Impulsivity and Overall Similarity Classification

Impulsivity and Overall Similarity Classification Andy J. Wills (andy.wills@plymouth.ac.uk), Chris A. Longmore Department of Psychology, Plymouth University, UK. Fraser Milton Department of Psychology, Exeter University, UK. Abstract Ward (1983) that highly impulsive individuals are more likely to classify on the basis of overall similarity than individuals with low impulsivity. This result appears to support the less-is-more hypothesis because, presumably, impulsive individuals devote fewer cognitive resources to the categorization task than do reflective individuals. We had two concerns about Ward’s demonstration— the validity of the measure of impulsivity, and the va- lidity of the measure of overall similarity classification. Below, we outline those concerns, and describe how we addressed them in the current study. It is sometimes argued that implementation of an overall similarity classification is less effortful than implemen- tation of a single-dimension classification. One piece of evidence taken to be in support of this argument is that highly impulsive individuals appear to be more likely to sort on the basis of overall similarity than individuals with low impulsivity (Ward, 1983); presumably, higher impulsivity results in lower effort. In the current arti- cle, we identify some limitations in Ward’s procedure and, using a more standard measure of impulsivity and a less ambiguous measure of overall similarity classifica- tion, re-investigate the relationship between impulsivity and overall similarity classification. Using a match-to- standard procedure, the current experiment finds that overall similarity classification is less prevalent in highly impulsive individuals. The implications of this result, which is opposite to that reported by Ward (1983), are discussed. Keywords: impulsivity; categorization; overall similar- ity; family resemblance. Impulsivity In a seminal article, Brooks (1978) argued for two dif- ferent processes of categorization. In analytic catego- rization, the participant separates aspects of the stimu- lus and evaluates their ability to predict category mem- bership. This process of analysis, Brooks assumed, will typically lead to a subset of the stimulus attributes con- trolling responding. In contrast, nonanalytic categoriza- tion is the process of predicting category membership on the basis of overall similarity to known examples— a process that results in all stimulus attributes having some control over responding. Brooks hypothesized that nonanalytic categorization would be more likely to occur where cognitive resources were limited. Brooks’s hypothesis is striking because it assumes that a categorization process that employs all the informa- tion in the stimulus (overall similarity) is less effortful than a categorization process that employs a subset of that information (analytic, or “rule-based”, categoriza- tion). Following Wills, Milton, Longmore, Hester, and Robinson (2013), we describe this as the less-is-more hypothesis—for example, less time spent categorizing objects results in more information from those objects having control over responding (Smith & Kemler Nel- son, 1984). We contrast this with the more-is-more hypothesis—for example, more time spent categorizing objects results in more information from those objects having control over responding (Milton, Longmore, & Wills, 2008). The current paper revisits one particular plank in the less-is-more argument; namely, the result reported by Ward used the Matching Familiar Figures measure of impulsivity (Kagan, 1965), a measure whose validity has been questioned (e.g. Block, Block, & Harrington, 1974) and which appears to be largely uncorrelated with better validated measures of impulsivity (Helmers, Young, & Pihl, 1995). In the current study, we employed the Bar- ratt Impulsivity Scale (BIS-11), which is the most widely used measure of impulsivity (Stanford et al., 2009). It has high reliability and good external validity (Patton, Stanford, & Barratt, 1995). The Barratt Impulsivity Scale is a self-report measure that includes statements such as, “I concentrate easily” and “I am happy-go- lucky”. Overall similarity classification Ward employed the triad procedure as a measure of the prevalence of overall similarity classification. In this pro- cedure three stimuli, whose relationship to each other is illustrated in Figure 1, are presented simultaneously and participants are asked to decide which two stimuli go together best. Stimuli B and C are similar on both stimulus dimensions, but not identical on either, while stimuli A and B are identical on one stimulus dimension but quite dissimilar on the other. Three responses are possible—an AB response (A and B go together best), a BC response or an AC response. Time pressure, concur- rent load, impulsivity, and instructions to respond im- pressionistically, all increase BC responses and decrease AB responses (Smith & Kemler Nelson, 1984; Ward, 1983; Ward, Foley, & Cole, 1986). AB responding is typically described as “dimensional” responding and BC responding is typically described as “overall similarity” responding, hence leading to the claim that overall sim- ilarity (BC) responding increases as cognitive resources