Blocking Effect in Humans

The apparent influence of informational factors on associative learning has been the focus of much attention by investigators who wished to account for this phenomenon within the classical Pavlovian conditioning paradigm. One of the most influential concepts in this area has been Kamin's (1969) notion of the blocking effect which he identified in animal experiments. Blocking describes the situation in which the prior conditioning of a subject to a conditioned stimulus (A) of a stimulus compound (AB) inhibits conditioning to the second conditioned stimulus B when the compound is paired with an unconditioned stimulus (US). The 'proof' of the blocking effect is provided by trials in which blocking does not take place when an unconditioned stimulus other than the one for which A had been previously conditioned is introduced to the compound AB (Dickinson, 1977, cited by Bonardi & Hall, 1994, p. 107). Kamin's (1969) findings were similar to the concept of overshadowing which had been described by Pavlov (1927). Overshadowing also takes place when a stimulus compound is paired with an unconditioned stimulus but without prior conditioning to either stimulus. In this case the difference arises when one stimulus is more salient than the other and the more salient stimulus may prevent conditioning to the less salient stimulus (Pavlov, 1927, cited by Hammerl, 1989, p. 74).

Basically it can be said that "the animal will not condition readily to B because it has been made redundan

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weak, easily disrupted phenomenon" (Martin & Levey, 1991, p. 127) or, when they demonstrated that blocking "can occur under certain conditions in classical autonomic conditioning in humans," found that the conditions under which the phenomenon occurred were at variance with those found in animal experiments, leaving open the question of what conditions are actually involved in blocking (Kimmel & Bevill, 1991). Hinchy, Lovibond and Ter-Horst contended, however, that since the effect had been demonstrated in animals and subsequently led to the assumption of much greater cognitive complexity in their associative learning, it was "surprising that this phenomenon has been difficult to demonstrate in humans" and suggested that an improved procedure and greater sensitivity of measures would demonstrate blocking in humans (1995, p. 2). Hinchy et al. (1995) noted, for example, that cognitive research designs have produced solid evidence of the effect in a different setting (e.g., Jones, Gray & Hemsley, 1990; Jones, Gray & Hemsley, 1992a). Jones, Gray and Hemsley developed an effective "paradigm with which to demonstrate the Kamin blocking effect with human subjects" in 1990. They have since gone on to use the Kamin blocking paradigm a

Category: Psychology - B