Wednesday, October 08, 2008

Does working memory belong in the CHC taxonomy?

Working memory---does it belong in the CHC taxonomy?

Recently, on either the CHC or NASP listservs (I can't recall which...poor Glr this morning), there was a brief thread re: the CHC classification of a test (I believe it was a Wechsler subtest) as measuring working memory (or not). I chimed in to remind people that working memory (Gsm-MW) is NOT like most other narrow abilities in the individual differences trait-type CHC taxonomy. At this time, I'd like to again reinforce this point with reference to more exteneded comments I made in McGrew (2005). Also, last evening I reread a very good article where similar comments where articulated by a leading group of working memory researchers (this information is presented below).

First, immediately below is how working memory was defined in my last web-based listing of the CHC broad and narrow abilities (and in my 2005 CHC: Past, Present, Future chapter in Flanagan and Harrison's CIA2 book). I've added italics/bold to reinforce the point I'm trying to articulate in the current post.

  • Working Memory (MW): Ability to temporarily store and perform a set of cognitive operations on information that requires divided attention and the management of the limited capacity resources of short-term memory. Is largely recognized to be the mind's "scratchpad" and consists of up to four subcomponents. The phonological or articulatory loop processes auditory-linguistic information while the visuo-spatial sketch/scratchpad is the temporary buffer for visually processed information. The central executive mechanism coordinates and manages the activities and processes in working memory. The most recent component added to the model is the episodic buffer. Recent research (see chapter text) suggests that MW is not of the same nature as the other 60+ narrow factor-based trait-like individual difference constructs included in this table. MW is a theoretically developed construct (proposed to explain memory findings from experimental research) and not a label for an individual-differences type factor. MW is retained in the current CHC taxonomy table as a reminder of the importance of this construct in understanding new learning and performance of complex cognitive tasks (see chapter text).
In the body of the McGrew (2005) chapter I explained this point further (again--I've added italic and bold to emphasize my current points)

  • "Although Flanagan and I (McGrew & Flanagan, 1998; Flanagan et al. 2000) previously argued for MW’s preliminary “membership” status in the CHC taxonomy, this recommendation was based primarily on logical and rational considerations. Our recommendation was tempered by Carroll’s (1993) skepticism toward the working memory construct. Carroll (1993) stated that 'although some evidence supports such a speculation, one must be cautious in accepting it because as yet there has not been sufficient work on measuring working memory, and the validity and generality of the concept have not yet been well established in the individual differences research' (p. 647)."
  • "Although MW is undeniably a valid and important psychological construct, this does not necessarily mean MW is a factor analytic, latent trait, individual differences type construct similar to the 60+ narrow cognitive abilities that are the cornerstone of the CHC taxonomy (see Table 3). According to Carroll (1993), 'evidence for the existence of a latent trait derives from a demonstration that a number of similar task sets are highly correlated, or in factor- analytic terms, have weights on the same factor. A factor, if it is well established in a number of empirical investigations, is in essence a latent trait reflecting differences over individuals in ability characteristics or potentials' (p. 22). According to Carroll’s definition, the trait-factor evidence for MW is still questionable."
In the following article, which was in response to a meta-analytic article by Ackerman et al. (2005), Oberauer et al. (2005) make the point much better than I do. I very much like the main essence of their comments--namely, working memory is an explantory theoretical construct that is attempting to explain intelligence. Again, italics/bold in the text below are added by the blogmaster (IQ McGrew)

Oberauer, K., Schulze, R., Wilhelm, O. & Suß, H-B. (2005). Working Memory and Intelligence—Their Correlation and Their Relation: Comment on Ackerman, Beier, and Boyle. Psychological Bulletin, 131(1), 61-65. (click to view/download)

  • Abstract: On the basis of a meta-analysis of pairwise correlations between working memory tasks and cognitive ability measures, P. L. Ackerman, M. E. Beier, and M. O. Boyle (2005) claimed that working memory capacity (WMC) shares less than 25% of its variance with general intelligence (g) and with reasoning ability. In this comment, the authors argue that this is an underestimation because of several methodological shortcomings and biases. A reanalysis of the data reported in Ackerman et al. using the correct statistical procedures demonstrates that g and WMC are very highly correlated. On a conceptual level, the authors point out that WMC should be regarded as an explanatory construct for intellectual abilities. Theories of working memory do not claim that WMC is isomorphic with intelligence factors but that it is a very strong predictor of reasoning ability and also predicts general fluid intelligence and g.
  • "Ackerman et al. (2005) treated WMC as one more beast in the zoo of ability constructs. They were content with giving it its place in the three-stratum theory of Carroll—with an inclination toward relegating it into the rank and file, together with lower level constructs such as psychometric speed. We think that this reflects a misunderstanding of why most researchers are interested in the correlation between WMC and intelligence. The aim of that research is to validate WMC as an explanatory construct for intellectual abilities. The psychometric ability constructs have been derived largely inductively, reflecting the common variance among tests that have been constructed as diagnostic tools for aspects of mental abilities as described in everyday language. In contrast, WMC is a construct that derives deductively from theories of the cognitive architecture in which a limited-capacity WM plays a central role, although not always under the same name, (Anderson & Lebiere, 1998; Atkinson & Shiffrin, 1968, to cite just the most prominent ones). These theories assign short-term memory or WM a crucial role for complex tasks such as reasoning and text comprehension."
  • "By treating WMC as another primary factor in the ability hierarchy, Ackerman et al. (2005) ignore its theoretical background. WMC is a construct that bridges the gap between research on individual differences in abilities and cognitive science, including experimental cognitive psychology and formal modeling of cognitive processes. The tasks used to measure WMC have been constructed to operationalize processes postulated in theories of WM, and although these theories are admittedly still in their infancy, they provide some guidance as to what features a good WM task should have."
  • "Among the theoretical constructs within current theories of information processing, WMC is the one parameter that correlates best with measures of reasoning ability, and even with gf and g. Therefore, investigating WMC, and its relationship with intelligence, is psychology’s best hope to date to understand intelligence. Stopping short at searching for the place of WMC among the factor hierarchy of ability constructs is like being satisfied with a Linne´an taxonomy of creatures and refusing to proceed toward explaining the origin of species."
Kudos to Obereaur et al. Well stated.

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