Reaction time (RT) and IQ: Shape of the task complexity function

The shape of the function relating reaction time (RT) and IQ was determined as complexity of the RT-tasks varied. At issue is whether the function is linear or U-shaped. Vernon and Weese (Personality and Individual Differences, 14, 413–419, 1993) posit a linear task complexity function; i.e. the magnitude of the correlation between RT and IQ increases as RT tasks resemble IQ tests in the demands placed upon Working Memory. Jensen (Current Directions in Psychological Science, 2, 53–56, 1993) posits a U-shaped function; too-easy and too-hard RT tasks measure non-information processing factors that interfere with the precise measurement of mental speed. Experiment 1 tested 105 university students with paper-and-pencil coding (RT) tests in which task complexity was defined by number of bits of information. Two procedures were used to reduce or eliminate motor time to obtain ‘purer’ measures of mental RT. The results did not support a linear task complexity function; nor were the RT tasks sufficiently difficult to adequately test Jensenʹs U-shaped function. In Experiment 2, 90 university students were tested with more difficult RT tasks. A definite U-shaped function was obtained with the highest correlation between RT and IQ at an intermediate level of task complexity. When the results of Experiments 1 and 2 were combined, the U-shaped function became even clearer. The results strongly support Jensenʹs notion that the highest correlation between RT and intelligence is found just below the point at which Working Memory is strained to the point of breakdown and loss of information. The results also support the conception of the Erlangen School that capacity of Working Memory and speed of information processing are determinants of IQ.