All that weekend I crossed streets with particular care and avoided all unnecessary risks to protect my discovery from loss through my accidental death. Let's take a closer look at a few more examples of extinction. Imagine that a researcher has trained a lab rat to press a key to receive a food pellet. What happens when the researcher stops delivering the food?
While extinction will not occur immediately, it will after time. If the rat continues to press the key but does not get the pellet, the behavior will eventually dwindle until it disappears entirely. Conditioned taste aversions can also be affected by extinction. Imagine that you ate some ice cream right before getting sick and throwing it up.
As a result, you developed a taste aversion to ice cream and avoided eating it, even though it was formerly one of your favorite foods. One way to overcome this reluctance would be to expose yourself to ice cream, even if just the thought of eating it made you feel a little queasy. You might start by taking just a few small tastes over and over again.
As you continued to eat the food without getting sick, your conditioned aversion would eventually diminish. If the conditioned response is no longer displayed, does that really mean that it's gone forever? In his research on classical conditioning, Pavlov found that when extinction occurs, it doesn't mean that the subject returns to their unconditioned state.
Allowing several hours or even days to elapse after a response has been extinguished can result in the spontaneous recovery of the response.
Spontaneous recovery refers to the sudden reappearance of a previously extinct response. In his research on operant conditioning , Skinner discovered that how and when a behavior is reinforced could influence how resistant it was to extinction. He found that a partial schedule of reinforcement reinforcing a behavior only part of the time helped reduce the chances of extinction.
Rather than reinforcing the behavior each and every time it occurs, the reinforcement is given only after a certain amount of time has elapsed or a certain number of responses have occurred. This sort of partial schedule results in behavior that is stronger and more resistant to extinction. A number of factors can influence how resistant a behavior is to extinction.
The strength of the original conditioning can play an important role. The longer the conditioning has taken place and the magnitude of the conditioned response may make the response more resistant to extinction. Behaviors that are very well established may become almost impervious to extinction and may continue to be displayed even after the reinforcement has been removed altogether. Some research has suggested that habituation may play a role in extinction as well. For example, repeated exposure to a conditioned stimulus may eventually lead you to become used to it, or habituated.
This off-baseline procedure produces two primary problems that often make it impossible to judge the full extent of LI, or even its presence. First, as we discussed above, it obscures possible effects mediated by LTH of the UR to the preexposed stimulus. Second, differences that emerge during the course of extinction testing, which allows new learning to occur, are not an unambiguous test of LI during acquisition.
In the present experiments, we addressed both of these problems by using an on-baseline conditioned-suppression procedure to measure the response to repeated presentations of a white noise stimulus during the preexposure phase. In addition, the one-trial-per-day procedure prevented the loss of the baseline behavior due to repeated shock presentations, and thus provided a detailed look at the development of LI in acquisition. LI should take the form of slowed acquisition of conditioned suppression following stimulus preexposure.
However, any differences that occur on the first trial of conditioning, prior to reinforcement being presented, must be the result of LTH of unconditioned suppression in the preexposed group and the absence of habituation in the nonpreexposed controls. Following conditioning to asymptote, the possible effects of preexposure on the course of subsequent extinction were examined in daily sessions. Do the effects of preexposure survive conditioning to asymptote, and if so, what impact do they have on the new learning in extinction?
However, the impact of preexposure on extinction is not clear. Tests in extinction that follows conditioning are used to assess LI in off-baseline procedures, but following the course of extinction is not a routine feature of LI experiments. A few experiments have reported the course of extinction after LI e. The conditions of these experiments have varied widely. The extent of LI in acquisition is not always clear e. Through the present experiments, we tried to resolve some of these ambiguities.
In Experiment 1 , we used a lick-suppression procedure to measure, during preexposure, the response to repeated presentations of a white noise stimulus. Following conditioning to asymptote, we went directly to extinction to examine any enduring effects of preexposure that might be revealed in the course of extinction over days.
Experimentation took place during the light period of the cycle. Animals had ad lib access to food and water for three weeks after arrival before behavioral testing began. The two facing walls and the top were clear plastic.
The other walls were aluminum. The grid floor was stainless steel rods 5-mm diameter spaced 1. Rats were restricted to 60 min of water per day and given four days of preliminary lick training min sessions in operant chambers placed in an open room. This preliminary training was followed by seven daily min sessions in the operant chambers used for testing.
Two groups of rats were created, matched on their overall rates of licking. Minimum lick criteria were used for all trials in which suppression was measured. The first stimulus presentation of a session came no sooner than 60 s into the session and only after the animal had made licks. The animal had to have made 50 licks in the last 20 s and five in the last 1 s prior to stimulus onset.
These criteria were met on all first trials of each session for each rat. Licking remained strong throughout the experiment. The mean number of licks per min session was 2, range: 1,—2, Although the total number of licks declined over conditioning sessions and then recovered during extinction, F 6. Each session consisted of ten presentations of the white noise stimulus that would become the conditioned stimulus CS in the subsequent conditioning sessions.
The first three stimuli each day were presented only when the rat met the consistent-licking criteria, with a minimum s intertrial interval ITI. The additional seven stimuli were presented on a fixed s ITI without regard to behavior.
In each session, each animal received a single pairing of the CS with a 0. The CS duration was extended to The CS and US coterminated. Extinction sessions began 24 h after the last conditioning session. In each of six sessions, rats received three presentations of the s CS following the consistent-licking criteria. No shocks were delivered. Statistical analyses over trials or days were based on repeated measures analyses of variance ANOVAs with Group as a between-subjects factor.
The left panel of Fig. Only animals in Group PE received stimulus presentations on these days. Mean lick suppression ratios to the conditioned stimulus CS in Experiment 1. Only the first three CS presentations each day are shown. Both groups received one CS paired with a foot-shock unconditioned stimulus each day during conditioning center panel.
Both groups then received three CS presentations per day during extinction right panel. Only the first trial of each extinction day is shown. The vertical bars represent SEM s. Robust long-term habituation occurred across days, as measured by responsiveness on the first trial of each of the two preexposure sessions and the first conditioning trial, which occurred before the first foot shock.
Short-term habituation of lick suppression was observed over the first three measured trials within days for Group PE. The data from these two animals were excluded from the analysis of short-term habituation. Lick-suppression ratios for the one-trial-per-day conditioning phase are presented in the middle panel of Fig.
As is shown in Fig. The day main effect was also significant, F 2. This pattern of results suggests that LI was observed, but that conclusion is confounded by the significant first-day C1 difference.
Post-hoc t tests comparing the groups on each day produced significant differences indicative of LI on C2, t Baseline licking during the PreCS periods before each CS declined equally for the two groups across the four conditioning sessions, from a daily mean of Suppression ratios for the first trial of each extinction session are shown in the right panel of Fig.
Both groups began extinction with suppression ratios near zero, suggesting that they had reached a common asymptote, and we found no significant difference between groups on the first extinction session E1 , t Both groups exhibited significant extinction over the six extinction sessions, but Group PE extinguished significantly more slowly than did Group NPE.
The basic habituation and LI data are not surprising, but two elements of the results are worthy of note. First, a cautionary note: If the UR to the preexposed stimulus is not measured, and that preexposure produces LTH, much of what is considered LI may result from the difference between the preexposed and nonpreexposed animals in their URs to the initial presentations of the CS during conditioning.
Had we run preexposure and acquisition off-baseline, we would have been blind to the significant difference between the groups on the first conditioning trial, which was due solely to the UR to the CS in the nonpreexposed group and the LTH of that response in the preexposed group.
Had we run a two- or three-trial acquisition session off-baseline and then looked for LI in a subsequent test session, the group difference presumed to represent LI would be largely the result of the initial UR difference. All off-baseline LI procedures make interpretation of the extent of LI difficult e. In the typical off-baseline conditioned suppression design, it is impossible to know whether the brain or drug manipulation has affected LI, or disrupted habituation to the preexposed stimulus, or distorted the basic response to that stimulus.
Second, the slower extinction in the preexposed animals after both groups had been conditioned to a common asymptote was unexpected and potentially of theoretical importance. As we noted earlier, the relatively few LI experiments that have reported the course of extinction after LI e.
The robust and unexpected extinction effect found here is contrary to the published literature and demanded replication. Experiment 2 was an attempt at replication performed in a different laboratory with different experimenters using a slightly modified procedure and a different response measure.
Sixteen male Long Evans rats Harlan Laboratories, Indianapolis, IN , approximately 80 days old at the start of the experiment, were individually housed in a colony room maintained on a h light:dark cycle. The rats had performed in a previous experiment, in two different contexts in which they experienced shock. The contexts differed from the present contexts in terms of visual, tactile, and olfactory cues.
The rats had never been exposed to auditory stimuli prior to the present experiment. The chambers Med Associates, ENV consisted of aluminum front and back walls and clear acrylic sides and top.
Each chamber was outfitted with a food cup, recessed in the center of the front wall. The right lever remained retracted during the experiment. The chambers were illuminated by one 6-W bulb, with a red cover, mounted to the ceiling of the sound-attenuating chamber.
The apparatus was controlled by computer equipment located in an adjacent room. Establishing the neurocircuitry involved in inhibiting fear is important for understanding and treating anxiety disorders. To date, extinction procedures have been predominately used to examine the inhibition of learned fear, where fear is reduced to a conditioned stimulus CS by presenting it in the absence of the unconditioned stimulus US.
However, learned fear can also be reduced by habituation procedures where the US is presented in the absence of the CS. The effect of stimulus preexposure survived conditioning to asymptote and was reflected directly in extinction. These two experiments provide a cautionary procedural note for LI experiments and have shown an unexpected extinction effect that may provide new insights into the interpretation of LI.
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