Genes, cognition and dyslexia: learning to read the genome

Studies of dyslexia provide vital insights into the cognitive architecture underpinning both disordered and normal reading. It is well established that inherited factors contribute to dyslexia susceptibility, but only very recently has evidence emerged to implicate specific candidate genes. In this article, we provide an accessible overview of four prominent examples--DYX1C1, KIAA0319, DCDC2 and ROBO1--and discuss their relevance for cognition. In each case correlations have been found between genetic variation and reading impairments, but precise risk variants remain elusive. Although none of these genes is specific to reading-related neuronal circuits, or even to the human brain, they have intriguing roles in neuronal migration or connectivity. Dissection of cognitive mechanisms that subserve reading will ultimately depend on an integrated approach, uniting data from genetic investigations, behavioural studies and neuroimaging.     

For efficient navigational search, humans require full physical movement, but not a rich visual scene

During navigation, humans combine visual information from their surroundings with body-based information from the translational and rotational components of their movement. Theories of navigation focus on the role of visual and rotational body-based information, even though experimental evidence shows they are not sufficient for complex spatial tasks. To investigate the contribution of all three sources of information, we asked participants to search a computer-generated virtual room for targets. Participants were provided with only visual information or with visual information supplemented with body-based information for all movement (walk group) or rotational movement (rotate group). The walk group performed the task with near-perfect efficiency, irrespective of whether a rich or impoverished visual scene was provided. The visual-only and rotate groups were significantly less efficient and frequently searched parts of the room at least twice. These results suggest that full physical movement plays a critical role in navigational search, but only moderate visual detail is required.     

Effects of enclosure size on sexual behavior of Japanese quail (Coturnix japonica)

The authors determined whether results of experiments on copulatory and affiliative behavior of pairs of Japanese quail (Coturnix japonica) conducted in a closely confining apparatus would predict behavior in a large enclosure in which female quail could avoid contact with male quail. As found previously in studies of closely confined quail, in a large enclosure containing numerous barriers, both unmated female quail and mated female quail laying unfertilized eggs were more likely to remain near a confined male quail than were mated female quail laying fertilized eggs. Furthermore, the number of copulations that a pair engaged in when closely confined predicted the number of copulations that they engaged in when they were in the large enclosure. Patterns of affiliation and of mating in a confining laboratory apparatus thus predicted behavior in a larger enclosure that provided female quail with opportunity to avoid contact with male quail.     

Citation Analysis of Skinner's Verbal Behavior: 1984-2004

The present study undertook an updated citation analysis of Skinner's (1957)Verbal Behavior. All articles that cited Verbal Behavior between 1984 and 2004 were recorded and content analyzed into one of five categories; four empirical and one nonempirical. Of the empirical categories, studies that employed a verbal operant from Skinner's analysis were assigned to either basic, applied, or observational categories. Empirical studies that did not employ a verbal operant were categorized as other-empirical. The total number of citations remained stable across the review period and averaged just over 52 per year. Of these, 80% were from nonempirical articles, 13.7% were from other-empirical articles, 4% were from applied articles, 1.4% were from basic articles, and 0.9% were from observational articles. An "obliteration" analysis was also conducted to identify articles that employed Skinner's verbal operant terms but did not cite Verbal Behavior. This analysis identified 44 additional articles, suggesting that a degree of obliteration had occurred in the half century since the publication of Verbal Behavior. In particular, the analysis suggests that the verbal operant of manding has sufficient presence in the applied empirical literature to render citation of Verbal Behavior redundant. Overall, Verbal Behavior continues to make an important contribution to the psychological literature.     

Unsupervised discovery of nonlinear structure using contrastive backpropagation

We describe a way of modeling high-dimensional data vectors by using an unsupervised, nonlinear, multilayer neural network in which the activity of each neuron-like unit makes an additive contribution to a global energy score that indicates how surprised the network is by the data vector. The connection weights that determine how the activity of each unit depends on the activities in earlier layers are learned by minimizing the energy assigned to data vectors that are actually observed and maximizing the energy assigned to "confabulations" that are generated by perturbing an observed data vector in a direction that decreases its energy under the current model.     

Allocentric spatial memory in humans with hippocampal lesions

An immersive virtual reality (IVR) system was used to investigate allocentric spatial memory in a patient (PR) who had selective hippocampal damage, and also in patients who had undergone unilateral temporal lobectomies (17 right TL and 19 left TL), their performance compared against normal control groups. A human analogue of the Olton [Olton (1979). Hippocampus, space, and memory. Behavioural Brain Science, 2, 315] spatial maze was developed, consisting of a virtual room, a central virtual circular table and an array of radially arranged up-turned 'shells.' The participant had to search these shells in turn in order to find a blue 'cube' that would then 'move' to another location and so on, until all the shells had been target locations. Within-search errors could be made when the participants returned to a previously visited location during a search, and between-search errors when they revisited previously successful, but now incorrect locations. PR made significantly more between-search errors than his control group, but showed no increase in within-search errors. The right TL group showed a similar pattern of impairment, but the left TL group showed no impairment. This finding implicates the right hippocampal formation in spatial memory functioning in a scenario in which the visual environment was controlled so as to eliminate extraneous visual cues.     

Gender-typed play and amniotic testosterone

Sex differences in play are apparent in a number of mammalian species, including humans. Prenatal testosterone may contribute to these differences. The authors report the first attempt to correlate gender-typed play in a normative sample of humans with measurements of amniotic testosterone (aT). Testosterone was measured in the amniotic fluid of 53 children (31 boys and 22 girls). A strong sex difference was observed in aT and, at ages 4.75 to 5.8 years, on a modified version of the Child Game Participation Questionnaire. Hierarchical regression analyses on the entire group and within-sex correlations suggested that variations in aT did not contribute to individual differences in game participation as reported by the mother. A critique of explanations for this finding is presented.     

Assessing measurement equivalence across rating sources: a multitrait-multirater approach

Research examining the structure of multisource performance ratings has demonstrated that ratings are a direct function of both who is doing the rating (rating source) as well as what is being rated (performance dimension). A separate line of research has focused on the extent to which performance ratings are equivalent across sources. To date no research has examined the measurement equivalence of multisource ratings within the context of both dimension and rating source direct effects on ratings. We examine the impact of both performance dimension and rating source as well as the degree of measurement equivalence across sources. Results indicate that (a) the impact of the underlying performance dimension is the same across rating sources, (b) the impact of rating source is substantial and only slightly smaller than the impact of the underlying performance dimension, and (c) the impact of rating source differs substantially depending on the source.     

Derived stimulus relations, semantic priming, and event-related potentials: testing a behavioral theory of semantic networks

Derived equivalence relations, it has been argued, provide a behavioral model of semantic or symbolic meaning in natural language, and thus equivalence relations should possess properties that are typically associated with semantic relations. The present study sought to test this basic postulate using semantic priming. Across three experiments, participants were trained and tested in two 4-member equivalence relations using word-like nonsense words. Participants also were exposed to a single- or two-word lexical decision task, and both direct (Experiment 1) and mediated (Experiments 2 and 3) priming effects for reaction times and event-related potentials were observed within but not across equivalence relations. The findings support the argument that derived equivalence relations provides a useful preliminary model of semantic relations.     

Avoidance of relatively aggressive male Japanese Quail (Coturnix japonica) by sexually experienced conspecific females

Sexually experienced female Japanese quail (Coturnix japonica) that are offered a choice between 2 conspecific males previously observed engaging in an aggressive encounter prefer to affiliate with the less aggressive male. The authors determined whether this apparent preference for less aggressive males results from females approaching less aggressive individuals or avoiding more aggressive individuals. The authors found that females that had seen 2 males fight before choosing, in counterbalanced order, between each of them and a neutral stimulus were indifferent to less aggressive males but avoided more aggressive males. The results are consistent with the view that in species in which male courtship and mating are potentially harmful to females, females keep away from relatively aggressive males in order to avoid the physical punishment that can result from contact with them.