Placing inspection time, reaction time, and perceptual speed in the broader context of cognitive ability: The VPR model in the Lothian Birth Cohort 1936

The idea that information processing speed is related to cognitive ability has a long history. Much evidence has been amassed in its support, with respect to both individual differences in general intelligence and developmental trajectories. Two so-called elementary cognitive tasks, reaction time and inspection time, have been used to compile this evidence, but most studies have used either one or the other. Relations between speed and fluid intelligence have tended to be stronger than those between speed and crystallized intelligence, but studies testing this have confounded verbal abilities with crystallized intelligence and spatial/perceptual abilities with fluid intelligence. Questions have also been raised regarding whether speed contributes directly to general intelligence or to more specific cognitive abilities to which general intelligence also contributes. We used 18 ability and speed measures in the Lothian Birth Cohort 1936, assessed at approximately age 70, to construct alternative versions of the Verbal-Perceptual-Image Rotation (Johnson & Bouchard, 2005a) model of cognitive ability to test different hypotheses regarding these issues. Though differences in the extents to which our models fit the data were relatively small, they suggested that reaction and inspection time tasks were comparable indicators of information processing speed with respect to general intelligence, that verbal and spatial abilities were similarly related to information processing speed, and that spatial, verbal, and perceptual speed abilities were more directly related to information processing speed than was general intelligence. We discuss the theoretical implications of these results.     

The relationship between speed of information processing and cognitive ability

Speed of information processing as measured by various reaction time and inspection tasks has been shown to correlate with psychometric intelligence, and it has been suggested that general intelligence (g) is determined to some degree by the speed that information is processed. If this is so, then various measures of speed of information processing should correlate substantially with each other, and each should also correlate with a wide range of psychometric tests that load on g. Alternatively, intelligence may be considered to be a multi-faceted complex of partially related abilities with specific abilities being dependent upon specific cognitive processes. If this is the case, it should be possible to discover independent cognitive processes, some of which correlate with one facet or broad ability and some with another. This paper presents three experiments in which the relationship between intellectual ability and four speed of information processing measures was examined. These were rate of memory scanning, rate of retrieval of information from long term memory, speed of stimulus-response mapping and inspection time (IT). Results showed that correlations between IT and most reaction time measures of speed of information processing were low, and that correlations between different versions of IT were negligible. In addition, some cognitive tasks with verbal material (memory scanning rate for digits and Posner letter matching IT) correlated most substantially with Verbal Reasoning whereas non-verbal (two-line) IT consistently correlated with tests loading on g. It was thus suggested that while non-verbal IT may be a measure of a perceptual speed attribute that contributes to mental functioning, other “speed of information processing” parameters may be more specific to a subset of abilities.     

Speed of information-processing in an inductive reasoning task and its relationship to psychometric intelligence

The relationship between psychometric intelligence (measured by means of Raven's Advanced Progressive Matrices and two verbal subtests of the “Intelligenz-Struktur-Test-70”) and speed of information-processing in a newly developed computerized reaction time (RT) task called the Concept-Verification-Test (CVT) was investigated in a sample of 104 undergraduates. In this CVT, first, one of five possible conceptual rules is presented on a computer monitor. After reading the rule, the subject has to press a button and then one of 27 possible simple geometrical figures is presented, which either is an example of the concept or not. The subject has to press the true button if the presented figure is a positive instance of the rule or the false button if it is not. Two RTs were measured: The Comprehension Reaction Time (CRT) from the onset of the rule to the first button press and the Verification Reaction Time (VRT) from the onset of the figure until the response is given. The different complexity of the conceptual rules used also allowed us to examine the “complexity hypothesis” (i.e. correlations with intelligence should be higher for more complex RT tasks). As predicted, both CRTs and VRTs correlated negatively with intelligence, but we found no evidence for the validity of the complexity hypothesis.     

Intelligence and changes in regional cerebral glucose metabolic rate following learning

Positron emission tomography (PET) studies of brain glucose metabolic rate (GMR) in normal volunteers report inverse correlations between GMR and scores on the Raven's Advanced Progressive Matrices (RAPM) and verbal fluency. A new study in eight normal men reports widespread significant GMR decreases following learning a complex task (the computer game “Tetris”). The purpose of this study is to ascertain the correlations between GMR changes following learning “Tetris” and psychometric intelligence scores (RAPM and WAIS-R) to determine whether high-ability subjects show the largest GMR decreases, as predicted by a brain efficiency hypothesis. This hypothesis is supported with significant correlations between the magnitude of GMR change and intelligence scores in many brain areas that changed with learning. Some implications for the role of attention, memory, and speed of processing are discussed in view of the specific brain areas involved.     

Comparing subtest profiles of g loadings and correlations with RT measures

It is argued that if a response time (RT) measure correlates with psychometric test (PT) scores because it shares variance in common with general intelligence, g, then the profile of g loadings for a set of PTs would be predictable from the profile of correlations between the RT measure and the PT scores. On the other hand, if an RT correlates with PTs through variance not shared with g, the g loadings of the PTs should be unrelated to the correlations between RT and PTs. The profiles of g loadings and correlations with RT were compared for a set of 6 RT measures and 8 PT scores from Smith and Stanley (1983). To demonstrate statistical significance, standard errors of the statistics were generated by Efron's bootstrap technique (Efron, 1979). It was clearly shown that the profile of the PT's g loadings could be well predicted from the RT-PT correlations for four of the RT measures. It can be concluded that RT tasks do measure general intelligence. Analysis of the errors in prediction suggested that the RTs may correlate more with fluid than crystallized intelligence.     

Information processing abilities in twins reared apart

A battery of information processing measures and psychometric tests of specific and general cognitive abilities was administered to a sample of 105 individuals which included 34 monozygotic and 13 dizygotic reared apart twin pairs or triplets. Correlations between information processing parameters and psychometric abilities as well as twin resemblances for the information processing parameters were examined. In a principal components analysis of the information processing parameters, three components were identified which accounted for 67% of the total variation; Overall Speed of Response (OSR), Speed of Information Processing (SIP), and Speed of Spatial Processing (SSP). OSR was significantly correlated with WAIS IQ, and psychometric measures of verbal reasoning, spatial ability, and perceptual speed and accuracy. SIP was significantly correlated with WAIS IQ, measures of verbal reasoning, and one of the perceptual speed and accuracy measures. SSP was significantly correlated with measures of both spatial ability and perceptual speed and accuracy. Due to the small size of the dizygotic twin sample, no strong conclusions could be drawn regarding the magnitude of their resemblance. The correlation between component scores of reared apart monozygotic twins was significant for OSR, but not for SIP or SSP.     

Hippocampal structure and human cognition: Key role of spatial processing and evidence supporting the efficiency hypothesis in females

Here we apply a method for automated segmentation of the hippocampus in 3D high-resolution structural brain MRI scans. One hundred and four healthy young adults completed twenty one tasks measuring abstract, verbal, and spatial intelligence, along with working memory, executive control, attention, and processing speed. After permutation tests corrected for multiple comparisons across vertices (p < .05), significant relationships were found for spatial intelligence, spatial working memory, and spatial executive control. Interactions with sex revealed significant relationships with the general factor of intelligence (g), along with abstract and spatial intelligence. These correlations were mainly positive for males but negative for females, which might support the efficiency hypothesis in women. Verbal intelligence, attention, and processing speed were not related to hippocampal structural differences.     

Eliminating the IQ-RT correlation by eliminating an experimental confound

Three experiments investigated the relation between visual scanning demands, reaction time (RT), and psychometrically defined intelligence (IQ). Prior studies have shown reliable correlations between RT and IQ in the range of −.20 to −.80. However, these studies have confounded the number of possible stimuli (stimulus uncertainty) with the size of the area in which the stimuli may appear (visual angle). Experiment 1 replicated these studies retaining this confound. As the number of stimuli increased from one to eight, the visual angle was permitted to increase as well (from 0° to 30°). The results showed that RT varied in accord with Hick's (1952) law, and a median correlation between IQ and six RT parameters (subjects' mean RTs and standard deviations at three levels of stimulus uncertainty) of −.47 was observed. Experiment 2 removed the confound, varying only stimulus uncertainty, and the median IQ-RT correlation declined to −.02. Experiment 3 held stimulus uncertainty constant at 1 bit (two stimuli) and varied visual angle; a median correlation of −.19 was observed. It was concluded that many of the previously reported correlations may not have hinged on speed of information processing alone, but at least in part on subjects' abilities to scan the display across which the stimuli appeared.     

Intelligence, reaction times, and peripheral nerve conduction velocity

Two studies (with sample sizes of 85 and 88) are reported that investigated relationships among measures of intelligence, speed of information processing, and peripheral nerve conduction velocity (NCV). In both studies, NCV was significantly correlated with IQ scores (rs = .42 and .48) and with reaction times (RTs; rs = −.28 and −.18): Thus, faster NCV was associated with higher IQ scores and faster speed of processing. In both studies, NCV and RTs contributed significantly, in combination, to the prediction of fullscale IQ (shrunken multiple Rs = .53 and .57), but the expected pattern of causal relationships between the variables was not borne out. The results are interpreted in terms of a “neural efficiency” model of intelligence, which has recieved support from other studies of physiological correlates of human intelligence.     

Effects of divided attention in the word-fragment completion task with unique and multiple solutions

A study with 114 young adults investigated the correlations of intelligence factors and working-memory capacity with reaction time (RT) tasks. Within two sets of four-choice RT tasks, stimulus–response compatibility was varied over three levels: compatible, incompatible, and arbitrary mappings. Two satisfactory measurement models for the RTs could be established: A general factor model without constraints on the loadings and a nested model with two correlated factors, distinguishing compatible from arbitrary mappings, with constraints on the loadings. Structural models additionally including factors for working memory and intelligence showed that the nested model with correlated factors is superior in fit. Working-memory capacity and fluid intelligence were correlated strongly with the nested factor for the RT tasks with arbitrary mappings, and less with the general RT factor. The results support the hypothesis that working memory is needed to maintain arbitrary bindings between stimulus representations and response representations, and this could explain the correlation of working-memory capacity with speed in choice RT tasks.     

Reaction time correlations with intelligence test scores obtained under either timed or untimed conditions

One hundred and thirteen high school students were randomly assigned to one of two groups that were administered an intelligence test (the Multidimensional Aptitude Battery) under either timed or untimed conditions. Subsequently, all subjects were given a battery of 8 reaction time tests. Multiple regression analyses showed that combinations of RTs were approximately equally good predictors of IQ scores in both groups. Zero-order correlations between each RT test and IQ scores were also approximately equal for timed and untimed Verbal and Full-Scale scores but correlations with Performance scores were higher in the timed condition. The extent to which the different RT tests correlated with timed scores was quite highly related to the tests' loadings on a general speed factor but these loadings were not related to the tests' correlations with untimed scores. Rather, the relative complexity of the RT tests had a stronger influence on their correlations with IQ scores in the untimed condition. It is concluded that timed and untimed intelligence tests impose different information-processing demands on subjects but that the speed with which subjects can cope with these demands is equally important in both conditions.     

Relation between speed of reaction and psychometric tests of mental ability in musculoskeletal injury-prone subjects

Long reaction time (RT), long choice reaction time (CRT), and low scores on psychometric tests of mental ability (MA) have in previous studies been related to musculoskeletal injuries. There has been controversy concerning the relation between slow reaction and low-grade MA recently, the old hypothesis of negative correlation between RT and MA being discussed. The aim of this study was to analyze the relation between speed of reaction and MA. For a sample of 123 volunteer healthy young men simple RT, choice RT, and spatial (block design), verbal and arithmetic components of MA were tested. A principal component analysis was performed and the factor matrix was rotated orthogonally using the varimax method. Two factors were extracted accounting for 73% of the total variance in data space. The mental ability factor, which was responsible for 70% of the variance in factor space, was comprised of components of MA and choice RT. The speed of reaction factor accounted for the remaining 30% of the variance in factor space and was comprised of simple and choice RTs. As choice RT had significant loading on the mental ability factor, the subjects having scores in the lowest quartile on both choice RT and MA total score were compared with the independent expected value by using the chi-squared test. The results of low-grade MA and slow choice reaction were not independent. Accordingly, the results do not support the entire distinction between traditional mental ability or convergent thinking and speed of reaction in normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measuring Cognitive Aptitude Using Unobtrusive Knowledge Tests: A New Survey Technology

Five knowledge tests and one implicit-reasoning task were developed to be: (1) exceptionally short, (2) correlated with general cognitive aptitude, (3) unobtrusive, i.e., appear similar to attitudinal survey items as opposed to maximal performance measures, and (4) without formally “correct” answers. The intent was to design scales that could be administered in non-proctored environments to directly measure general cognitive aptitude while avoiding the possibility that participants could use references to provide “good” answers. The five knowledge tests used a Likert format to assess knowledge in verbal and practical domains, and were scored by computing distances between examinee and reference ratings. The implicit-reasoning task appeared to be a series completion “game” that required a dichotomous response. The scales were administered to 288 Air Force recruits and were validated against the Armed Services Vocational Aptitude Battery (ASVAB). Individual unobtrusive knowledge scales and ASVAB tests were substantially correlated with sample correlations ranging to .39 and population correlation estimates to .66 after correcting for range restriction. Two sets of factor scores, which were separately derived from the unobtrusive test battery and the ASVAB, were highly correlated in our sample, .54, yielding a population correlation of .80 after correcting for range restriction. This technology is important because few paper- or Internet-based surveys, and virtually no mail-based surveys accurately measure general cognitive aptitude, while many of these surveys address important social issues and commercial questions that could be better understood given an unobtrusive but accurate estimate of general cognitive aptitude.     

Cognitive abilities profiles of Caucasian vs Japanese subjects in the Hawaii Family Study of Cognition

General intelligence (the unrotated first principal component) was partialled out of the cognitive abilities factors—verbal ability, spatial ability, perceptual speed, and visual memory—obtained for the 15 tests of cognitive abilities used in the Hawaii Family Study of Cognition (HFSC). The resulting cognitive abilities profiles indicated that HFSC subjects of Caucasian ancestry scored higher relative to subjects of Japanese ancestry on the verbal and visual memory factors, but lower on the spatial and perceptual speed factors. This ethnic group difference in the shape of the cognitive abilities profiles was found to be highly consistent across sexes and generations, in spite of the large mean differences across these groups in factor scores.     

Differential construct validity of intelligence as popularly measured: Correlations of age with raw scores on the WISC-R for Blacks Whites, males, and females

Raw scores on the 12 WISC-R subtests and the verbal, performance, and full scale IQ scales were correlated with age in years separately for 938 White males, 137 Black males, 927 White females, and 153 Black females. Highest and lowest correlations from the four groups were then contrasted for each of the 15 WISC-R variables to determine whether the magnitude of the relationship between age and performance on current tests of intelligence is constant across race and sex. Regression coefficients between age and raw scores were also contrasted across groups. None of the 15 comparisons of corrections yielded differences that were statistically significant. Regression coefficients differed only with respect to the Full Scale IQ, showing smaller incremental changes with age for Black males than for other groups. The results indicated that the relationship between age and intelligence test performance is relatively constant across race and sex and supports the construct validity of the WISC-R as a measure of children's intelligence for Blacks, Whites, males, and females, though some evidence was found to indicate slower development of “g” in Black males as compared to the other groups.     

Intelligence, reaction time (RT) and a new ‘odd-man-out’ RT paradigm

A sample of adult Ss of reasonably normal intelligence were given an ‘IQ’ test, a series of RT tests using 0, 1, 2, 3 bits of information in a Hick paradigm and an RT task requiring choice of 1 of 3 lights as an ‘odd-man-out’ on the basis of its relative position. Negative correlations were found between both RT and measures of variation in RT and ‘IQ’ for both of the two tasks. Recent results showing no correlation between Hick slope and ‘IQ’ and no increase in correlation between ‘IQ’ and RT with increasing number of bits, are confirmed. An explanation for findings of Ss whose RT data do not conform to Hick's law is tested and found inadequate. The ‘odd-man-out’ task is found to show an effect of ‘learning’ across the period of the task, the size of the learning effect was found also to correlate with ‘IQ’, but no evidence for learning was found with the choice RT task.     

Visual information processing and intelligence

Measures of inspection time (IT) have robust, moderately-sized correlations with IQ-type test scores. However, the reason for the IT-IQ correlation is not understood. Although the original theory asserted that IT performance was based on a single parameter—essentially speed of visual processing—peculiarities of the task have afforded other interpretations of IT differences and the IT-IQ association. In the present report two new visual processing tasks, visual change detection (VCD) and visual movement detection (VMD) are found to be correlated at or above .4 with IT and with non-verbal scores from the Alice Heim 4 test of general intelligence. VCD and VMD, in common with IT, assess the stimulus duration that is required by subjects in order to make an accurate discrimination. VCD and VMD, however, require a broader attentional focus than IT and do not involve backward masking. Measures of contrast sensitivity, a difficult discrimination task in which stimuli are not time-limited, had near-to-zero correlations with other visual processing tasks and with IQ-type test scores. We tested the hypothesis that only the latent trait derived from the speeded visual processing tasks (rather than task-specific features) would correlate with cognitive ability, and this was supported. The present study adds weight to the view that it is the ability to make accurate discriminations in the face of limited stimulus time that causes IT to correlate with psychometric intelligence. The psychological correlates of VCD, in terms of neural circuits that detect “difference” suggest a new line of investigation into the psychobiological bases of human intelligence.     

Power and speed components of individual differences in letter matching

Several previous studies have reported a correlation (typically around −.30) between standardized verbal ability test scores and name identity minus physical identity reaction times (NI-PI) in a letter-matching task. This correlation has usually been thought to reflect the mutual dependence of both measures on long-term memory access time. The present research was designed to assess Carroll's (1981) suggestions that: (a) NI — PI may not be the optimal formula for predicting standardized test scores from letter matching data, and (b) NI — PI may actually be related to the speed rather than the power component of standardized tests. Fifty-one subjects previously tested with a standardized reading test participated in letter-matching and word-reading tasks. The latter tasks required subjects to read words and specially constructed pseudowords. Power and speed measures were derived from the word-reading tasks and the standardized test on theoretical grounds (and supported by a principal components analysis). The results supported both of Carroll's contentions. NI — PI reaction time was related more to speed than power and the NI — PI statistic (as usually used) was not the optimum formula for predicting standardized test scores.     

Aptitude Testing Inspired by Information Processing: A Test of the Four-Sources Model

The four-sources model of human abilities posits that individual differences in performance on cognitive tasks are due to differences in working-memory capacity, information-processing speed, the breadth of declarative knowledge, and the breadth of procedural knowledge. To test this model, 310 civilian volunteers were administered a 25-test battery, consisting of verbal, quantitative, and spatial tasks designed to reflect each of the four sources. Confirmatory factor analysis was performed on the variance-covariance matrix of test scores to test the four-sources model and plausible alternatives. The best-fitting model was one that included both the four-sources factors and three content factors. Hierarchical and nonhierarchical models fit about equally well. From additional data on the Armed Services Vocational Aptitude Battery, latent-factor correlations suggested that working-memory capacity overlapped considerably with psychometric general ability (r = .99) and breadth of declarative knowledge overlapped with psychometric verbal ability (r = .97), but information-processing speed was distinct from psychometric perceptual speed (r = .16).     

The relationship between three auditory inspection time tasks and general intelligence

Three inspection-time tasks measuring the amount of time required to discriminate differences in pitch, loudness and phase were administered alongside the Multidimensional Ability Battery and Raven’s Advanced Progressive Matrices to 75 undergraduate students. The auditory tasks were administered adaptively, and thresholds were estimated by fitting a logistic function to each set of data. After correcting for restriction of range the three thresholds intercorrelated significantly, and correlated between −0.33 and −0.68 with scores on the ability tests. A composite auditory inspection time score correlated between −0.35 and −0.42 with the ability measures (−0.50 to −0.54 after correction). Although strategy-use enhanced performance on the pitch inspection-time task, strategy use was unrelated to intelligence and did not mediate the correlation between inspection time and intelligence.