Classical Conditioning

It hath been observed that occurrences within the United States during the early twentieth century did serve to establish psychology as a science, and learning as a legitimate field of study. Concurrently, noteworthy advancements transpired in other nations. Of particular significance was the oeuvre of Ivan Pavlov (1849–1936), a Russian physiologist, laureate of the Nobel Prize in 1904 for his investigations into the processes of digestion.

Pavlov's enduring contribution to the theory of learning resides in his exposition of classical conditioning (Cuny, 1965; Hunt, 1993; Windholz, 1997). Whilst presiding as Director of the Physiological Laboratory at the Institute of Experimental Medicine in Petrograd, he discerned that canines would oft salivate upon perceiving the attendant bearing their sustenance, or even at the auditory perception of the attendant's footfalls. Pavlov apprehended that the attendant did not constitute a natural stimulus for the reflex of salivation; rather, the attendant acquired this potency through association with aliment.

Classical conditioning constitutes a multistage procedure commencing with the presentation of an unconditioned stimulus (UCS), thereby eliciting an unconditioned response (UCR). Consider Pavlov's experiment, wherein the presentation of meat powder (UCS) to a famished canine elicited salivation (UCR). The conditioning of the subject necessitates the iterated exposure to an initially neutral stimulus antecedent to the UCS. Pavlov, in many instances, employed a ticking metronome as the neutral stimulus. Initially, the metronome's ticking induced no salivation. Eventually, the canine exhibited salivation upon hearing the metronome, prior to the administration of the meat powder. The metronome thus transformed into a conditioned stimulus (CS), engendering a conditioned response (CR) akin to the original UCR (vide Table 3.1).

Repetitive presentations of the CS without reinforcement (i.e., devoid of the UCS) precipitates a diminution in the intensity of the CR, culminating in its disappearance—a phenomenon designated as extinction (Larrauri & Schmajuk, 2008; Pavlov, 1932b).

Spontaneous recovery ensues following an interval wherein the CS is withheld, and the CR ostensibly undergoes extinction. Should the CS subsequently be presented, and the CR reappears, it is deemed that the CR has spontaneously recovered from extinction. A CR thus recovered is not enduring, absent re-presentation of the CS. The re-establishment of CS–CR pairings reinstates the CR to its original potency. The relative ease with which CS–CR pairings are reinstated intimates that extinction does not involve the unlearning of the initial associations (Redish, Jensen, Johnson, & Kurth-Nelson, 2007).

Generalisation implies that the CR manifests in response to stimuli bearing resemblance to the CS (vide Figure 3.2). Once a canine is conditioned to salivate upon hearing a metronome ticking at a cadence of 70 beats per minute, it may also salivate in response to metronomes ticking at varying rates, as well as to clocks or timers that produce similar sounds. The degree of generalisation is inversely proportional to the dissimilarity between the novel stimulus and the CS or to the paucity of shared attributes (Harris, 2006).

Discrimination is the complementary process whereby the canine learns to respond exclusively to the CS, whilst disregarding other, analogous stimuli. To effect discrimination training, the experimenter might pair the CS with the UCS, whilst presenting other, similar stimuli absent the UCS. For instance, a metronome ticking at 70 beats per minute (the CS) is paired with the UCS, whilst other cadences (e.g., 50 and 90 beats per minute) are presented without concomitant pairing with the UCS.

Once a stimulus attains conditioned status, it may function as a UCS, thereby facilitating higher-order conditioning (Pavlov, 1927). If a canine has been conditioned to salivate to the sound of a metronome ticking at 70 beats per minute, that metronome may serve as a UCS for subsequent conditioning. A novel, neutral stimulus (such as a buzzer) is sounded for a brief interval, followed by the metronome's ticking. If, after several iterations, the canine commences salivating upon hearing the buzzer, the buzzer has transformed into a second-order CS. Conditioning of the third order involves the second-order CS serving as the UCS and a new neutral stimulus being paired therewith. Pavlov (1927) noted that conditioning beyond the third order proves challenging.

Higher-order conditioning is a complex process the full intricacies of which are not entirely elucidated (Rescorla, 1972). The theoretical implications are compelling, potentially offering an explanation for the induction of conditioned emotional reactions, such as stress and anxiety, by certain social phenomena (e.g., academic failure). In early stages of life, academic failure may be a neutral occurrence. It frequently becomes associated with parental and pedagogic disapproval, which functions as a UCS, eliciting anxiety. Through conditioning, failure can subsequently elicit anxiety. Cues associated with the situation may likewise become conditioned stimuli. Ergo, students may experience anxiety upon entering the examination room or upon the distribution of test papers.

CSs capable of eliciting CRs are termed primary signals. Humans, unlike animals, possess the capacity for speech, thereby augmenting the potential for conditioning (Windholz, 1997). Language constitutes the second signal system. Words, either spoken or conceived, serve as labels denoting events or objects and may function as CSs. Consequently, contemplating an examination or attending to the instructor's discourse on an impending test may instigate anxiety. It is not the test per se that induces anxiety in the students, but rather the words or thoughts pertaining thereto, that is, its linguistic representation or meaning.

Pavlov posited that conditioning is an automatic procedure which transpires with iterated pairings of the CS and UCS, and that repeated non-pairings serve to extinguish the CR. However, in humans, conditioning may occur with considerable rapidity, occasionally after but a solitary CS–UCS pairing. Repeated non-pairings of the CS and UCS may prove ineffectual at extinguishing the CR. Extinction doth seem highly context-dependent (Bouton, Nelson, & Rosas, 1999). Responses remain extinguished within the original context, yet should the setting be altered, CRs may recur. These findings cast doubt upon Pavlov's original description of conditioning.

Research subsequent to that of Pavlov hath demonstrated that conditioning dependeth less upon the CS–UCS pairing and more upon the extent to which the CS conveyeth information concerning the likelihood of the UCS occurring (Rescorla, 1972, 1976). As an illustration, let us assume the existence of two stimuli: the one invariably followed by a UCS, and the other but occasionally so. The first stimulus should, of necessity, result in conditioning, inasmuch as it reliably predicteth the onset of the UCS. It may not even be requisite to pair the CS and UCS; conditioning may transpire simply through informing individuals that they are related (Brewer, 1974). Likewise, repeated CS–UCS non-pairings may not be essential for extinction; advising individuals that the contingency is no longer in effect may diminish or extinguish the CR.

An elucidation for these results lieth in the notion that individuals form expectations regarding the probability of the UCS occurring (Rescorla, 1987). For a stimulus to assume the mantle of a CS, it must convey information to the individual concerning the time, place, quantity, and quality of the UCS. Even when a stimulus possesseth predictive power, it may fail to become conditioned should another stimulus prove a superior predictor. Rather than conditioning being an automatic process, it appeareth to be mediated by cognitive procedures. Should individuals fail to apprehend a CS–UCS link, conditioning shall not occur. Conversely, in the absence of a veritable CS–UCS link, conditioning may yet occur should individuals believe in its existence. Albeit this contingency view of conditioning may not be entirely accurate (Papini & Bitterman, 1990), it doth furnish an alternative explication for conditioning than that offered by Pavlov, and doth highlight the complexity thereof.

Pavlov (1927, 1928) posited that any perceived stimulus might be conditioned to elicit any response of which the organism is capable. Subsequent investigations, however, have revealed that the universality of conditioning is circumscribed. Within any given species, responses are conditionable to certain stimuli but not to others. The efficacy of conditioning hinges upon the congruity of the stimulus and response with reactions specific to the species (Hollis, 1997). All organisms are inherently endowed with fundamental behavioural patterns essential for survival within their ecological niches; yet, it is through the agency of learning that the requisite fine-tuning for successful adaptation is achieved (Garcia & Garcia y Robertson, 1985, p. 197).

An experiment conducted by Garcia and Koelling (1966) employing rats serves to illustrate the salience of biological factors. Certain rats were provided with water accompanied by bright illumination and auditory stimuli (an aversive stimulus—bright, noisy water). These rats were subsequently either subjected to immediate electric shock or treated in such a manner as to induce nausea after a temporal delay. Conversely, other rats were given regular (saccharin-sweetened) water and then either subjected to shock or induced to experience nausea. Bright, noisy water coupled with electric shock engendered a conditioned aversion to the water, whereas bright, noisy water coupled with nausea did not. Regular (saccharin) water coupled with nausea resulted in an aversion to the water, but regular water coupled with shock did not. The electric shock (an external event) was readily associated with the bright illumination and auditory stimuli (external cues), but not with nausea (an internal event). Nausea became a Conditioned Response (CR) to an internal stimulus (taste). Although the interval separating the consumption of water and the onset of nausea (one hour) exceeded the temporal parameters typically accommodated by a classical conditioning model, the findings underscore the complexity of classical conditioning by suggesting that rats have evolved an innate mechanism to forestall taste aversions. In summation, it appears that conditioning is contingent upon a certain degree of inherent association between stimuli, thereby facilitating the animal's adaptation to its environment (Hollis, 1997).

Pavlov (1932a, 1934) did apply the principles of classical conditioning to abnormal behaviours, and did discuss how neuroses and sundry pathological states might develop. His postulations were, admittedly, of a speculative nature and lacked substantiation; albeit, the very principles of classical conditioning have been applied by others in order to condition emotional reactions.

Watson did claim to demonstrate the potency of emotional conditioning in the well-recounted 'Little Albert' experiment (Watson & Rayner, 1920). Albert was an infant, some eleven months of age, who evinced no fear of a white rat. During the conditioning process, a hammer was struck against a steel bar behind Albert as he reached for the aforementioned rat. 'The infant jumped violently and fell forward, burying his face in the mattress' (p. 4). This sequence was forthwith repeated. A week hence, when the rat was presented anew, Albert did commence to reach out, but then withdrew his hand. The previous week's conditioning was, thus, apparent. Tests conducted over the subsequent few days did reveal that Albert reacted emotionally to the rat's presence. There was also a generalisation of fear observed, extending to a rabbit, a dog, and even a fur coat. When Albert was retested a month later with the rat, he manifested a mild emotional reaction.

Notwithstanding that this study is widely cited as demonstrating how conditioning may engender emotional reactions, the influence of conditioning is not usually of such magnitude (Harris, 1979). As we have observed in the preceding section, classical conditioning is a complex phenomenon; one cannot condition any response to any stimulus indiscriminately. Species have evolved mechanisms predisposing them to being conditioned in some ways and not in others (Hollis, 1997). Amongst humankind, conditioning transpires when individuals are cognisant of the relation between the CS and the UCS, and information indicating that the UCS may not invariably follow the CS can induce extinction. Attempts to replicate Watson and Rayner's findings were not uniformly successful. Valentine (1930a), for example, found no evidence of conditioning when he employed inanimate objects as the CS in lieu of animals.

A more reliable means of producing emotional conditioning resides in systematic desensitisation, which is frequently employed with individuals who harbour debilitating fears (Wolpe, 1958; vide Application 3.3). Desensitisation comprises three distinct phases. In the first phase, the therapist and the client jointly develop an anxiety hierarchy, consisting of several situations graded from least-to-most anxiety-producing for the client. For a test-anxious student, situations of low anxiety might encompass hearing a test announcement in class, and gathering together materials for study. Situations of moderate anxiety might be studying the night before the test, and walking into class on the day of the test. High-anxiety situations could include receiving a copy of the test in class, and being unable to answer a test question.

In the second phase, the client learns to relax by imagining pleasant scenes (e.g., lying on a beach) and cuing relaxation (saying 'relax'). In the third phase, the client, whilst relaxed, imagines the lowest (least-anxious) scene on the hierarchy. This may be repeated several times, after which the client imagines the next scene. Treatment proceeds up the hierarchy until the client can imagine the most anxiety-producing scene without feeling anxious. Should the client report anxiety whilst imagining a scene, the client drops back down the hierarchy to a scene that does not produce anxiety. Such treatment may require several sessions.

Desensitisation involves counterconditioning. The relaxing scenes that one imagines (UCS) produce relaxation (UCR). Anxiety-producing cues (CS) are paired with the relaxing scenes. Relaxation is incompatible with anxiety. By initially pairing a weak anxiety cue with relaxation, and by slowly working up the hierarchy, all of the anxiety-producing cues should eventually elicit relaxation (CR).

Desensitisation is an effective procedure that can be accomplished in a therapist's or counsellor's office. It does not require the client to perform the activities on the hierarchy. A disadvantage, however, is that the client must be able to imagine scenes vividly. People differ in their ability to form mental images. Desensitisation also requires the skill of a professional therapist or counsellor, and should not be attempted by anyone unskilled in its application.