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CUE COMPETITION IN FUNCTION LEARNING: BLOCKING AND HIGHLIGHTING



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Submitted for publication Please do not quote Version of April 26 2001 Comments welcome Cue competition in function learning Blocking and highlighting John K Kruschke Indiana University Bloomington In function learning people learn to predict a continuous outcome from continuous cues In category learning people learn to predict a nominal outcome The present research demonstrates that two complementary forms of cue competition previously found in category learning also occur in function learning One form of cue competition is blocking of learning about a redundant cue Kamin 1968 A second form of cue competition is highlighting of a diagnostic cue a k a the inverse base rate effect Medin Edelson 1988 For tests with conflicting cues the results show bimodality of responses as opposed to averaging which implies exclusive selectivity that cannot be discerned from category learning paradigms It is argued that these effects are caused in both category and function learning by attentional shifts No previously published model of function learning can account for these effects but a model by Kalish Lewandowsky and Kruschke 2001 is promising This article reports evidence of two types of strong cue competition in function learning One effect is blocking of learning about a redundant relevant cue Kamin 1968 The other effect is what I call highlighting previously referred to as the inverse base rate effect Medin Edelson 1988 There are two main implications of this work First because the effects are now evident in both function learning and category learning the results suggest that future theories of learning in either domain should be designed to address the other domain as well Second because theories of these cue competition effects in category learning posit a central role for selective attention Kruschke 1996 Kruschke Blair 2000 theories of function learning should also incorporate selective attention The new data also indicate mutual exclusivity in cue competition as opposed to averaging that cannot be measured in category learning paradigms Consider what might happen when an observer is confronted by two conflicting cues simultaneously For example suppose that the person has previously learned that cue A indicates outcome 1 and cue C indicates outcome 3 where outcomes 1 and 3 are values on a metric scale Suppose that the person is then confronted by a test case in which the conflicting cues A and C are paired The observer might contemplate the responses for both cues and generate a response that best reflects an average of the two i e response 2 Alternatively the observer might exclusively select one or the other cue or cue outcome link and generate either response 1 or response 3 perhaps bimodally Yet another possibility is that the person could just decide that the conflicting cues imply that all bets are off and so s he just chooses randomly uniformly from the available response options Still other possibilities exist of course My point is that these three different response tendencies which leave different signatures in the function learning paradigm cannot be so easily distinguished in the standard category learning paradigm This is because in category learning there are no intermediate response options between the nominal category labels The results reported below are most consistent with mutual exclusivity in cue selection as opposed to averaging Background Function learning is common in everyday tasks As just a few examples consider that people can learn how hard to throw a ball in response to visual cues about the distance of the catcher paramedics can learn how much medication to administer in response to cues about the weight of the patient and investors can learn how much stock to purchase in response to cues about market trends Category learning is distinct from function learning only in that the outcomes are categorical values instead of metric values That is the outcomes are merely labels without size or order instead of magnitudes This seemingly small difference suggests that similar psychological mechanisms should be involved in both and that research about the two types of learning should mutually inform each other see review by Busemeyer Byun Delosh McDaniel 1997 One of the central types of phenomena observed in category learning is cue competition wherein alternative cues apparently compete to gain associative predictiveness of the outcome It seems reasonable to expect that cue competition should also occur in function learn This research was supported in part by NSF grant BCS 9910720 The author thanks Michael Kalish and Stephan Lewandowsky for motivation to pursue this research For helpful comments on drafts of this article the author thanks Jerome Busemeyer and Stephan Lewandowsky For assistance administering the experiment the author thanks Twanna Allen Colin Campbell Dan Hall Kara Kohnen Indya Watts and Maxine Weiss Correspondence can be addressed to John K Kruschke Department of Psychology 1101 E 10th St Indiana University Bloomington IN 47405 7007 or via electronic mail to kruschke indiana edu The author s world wide web page is at http www indiana edu kruschke 1 2 KRUSCHKE ing Cue competition is fundamental in associative learning but only a little work has found cue competition in function learning e g Birnbaum 1976 Busemeyer Myung McDaniel 1993 Mellers 1986 Perhaps the most well known example of cue competition in category learning is blocking which has been observed in a variety of species and procedures e g Dickinson Shanks Evenden 1984 Kamin 1968 Kruschke Blair 2000 Shanks 1985 and which revolutionized theories of associative learning In blocking the participant first learns that a cue denoted here as A perfectly predicts an outcome In subsequent training the participant experiences cases of cue A paired with another cue denoted B still perfectly predictive of the outcome Despite the fact that B perfectly predicts the outcome people apparently do not learn to strongly associate it with the outcome That is learning about B has been blocked by previous learning about A To my knowledge blocking has never been sought in the context of function learning yet it should exist if blocking is truly a fundamental and pervasive phenomenon in learning Another dramatic case of cue competition in category learning is what I call highlighting previously referred to as the inverse base rate effect Medin Edelson 1988 In this paradigm people initially learn that a pair of


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