What is it called when an organism responds to a specific stimulus or conditioned stimulus and doesnt respond to another stimulus that is similar to the conditioned stimulus?

3 Conclusion

A CS can behave either as a simple CS or as an occasion setter. In the first case, the CS acquires excitatory or inhibitory associations with the US, in the second case the CS might enhance or depress the effect of the simple association accrued by another CS. The properties of simple CSs and occasion setters have been thoroughly studied (for a review see Swartzentruber 1995).

A neural network model presented by Schmajuk et al. (1998) can accurately describe most of the available data. Other learning models that also include direct and indirect associations between CS inputs and CR outputs (e.g., Bouton 1994) also provide correct depictions of the phenomena. Neural networks without direct connections (e.g., Gluck and Myers 1993, Wagner 1992) can only describe some of the experimental results. Some of the physiological mechanisms of occasion setting have been addressed in terms of neural networks (Gluck and Myers 1994, Schmajuk and Buhusi 1997). A recent volume, published by Schmajuk and Holland (1998) presents the latest data and theoretical approaches to the subject.

1.2.3 The role of the anterior perirhinal and insular cortex

The perirhinal cortex, which receives either visual or auditory CS information, projects directly to the lateral and basolateral amygdala. Post-training lesions of the anterior perirhinal cortex completely blocked the expression of fear-potentiated startle using a visual CS (Rosen et al. 1992), provided the lesion destroyed both the dysgranular and agranular portions of the perirhinal cortex. Post-training lesions of the perirhinal area (including secondary auditory cortices) blocked fear-potentiated startle to both auditory and visual CS (Campeau and Davis 1995a). However, reliable potentiated startle was observed after retraining in animals that had sustained main geniculate body lesions (which would destroy cortical connections between the thalamus and perirhinal cortex), or following pretraining lesions of the perirhinal area. These data suggest that cortical areas are normally used for the expression of fear conditioning, but that subcortical areas can take over if the cortex is damaged. Finally, as mentioned before, shock information seems to require the insular cortex, which in turn projects directly to the lateral nucleus of the amygdala.

1 Basic Terms

The pairing of an initially neutral stimulus (the conditioned stimulus—CS) with a biologically relevant stimulus (the unconditioned stimulus—US) comes to elicit a response (conditioned response—CR) that is usually but not always similar to the response previously associated with the unconditioned stimulus (the unconditioned response—UR). In fear conditioning, the US is an aversive fear-eliciting stimulus such as painful electric shock or loud noise, the CS is a neutral tone or light stimulus. The unconditioned and the conditioned response consist of changes on the subjective, the behavioral and the physiological level and include (in humans) enhanced subjective fear and responses such as freezing, changes in heart rate and skin conductance, the release of stress hormones, reduced pain sensitivity and startle reflex potentiation.

The development of the CR is based on the formation of an association between a neutral stimulus and a stimulus with innate biological significance (Rescorla 1988). Most studies involving fear conditioning have used cue rather than context conditioning, i.e., discrete CSs were presented rather than using the environment of the animal (e.g., the cage) as CS. In addition, delay conditioning where the CS terminates with the US rather than trace conditioning where the CS and US are separated in time were used in most studies. Fear can be viewed as a specific reaction to threatening stimuli. It can turn into an anxiety disorder when the fear becomes disproportionate to the stimulus that elicits it or when fear is experienced in inappropriate situations.

3 Conclusion

With classical conditioning of the Aplysia withdrawal reflex, the paired CS and US form an association by converging on a second messenger cascade within a single cell. This convergence results in the enhancement of a specific synapse. With operant conditioning of Aplysia feeding behavior, the association is made through contingent reinforcement. Contingent reinforcement of the response results in the alteration of a cell that mediates the expression of that response. Conditioning occurs through a modulation of the membrane properties of this single cell. Thus, modifications made to individual neurons (via intrinsic membrane properties and synapses) can account for both types of associative learning phenomena.

2.3 Classical Conditioning

Classical conditioning is the simplest form of associative learning. It occurs when a conditioned stimulus is observed within a certain time period before the observation of an unconditioned stimulus. After such a temporal pairing has occurred repeatedly, the conditioned stimulus itself produces a response. This learned response is known as the conditioned response (CR) and it can occur even in the absence of the unconditioned stimulus. The original experiment that demonstrated this type of behavior was performed by Pavlov [Pav27]. Such behavior has long been observed in higher animals, but Bailey and Kandel were among the first to discover classical conditioning in simple organisms such as Aplysia[BK85]. Because of the relatively simple neural structure of Aplysia, Bailey and Kandel were able to qualitatively discuss the biological mechanisms which produced the behavior. Byrne and Gingrich then took Bailey and Kandeľs qualitative discussion and used it to build a mathematical model[BG89]. The behavior of the model was then compared to Bailey and Kandeľs experimental results. According to this model, cAMP levels are enhanced even more strongly by an unconditioned stimulus, when Ca2 + levels are high as the result of a recently occurring conditioned stimulus. In this manner, the same mechanism responsible for sensitization results in even greater enhancement of the neural response when the unconditioned stimulus is temporally paired with the conditioned stimulus.

2.2 Operant Conditioning

In contrast to classical conditioning, which maintains that behaviors can be elicited by preceding conditioned stimuli, operant learning principles hold that behaviors are emitted from within, in response to the environmental stimuli that follow them. Operants themselves consist of actions that are performed on the environment that produce some consequence. Operant behaviors that bring about reinforcing environmental changes (i.e., if they provide some reward to the individual or eliminate an aversive stimuli) are likely to be repeated. In the absence of reinforcement, operants are weakened. Removing consequences (ignoring) can decrease or completely eliminate many annoying child behaviors such as whining.

B. F. Skinner, an experimental psychologist considered to be the primary proponent of operant learning theory, distinguished between two important learning processes: reinforcement (both positive and negative) and punishment. Positive reinforcement is the process by which a stimulus or event, occurring after a behavior, increases the future occurrence of a behavior. Negative reinforcement also results in an increase in the frequency of a behavior, but through a process of contingently removing an aversive stimulus following a behavior. Punishment refers to the introduction of an aversive stimulus, or removal of a positive one, following a response, resulting in a decrease in the future probability of that response. Skinner also observed that extinction occurs when the absence of any reinforcement results in a decrease or a reduction in response frequency.

3.2 Classical Conditioning

Classical conditioning is recognized as the simplest form of associative learning. An association between a signaling stimulus (conditioned stimulus or CS) and a response producing stimulus (unconditioned stimulus or UCS) forms when the CS is presented shortly before UCS onset. The CS gradually comes to elicit a response (CR) similar to that evoked initially by the UCS. A considerable body of research beginning in the 1930s (see Patterson 1976) attempted to demonstrate that spinal reflex circuits show the associational learning of classical conditioning. While beset with theoretical and methodological difficulties, the evidence supported the ability of spinal circuits to support long-lasting (days) changes due to temporal association. Other data (e.g., Beggs et al. 1985) indicate that classical conditioning procedures produce a variety of long-term neural alterations closely approximating associative learning in the intact animal. There is some suggestion that the ability of the spinal cord to sustain this neural plasticity decreases for several days after spinal transection, but may return within a few weeks, presumably after neural reorganization.

4 Clinical Interventions Involving Operant and Respondent Conditioning

Respondent (also known as classical, or Pavlovian) conditioning (see Classical Conditioning and Clinical Psychology) involves the pairing of unconditioned and conditioned stimuli, which ultimately leads to a conditioned stimulus that elicits a conditioned response. One of the more useful clinical heuristics has been research on how respondent and operant conditioning can combine to explain important clinical problems.

The best-known problem that has been addressed by considering both operant and respondent conditioning is the theory of the acquisition and maintenance of phobic behaviors. It has been suggested that phobic behaviors are acquired by classical conditioning but maintained by operant conditioning. Consider the simple example of someone bitten by a dog. In respondent conditioning terms, the dog bite is an unconditioned stimulus that produces the unconditioned response of pain and fear. Following such an incident, the next time the person approaches a dog, their fear and anxiety rises as the stimulus (the dog) gets closer. So far, the acquisition of the fearful response can be understood using a classical conditioning paradigm. If the person were to approach a variety of dogs, the fearful response would extinguish naturally, because extinction in classical conditioning is accomplished by presenting the conditioned stimulus (a dog) in the absence of the unconditioned stimulus (the dog bite). If this were the case, phobic responses would extinguish naturally over time. However, in many instances when one sees the dog and anxiety increases, a person simply turns around and walks away, thus avoiding the feared object. When that happens, the avoidance behavior is negatively reinforced (increased) by the removal of the anxiety. This increases the probability of avoiding the dog the next time such a stimulus is encountered. The avoidance of the phobic object prevents the natural extinction of phobic anxiety, because the phobic object (now a conditioned stimulus) is avoided and therefore extinction cannot occur.

Avoidance is an important issue in clinical psychology. Avoidance responses are operants that prevent the occurrence of aversive consequences before they are actually experienced. This behavior is maintained by negative reinforcement. Clinically, the liability of avoidance behavior is that the person engaging in such behavior does not experience the opportunity to test whether the anticipated aversive consequences are still in effect. Thus, the circumstances that led to the initial aversive consequences may have changed, but if the person continues to avoid the original stimulus conditions, the changes will go undetected. There may also be avoidance of other stimuli due to generalization that leads to additional restrictions in healthy functioning.

Several clinical interventions address such problems. Treatments for phobias involve therapeutic interventions that prevent or remove the instrumental benefits of avoidance. Phobia treatment involves a classical conditioning paradigm in which the behavior therapist uses exposure to the conditioned stimulus to bring about extinction (see Behavior Therapy: Psychological Perspectives). The key to successful treatment is the prevention of avoidance, which would negatively reinforce the phobic behavior (Barlow 1990).

Another clinical problem that is treated, in part, by preventing avoidance behavior is obsessive-compulsive disorder (OCD). In OCD, the client experiences intrusive thoughts or images that produce anxiety. For example, someone might be obsessed with a concern that they have failed to lock their house adequately. The thoughts are high in frequency, do not feel natural to the client, and are not under the voluntary control of the client. Obsessions are thoughts or images. They are often accompanied by compulsive behaviors that serve to reduce the obsessive thoughts. In this example, a client may go back repeatedly to check that the front door is locked, preventing them from going to work. The psychological intervention used to treat OCD is exposure to the situation that produces the obsessive behavior and response prevention so that the compulsive behaviors are not emitted (Foa et al. 1980). Eventually, the anxiety associated with the problematic stimulus extinguishes, because the function of acting to reduce the distress extinguishes.

3.2 Classical Conditioning

A paradigm in which stimulus-elicited responses are studied that has been of continuing interest to psychophysiologists is classical conditioning. In paradigms in which the conditioned stimulus (CS) is several seconds long, with the unconditioned stimulus (UCS) occurring at CS offset, the form of the conditioned response (CR) is generally observed to be that of a heightened orienting response to the CS (Hugdahl 1995). A general question frequently investigated has concerned the relationship between classical conditioning, a very simple form of learning, and the more complex forms of learning of which humans are capable, including verbally mediated processes. For instance, Dawson and his colleagues (Dawson and Schell 1985) studied the relationship between acquisition of the conditioned skin conductance response and the human subject's conscious awareness of the relationship between the CS and the UCS, asking whether a person who is unaware of the CS–UCS contingency will show conditioning. In a series of studies in which awareness of the CS–UCS relation was prevented or delayed by a distracting secondary task, they found that a CR was seen only in subjects who became aware of the CS–UCS relation. Moreover, CRs developed only at or after the point in time in a series of CS–UCS trials when subjects indicated awareness. Thus, these results indicate that conscious relational learning is necessary for human classical conditioning of ANS responses with neutral CSs. On the other hand, the relationship between awareness and conditioning may be different with certain paradigms used to establish the skeletal eyeblink conditioned response (Clark and Squire 1999).

In most psychophysiological studies of classical conditioning, the CSs have been fairly neutral stimuli such as simple tones or colored lights. In contrast, Öhman and his colleagues (see Hugdahl 1995) conducted a series of interesting studies of a different class of CSs, those variously characterized as potentially phobic, fear-relevant, or biologically prepared, such as pictures of spiders, snakes, or angry faces. Öhman and his colleagues have found that CRs (usually the conditioned skin conductance response) conditioned to potentially phobic stimuli (a picture of a snake) are harder to extinguish than are CRs conditioned to neutral stimuli (a picture of a flower). They require more non-reinforced presentations of the CS, and are resistant to instructional manipulation. That is, while responses conditioned to neutral stimuli can usually be abolished by instructing the subject that the UCS will no longer be delivered, so that the subject no longer has any cognitive expectancy that the UCS will follow the CS, responses conditioned to potentially phobic stimuli remain after such instructions, even in the absence of conscious expectancy of the UCS. Thus, psychophysiological techniques can be used in the laboratory to study the dynamics of ‘irrational’ conditioned responses, such as one may encounter in clinical phobias where the patient fears an object while realizing rationally that the object is harmless.

2.4 Operant–Pavlovian Interactions

Conditioned reinforcers and conditioned punishers can be generated by Pavlovian procedures. For example, if an odor is paired with food, the odor will elicit salivation as a CS but it can also serve as a conditioned reinforcer for an operant response. Conditioned punishers are created in the same way. Conditioned stimuli greatly enhance delayed consequences, for example, a delayed reinforcer will still be very effective as long as a stimulus bridges the gap between the response and the reinforcer (as in long-delay conditioning in Fig. 5). However, the effects are transitory unless the association between the conditioned stimulus and the reinforcer is maintained.

An operant SD can become a Pavlovian CS for operant consequences such as food. The SD then serves two functions that may produce competition between elicited and emitted responses. An example from the animal-training literature is shown in Fig. 6. A pig was reinforced with food for depositing coins in a bank. Shortly after learning the operant, the pig began ‘rooting’ the coins—pushing them along the ground, the pig's species-typical food handling behavior. As a result of the operant contingency the coin enters into a positive Pavlovian contingency with food and elicits rooting.

Punishment can reduce the frequency of operant behavior for a similar reason—a painful, punishing consequence reduces behavior because it elicits species-typical defensive behavior such as escape and avoidance. The result is that ‘punisher’ reduces the target behavior but not just by being a consequence of that behavior; it would still reduce the operant behavior even if arranged in a zero contingency. A conditioned aversive stimulus, such as a tone paired with shock, will similarly interfere with operant behavior. As a rule, reinforcers are most effective when the responses they elicit are identical to or compatible with a reinforced response and punishers are most effective when the responses they elicit are incompatible with the punished response. For example, it is easy to reinforce pecking in the pigeon with food because food elicits pecking.