| Summary: | This thesis studied the association between auditory inspection time (AIT) and psychometric measures of verbal and non-verbal cognitive abilities. I review attempts to search for basic information processing components that predict intelligence (Chapter 1), attempts to relate auditory processing speed to intelligence (Chapter 2), and attempts to relate acuity of sensory discrimination to intelligence (Chapter 3). These reviews establish certain essential requirements for a plan of research on auditory inspection time. Chapter 4 described the development of a modified AIT test. In a study of 120 undergraduates, the modified AIT test showed improved subject performance characteristics over previous AIT tasks, and AIT thresholds had low to moderate correlations with visual IT thresholds and with verbal and non-verbal cognitive ability scores. Chapter 5 described two studies. Study 1 included 84 undergraduates and showed that the AIT test had a very high split-half reliability and that about two-thirds of subjects who could perform the AIT task had response performance curves which fitted a cumulative normal ogive. The association between AIT and verbal ability appeared stronger than the AIT-non-verbal ability association in 34 of the subjects; this was also found in Study 2 which tested 119 11-year-olds. Unspeeded pitch discrimination showed a small but significant association with verbal ability in children but not in undergraduates. Results from neither study supported the suggestion that pitch discrimination was the basis for the AIT-cognitive ability association. Chapters 6 and 7 examined the associations among AIT, unspeeded pitch discrimination and an auditory backward masking recognition task which was dubbed the 'Raz' task. It was found that all three tasks were reliable, prone to practice effects and showed high intercorrelations. The AIT and Raz tasks appeared to share common variance not related to pitch discrimination. In a confirmatory factor analysis of over 100 13-year-olds latent variables from the three auditory tests representing auditory processing speed and pitch discrimination both had significant associations with a factor common to verbal and non-verbal intelligence, though speed was the more important factor. Chapter 8 reported the results of a longitudinal study of AIT and cognitive ability in over 100 children from age 11 to age 13. Using structural modelling techniques to create competing causal models and then testing these for goodness-of-fit to the data, some support was found for the suggestion that auditory processing abilities at age 11 might have a causal influence on later verbal and non-verbal abilities rather than the converse. Chapter 9 provided a thematic resume of the studies conducted in the thesis. It was concluded that the corrected AIT-cognitive ability association was in the region of -0.5, and that some progress had been made in explaining this association. In addition, a strong plea was made for AIT and visual IT to be integrated with other models of auditory and visual information processing which exist. Suggestions were made for future research on auditory and visual processing and intelligence.
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