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Abstract

Individual differences in inspection time explain about 20% of IQ test variance. To determine whether the association between inspection time and IQ is mediated by common genes or by a common environmental factor, inspection time and IQ were assessed in an extended twin design. Data from 688 participants from 271 families were collected as part of a large ongoing project on the genetics of adult brain function and cognition. The sample consisted of a young adult cohort (mean age 26.2 years) and an older adult cohort (mean age 50.4 years). IQ was assessed with the Dutch version of the WAIS-3R. Inspection time was measured in the so-called II-paradigm, in which a subject is asked to decide which leg of the II-figure is longest at varying display times of the II-figure. The number of correct inspections per second (i.e., the reciprocal of inspection time) was used to index perceptual speed. For Verbal IQ and Performance IQ, heritabilities were 85% and 69%, respectively. For perceptual speed, 46% of the total variance was explained by genetic variance. No differences in heritability estimates across age cohorts or sexes were found. Across the whole sample, a significant phenotypic correlation was found between perceptual speed and Verbal IQ (0.19) and between perceptual speed and Performance IQ (0.27). These correlations were entirely due to a common genetic factor that accounted for 10% of the genetic variance in verbal IQ and for 22% of the genetic variance in performance IQ. This factor is hypothesized to reflect the influence of genetic factors that determine axonal myelination in the central nervous system.

The association between brain volume and intelligence is of genetic origin

“…The subjects for whom MRI scans were available partly overlapped with a sample of extended twin families from a large study on cognition 4 . In the latter study, we found a heritability of g of 0.86, which is consistent with previous reports 5 .…”

Psichikos sveikatos sutrikimų turinčių asmenų paprastos ir sudėtingos informacijos apdorojimo greitis

“…The importance of studying individual difference in IPS was emphasized by Wilhelm Wundt, Sir Francis Galton, and James Mckenn Cattell during the late 1800s and early 1900s. However, due to general decline in IPS research up until late nineteenth century only during the past decades IPS changes in clinical populations began to be understood (O'Brien & Tulsky, 2008).…”

“…General slowing of information processing is also related to psychia tric disorders, such as depression (Reppermund et al, 2007;Tsourtos, Thompson, & Stough, 2002), schizophrenia (Brebion et al, 2015;Cella & Wykes, 2013), schizoaffective disorder (Fryar-Williams & Strobel, 2015;Simonsen et al, 2011) and others. These relatively consistent findings of IPS group differences between healthy controls and mental illness could contribute to more general investigations of mechanisms underlying individual differences in IPS.…”

“…It has been shown that in mental disorders, such as schizophrenia (Antonova et al, 2005), and depression (Lesser, Boone, Mehringer, & Wohl, 1996) white matter disintegration is related to IPS. This similarity of cognitive deficits despite heterogeneity of conditions might be explained by common genetic determinants of processing speed decreasing in aging and in many brain disorders, which are mediated by structural white matter changes (Kochunov et al, 2016;Posthuma, De Geus, & Boomsma, 2001). So, now we are beginning to understand that the same biological processes that enabled quick and efficient information processing in vertebrates, lead to possibility of more complex disorders, such as psychiatric illness (Nave, 2010).…”

“…Also, as the literature suggests (Lennertz et al, 2015), sampling procedures might be important in these investigations as hospitalized samples might overestimate cognitive deficits. Furthermore, due to the psychometric nature of IPS tasks, other cofounding variables, such as gender, age, education, and native language (Ruff & Parker, 1993;Salthouse, 1996;Wagenmakers, Ratcliff, Gomez, & McKoon, 2008) should be analysed before drawing conclusions about the importance of IPS in psychiatric samples.…”