec trace interval followed CS termination. The long-delay groups received
a 20-sec CS paired with shock, to equate for the longer interstimulus interval (ISI) in the trace group. Trace conditioning
emerged later in development than did short-delay conditioning (see Moye & Rudy, 1987). Importantly, long-delay conditioning
emerged in parallel with trace conditioning, at a similar time, and with similar strength. These findings suggest a role for
the longer ISI, as opposed to the unfilled gap per se, in the late emergence of trace conditioning. The role of the hippocampus
in trace conditioning and the possibility that young rats encode the temporal relationship between CSs and unconditioned stimuli
are also considered. 相似文献
17.
Four experiments used a within-subjects design with rats to study the effects of preexposure on the restoration of fear responses
(freezing) to an extinguished conditioned stimulus (CS). In each experiment, rats were preexposed to one CS (A), but not to
another (B), and then were exposed to pairings of each of these CSs with an aversive unconditioned stimulus (US). In each
experiment, there was less freezing to A than to B across extinction, showing a latent inhibitory effect of preexposure. There
was no differential recovery to A and B following either a US reexposure (Experiment 1) or a delay interval (Experiment 2). However, when a delay interval included US reexposure, there was greater recovery to the preexposed CS, A, than to the
nonpreexposed CS, B (Experiments 1, 3, and 4). These results suggest that the effects of US reexposure and delay combine to affect recovery from the depressive effects
of CS-alone exposure. The results are consistent with the view that US reexposure produces better mediated conditioning of
CSs that are strongly associated with the context. The results may additionally reflect an effect of preexposure on the learning
produced by extinction. 相似文献
18.
Two rat experiments were run to study the effects of a wide range of signal (CS) intensities on the suppression of licking. In Experiment 1, a light CS was varied over five levels, including zero intensity. Conditioned suppression was found to vary directly with CS intensity, but basal lick rates were not different among groups. In Experiment 2, an attempt was made to disturb the basal rate of licking, while a tone CS was varied over four levels, including zero intensity. Here the suppression of the CS rates was found to be directly related and basal rates inversely related to CS intensity. The results as a whole were consistent with the Perkins-Logan hypothesis regarding the effects of CS intensity upon conditioning, but not with the Rescorla-Wagner model of classical conditioning. 相似文献
19.
Although a number of studies have demonstrated nearly complete retention of fear in a conditioned suppression task, they provide little information about the nature of the memory for the CS. The purpose of the present experiment was to investigate the retention of an attribute of a tonal CS that had been paired with shock and was thus capable of eliciting a conditioned emotional response (CER) in rats. The Kamin blocking effect was utilized to detect changes in the memory of CS attributes. Either 1 or 21 days following conditioning to a tone, separate groups of rats received compound conditioning in which either the original or a novel tone was combined with a light. Subsequent measurement of suppression to the added element (light) indicated that only the original CS produced blocking at the short delay, but that both original and novel tones resulted in blocking at the 21-day interval. This increase in the extent of blocking suggests that memory for specific attributes of the CS does diminish as a function of time. 相似文献
20.
The expression of cardiac responses to sequences of two sounds was studied in restrained rats following discriminative trace or delay conditioning. Stimuli paired with a tail shock 10 sec later (CS1) elicited conditioned bradycardia. Unpaired or neutral stimuli (CS0) elicited mostly tachycardia. Rats did not learn to suppress responding to nonreinforced sequences with an interval of 6 sec between sounds. Responses to the second stimulus were significantly augmented following a CS1 stimulus, but not following a CS0 stimulus. Real-time summation of simple responses provided a more complete and quantitative prediction of dual responses than did resetting or facilitation. These results extend the time range over which summation may be observed from less than 2 sec to at least 16 sec. They appear to be inconsistent with models involving competition between unitary representations of stimuli in short-term memory and suggest the existence of multiple stimulus traces with independent time courses. 相似文献