Inspection time and WAIS-R IQ subtypes: A confirmatory factor analysis study

P3b correlates of inspection time

Both P3b and the inspection time (IT) are related with intelligence, yet the P3b correlates of IT are not well understood. This event-related potential study addressed this question by asking participants (N = 28) to perform an IT task. There were three IT conditions with different levels of discriminative stimulus duration, i.e., 33 ms, 67 ms, and 100 ms, and a control condition with no target presentation (0 ms condition). We also measured participants' processing speed with four Elementary Cognitive Tests (ECTs), including a Simple Reaction Time task (SRT), two Choice Reaction Time tasks (CRTs), and a Pattern Discrimination task (PD). Results revealed that an increase in P3b latency with longer duration of the discriminative stimulus. Moreover, the P3b latency was negatively correlated with the accuracy of the IT task in the 33 ms condition, but not evident in the 67 and 100 ms conditions. Furthermore, the P3b latency of the 33 ms condition was positively correlated with the RT of the SRT, but not related with the RTs of CRTs or PD. A significant main effect of duration on the amplitude of P1 was also found. We conclude that the present study provides the neurophysiological correlates of the IT task, and those who are able to accurately perceive and process very briefly presented stimuli have a higher speed of information process, reflected by the P3b latency, yet this relationship is more obvious in the most difficult condition. Combined, our results suggest that P3b is related with the closure of a perceptual epoch to form the neural representation of a stimulus, in support of the "context closure" hypothesis.

Perceptual Grouping and High-Order Cognitive Ability

High-order cognitive functions require the integration of information across functionally related modules. This relationship suggests that cognitive ability is related to the efficiency and processing speed of basic integrative function. In order to examine individual differences for this relationship, we compared standardized tests of intelligence to visual perceptual grouping abilities, which represents a basic process of integration. Sixty participants discriminated perceived grouping of dot patterns based upon similarity in luminance. Psychophysical measurements were made of the functional limits and processing speed of grouping. We assessed cognitive abilities with the Wechsler Abbreviated Scale of Intelligence (WASI) and found that measures of grouping efficiency as well as speed varied considerably across subjects, indicating substantial individual differences at this relatively early level of visual processing. Faster grouping speed was associated with higher scores on all WASI subtests, whereas grouping ability, when not restricted by time, was associated only with the performance IQ components. These results demonstrate an association between a basic integrative function, in which cognitive and motoric factors were minimized, with measures of high-order cognition, which include both verbal and spatial cognitive components.

Genetics of Cognition: Outline of a Collaborative Twin Study

Amultidisciplinary collaborative study examining cognition in a large sample of twins is outlined. A common experimental protocol and design is used in The Netherlands, Australia and Japan to measure cognitive ability using traditional IQ measures (i.e., psychometric IQ), processing speed (e.g., reaction time [RT] and inspection time [IT]), and working memory (e.g., spatial span, delayed response [DR] performance). The main aim is to investigate the genetic covariation among these cognitive phenotypes in order to use the correlated biological markers in future linkage and association analyses to detect quantitativetrait loci (QTLs). We outline the study and methodology, and report results from our preliminary analyses that examines the heritability of processing speed and working memory indices, and their phenotypic correlation with IQ. Heritability of Full Scale IQ was 87% in the Netherlands, 83% in Australia, and 71% in Japan. Heritability estimates for processing speed and working memory indices ranged from 33–64%. Associations of IQ with RT and IT (−0.28 to −0.36) replicated previous findings with those of higher cognitive ability showing faster speed of processing. Similarly, significant correlations were indicated between IQ and the spatial span working memory task (storage [0.31], executive processing [0.37]) and the DR working memory task (0.25), with those of higher cognitive ability showing better memory performance. These analyses establish the heritability of the processing speed and working memory measures to be used in our collaborative twin study of cognition, and support the findings that individual differences in processing speed and working memory may underlie individual differences in psychometric IQ.

Speed of processing and individual differences in IQ in schizophrenia: General or specific cognitive deficits?

INTRODUCTION

The aim of this study was to re-examine the role of cognitive processing speed in the vulnerability to schizophrenia, using an inspection time (IT) task that does not require a speeded manual response. Since IT consistently correlates with intelligence, the relationship between IT and general intelligence was also explored.

METHODS

Patients with schizophrenia were compared with unaffected siblings of schizophrenia patients and healthy controls on a visual IT task. Both speed and variability of IT performance were examined. Current intellectual ability (IQ) was estimated with the Shipley Institute of Living Scale (SILS), which yields separate assessments of verbal and abstraction abilities.

RESULTS

Schizophrenia patients produced ITs that were significantly slower and more variable than either unaffected siblings or healthy controls. These results are not related to demographic or clinical variables. A significant negative correlation was obtained between IT and IQ; specifically, longer IT values were associated with abstraction scores only.

CONCLUSIONS

These findings confirm that basic cognitive processing efficiency is impaired in patients with schizophrenia. In contrast, ITs in unaffected siblings did not differ from healthy controls, in line with their better IQ test scores. Implications for models of general and specific heritable dimensions in schizophrenia are discussed.

Intracranial capacity and brain volumes are associated with cognition in healthy elderly men

BACKGROUND

Brain size and intracranial capacity are correlated with cognitive performance in young healthy adults, but data are lacking on these relationships in older healthy adults.

OBJECTIVE

To test the hypotheses that intracranial capacity, volumes of specific brain regions, and a measure of the shared variance between brain regions are positively associated with cognitive function in a sample of healthy, unmedicated elderly men (n = 97; mean age 67.8, SD 1.3).

METHODS

Individuals underwent MRI, with measurements of intracranial area and volumetric measurements of hippocampi, temporal lobes, and frontal lobes. Cognitive testing included measures of premorbid intelligence, fluid intelligence, verbal memory, visuospatial memory, verbal fluency, and attention and processing speed.

RESULTS

Cognitive tests showed significant positive intercorrelations throughout, and regional brain volumes were also universally, significantly, and positively intercorrelated. Intracranial area and several regional brain volumes correlated with tests of premorbid and fluid intelligence and tests of visuospatial memory. Tests of verbal memory and verbal fluency did not correlate significantly with brain volumes. Structural equation modeling demonstrated that the relationships between specific cognitive tests and regional brain volumes could best be summarized by a significant positive relationship between a general brain size factor and a general cognitive factor, and not by associations between individual tests and particular brain regions.

CONCLUSIONS

In healthy elderly men, there are significant relationships between multiple cognitive tests and both intracranial capacity and regional brain volumes. These relationships may be largely due to longstanding associations between general cognitive ability and overall brain size.

Temporal processing ability in above average and average readers

In the present study, we compared the rapid visual and auditory temporal processing ability of above average and average readers. One hundred five undergraduates participated in various visual and auditory temporal tasks. The above average readers exhibited lower auditory and visual temporal resolution thresholds than did the average readers, but only the differences in the auditory tasks were statistically significant, especially when nonverbal IQ was controlled for. Furthermore, both the correlation and stepwise multiple regression analyses revealed a relationship between the auditory measures and the wide range achievement test (WRAT) reading measure and a relationship between the auditory measures and a low spatial frequency visual measure and the WRAT spelling measure. Discriminant analysis showed that together both the visual and auditory measures correctly classified 75% of the subjects into above average and average reading groups, respectively. The results suggest that differences in temporal processing ability in relation to differences in reading proficiency are not confined to the comparison between poor and normal readers.

The Raven's progressive matrices: change and stability over culture and time

Data relating to the stability and variation in the norms for the Raven's Progressive Matrices Test (a well-validated measure of basic cognitive functioning) for different cultural, ethnic, and socioeconomic groups on a worldwide and within-country basis are first summarized. Subsequent sections deal with variation over time. A possible explanation for the variation in norms over time and between ethnic groups within countries is offered.

Reductionism and intelligence: the case of inspection time

Successes in science tend to be successful attempts at reduction and causal interaction. The reduction of the interaction of bodies to the laws of motion and the reduction of chemical phenomena to elements and their interactions are good examples. In these cases reductionism leads to observed phenomena being explained by a relatively small number of basic concepts and the laws which govern the interaction of the concepts. The spectrum of inquiry that stretches from common sense to scientific psychology is infused with a tendency toward reductionism. Hippocrates and Galen originated and developed, respectively, the notion that temperamental differences might be reducible to the amounts of four bodily fluids, or humours (black bile, yellow bile, blood and phlegm), that a person produced. Astrologers reduced stable personality differences to the positions of the stars and planets at the time of birth. And differential psychologists have reduced the personality trait adjectives contained in the lexicon to about five major dimensions.

Cerebral asymmetries in inspection time?

Recent studies have suggested that there are low-level processing asymmetries across the cerebral hemispheres, with a right visual field-left hemisphere advantage in tasks involving temporal resolution. In the present report, one such task, inspection time, was measured separately for each cerebral hemisphere in 10 right-handed male subjects over 5 days. A number of methodological improvements were made on previous studies in which a general right visual field-left hemisphere advantage had been found relative to the left visual field-right hemisphere in inspection time performance. The present results suggest that there is no general left hemisphere advantage in inspection time, although there might be asymmetries in practice effects across the hemispheres. The findings also suggest the existence of individual differences in the extent and direction of hemispheric specialisation for this task (ranging from left hemisphere dominance to marked right hemisphere dominance for some subjects) even in right-handed subjects.

Effects of nicotine on perceptual speed

Two experiments investigating the effects of nicotine on performance in the inspection time (IT) procedure are reported. Experiment 1 compared ITs in smoking (0.8 mg nicotine cigarette), sham-smoking, and no-smoking conditions. IT was significantly shorter in the smoking condition as compared to both the no-smoking or sham-smoking conditions, suggesting that nicotine enhances early information processing. This result is of particular interest because of the correlation between IT and IQ reported in previous experiments. The nicotine related decrease in IT raises the possibility that nicotine enhances at least a subset of the physiological processes underlying intellectual performance. Experiment 2 examined the persistence of this nicotine related enhancement in IT, and investigated the effects of nicotine across 480 IT trials. Results suggested that ITs derived from the last third of the 480 trials were significantly shorter in the 0.8 mg cigarette condition than in no-smoking condition. The results from these two experiments, taken together with recent work examining the effects of nicotine on the string length measure of AEP waveform complexity and Hick decision time (DT), and studies investigating cognitive functioning and cholinergic system dysfunction in dementia, suggest a role of the cholinergic system in intellectual performance.