New and Emerging Models of Human Intelligence Andrew R

Overview New and emerging models of human intelligence Andrew R. A. Conway1 and Kristof Kovacs2,3 In the last decade, new models of human intelligence have altered the theoretical landscape in psychometrics and cognitive science. In the current article, we provide an overview of key distinguishing features of these new models. Compared to 20th century models of intelligence, the new models proposed in the 21st century are unique for three primary reasons; (1) new models interpret the general factor, or g,asanemergentpropertyreﬂectingthepatternofpositivecorrelationsobserved among test scores, not as a causal latent variable, and therefore challenge the notion of general ability, (2) new models bridge correlational and experimental psychology and account for inter-individual differences in behavior in terms of intra-individual psychological processes, and (3) new models make novel predictions about the neural correlates of intelligent behavior. © 2015 Wiley Periodicals, Inc. How to cite this article: WIREs Cogn Sci 2015. doi: 10.1002/wcs.1356 INTRODUCTION afreshperspectiveandnewapproachtothescienceof intelligence. ntelligence is one of the most extensively investi- The article also does not provide a formal gated constructs in the history of cognitive science. I defnition of intelligence. As mentioned, there is no Despite this research effort, or perhaps because of it, consensus defnition of the term. Thus, in order there is still no single consensus defnition, model, or to be objective here, we could only provide a list theory of human intelligence. The purpose of the cur- of acceptable defnitions, rather than the defnition. rent article is to provide an overview of new models More importantly, most previous defnitions (apart of intelligence. The feld of intelligence is currently in from the one, ‘Intelligence is what IQ tests measure’,1) a stage of signifcant progress, so our goal here is to revolve around the interpretation of the general factor convey to a broad audience what is novel and exciting of intelligence as something that is refected by IQ about these so-called new models. tests. That is, these defnitions implicitly adhere to the Given the focus on what is new, the current idea that there is something out there that we can call article does not address old controversies or political intelligence, and this single construct is measured by a arguments about intelligence research. In our opin- variety of different ability tests. In this article, we argue ion, the feld has fnally moved beyond all that. A that this interpretation is incorrect: intelligence, best new generation of intelligence researchers, equipped defned, is a set of different cognitive abilities rather with more advanced statistical methods and a more than an overarching, general mechanism involved in sophisticated understanding of the brain, are asking all cognitive activity. much more compelling questions about cognitive abil- Of course, the debate on general ability versus ities. As we embark upon the second century of intel- multiple abilities has been around for over a century ligence research, there is opportunity, and reason, for now, so what is new, or different, about ‘new models’ of intelligence? In our view, a lot, but let us start with ∗Correspondence to: [email protected] a glimpse of just three recent developments in the feld 1Department of Psychology, Princeton University, Princeton, NJ, USA of intelligence research. We will elaborate upon each 2Department of Psychology, Eszterházy Károly College, Hungary of these topics later. 3Department of Psychological Methods, University of Amsterdam, Amsterdam, Netherlands • The general factor of intelligence, or g, which Confict of interest: The authors have declared no conficts of interest is reliably observed when the all-positive for this article. covariance matrix of mental test scores is ©2015WileyPeriodicals,Inc. Overview wires.wiley.com/cogsci factor analyzed, is interpreted as an emergent of intelligence. A theory is a set of ideas intended to rather than a latent property. That is, instead explain something or some type of phenomenon and of interpreting g as a causal general ability, is based on general principles independent of the thing, implicitly linked to a unitary psychological trait, or the phenomenon, being explained. Strong theories new models interpret g as an emergent property make empirical predictions and are therefore falsif- and individual scores on g as an index of the able. In contrast, a model is an implementation of collective performance on a battery of tests. In the theory. In order to implement a theory, a particu- less technical terms, according to new models of lar modeling framework must be adopted, and certain intelligence, g does not have a causal infuence assumptions may be necessary for the model to oper- on test scores, which means that the concept ate in a manner consistent with the theory. of ‘general ability’ is not a necessary feature It is also important here at the outset to clarify of a theory of intelligence. To be clear, new the distinction between two broad categories of mod- models of intelligence do not deny the existence els in cognitive science: psychometric and cognitive. of g, it clearly exists, and is predictive of many Psychometric models have dominated the landscape important life outcomes.2 of intelligence research and will be described in more • New models of intelligence can formally connect detail below. In short, psychometric models attempt psychometrics and cognitive science in a com- to capture the structure of intelligence but often times putational manner. In psychometrics, the pur- fail to convey much information about function. In pose of a ‘model’ is to explain the pattern of contrast, cognitive models of intellectual behavior, correlations among test scores, i.e., the covari- such as reasoning and working memory, attempt ance structure, in terms of a latent variable to capture the cognitive processes involved in com- model and to explain responses to test items plex cognition but often fail to explain individual in terms of item response models. In cogni- differences in performance. tive science, the goal of a ‘model’ is to provide To appreciate the divide between psychomet- acomputationalaccountofthecognitivepro- ric models of intelligence and computational models cesses involved in the performance of some cog- of cognition, let us take a look at two contem- nitive task. It has been argued that computational porary and highly infuential models: the Cattell- models have greater scientifc potential in cogni- Horn-Carroll (CHC) model of intelligence3–5 and the tive science than theoretical frameworks because embedded-process model of working memory.6–8 The they make more specifc, quantifable predic- CHC model is presented in Figure 1 and the working tions about the processes being modeled. New memory process model is presented in Figure 2. models of intelligence are attempting to connect The CHC model provides an excellent ft to these different modeling approaches. The goal a broad range of individual differences data and is is to ft psychometric models with parameters therefore considered one of the best, if not the best, from cognitive models and thereby account for latent variable models of intelligence in the psycho- inter-individual differences in behavior in terms metric literature. According to the hierarchical model, of intra-individual psychological processes, and there is a general factor at the apex, which has a do so in formal mathematical fashion, such that causal infuence on several ‘broad stratum’ factors, proposed models can be subject to novel predic- and these factors in turn have a causal infuence on tions, objectively falsifed, and updated. ‘narrow stratum’ factors, and these factors in turn • New models of intelligence make novel predic- have a causal infuence on test scores. As mentioned, tions about the neural bases of intelligence and the CHC provides a comprehensive account of covari- these predictions are being met with a staggering ance structures, but it does not translate well into a amount of new data from neuroscience. Theo- cognitive process model. For instance, Carrol4 does ries of intelligence have always been informed not specify what g represents in terms of a cognitive by our scientifc understanding of the brain but process, nor does he explain the causal mechanism now, with the rise of neuroimaging methods, neu- relating g to other factors. To be fair, that is not the ral data from large samples of healthy subjects primary goal of a latent variable model. are being combined with behavioral data, allow- In contrast, consider the working memory model ing for much more accurate predictions about the in Figure 2. It provides a detailed account of the neural bases of intelligent behavior. cognitive processes involved in perception, attention, and memory, and each component of the model It is important here at the outset to clarify the dis- is supported by decades of cognitive experimental tinction between a theory of intelligence and a model psychological research. For example, the focus of ©2015WileyPeriodicals,Inc. WIREs Cognitive Science New and emerging models FIGURE 1 The Cattell-Horn-Carrol (CHC) latent variable model of intelligence. | FIGURE 2 The embedded-process model of working memory.6 attention is| limited to a small number of mem- there are many other models of working memory, ory representations, and information maintained in with similar features, but it is fair to say that the this state is more readily accessible than informa- embedded-process model is among the most infu- tion represented in the short-term store, and this ential models of working memory in cognitive sci- information is more readily accessible than infor- ence. Yet, looking at the model, one is left guessing mation represented in the long-term memory.6 As as to which of the components gives rise to varia- another example, note that novel stimuli, unlike habit- tion in task performance across individuals. Again, to uated stimuli, can capture attention and gain imme- be fair, that is not the primary goal of this type of diate access into the focus of attention.

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