Reaction Time

The relationship between reaction time, or the speed at which individuals respond to sensory information, and intelligence has long been a topic of debate among researchers in the fields of education and psychology. Discussion on the topic dates back to Sir Francis Galton, who hypothesized that intelligence was a manifestation of efficiency in underlying motor and perceptual abilities. To test his hypothesis, he assessed the reaction times and sensory discrimination abilities of thousands of [Page 723]individuals in his laboratories. His work, though anecdotal and inconclusive, inspired American researcher James Cattell to incorporate speeded sensory discrimination tasks into his own research on intelligence. These tasks included purely physical reactions to stimuli, such as measuring how quickly subjects could respond to sound, and more mental tasks, such as measuring how quickly subjects could name colors as they were presented. Their combined work inspired a wave of interest in sensory/motor or psychophysical tests of intelligence that lasted until the early 20th century.

One of Cattell's own graduate students, Clark Wissler, is credited with striking a powerful blow to this line of inquiry. In 1901, Wissler published research suggesting little to no correlation between academic performance and reaction time. This finding was widely accepted, and helped to curtail interest in the topic of reaction time for a number of years. In the meantime, interest and support were on the rise for Alfred Binet's intelligence scales, further decreasing attention to chronometric measures of intelligence.

Since that time, however, various researchers have found support for a link between reaction time and cognitive ability, including Charles Spearman and Cyril Burt. Arthur Jensen, who has conducted numerous studies of reaction time, has been one of the best known proponents of this link. Jensen, like Galton, hypothesized speed and efficiency of underlying neurological mechanisms as key to the relationship between reaction time and intelligence. To study reaction time, Jensen created an apparatus that timed subjects' responses to various sized sets of stimuli. The apparatus had a home button on which the subject placed his or her finger, and buttons corresponding to eight different lights. When a light was activated on the panel, the subject moved his or her finger from the home button to the button associated with that light. Subjects were timed in their response to a single light, or asked to make a choice between multiple lights. The apparatus allowed Jensen to test the amount of time needed for removal of the finger from the home button (reaction time), and movement of the finger to the appropriate button (movement time). It also allowed measurement of differences in response time to one versus many stimuli. Subjects' times were correlated to their scores on intelligence tests.

Jensen found that reaction time was indeed significantly and negatively correlated with intelligence (i.e., faster response times equated to higher scores on IQ tests). Detailing his research, Jensen reports average correlations between reaction time and intelligence of −.19, −.21, −.24, and −.26, for no-choice, two-choice, four-choice, and eight-choice trials, respectively, on his apparatus. Other researchers have found average reaction time/intelligence correlations ranging from approximately −.22 for no-choice trials to −.40 for eight-choice trials. Most researchers accept the premise that reaction time increases as the complexity of the task increases; for example, people react more quickly to one light on Jensen's apparatus than to four lights. Some evidence has been found to suggest that more intelligent people require less additional time to respond to added information than do average individuals, creating a flatter slope to the linear relationship between reaction time and information. This finding, however, remains inconclusive and controversial.

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