Reaction time and intelligence: A replicated study

Two samples of adult subjects of reasonably average intelligence were given IQ tests and a series of RT tests using 0, 1, 2, and 3 bits of information in a Hick paradigm. Both series showed negative correlation between IQ on the one hand, and RT and σRT, on the other, confirming earlier work. On the other hand, there was no evidence of correlation between the Hick slope and IQ, and the correlation between IQ and RT of σRT did not increase from 1 to 3 bits of information. It was found that the Hick paradigm did not apply to some 20% of the samples, and that the exclusion of these nonconformists increased the correlation between IQ and RT/σRT.     

Reaction time,movement time,and intelligence

Speed of information processing is measured in terms of reaction time (RT) and movement time (MT) to five stimulus displays which differ in the amount of information transmitted, over a range from 0 to 3 bits of information. RT, but not MT, increases as a linear function of the number of bits in the stimulus display. RT and MT show reliable individual differences which are significantly correlated with intelligence as measured by Raven's Standard Progressive Matrices.     

The real and the unreal: A reply to Jensen and Vernon

Jensen and Vernon (1986) have written a detailed reply to my critique of Jensen's reaction-time research (Longstreth, 1984). Their reply seems little short of a complete annihilation of my article. My critique is said to be full of inaccuracies, half-truths, false reasoning, wrong conclusions, and statistical naivete. But it just isn't so. I now explicate my concerns, and show that, particularly with respect to the major theoretical questions, there is little reason for accepting Jensen's claims.     

Inspection time: Does it measure intelligence?

The relationship between inspection time (IT) and intelligence id discussed in the context of the more general relationship between measures of mental speed and mental ability. Six issues are raised concerning IT, mental speed and intelligence: the size of the sample that have been studied; the inclusion of mentally-retarded Ss in these samples; the generality of IT; reaction time (RT) correlations with intelligence; IT and timed vs untimed IQ tests; and theoritical implications of the IT/IQ relationship. In the latter section, it is concluded that IT does not fit neatly into models accounting for RT/IQ correlates and that additional research will be required to obtain a better understanding of the nature of its relationship with intelligence.     

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.     

Inspection time and response strategies in a choice response task

The effects of varying stimulus duration on two response measures, percentage correct (p_c) and mean reaction time (RT) were investigated in a lights-keys RT task similar to an inspection time (IT) task. One of either N = 2, 4 or 8 lights came on as the stimulus, followed after a range of stimulus exposure durations (D) by all 8, as a backward mask. It was found that p_c was an ogival function of D for all three levels of choice, and that the standard deviations of the best-fitting normal ogives were equal. It is argued that the standard deviation can be taken as a measure of the neural noise, or error-inducing variability introduced by processing the stimulus, and so this result indicated that noise in the choice reaction task is independent of N. The effect of D on RT was as predicted by an optional accumulator model for 7 Ss with RT decreasing as D increased, while another 2 Ss appeared to have adopted a temporal deadline criterion giving RTs independent of D and equal error and correct RTs. The same two response styles were found in a re-analysis of RT data from an IT study. The p_c vs D curves were comparable for both response styles. The accumulator model commonly assumed to underly IT tasks thus does not describe the behaviour of all Ss. Such individual differences in strategic approach to the IT task should be investigated further, since assuming that all Ss use one approach may hide or confound relationships between IT and other measures of individual difference, such as intelligence. Recommendations for better IT measurement techniques are given.     

Investigating Group Differences on Cognitive Tests Using Spearman's Hypothesis: An Evaluation of Jensen's Method

Jensen has posited a research method to investigate group differences in cognitive tests. This method consists of first extracting a general intelligence factor by means of exploratory factor analysis. Secondly, similarity of factor loadings across groups is evaluated in an attempt to ensure that the same constructs are measured. Finally, the correlation is computed between the loadings of the tests on the general intelligence factor and the mean differences between groups on the tests. This part is referred to as a test of "Spearman's Hypothesis", which essentially states that differences in g account for the main part of differences in observed scores. Based on the correlation, inferences are made with respect to group differences in general intelligence.

The validity of these inferences is investigated and compared to the validity of inferences based on multi-group confirmatory factor analysis. For this comparison, population covariance matrices are constructed which incorporate violations of the central assumption underlying Jensen's method concerning the existence of g and/or violations of Spearman's Hypothesis. It is demonstrated that Jensen's method is quite insensitive to the violations. This lack of specificity is observed consistently for all types of violations introduced in the present study. Multi-group confirmatory factor analysis emerges as clearly superior to Jensen's method.     

Psychometric g and mental processing speed on a semantic verification test

The Semantic Verification Test (SVT) consists of brief, simple statements, which are either true or false, about various arrangements of the letters ABC (e.g. B after A). Mean reaction time (RT) for confirming or disconfirming the various statements varies according to their complexity. In independent studies of university students and Navy recruits, RT and other response latency parameters (intraindividual variability and movement time) from SVT performance show significant correlations of about -0.40 with nonspeeded tests of psychometric g. The mean RTs of adults to the various SVT item types are highly related to the mean error rates on these item types when the SVT is taken by elementary school children as a nonspeeded paper-and-pencil test. RT is correlated with the general cognitive ability factor (g) and not with the test-taking speed factor that is found in speeded paper-and-pencil tests. The degree of correlation between RT and psychometric g does not show any regular relationship to differences in the SVT item-type's complexity or difficulty as indicated by mean RT.     

Inspection time and IQ: Evidence for a mental speed—ability association

Two studies have tested a theory that individual differences in mental speed constitute an important component of differences in general intelligence by examining patterns of correlation between ‘inspection time’ (IT) and various ability measures assumed to reflect different kinds of speed. The first study was set within the framework of Cattell's theory about the structure of abilities. Results from 30 adult Ss whose IQs (Raven Advanced Progressive Matrices, RAPM) were in the average to above-average range suggested that IT is associated with a broad general ability variable and not with the primary abilities ‘perceptual speed’ or ‘speed of closure’. However, IT was significantly correlated with only a subgroup of those primary abilities that were significantly intercorrelated, and the outcome did not further elucidate the nature of speed as discussed within Cattell's formulation. The second study tested a relationship between IT and a measure of general ‘intellectual speed’, previously described as the major determinant of intellectual differences in a situation where two other critical variables, ‘accuracy’ and ‘continuance’ can exert no influence. It was measured for more than 40 adult Ss, whose IQs (Wechsler Adult Intelligence Scale—Revised) ranged from 81 to 138, and compared with times to produce the correct solution to individual items from the RPM. IT, IQ and solution times were all significantly intercorrelated but, nonetheless, IT and solution times appeared to be substantially reflecting different processes. It is concluded that IT can account for more than the 10% of variance in IQ commonly found to be shared with simple information-processing tasks. The present result of approx. 17% shared variance is probably an underestimate, given the restricted IQ samples used and certain procedural shortcomings. The nature of speed reflected by IT has not been determined and current measurement procedures may be confounded by internal noise.     

Early electro-cortical correlates of inspection time task performance

The concept of general intelligence (g) summarizes the well established finding that scores on separate cognitive tasks are positively correlated, indicating a trait common to many aspects of information processing. Inspection time is a well-established correlate of IQ, where those of a higher IQ can correctly identify a briefly presented stimulus with a greater level of accuracy than those of a lower IQ. This study used two age-matched samples, selected on the basis of their scores on Raven's Advanced Progressive Matrices from the undergraduate population of Bangor University. In order to address the confound of inspection time and IQ of previous ITT-ERP research, each participant of the presented study performed an IT task with the same five levels of stimulus duration while undergoing 64-channel EEG recording. The high IQ group made significantly fewer errors at each level of stimulus duration and exhibited a significantly larger N1 response. N1 latency and other ERP components did not distinguish the two IQ groups. Given the specificity of ERP group differences to the N1, the results of the present study suggest that the link between IT performance and g is attributable to individual differences in directing attention to a spatial region.     

The theory of intelligence and its measurement

Mental chronometry (MC) studies cognitive processes measured by time. It provides an absolute, ratio scale. The limitations of instrumentation and statistical analysis caused the early studies in MC to be eclipsed by the ‘paper-and-pencil’ psychometric tests started by Binet. However, they use an age-normed, rather than a ratio scale, which severely limits the ability of IQ tests to probe the physical basis of differences in cognition. For this reason, Arthur Jensen reinitiated mental chronometry in the 1970s. He designed an apparatus that measures reaction time to a task known as the Hick paradigm that requires the testee to respond to a display of 1 to 8 lights. Faster decision times were related to psychometric g, with theoretically important consequences. He was able to do this, where many other studies had failed, mainly because his apparatus clearly separated movement (MT) from reaction time (RT, also called ‘decision time’.) Interestingly, while RT is clearly related to IQ, MT is not. Principal components analysis reveals RT to be a cognitive variable and MT a motor variable. Failure to distinguish between them drastically obscures the correlation between composite RT (i.e., RT + MT) and cognitive variables. When Jensen (2006) reviewed the literature on MC he found there was a shocking lack of standardization in the administration, recording, and analysis. Consequently, the results of a study conducted in one lab, even though measured in absolute time, could not be compared directly against those from another. Termed “method variance,” this is a major obstacle to the advancement of MC. For that reason, Jensen's Institute of Mental Chronometry commissioned a leading electronics firm to construct a state-of-the-art apparatus to administer, record, and analyze MC experiments.     

Process differences and individual differences in some cognitive tasks

This study is based on three distinct elementary cognitive tasks (ECTs) using chronometric techniques: (a) the S. Sternberg memory scan task, (b) a visual scan task which is perfectly analogous to the memory scan, except that the target digit is presented first and the subject must then scan a set of digits and indicate the presence or absence of the target digit in the set, and (c) the Hick paradigm, which involves responding to a visual stimulus (a light going “on”) when the stimulus is one among sets of either 1, 2, 4, or 8 equally probable alternatives. Certain parameters of all three tasks, such as intercept and slope of RT as a function of set size, from which different cognitive processes are inferred, are compared experimentally and correlationally. Subjects were 48 university students, tested and retested on the three tasks in a counterbalanced design on two separate days to obtain the retest reliabilities needed to correct all correlations for attenuation. Subjects were also given Raven's Advanced Progressive Matrices as a measure of psychometric g. Parameters of the ECTs are significantly and, in some cases, quite substantially correlated with g. Virtually all of this correlation is due to the general factor of the various ECTs, rather than to specific processing components (independent of the general factor). The results also indicate that different ECT paradigms (e.g., visual search and memory search tasks) may yield markedly different values in terms of the group means of analogous parameters, indicating different processes, and yet not show independence of the parameters in terms of individual differences; that is, measurements of the different parameters in individuals are perfectly correlated (i.e., disattenuated correlations do not differ significantly from r = 1). This is found for the intercept parameter of visual and memory search. The reverse condition is also found for the other parameters (e.g., slope); that is, their mean values are nearly identical, suggesting the same processes, yet disattenuated correlations between individual differences are relatively low, or even negative, indicating different processes. Although the general factor clearly predominates, it does not completely overwhelm individual differences in various component processes that are distinct from the general factor.     

Meta‐Analyses of the Relationship of Creative Achievement to Both IQ and Divergent Thinking Test Scores

There is disagreement among researchers about whether IQ tests or divergent thinking (DT) tests are better predictors of creative achievement. Resolving this dispute is complicated by the fact that some research has shown a relationship between IQ and DT test scores (e.g., Runco & Albert, 1986; Wallach, 1970). The present study conducted meta‐analyses of the relationships between creative achievement and both IQ and DT test scores. The analyses included 17 studies (with 5,544 participants) that established the correlation coefficients between IQ and creative achievement and 27 studies (with 47,197 participants) that established the correlation coefficients between DT test scores and creative achievement. Marginal, but statistically significant, Fisher's Z‐transformed correlation coefficients were revealed. The analysis found a significantly higher relationship between DT test scores and creative achievement (r = .216) than between IQ test scores and creative achievement (r = .167). The differences in the correlation coefficients were explained by differences in DT tests, creative achievement types, predicted time periods, and creativity subscales. The significant independent moderator effect for different DT tests indicates that the Torrance Tests of Creative Thinking (TTCT) predict creative achievement better than any other DT test included in this study. Among the creative achievement types, music is predicted the best by IQ and all others are predicted best by DT tests. Among the time periods evaluated, the relationship between DT test scores and creative achievement had the highest correlation at the period of 11–15 years.     

OSP parameters and the cognitive component of reaction time to a missing stimulus: Linking brain and behavior

This within-subjects experiment tested the relationship between the premotor (cognitive) component of reaction time (RT) to a missing stimulus and parameters of the omitted stimulus potential (OSP) brain wave. Healthy young men (N = 28) completed trials with an auditory stimulus that recurred at 2 s intervals and ceased unpredictably. Premotor RT and Motor RT were measured on active trials that required an immediate response to a missing stimulus. Passive trials required no response in order to measure the complete set of OSP parameters (i.e., onset, rate of rise, amplitude and peak latency). The results showed that faster Premotor RT was strongly associated with a faster rate of rise in the OSP wave. Motor RT was unrelated the OSP parameters. This new evidence is consistent with the occurrence of some common cognitive processes generating behavioral and brain reactions to a missing stimulus.     

Age, information processing speed, and intelligence

Two parallel, but independent, literatures have grown out of observations that individual differences in information processing speed, as expressed in performance on choice reaction time (C RT) tasks, modestly correlate with individual differences in age and IQ test performance. These associations have prompted theories that individual differences in information processing speed functionally determine individual differences in performance of all cognitive skills by people of different general intellectual ability (Eysenck, 1986; Jensen, 1985) or age (Salthouse, 1982, 1985).

The experiments on which this literature has been based suffer from methodological weaknesses, such that comparisons have only been made very early in practice and have only concerned mean latencies for correct responses. An experiment compared 90 volunteers aged from 50 through 79 years who were grouped in terms of their performance on the AH 4 (Heim, 1968) IQ test. It explored the joint and independent effects of individual differences in age and in IQ test score and the effects of practice on mean latencies (C RTs) on the shapes of distributions of correct and incorrect responses and on the limiting speeds with which accurate responses can be made (speed/error trade-off functions). We suggest that a plausible explanation for the results is that individual differences in age and in general ability influence C RTs mainly because they affect the efficiency with which responses can be controlled to maximize speed while maintaining accuracy.     

Probability effects in choice reaction time tasks

This paper contains a short review of the main results that were obtained by the author in a series of experiments that constituted a study of the effects of signal probability on choice reaction time. The effects of stimulus probability are shown to be influenced by the following variables: (1) differences in the method of varying stimulus probability, (2) differences in task complexity, (3) differences in S-R code, and (4) differences in Ss’ motivation. The data that are considered here are the overall mean RT for particular signals and the mean RT for sequential repetitions. Two questions, related to the psychological “nature” of the probability effects in choice RT are discussed: (1) The question of the relationship between the relative frequency and the number of alternatives as two different ways of determining the probability effect in choice RT; and (2) the question of identifying the main determinants of the trial-to-trial variability of RT in such experiments.

     

The g-loading of intelligence tests and their relationship with reaction times: A comment on Ruchalla et al.

Ruchalla, Schalt, and Vogel (1985) reported a negative correlation between the g-loadedness of a number of intelligence test subtests and the extent to which the subtests correlated with reaction times (RTs), a result contrary to the position of Jensen and others. A number of possible methodological problems with Ruchalla et al. are described, as are the results of two other studies pertinent to the issue. These results indicate that the g-loadedness of different subtests is in some cases highly positively correlated with the subtests' correlations with RTs, whereas in other cases the relationship is negligible or negative. The key factor appears to be the relative complexity of the RT test: more complex tests showing a strong positive correlation. In the context of these findings, Ruchalla et al.'s results are not out of line—they simply do not tell the whole story.     

Identification of sensorimotor components accounting for individual variability in Zahlen–Verbindungs-Test (ZVT) performance

The Zahlen–Verbindungs-Test (ZVT) represents a highly feasible measure of information-processing speed that correlates quite highly with standard psychometric tests of intelligence. The present study was designed to identify specific stages of the sensorimotor processing system that may account for individual differences in overall variability of ZVT performance. For this purpose, ZVT, reaction time (RT), lateralized readiness potential (LRP), and electromyogram (EMG) measures were obtained in 48 female participants. While faster RT, smaller intraindividual variability in RT, shorter response-locked LRP and EMG latencies were associated with superior ZVT performance, speed of stimulus analysis, as reflected by stimulus-locked LRP latency, was unrelated to ZVT performance. Additional commonality analyses suggested a functional relationship between ZVT performance and the time course of central aspects of response organization rather than the time required for execution of the overt motor response. These findings provide converging evidence for the general notion of an association between speed of motor processing and intelligence.     

IQ/fertility relationships in Japan and Sweden

This study explores the relationship between intelligence and family size in Japan and Sweden. In Japan, there is no relationship, once father's education is controlled for. However, if father's education is not controlled for, then there is a negative relationship between IQ and number of siblings. In Sweden, there is a positive relationship between IQ and fertility only for the male cohort born between 1915 and 1924. The remaining relationships, for both females and males, are neither negative nor positive.     

GRADIVA: FREUD,FETISHISM, AND POMPEIAN FANTASY

This paper is a critical reconsideration of Freud's analysis (1907) of Wilhelm Jensen's novella Gradiva: A Pompeian Fantasy (1903). Freud's interest was aroused by the parallels between Jensen's presentation of dreams and Freud's model of dream formation just published in The Interpretation of Dreams (1900). Freud also acclaims Jensen's presentation of the formation and “cure” of his protagonist's delusion about a marble bas‐relief of a woman walking. This paper argues for the centrality of the phenomenon of fetishism, briefly considered but excluded from Freud's analysis. The fantasy of Gradiva as “the necessary conditions for loving” (Freud 1910, pp. 165–166) is also a key thesis of the essay, which makes use of the newly translated Freud–Jensen correspondence contained in this article's Appendix.