Intelligence and auditory discrimination: separating processing speed and fidelity of stimulus representation

Significant associations have been reported between several different measures of auditory information-processing ability and measures of cognitive ability derived from IQ-type tests. The explanation for these correlations was originally based on the hypothesis that brighter individuals were relatively fast in their processing of auditory information. However, there is a growing body of evidence that supports a competing hypothesis, viz. that the auditory processing-ability-intelligence association is explained by the fact that individuals with higher ability scores have superior pitch discrimination ability. Using structural equation-modeling techniques, this study attempts to test these hypotheses. Three psychophysical auditory processing tests, which varied in the degree to which they emphasized speed of processing and pitch discrimination, and tests of verbal and nonverbal ability were administered to 108 thirteen-year-olds. All three auditory tests were significantly correlated with the IQ-type tests. Factor analysis of the three auditory tests revealed two underlying factors, which appeared to reflect speed of processing and pitch discrimination abilities. A well-fitting structural equation model suggested that information-processing speed and pitch discrimination ability were both significantly associated with nonverbal and verbal IQs, and that speed was the more important factor.