Failure of retrospective revaluation to influence blocking.

Abstract

In the blocking paradigm, subjects receive reinforced presentations of a compound, AX, after reinforced presentations of A alone. Following this training, responding to X is often diminished relative to a control group, which did not receive the prior training with A. Standard associative theories of learning such as the Rescorla-Wagner model (Rescorla & Wagner, 1972) explain this effect by assuming that A and X compete for control over behavior. In contrast, theories such as the comparator hypothesis assume that learning about X is unaffected by the properties of A, but it is the expression of this learning at test that is affected by the blocking manipulation. The aim of the 3 reported experiments was to distinguish between these 2 accounts. According to the comparator hypothesis, devaluing A following blocking should increase subsequent responding to X. In all 3 experiments the blocking effect was found to persist following devaluation of A, providing support for standard associative theories.Keywords: conditioning, blocking, comparator hypothesis Effects such as blocking (Kamin, 1969) have been taken as evidence that cues compete for the control they acquire over behavior. In a typical blocking experiment, pairings of a compound comprising two stimuli, A and X, with an unconditioned stimulus (US) are preceded by pairings of just A with the US (Aϩ then AXϩ). Subsequent responding to X is then found to be weaker than if the original training with A is omitted. According to one influential class of theories, blocking is a consequence of cues competing for a limited pool of associative strength (e.g., Pearce, 1994;Rescorla & Wagner, 1972). The Rescorla-Wagner theory, for example, explains blocking by assuming that the initial training with A allows this stimulus to acquire considerable associative strength, leaving little to be gained by X during compound conditioning. This idea is expressed formally by Equation 1, in which the rate of learning about X, ⌬V X , is determined by the discrepancy between the maximum associative strength that the US is able to support on a given trial, , and the aggregate associative strength of all cues present on that trial, ⌺V. The learning rate parameters ␣ and ␤ represent the salience of X and the US respectively. If pretraining with A results in it gaining high associative strength, then the value of ⌺V will be close to when X is introduced and according to Equation 1 there will be little scope for conditioning with X.An implication of the foregoing explanation concerns the effect on X of presenting A by itself after the blocking treatment. Standard theories of associative learning, including the RescorlaWagner (1972) theory, assume that the associative strength of a stimulus can be modified only if it is physically present. Thus presentations of A, either by itself or paired with the US, after blocking should have no impact on responding to X. In contrast, other theories allow that performance to X can be affected by subsequent manipulations of the associative strength of A.Th...

The elusive nature of the blocking effect: 15 failures to replicate.

“…Other researchers have replaced elemental training by discrimination training (A+/B-in the experimental group and B+/A-in the control group; e.g. Dopson, Pearce, & Haselgrove, 2009). However, such designs empirically conflate blocking and reduced overshadowing: higher responding to X in the control group than in the experimental group may reflect enhanced responding in the former rather than reduced responding in the latter, relative to mere compound training.…”

An instance theory of associative learning

“…Minerva-AL has trouble with peak shift (see McLaren, Bennett, Guttman-Nahir, Kim, & Mackintosh, 1995). Minerva-AL predicts that some examples of retrospective revaluation (e.g., backward blocking) ought to be strong and reliable when, in fact, retrospective revaluation is experimentally elusive (see Blaisdell et al, 1999;Dopson, Pearce, & Haselgrove, 2009;Holland, 1999). Minerva-AL fails to acknowledge mediated conditioning due to its explanation for retrospective revaluation-a confusion recognized elsewhere (see Dwyer, 1999;Graham, Jie, Chan, McLaren, & Wills, 2011).…”

The fate of redundant cues during blocking and a simple discrimination.

“…This treatment, rather than the more conventional methodology of presenting Aϩ trials before but not intermingled with AXϩ trials, was adopted to encourage conditioning with A to reach asymptote. It was also adopted because we have found it to be successful in obtaining reliable blocking with appetitive Pavlovian conditioning (Dopson, Pearce & Haselgrove, 2009). A discrimination group received an AXϩ BXϪ discrimination in Stage II.…”