Head strong
The Wages of Sinistrality: Handedness, Brain Structure, and Human Capital Accumulation
Joshua Goodman, Journal of Economic Perspectives, Fall 2014, Pages 193-212
Abstract:
Left- and right-handed individuals have different neurological wiring, particularly with regard to language processing. Multiple datasets from the United States and the United Kingdom show that lefties exhibit significant human capital deficits relative to righties. Lefties score 0.1 standard deviations lower on cognitive skill measures, have more behavioral problems, have more learning disabilities such as dyslexia, complete less schooling, and work in occupations requiring less cognitive skill. Most strikingly, lefties have 10-12 percent lower annual earnings than righties, much of which can be explained by observable differences in cognitive skills and behavioral problems. Lefties work in more manually intensive occupations than do righties, further suggesting their primary labor market disadvantage is cognitive rather than physical. I argue here that handedness can be used to explore the long-run impacts of differential brain structure generated in part by genetics and in part by poor infant health.
----------------------
Dorian Mitchem et al., Evolution and Human Behavior, forthcoming
Abstract:
Theories in both evolutionary and social psychology suggest that a positive correlation should exist between facial attractiveness and general intelligence, and several empirical observations appear to corroborate this expectation. Using highly reliable measures of facial attractiveness and IQ in a large sample of identical and fraternal twins and their siblings, we found no evidence for a phenotypic correlation between these traits. Likewise, neither the genetic nor the environmental latent factor correlations were statistically significant. We supplemented our analyses of new data with a simple meta-analysis that found evidence of publication bias among past studies of the relationship between facial attractiveness and intelligence. In view of these results, we suggest that previously published reports may have overestimated the strength of the relationship and that the theoretical bases for the predicted attractiveness-intelligence correlation may need to be reconsidered.
----------------------
Saving-Enhanced Memory: The Benefits of Saving on the Learning and Remembering of New Information
Benjamin Storm & Sean Stone, Psychological Science, forthcoming
Abstract:
With the continued integration of technology into people’s lives, saving digital information has become an everyday facet of human behavior. In the present research, we examined the consequences of saving certain information on the ability to learn and remember other information. Results from three experiments showed that saving one file before studying a new file significantly improved memory for the contents of the new file. Notably, this effect was not observed when the saving process was deemed unreliable or when the contents of the to-be-saved file were not substantial enough to interfere with memory for the new file. These results suggest that saving provides a means to strategically off-load memory onto the environment in order to reduce the extent to which currently unneeded to-be-remembered information interferes with the learning and remembering of other information.
----------------------
Michael Woodley, Personality and Individual Differences, March 2015, Pages 80–84
Abstract:
Two dysgenic models of declining general intelligence have been proposed. The first posits that since the Industrial Revolution those with low g have had a reproductive advantage over those with high g. The second posits that relaxed purifying selection against deleterious mutations in modern populations has led to g declining due to mutation accumulation. Here, a meta-analytic estimate of the decline due to selection is computed across nine US and UK studies, revealing a loss of .39 points per decade (combined N = 202,924). By combining findings from a high-precision study of the effects of paternal age on offspring g with a study of paternal age and offspring de novo mutation numbers, it is proposed that, 70 de novo mutations per familial generation should reduce offspring g by 2.94 points, or .84 points per decade. Combining the selection and mutation accumulation losses yields a potential overall dysgenic loss of 1.23 points per decade, with upper and lower bound values ranging from 1.92 to .53 points per decade. This estimate is close to those from studies employing the secular slowing of simple reaction time as a potential indicator of declining g, consistent with predictions that mutation accumulation may play a role in these findings.
----------------------
Selection and the Age-Productivity Profile. Evidence from Chess Players
Marco Bertoni, Giorgio Brunello & Lorenzo Rocco, Journal of Economic Behavior & Organization, February 2015, Pages 45–58
Abstract:
We use data on professional chess tournaments to study how endogenous selection affects the relationship between age and mental productivity in a brain-intensive profession. We show that less talented players are more likely to drop out, and that the age-productivity gradient is heterogeneous by ability, making fixed effects estimators inconsistent. Since we do not observe the players who dropped out of chess before the beginning of our sampling period, we cannot exploit the standard Heckman sample selection correction procedure. Therefore, we correct for selection by using an imputation method that repopulates the sample by applying to older cohorts the self-selection patterns observed in younger cohorts. We estimate the age-productivity profile on the repopulated sample using median regressions, and find that median productivity increases by close to 5 percent from initial age (15) to peak age (21.6), and declines substantially after the peak. At age 50, it is about 10 percent lower than at age 15. We compare profiles in the unadjusted and in the repopulated sample and show that failure to adequately address endogenous selection in the former leads to substantially over-estimating productivity at any age relative to initial age.
----------------------
Mapping the unconscious maintenance of a lost first language
Lara Pierce et al., Proceedings of the National Academy of Sciences, 2 December 2014, Pages 17314–17319
Abstract:
Optimal periods during early development facilitate the formation of perceptual representations, laying the framework for future learning. A crucial question is whether such early representations are maintained in the brain over time without continued input. Using functional MRI, we show that internationally adopted (IA) children from China, exposed exclusively to French since adoption (mean age of adoption, 12.8 mo), maintained neural representations of their birth language despite functionally losing that language and having no conscious recollection of it. Their neural patterns during a Chinese lexical tone discrimination task matched those observed in Chinese/French bilinguals who have had continual exposure to Chinese since birth and differed from monolingual French speakers who had never been exposed to Chinese. They processed lexical tone as linguistically relevant, despite having no Chinese exposure for 12.6 y, on average, and no conscious recollection of that language. More specifically, IA participants recruited left superior temporal gyrus/planum temporale, matching the pattern observed in Chinese/French bilinguals. In contrast, French speakers who had never been exposed to Chinese did not recruit this region and instead activated right superior temporal gyrus. We show that neural representations are not overwritten and suggest a special status for language input obtained during the first year of development.
----------------------
Using Participant Choice to Enhance Memory Performance
Ulrich Weger & Stephen Loughnan, Applied Cognitive Psychology, forthcoming
Abstract:
When patients are involved in deciding the course of treatment for their ailment and are given a chance to choose between different treatment options, the success of the intervention typically increases. In our study we transferred this approach to a cognitive psychology task and investigated whether treatment choice can enhance participants' memory performance. Participants who were free to choose one out of a selection of alleged cognitive enhancers showed better performance than those who were assigned an enhancer. We also found that performance-expectations have a stronger impact when triggered prior to the encoding as opposed to the retrieval stage and thus appear to be more effective at a point when participants exercise a greater degree of cognitive control. The findings are of relevance in contexts where it can be assumed that participants have knowledge about their own needs and can in turn capitalize on this knowledge when given the opportunity.
----------------------
Marco Sandrini et al., Frontiers in Aging Neuroscience, October 2014
Abstract:
Memory consolidation is a dynamic process. Reactivation of consolidated memories by a reminder triggers reconsolidation, a time-limited period during which existing memories can be modified (i.e., weakened or strengthened). Episodic memory refers to our ability to recall specific past events about what happened, including where and when. Difficulties in this form of long-term memory commonly occur in healthy aging. Because episodic memory is critical for daily life functioning, the development of effective interventions to reduce memory loss in elderly individuals is of great importance. Previous studies in young adults showed that the dorsolateral prefrontal cortex (DLPFC) plays a causal role in strengthening of verbal episodic memories through reconsolidation. The aim of the present study was to explore the extent to which facilitatory transcranial direct current stimulation (anodal tDCS) over the left DLPFC would strengthen existing episodic memories through reconsolidation in elderly individuals. On Day 1, older adults learned a list of 20 words. On Day 2 (24 h later), they received a reminder or not, and after 10 min tDCS was applied over the left DLPFC. Memory recall was tested on Day 3 (48 h later) and Day 30 (1 month later). Surprisingly, anodal tDCS over the left DLPFC (i.e., with or without the reminder) strengthened existing verbal episodic memories and reduced forgetting compared to sham stimulation. These results provide a framework for testing the hypothesis that facilitatory tDCS of left DLPFC might strengthen existing episodic memories and reduce memory loss in older adults with amnestic mild cognitive impairment.
----------------------
Chinese sex differences in intelligence: Some new evidence
Jianghong Liu & Richard Lynn, Personality and Individual Differences, March 2015, Pages 90–93
Abstract:
Sex differences on the WISC-R in Chinese children were examined in a sample of 788 aged 12 years. Boys obtained a higher mean full scale IQ than girls of 3.75 IQ points, a higher performance IQ of 4.20 IQ points, and a higher verbal IQ of 2.40 IQ points. Boys obtained significantly higher means on the information, picture arrangement, picture completion, block design, and object assembly subtests, while girls obtained a significantly higher mean on coding. The results were in general similar to the sex differences in the United States standardisation sample of the WISC-R. Boys showed greater variability than girls.
----------------------
The Smarter, the Stronger: Intelligence Level Correlates With Brain Resilience To Systematic Insults
Emiliano Santarnecchi, Simone Rossi & Alessandro Rossi Cortex, forthcoming
Abstract:
Neuroimaging evidences posit human intelligence as tightly coupled with several structural and functional brain properties, also suggesting its potential protective role against aging and neurodegenerative conditions. However, whether higher-order cognition might in fact lead to a more resilient brain has not been quantitatively demonstrated yet. Here we document a relationship between individual intelligence quotient (IQ) and brain resilience to targeted and random attacks, as measured through resting-state fMRI graph-theoretical analysis in 102 healthy individuals. In this modeling context, enhanced brain robustness to targeted attacks in individuals with higher IQ is supported by an increased distributed processing capacity despite the systematic loss of the most important node(s) of the system. Moreover, brain resilience in individuals with higher IQ is supported by a set of neocortical regions mainly belonging to language and memory processing network(s), whereas regions related to emotional processing are mostly responsible for lower IQ individuals. Results suggest intelligence level among the predictors of post-lesional or neurodegenerative recovery, also promoting the evolutionary role of higher order cognition, and simultaneously suggesting a new framework for brain stimulation interventions aimed at counteract brain deterioration over time.
----------------------
Nicola Paine et al., Psychophysiology, forthcoming
Abstract:
Elevated inflammatory levels are linked to poorer cognition, but experimental confirmation is lacking. This report examined associations between cognitive performance and inflammation induced by exercise and vaccination. Thirty-six (exercise N = 18, vaccination N = 18) healthy males completed a paced auditory serial addition test (PASAT), which is a multifaceted measure of cognitive function. The task was completed in placebo and elevated inflammation states. Improvements in PASAT performance were related to inflammation. In the exercise study, IL-6 during the first PASAT negatively correlated with PASAT improvement (p = .022). In the vaccination study, increases in C-reactive protein between PASATs correlated with reduced PASAT improvement (p < .001). Inflammation was linked to reduced improvements in cognitive performance. Further research should identify the specific cognitive functions affects and the underlying mechanisms.