Academic journal article Psychonomic Bulletin & Review

Learning with Arbitrary versus Ecological Conditioned Stimuli: Evidence from Sexual Conditioning

Academic journal article Psychonomic Bulletin & Review

Learning with Arbitrary versus Ecological Conditioned Stimuli: Evidence from Sexual Conditioning

Article excerpt

Laboratory investigations of Pavlovian conditioning typically involve the association of an arbitrary conditioned stimulus (CS) with an unconditioned stimulus (US) that has no inherent relation to the CS. However, arbitrary CSs are unlikely to become conditioned outside the laboratory, because they do not occur often enough with the US to result in an association. Learning under natural circumstances is likely only if the CS has a preexisting relation to the US. Recent studies of sexual conditioning have shown that in contrast to an arbitrary CS, an ecologically relevant CS is resistant to blocking, extinction, and increases in the CS-US interval and results in sensitized responding and stronger second-order conditioning. Although the mechanisms of these effects are not fully understood, these findings have shown that signature learning phenomena are significantly altered when the kinds of stimuli that are likely to become conditioned under natural circumstances are used. The implications of these findings for an ecological approach to the study of learning are discussed.

To study Pavlovian conditioning, one has to select an unconditioned stimulus (US) and a potential conditioned stimulus (CS) and then arrange for the CS and the US to become associated with each other. Common definitions of Pavlovian conditioning tell us how to do this. Mackintosh (1974), for example, wrote, "Experiments on classical conditioning may be defined as those in which a contingency is arranged between a stimulus and an outcome" (p. 4). According to Bower and Hilgard (1981), "some arbitrary stimulus, such as a light, is combined with the presentation of food. Eventually, after repetition and the correct time relationships, the light will evoke salivation independently of the food" (p. 49). In a similar definition, Anderson (1995) specified that "the US is paired with a neutral conditioned stimulus (CS), such as a bell. After a number of such pairings, the CS acquires the ability to evoke a response by itself" (p. 10).

The emphasis in these definitions is that before being used in a conditioning procedure, the CS should be unrelated to the US. Terms such as arbitrary (Bower & HiIgard, 1981) and neutral (Anderson, 1995; Papini, 2002, p. 491; Shettleworth, 1998, p. 109; Staddon, 1983, p. 102) have been used to describe the initial independence of the CS from the US. This emphasis on arbitrary or neutral CSs has been encouraged by the fact that investigators have been interested primarily in the establishment of new associations. Selecting a CS that is initially unrelated to the US helps to ensure that the responses that develop reflect the newly acquired CS-US association, rather than a preexisting relation between the events.

Another point that has become increasingly popular to emphasize is that Pavlovian conditioning can be characterized as an adaptive process that promotes efficient interactions of the organism with significant biological events in its natural environment (Domjan, Cusato, & ViIlarreal, 2000; Hollis, 1982,1997). This ecological view is especially appealing to those interested in functional considerations, but it may not be easily reconciled with definitions of Pavlovian conditioning that emphasize the use of arbitrary CSs. The terms arbitrary and neutral imply that the CS is unrelated to the US and, therefore, rarely occurs in conjunction with that US under natural circumstances. An arbitrary CS may coincide with a US occasionally, but without the interventions of an experimenter, such accidental pairings will be rare. In addition, the accidental pairings will be preceded and followed by unpaired CS and US encounters, which would undermine the development of conditioned responding (e.g., Benedict & Ayres, 1971; Rescorla, 2000).

A CS will occur reliably with a US outside the laboratory only if there is a preexisting or inherent relation between the two events. Consider, for example, a hawk that preys on mice for food. …

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