Dec 26 2011

Reaction Times and IQ Tests

As Bryan Pesta recently commented that his attempts to attack my expertise rather than my arguments on IQ is justified by my treatment of him, I thought I’d pull this out of the archive so everyone could judge it. This was originally published on Greg Laden’s Blog, with much additional discussion (with most of Bryan Pesta’s comments on the post, including his intimating that I could get into trouble for linking his study) on my old blog. The discussion of practice effects has been tweaked here for clarity.

In the ongoing discussion about disparities between racial classifications on IQ tests, Dr. Bryan Pesta requested that we consider his paper, “Black-White differences on IQ and grades: The mediating role of elementary cognitive tasks.” Because as he rightly points out, not everyone will have the background to evaluate the paper, I thought it would be helpful to discuss the paper in the context of the cognitive science literature.

The Study

There were three tests given to the participants (139 white and 40 black students who received course credit for participation). The first was a very short IQ test, clocking in at 12 minutes. However, its creators do say (it’s a proprietary test) that it has a high g factor loading. This means that it correlates strongly with other IQ tests despite its brevity. For a good discussion of the history of g and what this correlation means on its own without further study, I highly recommend this post by Three-Toed Sloth. The study currently under discussion was an attempt to show what g is in more concrete terms.

The other two tests were computer-based reaction-time tests. Test one was an inspection time test, in which participants were shown a pair of lines for a set, very brief time and asked to indicate which was shorter. Series of correct answers resulted in the time being shortened. Any incorrect answer would result in the the time being lengthened. Test two was a reaction time test, in which participants were asked to indicate the position of the stimulus (a letter A in this case) as quickly as they could.

There were significant differences between race groups on all measures, with blacks scoring worse than whites on average, and the authors found that the variability in a factor derived from the timing test scores accounted for the variability in IQ test results.

The Context

Reaction time experiments have a long history in cognitive psychology. If you want to know more about it in detail, Dr. Andries F. Sanders literally wrote the book on the subject, Elements of Human Performance: Reaction Processes and Attention in Human Skill. If you’re interested in a somewhat lighter overview than nearly 600 pages, Dr. Robert J. Kosinski maintains a good bibliography and overview.

What is important to take away from either the short version or the long? Two things. The first is that reaction time is largely a function of attention (thus the title of Dr. Sanders’ book). This means that reaction time is strongly influenced by factors such as fatigue, stress and distraction. This study makes no effort to control for these factors despite the existence of an extensive literature on this subject, and despite their being racial differences in hours worked by college students (although what the exact direction of the difference would be in this case is unclear). They do control for age and sex, which are also known to affect reaction time.

The second is that, with practice, reaction time tasks show a decrease in errors, reaction time, and variability in reaction time. Because of this effect, Sanders stresses the importance of adequate practice times. Pesta’s study included three practice trials for the first timed test and six for the second, which may not be enough if one group of students has significantly more practice outside the study in reaction time tasks, like high-twitch sports or video games, as reaction time tests do show some transfer of practice effects between related tasks. Although the authors do not discuss it, the case for more pre-data-collection practice is also supported by the fact that the group with the longer reaction times showed a higher variability in times.

The Claims

There is an additional context to be considered with regard to this study, which is the difference between the claims made in a modest, undercontrolled study like this one and the claims made by the scientists outside the journals in which these studies are published. In building the case that racial-grouping IQ test differences are immutable or genetic in origin, qualifiers get left out and connections are made that aren’t supported by the literature.

What does Pesta have to say in the Discussion section of his paper?

The variation in both ECT performance and IQ scores seems largely driven by individual and group differences in the general factor. On the other hand, more than g contributes to a person’s GPA, including variables like motivation, conscientiousness, family environment, work status, etc. (though recent research also points to a genetic cause for within-group differences in academic achievement, see, e.g., Luo, Thompson, & Detterman, 2003; Wainwright, Wright, Geffen, Luciano, & Martin, 2005; Wainwright et al., 2006). Considering just the present data set, however, basic measures of information processing do little to explain the Black-White difference on GPA.Although consistent with Spearman’s hypothesis, our data offer no insights as to possible causes for race differences on the ECTs. Whether these differences might arise from differences in environment, nutritional levels, genes or some other factor is an issue in need of further study. Further limits to the present study include: (1) a relatively small sample size for Black students, though statistical power did not seem to be an issue given the pattern of consistent, significant results was found. (2) A restricted range of participants, as we ran only college students. (3) Use of WPT scores as a proxy for g (i.e., we did not derive g factorially). Future studies with multiple measures of g might show an even clearer picture of the mediation effects reported here. (4) For unknown reasons, both age and gender differed by race. Although we included each as control variables in the mediated regressions, a more random sampling of race in a future study would offer stronger evidence that neither played a role in the data patterns reported here.

What does he have to say when he discusses the study elsewhere?

Easy to explain (though the explanation may not be correct) if you believe that IQ is some basic index of how people differ in how fast and capable their brains process info.

I really think my one study in the area cannot speak to the cause of the difference. It was never intended to do that. It shows that paper and pencil differences are explained by information processing ability, but not why.No single study is obligated to answer all questions that might arise, especially those it was never designed to address.

So, I really don’t know why races differ on average in cognitive speed. I suspect it could be nutrition, prenatal development or something else– possibly genetics, but I don’t know.

I take how fast a neuron fires to be fairly biological, but not necc. genetic.

You can trace the raw paper and pencil IQ difference back to race differences in performance on tasks requiring nothing but mental speed. Even the speed with which one neuron in the brain fires correlates with IQ.My measures are cognitive (reaction time) and not biological (some type of blood test or whatever) but I think the inference that choice reaction time reliably and validly measures brain speed is reasonable.

So now we’ve moved from a measure of attentiveness to a measure of information processing ability, specifically the speed at which neurons fire. Where is the evidence to support this? Um, evidence? You know that it’s awfully invasive to measure the speed of individual neurons, right?

There is a recent technique that can measure the myelination (insulation by fat that causes impulses to be conducted more quickly in nerve cells) of various parts of the brain, however, and a study has found increased myelination in the brains of people who perform better on reaction time tests. On the other hand, given that the conduction boost was found in the areas of the brain related to vision, it would be premature to take these results as a confirmation of g as a measure of intelligence. And given the plasticity of the developing brain, it certainly has nothing to say on whether there is a genetic link to performance on these tests.

PESTA, B., & POZNANSKI, P. (2008). Black-White differences on IQ and grades: The mediating role of elementary cognitive tasks Intelligence, 36 (4), 323-329 DOI: 10.1016/j.intell.2007.07.004

Planty, M., Hussar, W., Snyder, T., Kena, G., KewalRamani, A., Kemp, J., Bianco, K., Dinkes, R. (2009). The Condition of Education 2009 (NCES 2009-081). National Center for Education Statistics, Institute of Education Sciences, U.S. Department of Education. Washington, DC.

Sanders, A. F. 1998. Elements of Human Performance: Reaction Processes and Attention in Human Skill. Lawrence Erlbaum Associates, Publishers, Mahwah, New Jersey.

Tuch, D. (2005). Choice reaction time performance correlates with diffusion anisotropy in white matter pathways supporting visuospatial attention Proceedings of the National Academy of Sciences, 102 (34), 12212-12217 DOI: 10.1073/pnas.0407259102


Skip to comment form

  1. 1

    Thanks for the attention.

    I really don’t know whether linking the article here is a copyright violation. It doesn’t bother me, but Elsevier might disagree.

  2. 2
    Dan J

    I really don’t know whether linking the article here is a copyright violation. It doesn’t bother me, but Elsevier might disagree.


    I really have no words.

  3. 3

    All work that is not Stephanie’s appears to have been quoted, referenced, and/or linked. It has all been handled properly to avoid copyright issues. Suggesting otherwise could make one look …uneducated.

    If you truly don’t get it: linking cannot be a copyright violation because people are being sent to the original article. It’s free advertisement.

  4. 4
    Stephanie Zvan

    Bryan, you had plenty of people explain fair use to you two years ago when this was originally posted. I can understand you not caring enough during that time to find out how copyright works. Maybe you never talk about papers in public venues. Whatever.

    I do not remotely understand showing up after two years to reassert your maintained ignorance.

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