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File:Jensen box.gif

The Jensen box.

The Jensen box was developed by University of California, Berkeley psychologist Arthur Jensen as a standard apparatus for measuring choice reaction time, especially in relationship to differences in intelligence.[1] Since Jensen created this approach, correlations between simple and choice reaction time have been demonstrated in many hundreds of studies. Perhaps the best was reported by Ian Deary and colleagues, in a population-based cohort study of 900 individuals, demonstrating correlations between IQ simple and choice reaction time of –0.3 and –0.5 respectively, and of –0.26 with the degree of variation between trials shown by an individual.[2]

The standard box is around 20 inches wide and 12 deep, with a sloping face on which 8 buttons are arrayed in a semicircle, with a 'home' key in the lower center. Above each response button lies a small Light-emitting diode (LED) which can be illuminated, and the box contains a loudspeaker to play alerting sounds.

Following Hick's law,[3] reaction times (RTs) slow as a log2 of the number of choices are presented. Thus when all but one button is covered responses are fastest, and slowest when all 8 responses are available.

Several parameters can be extracted: The mean 1-choice RT gives simple reaction time. The slope of the function across 1, 2, 4, and 8 lights gives the rate of information processing, an variance or standard deviation in RTs can be extracted to give a measure of response variability within subjects.

Finally, the time to lift off the home button and the time to hit the response button can be measured separately, and these are typically thought of as assessing decision time, and movement time, though in the standard paradigm, subjects can shift decision time into the movement phase by lifting off the home button while the location computation is still incomplete. Masking the stimulus light can eliminate this artifact.[4]

Simple reaction time correlates around .4 with general ability,[2] and there is some evidence that the slope of responding does also, so long as access to the stimulus is controlled.[4]

See also


  1. A. R. Jensen. (1987). Individual differences in the Hick paradigm. In Speed of information-processing and intelligence. P. A. Vernon and et al., Norwood, NJ, USA, Ablex Publishing Corp, 101-175.
  2. 2.0 2.1 I. J. Deary, G. Der and G. Ford (2001). Reaction times and intelligence differences: A population-based cohort study. Intelligence 29 (5): 389–399.
  3. W. E. Hick (1952). On the rate of gain of information. Quarterly Journal of Experimental Psychology 4 (1): 11–26.
  4. 4.0 4.1 T. C. Bates, C. Stough (1998). Improved Reaction Time Method, Information Processing Speed, and Intelligence. Intelligence 26 (1): 53–62.
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