Sunday, October 25, 2015

Measurement: IQ and 5 Personality Factors

I've been reading around in Joseph Carroll recently, Graphing Jane Austen (2012) in particular, which he coauthored with John Johnson, Jonathan Gottschall, and Daniel Kruger. As you may know, the book reports results of an empirical study of how readers assess roughly 2000 characters in 202 19th century British novels. (FWIW, I'm one of 1,492 people who filled out a protocol for this study.) One aspect of the study was to assess the personality of each character. We did this using an instrument based on the so-called five factors model of personality, which, we're told is the preferred model these days. This post represents a speculation of mind about what's going on "under the hood" in this kind of assessment.  My key notion is tricked out in orange text. [This is a repost from 2011.]

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One of the things psychologists like to do is measure things: reaction time, sensitivity to temperature, racial bias, or, say, personality and intelligence. The last, of course, is one of the most contentious topics in psychology: Just what is intelligence anyhow? Does IQ measure it? Does IQ measure anything at all? Are IQ tests little more than a means by which elites dominate others? The measurement of personality hasn’t produced so much controversy, but it’s still an iffy business.

This post is an oblique comment on those two types of measurement: IQ and personality. Both involve complex technical issues that I’m not qualified to judge. So, for the purposes of this post I’m simply going to assume that IQ tests and personality inventories do in fact measure something real. Given that, what might those somethings be?

I ask that question in the context of contemporary cognitive science and neuroscience. Cognitive science is rich in models of mental processes that are based on an analogy with computing. Such models typically consist of ‘modules’ each of which performs a specific and limited task. A model capable of simulating or explaining interesting behavior is likely to consist of several to many interacting modules. Similarly, the neurosciences give evidence of a wide variety of functional capabilities variously localized throughout the brain.

Against THAT background, one is tempted to ask: Which are the modules responsible for intelligence and which for personality? The point of the analogy I’m about to suggest is that these tests don’t measure the performance of any specific modules at all. Rather, they measure the joint performance of all modules taken together.

The Analogy: Automobile Performance

The analogy I have in mind is that of automobile performance. Automobiles are complex assemblies of mechanical, electrical, electronic and (these days) computational devices. We have various ways of measuring the overall performance of these assemblages.

Think of acceleration as a measurement of an automobile’s performance. It’s certainly not the only measurement; but it is real, and that’s all that concerns me, As measurements go, this is a pretty straightforward one. There’s no doubt that automobiles do accelerate and that one can measure that behavior. But, just where in the overall assemblage is one to locate that capability?

Does the automobile have a physically compact and connected acceleration system? No. Given that acceleration depends, in part, on the mass of the car, anything in the car that has mass has some effect on the acceleration. Obviously enough the engine has a much greater effect on acceleration than the radio does. Note only does the engine contribute considerably more mass to the vehicle, but it is the source of the power needed to move the car forward. The transmission is also important, but so is the car’s external shape, which influences the amount of friction it must overcome. And so forth.

Some aspects of the automobile are clearly more important than others in determining acceleration. But, as a first approximation, it seems best to think of acceleration as a diffuse measure of the performance of the entire assemblage. As I’ve already indicated, there’s nothing particularly mysterious about what acceleration is, why it’s important, or how you measure it. Nor, for that matter, is there any particular mystery about how the automobile works and how various traits of components and subsystems affect acceleration. This is all clear enough, but that doesn’t alter the fact that we cannot clearly assign acceleration to some subsystem of the car. Acceleration is a global measure of performance.

The Analogy Applied

And so, it seems to me, that if intelligence is anything at all, it must be a global property of the mind/brain. You aren’t going to find any intelligence module or intelligence system in the brain. IQ instruments require performance on a variety of different problems such that a wide repertoire of cognitive modules embedded in many different neurofunctional areas are recruited. The IQ score measures the joint performance of all those areas.

The same, I suggest, is true of personality. However, whereas intelligence is generally measured by a single number, an IQ score, these days personality is measured by five numbers, one each for five factors: extroversion-introversion, neuroticism, agreeableness, conscientiousness, and openness. My sense is that the neural correlates to these things are likely to be distribution of neuro-chemicals and relative sizes of various neural regions. That is, they’re going to be diffuse properties of the nervous (and endocrine) system, not the properties of a specific personality subsystem.

The five factors are simply measures of how the whole system performs in various situations. We can’t track any factor down to some particular subsystem; we aren’t going to find the personality module by dissecting the brain. Nonetheless it makes perfectly good sense to talk of personality as a real thing as long as we don’t reify the dimensions of measurement.

In this case, however, I want to offer one further suggestion. We are social creatures. We are constantly interacting with one another. And so we must be constantly appraising one another’s moods and desires and forming estimates of how others are likely respond if we act in this or that way. In making such estimates, such guesses, such predictions, it would certainly be useful to have some representation, some sense, of the other’s personality in order to do so.

So, how is it that we acquire a sense of someone’s personality? What are the terms, in ‘mentalese’ if you will, in which we represent that sense? Where in the brain do we perform such estimates and retain the results? Note that this last question is QUITE DIFFERENT from the question of what brain system generates or performs personality. I’ve already rejected the notion that such a system exists; that was the point of the automobile analogy. No, the system I’m talking about is quite different. It is, in effect, a bit like a sensory system.

We have a visual system that detects shapes and colors. The auditory system detects sounds, pitches, volumes, timbres. Well, why not a personality appraisal system? Let us put aside the question of just how such a system might work and simply assume that such a system exists. My suggestion about the five-factory personality model, then, is simply that those five factors are the dimensions (in Gärdenfors’s* sense) along which we evaluate and retain personality judgments.

In support of this guess I note that the whole business of personality measurement started with “what is now known as the Lexical Hypothesis. This is the idea that the most salient and socially relevant personality differences in people’s lives will eventually become encoded into language. The hypothesis further suggests that by sampling language, it is possible to derive a comprehensive taxonomy of human personality traits.” Just as language encodes color and shape in visual space, and pitch, loudness, and timbre in auditory space, so it encodes extroversion-introversion, neuroticism, agreeableness, conscientiousness, and openness in personality space.

If I’m right about this, then we aren’t going to find any personality modules. But we should find some brain region or regions specialized for global assessments of people’s behavioral proclivities, that is, personality. For all I know, such a region or regions has already been identified.

Does anyone know the relevant literature?

*Peter Gärdenfors, Conceptual Spaces: The Geometry of Thought, MIT Press 2000; The Geometry of Meaning, MIT Press 2014.

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