PROCESSING SPEED, ATTENTION, AND INTELLIGENCE - EFFECTS OF SPATIAL ATTENTION ON DECISION TIME IN HIGH AND LOW IQ SUBJECTS

Mental-speed theories of intelligence (Spearman, The abilities of man, 1927; Lemmon, Archives of Psychology, 15, 5-38, 1927-28; Jensen, Jour nal of Social and Biological Structures, 3, 103-122, 1980; Jensen, Spe ed of information processing and intelligence, 1987) are challenged by the finding that, in some methods, bright subjects do not appear to p rocess information at an increased speed. The present experiment was d esigned to explore new RT measures which might relate more strongly to IQ while possessing a clear theoretical relationship to biological th eories of intelligence. One direct measure of information processing s peed is the rate at which choice reaction time (RT) increases with inc reasing stimulus information content (RT slope). While RT slope is a c ritical variable in mental-speed models of intelligence, the results o f several experiments, since Jensen proposed his model, suggest that s lope does not correlate strongly with intelligence. We investigated th e possibility that spatial attention affects the relationship between RT and re in the traditional Jensen paradigm. Thirty-five subjects per formed an RT task with two and four choice stimuli presented in narrow and wide spatial configurations. Correlations between Raven's Advance d Progressive Matrices (APM) scores and RT were in line with previous reports of a moderate negative relationship between IQ and RT. However , a much stronger effect was found in the relative speed in the narrow and wide spatial display conditions. The wide minus narrow RT differe nce in the two-choice condition correlated 0.71 with APM scores. This result suggests that the processing speed advantage of high IQ subject s is best revealed under optimal attentional conditions. It is suggest ed that this result supports the speed of processing model of intellig ence. Paradoxically, the traditional Jensen paradigm confounds the hig h choice orders with increased spatial attention demands, thus artifac tually increasing the RT slope in high, but not in low, IQ subjects. E xplicit control of spatial attention requirements indicates that indiv idual differences in intelligence are substantially underpinned by dif ferences in the speed of information processing mechanisms which, in h igh IQ subjects, require focused attention if they are to be deployed adequately. (C) 1997 Elsevier Science Ltd.