Dumb and dumber
Michael Woodley, Jan te Nijenhuis & Raegan Murphy
Intelligence, forthcoming
Abstract:
The Victorian era was marked by an explosion of innovation and genius, per capita rates of which appear to have declined subsequently. The presence of dysgenic fertility for IQ amongst Western nations, starting in the 19th century, suggests that these trends might be related to declining IQ. This is because high-IQ people are more productive and more creative. We tested the hypothesis that the Victorians were cleverer than modern populations, using high-quality instruments, namely measures of simple visual reaction time in a meta-analytic study. Simple reaction time measures correlate substantially with measures of general intelligence (g) and are considered elementary measures of cognition. In this study we used the data on the secular slowing of simple reaction time described in a meta-analysis of 14 age-matched studies from Western countries conducted between 1884 and 2004 to estimate the decline in g that may have resulted from the presence of dysgenic fertility. Using psychometric meta-analysis we computed the true correlation between simple reaction time and g, yielding a decline of - 1.23 IQ points per decade or fourteen IQ points since Victorian times. These findings strongly indicate that with respect to g the Victorians were substantially cleverer than modern Western populations.
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Long-Term Enhancement of Brain Function and Cognition Using Cognitive Training and Brain Stimulation
Albert Snowball et al.
Current Biology, forthcoming
Abstract:
Noninvasive brain stimulation has shown considerable promise for enhancing cognitive functions by the long-term manipulation of neuroplasticity. However, the observation of such improvements has been focused at the behavioral level, and enhancements largely restricted to the performance of basic tasks. Here, we investigate whether transcranial random noise stimulation (TRNS) can improve learning and subsequent performance on complex arithmetic tasks. TRNS of the bilateral dorsolateral prefrontal cortex (DLPFC), a key area in arithmetic, was uniquely coupled with near-infrared spectroscopy (NIRS) to measure online hemodynamic responses within the prefrontal cortex. Five consecutive days of TRNS-accompanied cognitive training enhanced the speed of both calculation- and memory-recall-based arithmetic learning. These behavioral improvements were associated with defined hemodynamic responses consistent with more efficient neurovascular coupling within the left DLPFC. Testing 6 months after training revealed long-lasting behavioral and physiological modifications in the stimulated group relative to sham controls for trained and nontrained calculation material. These results demonstrate that, depending on the learning regime, TRNS can induce long-term enhancement of cognitive and brain functions. Such findings have significant implications for basic and translational neuroscience, highlighting TRNS as a viable approach to enhancing learning and high-level cognition by the long-term modulation of neuroplasticity.
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Spearman's Law of Diminishing Returns and national ability
Thomas Coyle & Heiner Rindermann
Personality and Individual Differences, forthcoming
Abstract:
This research examined Spearman's Law of Diminishing Returns (SLODR) using national ability as the unit of analysis. National ability was estimated using international standardized tests such as the Programme for International Student Assessment (PISA), Trends in International Mathematics and Science Study (TIMSS), and Progress in International Reading Literacy Study (PIRLS). Factor analysis estimated the national G loadings of tests for high and low ability nations. Consistent with SLODR, the G loadings of tests were lower for higher ability nations. The pattern was confirmed after correcting for school attendance and age biases. Because a test's g loading is directly related to its predictive validity (correlation with outcomes), our results imply that the predictive validity of tests may be lower for higher ability nations.
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Are cognitive differences between countries diminishing? Evidence from TIMSS and PISA
Gerhard Meisenberg & Michael Woodley
Intelligence, forthcoming
Abstract:
Cognitive ability differences between countries can be large, with average IQs ranging from approximately 70 in sub-Saharan Africa to 105 in the countries of north-east Asia. A likely reason for the great magnitude of these differences is the Flynn effect, which massively raised average IQs in economically advanced countries during the 20th century. The present study tests the prediction that international IQ differences are diminishing again because substantial Flynn effects are now under way in the less developed "low-IQ countries" while intelligence is stagnating in the economically advanced "high-IQ countries." The hypothesis is examined with two periodically administered scholastic assessment programs. TIMSS has tested 8th-grade students periodically between 1995 and 2011 in mathematics and science, and PISA has administered tests of mathematics, science and reading between 2000 and 2009. In both TIMSS and PISA, low-scoring countries tend to show a rising trend relative to higher-scoring countries. Despite the short time series of only 9 and 16 years, the results indicate that differences between high-scoring and low-scoring countries are diminishing on these scholastic achievement tests. The results support the prediction that through a combination of substantial Flynn effects in low-scoring countries and diminished (or even negative) Flynn effects in high-scoring countries, cognitive differences between countries are getting smaller on a worldwide scale.
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Shana Carpenter et al.
Psychonomic Bulletin & Review, forthcoming
Abstract:
The present study explored the effects of lecture fluency on students' metacognitive awareness and regulation. Participants watched one of two short videos of an instructor explaining a scientific concept. In the fluent video, the instructor stood upright, maintained eye contact, and spoke fluidly without notes. In the disfluent video, the instructor slumped, looked away, and spoke haltingly with notes. After watching the video, participants in Experiment 1 were asked to predict how much of the content they would later be able to recall, and participants in Experiment 2 were given a text-based script of the video to study. Perceived learning was significantly higher for the fluent instructor than for the disfluent instructor (Experiment 1), although study time was not significantly affected by lecture fluency (Experiment 2). In both experiments, the fluent instructor was rated significantly higher than the disfluent instructor on traditional instructor evaluation questions, such as preparedness and effectiveness. However, in both experiments, lecture fluency did not significantly affect the amount of information learned. Thus, students' perceptions of their own learning and an instructor's effectiveness appear to be based on lecture fluency and not on actual learning.
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Nicolas Déry et al.
Frontiers in Neuroscience, April 2013
Abstract:
Since the remarkable discovery of adult neurogenesis in the mammalian hippocampus, considerable effort has been devoted to unraveling the functional significance of these new neurons. Our group has proposed that a continual turnover of neurons in the DG could contribute to the development of event-unique memory traces that act to reduce interference between highly similar inputs. To test this theory, we implemented a recognition task containing some objects that were repeated across trials as well as some objects that were highly similar, but not identical, to ones previously observed. The similar objects, termed lures, overlap substantially with previously viewed stimuli, and thus, may require hippocampal neurogenesis in order to avoid catastrophic interference. Lifestyle factors such as aerobic exercise and stress have been shown to impact the local neurogenic microenvironment, leading to enhanced and reduced levels of DG neurogenesis, respectively. Accordingly, we hypothesized that healthy young adults who take part in a long-term aerobic exercise regime would demonstrate enhanced performance on the visual pattern separation task, specifically at correctly categorizing lures as "similar." Indeed, those who experienced a proportionally large change in fitness demonstrated a significantly greater improvement in their ability to correctly identify lure stimuli as "similar." Conversely, we expected that those who score high on depression scales, an indicator of chronic stress, would exhibit selective deficits at appropriately categorizing lures. As expected, those who scored high on the Beck Depression Inventory (BDI) were significantly worse than those with relatively lower BDI scores at correctly identifying lures as "similar," while performance on novel and repeated stimuli was identical. Taken together, our results support the hypothesis that adult-born neurons in the DG contribute to the orthogonalization of incoming information.
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Increased morphological asymmetry, evolvability and plasticity in human brain evolution
Aida Gómez-Robles, William Hopkins & Chet Sherwood
Proceedings of the Royal Society: Biological Sciences, 22 June 2013
Abstract:
The study of hominin brain evolution relies mostly on evaluation of the endocranial morphology of fossil skulls. However, only some general features of external brain morphology are evident from endocasts, and many anatomical details can be difficult or impossible to examine. In this study, we use geometric morphometric techniques to evaluate inter- and intraspecific differences in cerebral morphology in a sample of in vivo magnetic resonance imaging scans of chimpanzees and humans, with special emphasis on the study of asymmetric variation. Our study reveals that chimpanzee-human differences in cerebral morphology are mainly symmetric; by contrast, there is continuity in asymmetric variation between species, with humans showing an increased range of variation. Moreover, asymmetric variation does not appear to be the result of allometric scaling at intraspecific levels, whereas symmetric changes exhibit very slight allometric effects within each species. Our results emphasize two key properties of brain evolution in the hominine clade: first, evolution of chimpanzee and human brains (and probably their last common ancestor and related species) is not strongly morphologically constrained, thus making their brains highly evolvable and responsive to selective pressures; second, chimpanzee and, especially, human brains show high levels of fluctuating asymmetry indicative of pronounced developmental plasticity. We infer that these two characteristics can have a role in human cognitive evolution.
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Changes in test-taking patterns over time
Olev Must & Aasa Must
Intelligence, forthcoming
Abstract:
The current study aims to investigate the relationship between right, wrong and missing answers to cognitive test items (test-taking patterns) in the context of the Flynn Effect (FE). We compare two cohorts of Estonian students (1933/36, n = 890; 2006, n = 913) using an Estonian adaptation of the National Intelligence Tests and document three simultaneous trends: fewer missing answers (- 1 Cohen's d averaged over subtests), and a rise in the number of right and wrong answers to the subtests (average ds of .86 and .30, respectively). In the Arithmetical Reasoning and Vocabulary subtests, adjustments for false-positive answers (the number of right minus the number of wrong answers) reduced the size of the Flynn Effect by half. These subtests were supposed to be high g-loading subtests. Our conclusion is that rapid guessing has risen over time and influenced tests scores more strongly over the years. The FE is partly explained by changes in test-taking behavior over time.
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Human frontal lobes are not relatively large
Robert Barton & Chris Venditti
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
One of the most pervasive assumptions about human brain evolution is that it involved relative enlargement of the frontal lobes. We show that this assumption is without foundation. Analysis of five independent data sets using correctly scaled measures and phylogenetic methods reveals that the size of human frontal lobes, and of specific frontal regions, is as expected relative to the size of other brain structures. Recent claims for relative enlargement of human frontal white matter volume, and for relative enlargement shared by all great apes, seem to be mistaken. Furthermore, using a recently developed method for detecting shifts in evolutionary rates, we find that the rate of change in relative frontal cortex volume along the phylogenetic branch leading to humans was unremarkable and that other branches showed significantly faster rates of change. Although absolute and proportional frontal region size increased rapidly in humans, this change was tightly correlated with corresponding size increases in other areas and whole brain size, and with decreases in frontal neuron densities. The search for the neural basis of human cognitive uniqueness should therefore focus less on the frontal lobes in isolation and more on distributed neural networks.
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Krista Macpherson & William Roberts
Learning and Motivation, forthcoming
Abstract:
Numerical competencies have been thoroughly examined in several species, yet relatively few studies have examined such processes in the domestic dog. In an initial experiment, procedures from numerical studies of chimpanzees (0010 and 0015) were adapted for use with 27 domestic dogs. Subjects in these experiments watched as different quantities of food were sequentially dropped into each of two bowls. The subjects were then allowed to select and consume the contents of one of the bowls. Although dogs excelled in a 1 vs 0 condition, their performance failed to significantly surpass chance across all other ratios. In a second experiment with a single subject (a rough collie named Sedona), the procedure was revised so that non-food stimuli were presented simultaneously to the dog on two magnet boards. If Sedona chose the board with the majority of the items, she was rewarded with a piece of food hidden underneath the board. If she made an incorrect choice, she received no reinforcement. Interestingly, Sedona's performance far exceeded that of the dogs in Experiment 1. Implications of these findings for the study of domestic dogs are discussed.
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Deliberate practice: Is that all it takes to become an expert?
David Hambrick et al.
Intelligence, forthcoming
Abstract:
Twenty years ago, Ericsson, Krampe, and Tesch-Römer (1993) proposed that expert performance reflects a long period of deliberate practice rather than innate ability, or "talent". Ericsson et al. found that elite musicians had accumulated thousands of hours more deliberate practice than less accomplished musicians, and concluded that their theoretical framework could provide "a sufficient account of the major facts about the nature and scarcity of exceptional performance" (p. 392). The deliberate practice view has since gained popularity as a theoretical account of expert performance, but here we show that deliberate practice is not sufficient to explain individual differences in performance in the two most widely studied domains in expertise research - chess and music. For researchers interested in advancing the science of expert performance, the task now is to develop and rigorously test theories that take into account as many potentially relevant explanatory constructs as possible.
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R.C. Veasey et al.
Appetite, 1 September 2013, Pages 38-44
Abstract:
The current study assessed the interactive effect of breakfast and exercise on cognition and mood. Twelve active males completed four trials; no breakfast-rest, breakfast-rest, no breakfast-exercise or breakfast-exercise in a randomized, cross-over design. The trials consisted of; breakfast or fast, a 2h rest, exercise (treadmill run) or equivalent rest, a chocolate milk drink, a 90min rest and an ad libitum lunch. Cognitive performance and mood were recorded frequently throughout each trial. Data was analysed as pre-exercise/rest, during and immediately post exercise/rest and post-drink. No effects were found prior to consumption of the drink. Post-drink, fasting before exercise increased mental fatigue compared to consuming breakfast before exercise and fasting before rest. Tension increased when breakfast was consumed at rest and when exercise was undertaken fasted compared to omitting breakfast before rest. Breakfast before rest decreased Rapid Visual Information Processing task speed and impaired Stroop performance. Breakfast omission improved Four Choice Reaction Time performance. To conclude, breakfast before exercise appeared beneficial for post-exercise mood even when a post-exercise snack was consumed. Exercise reversed post-breakfast cognitive impairment in active males.
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Music training, cognition, and personality
Kathleen Corrigall, Glenn Schellenberg & Nicole Misura
Frontiers in Psychology, April 2013
Abstract:
Although most studies that examined associations between music training and cognitive abilities had correlational designs, the prevailing bias is that music training causes improvements in cognition. It is also possible, however, that high-functioning children are more likely than other children to take music lessons, and that they also differ in personality. We asked whether individual differences in cognition and personality predict who takes music lessons and for how long. The participants were 118 adults (Study 1) and 167 10- to 12-year-old children (Study 2). We collected demographic information and measured cognitive ability and the Big Five personality dimensions. As in previous research, cognitive ability was associated with musical involvement even when demographic variables were controlled statistically. Novel findings indicated that personality was associated with musical involvement when demographics and cognitive ability were held constant, and that openness-to-experience was the personality dimension with the best predictive power. These findings reveal that: (1) individual differences influence who takes music lessons and for how long, (2) personality variables are at least as good as cognitive variables at predicting music training, and (3) future correlational studies of links between music training and non-musical ability should account for individual differences in personality.
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Emergence of Individuality in Genetically Identical Mice
Julia Freund et al.
Science, 10 May 2013, Pages 756-759
Abstract:
Brain plasticity as a neurobiological reflection of individuality is difficult to capture in animal models. Inspired by behavioral-genetic investigations of human monozygotic twins reared together, we obtained dense longitudinal activity data on 40 inbred mice living in one large enriched environment. The exploratory activity of the mice diverged over time, resulting in increasing individual differences with advancing age. Individual differences in cumulative roaming entropy, indicating the active coverage of territory, correlated positively with individual differences in adult hippocampal neurogenesis. Our results show that factors unfolding or emerging during development contribute to individual differences in structural brain plasticity and behavior. The paradigm introduced here serves as an animal model for identifying mechanisms of plasticity underlying nonshared environmental contributions to individual differences in behavior.
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Developmental constraints on behavioural flexibility
Kay Holekamp, Eli Swanson & Page Van Meter
Philosophical Transactions of the Royal Society: Biological Sciences, 19 May 2013
Abstract:
We suggest that variation in mammalian behavioural flexibility not accounted for by current socioecological models may be explained in part by developmental constraints. From our own work, we provide examples of constraints affecting variation in behavioural flexibility, not only among individuals, but also among species and higher taxonomic units. We first implicate organizational maternal effects of androgens in shaping individual differences in aggressive behaviour emitted by female spotted hyaenas throughout the lifespan. We then compare carnivores and primates with respect to their locomotor and craniofacial adaptations. We inquire whether antagonistic selection pressures on the skull might impose differential functional constraints on evolvability of skulls and brains in these two orders, thus ultimately affecting behavioural flexibility in each group. We suggest that, even when carnivores and primates would theoretically benefit from the same adaptations with respect to behavioural flexibility, carnivores may nevertheless exhibit less behavioural flexibility than primates because of constraints imposed by past adaptations in the morphology of the limbs and skull. Phylogenetic analysis consistent with this idea suggests greater evolutionary lability in relative brain size within families of primates than carnivores. Thus, consideration of developmental constraints may help elucidate variation in mammalian behavioural flexibility.