The genetic architecture of correlations between perceptual timing, motor timing, and intelligence
Introduction
Intelligence is correlated with performance in a range of behaviors that involve timing in the millisecond to second range. The most well-studied type of task in this context is presumably reaction time, where the participant produces a response (e.g. a key press) to a sensory stimulus in some modality (Jensen, 2006, Luce, 1986). A large variety of such paradigms have been employed, from simple reaction time, where both stimuli and responses are identical across trials, to complex choice reaction time tasks where several response alternatives are available, and the selection of the appropriate response may depend on instructions, stimulus features, and previous knowledge stored in long-term memory. To give an example, one common design of a choice reaction time task is that visual stimuli (e.g. from light emitting diodes) appear in two or more possible spatial positions; there is one response button corresponding to each stimulus position, and the participant responds by pressing the correct button (Jensen, 2006). Consistent findings in the literature are that the mean and the inter-trial variability of reaction time correlate negatively with intelligence, and that correlations tend to be larger for more complex tasks (Jensen, 2006, Sheppard, 2008). Sheppard (2008), in a comprehensive review of studies reporting correlations between reaction time and general intelligence, found average correlations for different reaction time paradigms to range between − 0.22 and − 0.40, with stronger associations for paradigms involving more choice alternatives. In a population representative sample of 900 Scottish individuals, Deary and coworkers found correlations with intelligence of − 0.31 for simple reaction time, − 0.49 for 4-choice reaction time, and − 0.26 for intraindividual trial-to-trial variability (standard deviation) of reaction time in both tasks (Deary, Der, & Ford, 2001).
Another chronometric task which has been frequently studied in relation to intelligence, is the inspection time task (Grudnik and Kranzler, 2001, Vickers et al., 1972). In a standard version of this paradigm, a π-shaped visual stimulus with two parallel vertical lines connected by a horizontal line at the top is presented for a brief period of time before it is covered by a masking stimulus. In different trials, the stimulus randomly appears in one of two versions, where either the left or the right vertical line is longer than the other. The task of the participant is to indicate which line is longer by pressing one of two response buttons. Inspection time has been interpreted as a measure of visual processing speed, and can be considered as an example of a visual backward masking task, where the perceptual processing of a briefly presented target stimulus is influenced by the subsequent presentation of a masking stimulus; also other backward masking tasks, using e.g. alphanumeric stimuli, correlate with intelligence (Burns and Nettelbeck, 2003, Burns et al., 1998). Unlike in a reaction time task, in inspection time only the timing of the target and mask stimuli are timed, not the responses of the participant. The stimulus duration is modified from trial to trial, using an adaptive procedure, in order to estimate the participant's inspection time. This is conventionally defined as the stimulus duration at which the participant makes a correct discrimination with a certain predefined probability (commonly chosen as 97.5%; Jensen, 2006). Correlations between inspection time and intelligence typically fall in the same range as for reaction time, i.e. between − 0.2 and − 0.4 (Grudnik and Kranzler, 2001, Sheppard, 2008). Auditory versions of the inspection time task have been constructed; these show similar relations to intelligence (Bates, 2005, Sheppard, 2008).
Here, we will focus on a third type of timing task that has been studied in relation to intelligence: perceptual and motor paradigms where the task involves processing and discriminating durations and rhythmic structures. Rammsayer and coworkers have demonstrated that intelligence correlates with performance on various perceptual timing tasks, including duration discrimination of single intervals, rhythm perception, temporal order judgment, and temporal generalization (Helmbold et al., 2007, Rammsayer and Brandler, 2002, Troche and Rammsayer, 2009). As for reaction time and inspection time, correlations between accuracy in these tasks and measures of intelligence typically fall in the range 0.2–0.4 (Haldemann et al., 2011, Rammsayer and Brandler, 2002, Rammsayer and Brandler, 2007). Similar correlations have been found between rhythm discrimination subscales of music aptitude tests and intelligence (Lynn et al., 1989, Mosing et al., 2014b, Schellenberg and Weiss, 2013). Associations between motor timing and intelligence have been studied using the isochronous serial interval production (ISIP) paradigm (Madison, 2001) — a simple, repetitive task where the participant performs self-paced isochronous (regular) tapping movements, e.g. with a finger. Several studies have demonstrated that temporal variability in this task, operationalized e.g. as the coefficient of variation of the produced intervals, is negatively correlated with intelligence, with r values typically around −.30 (Holm et al., 2011, Madison et al., 2009, Ullén et al., 2012b).
The various timing tasks discussed above are also correlated with each other. Several larger studies have included both reaction time and inspection time, and in psychometric models of cognitive abilities these tasks load significantly on a common broad ability factor (Gt — Reaction and Decision Speed), which is often interpreted as speed of information processing (Johnson and Deary, 2011, McGrew, 2009, Roberts and Stankov, 1999). However, inspection time and reaction time also have independent contributions to intelligence (Kranzler and Jensen, 1991, Nettelbeck and Rabbitt, 1992, Petrill et al., 2001). Perceptual tasks involving manipulation of temporal information are correlated with reaction time measures – i.e. a faster reaction time is related to better performance in perceptual timing task – with the magnitude of most reported r values in the 0.1–0.3 range (Helmbold et al., 2007, Rammsayer and Brandler, 2002, Rammsayer and Brandler, 2007). Helmbold and coworkers modeled these relations with structural equation modeling, and found good fit for a model where a common temporal factor mediated the effects of both reaction time and perceptual timing on intelligence (Helmbold et al., 2007). Holm and coworkers (Holm et al., 2011) studied relations between motor timing in the ISIP, reaction time, and intelligence. Correlations between reaction time measures and motor timing were mostly in the range 0.2 to 0.4, and a commonality analysis indicated that the associations of these tasks with intelligence involved both overlapping and unique components. When the ISIP task is performed with different effectors by the same individual, reported correlations in motor timing accuracy range from r = 0.36 for speech-jaw movement correlations (Franz, Zelaznik, & Smith, 1992) to r = 0.90 for finger-forearm correlations (Keele, Ivry, & Pokorny, 1987). A correlation of r = 0.53 has been reported between ISIP accuracy and performance in a perceptual timing task (auditory duration discrimination) (Keele, Pokorny, Corcos, & Ivry, 1985). These modest-to-high correlations suggest that common mechanisms could be involved in timing tasks in different modalities.
To summarize, analyses on the phenotypic level suggest that associations between intelligence and timing are weak to moderate in magnitude, and likely to involve common mechanisms as well as more narrow and task specific components. Analyses of timing-intelligence relations in genetically informative samples have mainly focused on reaction time. Early twin studies of reaction time have been reviewed by Jensen (2006) and Beaujean (2005). Jensen (2006) reports a mean heritability of reaction time across studies of 0.44 (SD = 0.19), while the association between reaction time and intelligence appears essentially driven by genetic pleiotropy, i.e. common genes influencing different phenotypic variables (mean genetic correlation = 0.90, SD = 0.13). In a more recent study, Lee and coworkers, in a study of older (age > 65 years) Australian twins, found a genetic correlation of r = 0.32 between simple reaction time and intelligence, with overlapping genes explaining a substantial part of the association between the two variables (Lee et al., 2012b). Several twin studies have also been performed on inspection time and intelligence (Luciano et al., 2001, Luciano et al., 2004, Luciano et al., 2005). Luciano and coworkers (Luciano et al., 2005) analyzed the association between these variables using directional causation modeling, a method which can be used to analyze direction of causation for correlated traits in genetically related individuals, provided that genetic influences on one of the traits are sufficiently different in magnitude from genetic influences on the other trait. The results showed a heritability of 0.57 for inspection time, and that the covariation between the traits was best explained by pleiotropic genetic effects.
A striking feature of this literature is that intelligence is related to performance in a wide range of diverse tasks, that include elementary cognitive tasks measuring information processing speed, perceptual and cognitive tasks involving online manipulation of temporal information, and repetitive rhythmic motor behaviors. With regard to the latter, we have earlier argued that the association between intelligence and rhythmic accuracy in a simple, automatic motor behavior such as the ISIP supports that the intelligence-timing relation may involve bottom-up mechanisms that are distinct in nature from top-down phenomena such as fluctuations in attention (see Discussion) (Holm et al., 2011, Madison et al., 2009, Ullén et al., 2012b). To analyze the biological underpinnings of the association between motor timing and intelligence is therefore of particular interest. However, this association has not been studied previously in a genetically informative sample.
Here, we use twin modeling in a large cohort of Swedish twins, to analyze the genetic architecture of the associations between IQ, motor timing (ISIP), and an auditory rhythm discrimination task (Rhythm). Specifically, we tested whether common genetic factors influence intelligence, motor timing and perceptual timing. Furthermore, as summarized above, correlations between motor and perceptual timing tasks have been found to be stronger than what is typically found for timing-intelligence relations (Keele et al., 1985). A second hypothesis was therefore that associations between motor and perceptual timing also involve genetic factors that have more specific effects on temporal processing, independently of cognitive ability.
Section snippets
Participants
The participants were twins born between 1958 and 1985, recruited from the Swedish Twin Registry (STR) (Magnusson et al., 2013). The data were acquired as part of a larger online survey which also included numerous other tests and questionnaires on music related traits. Informed consent to participate was obtained from all participants. The study was conducted according to the principles expressed in the Declaration of Helsinki, and was approved by the Regional Ethics Review Board in Stockholm
Phenotypic analyses
Descriptive statistics for the outcome variables are summarized in Table 1. Preliminary analyses (assumption testing) showed that sex had a significant mean effect on IQ and ISIP, with men on average scoring slightly higher on IQ and having a slightly lower ISIP than females. Further, age had a significant mean effect on IQ and Rhythm with a lower performance on both tests with higher age. For all three variables, there were no significant differences in means and variances between MZ and DZ
Discussion
We have studied, for the first time, the associations between both motor and perceptual timing accuracy and intelligence in a genetically informative sample. The results of the multivariate twin modeling indicate that these associations are primarily driven by genetic influences. Shared environmental effects as well as non-shared environmental cross-paths could be removed from the full model without any significant decrease of goodness-of-fit. Only the genetic components of the correlations
Acknowledgments
The present work was supported by the Bank of Sweden Tercentenary Foundation (M11-0451:1) and the Sven and Dagmar Salén Foundation. We would also like to thank the Swedish twins for their participation.
References (80)
Auditory inspection time and intelligence
Personality and Individual Differences
(2005)Heritability of cognitive abilities as measured by mental chronometric tasks: A meta-analysis
Intelligence
(2005)- et al.
Listening to rhythms activates motor and premotor cortex
Cortex
(2009) - et al.
Inspection time in the structure of cognitive abilities: Where does IT fit?
Intelligence
(2003) - et al.
Testing the interpretation of inspection time as a measure of speed of sensory processing
Personality and Individual Differences
(1998) - et al.
Heritability of EEG coherence in a large sib-pair population
Biological Psychology
(2007) A review of the worst performance rule: Evidence, theory and alternative hypotheses
Intelligence
(2003)- et al.
Reaction times and intelligence differences — A population-based cohort study
Intelligence
(2001) - et al.
Meta-analysis of the relationship between intelligence and inspection time
Intelligence
(2001) - et al.
Structural brain variation and general intelligence
NeuroImage
(2004)
Placing inspection time, reaction time, and perceptual speed in the broader context of cognitive ability: The VPR model in the Lothian birth cohort 1936
Intelligence
Dendritic mechanisms controlling spike-timing-dependent synaptic plasticity
Trends in Neurosciences
The dorsal auditory pathway is involved in performance of both auditory and visual rhythms
NeuroImage
Do perception and motor production share common timing mechanisms: A correlational analysis
Acta Psychologica
The nature of psychometric g: Unitary process or a number of independent processes?
Intelligence
A smarter brain is associated with stronger neural interaction in healthy young females: A resting EEG coherence study
Intelligence
Distinct systems for automatic and cognitively controlled time measurement: Evidence from neuroimaging
Current Opinion in Neurobiology
On the heritability of inspection time and its covariance with IQ: A twin study
Intelligence
Perceptual speed does not cause intelligence, and intelligence does not cause perceptual speed
Biological Psychology
Simple musical tests as measures of Spearman's g
Personality and Individual Differences
Correlations between general intelligence and components of serial timing variability
Intelligence
CHC theory and the human cognitive abilities project: Standing on the shoulders of the giants of psychometric intelligence research
Intelligence
Aging, cognitive performance, and mental speed
Intelligence
Intelligence and neural efficiency: Measures of brain activation versus measures of functional connectivity in the brain
Intelligence
Inspection time and the relationship among elementary cognitive tasks, general intelligence, and specific cognitive abilities
Intelligence
On the relationship between general fluid intelligence and psychophysical indicators of temporal resolution in the brain
Journal of Research in Personality
Performance on temporal information processing as an index of general intelligence
Intelligence
Beyond a bigger brain: Multivariable structural brain imaging and intelligence
Intelligence
Individual differences in speed of mental processing and human cognitive abilities: Toward a taxonomic model
Learning and Individual Differences
Music and cognitive abilities
Attention and working memory as predictors of intelligence
Intelligence
The structure of the relationship between attention and intelligence
Intelligence
Brain spontaneous functional connectivity and intelligence
NeuroImage
The influence of temporal resolution power and working memory capacity on psychometric intelligence
Intelligence
Proneness for psychological flow in everyday life: Associations with personality and intelligence
Personality and Individual Differences
Bottom-up mechanisms are involved in the relation between accuracy in timing tasks and intelligence — further evidence using manipulations of state motivation
Intelligence
Psychometric properties and heritability of a new online test for musicality, the Swedish musical discrimination test
Personality and Individual Differences
Lapses in sustained attention and their relation to executive control and fluid abilities: An individual differences investigation
Intelligence
White matter volume predicts reaction time instability
Neuropsychologia
Quantitative genetic modeling of variation in human brain morphology
Cerebral Cortex
Cited by (18)
Beat alignment ability is associated with formal musical training not current music playing
2023, Frontiers in PsychologyUsing a polygenic score in a family design to understand genetic influences on musicality
2022, Scientific ReportsGenome-wide association study of musical beat synchronization demonstrates high polygenicity
2022, Nature Human Behaviour