Asymmetry and performance: toward a neurodevelopmental theory

Hemispheric asymmetry implies the existence of developmental influences that affect one hemisphere more than the other. However, those influences are poorly understood. One simple view is that asymmetry may exist because of a relationship between a mental process' degree of lateralization and how well it functions. Data scaling issues have largely prevented such investigations, but it is shown that scaling effects are minimized after correction for ceiling and floor effects. After correction, lateralization-performance correlations are pervasive. However, while some correlations are positive, others are negative, with the direction depending on the underlying lateralized process. Two hypotheses are proposed that can account for these relationships by pointing either to individual differences in maturation of the corpus callosum or to developmental limits encountered at different ages of childhood. Their investigation should contribute toward a neurodevelopmental theory of hemispheric asymmetry.     

The advantage of mentally rotating clockwise

The time taken to decide whether a character is shown in its mirror or normal version has been shown to increase approximately linearly with the angular departure from an up-right position. Additionally, in some studies, decisions took longer for clockwise tilted characters than for counterclockwise tilted ones. Other studies do not report the latter effect. We argue that inconsistencies across studies are caused by variance in participants' strategies. The task employed here was specifically designed to bring these strategies and thereby the direction of rotation under experimental control. From the EEG recorded during the rotation period, we extracted an event-related slow potential whose amplitude is sensitive to the amount of mental rotation. In both strategy conditions, the slow potential's amplitude was lower for clockwise than for counterclockwise rotations. We take this as evidence that mental rotation of alphanumeric characters is easier in a clockwise than in a counterclockwise direction.     

Fifty years of dichotic listening research - still going and going and…

This year celebrates 50 years of research in auditory laterality and hemispheric asymmetry, using a dichotic listening approach. The discovery of the "right ear advantage" in 1961 by Doreen Kimura to dichotic presentations of phonetic stimuli paved the way for new studies of how speech perception and related language processes are lateralized in the human brain. The articles in this special issue, celebrating the first 50 years of dichotic listening research, reveal both the breadth and depth of current research, with contributions spanning from basic research to clinical applications, from behavioral studies to studies using advanced neuroimaging techniques, and with contributions from all over the world. It is my hope as Guest Editor that the next 50 years will be as productive as the first 50 years.     

Oppositional Children Differ from Healthy Children in Frontal Brain Activation

An atypical EEG pattern of frontal brain activation, which has been found in children and adults with emotional disorders, also is hypothesized to be present in disruptive behavior disorders. One hundred nineteen children (4 $\frac{1}{2}$ and 8 years of age) were examined with regard to the following questions: (1) Do children who are diagnosed with oppositional defiant disorder (ODD) exhibit an atypical pattern of frontal brain activation? (2) Can this pattern be demonstrated in preschool children (4 $\frac{1}{2}$ years of age) as well as in school children (8 years)? (3) Are there gender differences in these patterns similar to those that have been demonstrated in adults? Spontaneous EEG activity was subjected to power spectral analysis. In oppositional preschool and elementary school girls, the well-known pattern of lower left frontal than right frontal activation emerged that has been found previously in emotionally disordered children. Healthy girls showed no frontal brain asymmetry at 4 $\frac{1}{2}$ years of age, and left frontal activation at 8 years. In contrast, healthy boys demonstrated a greater right than left frontal activation, whereas ODD boys did not display any frontal brain asymmetry. Thus, the pattern of frontal brain activation seems to be gender-specific. The atypical activation pattern in oppositional children is hypothesized to be a biological substrate of negative affective style.     

拓扑性质知觉的大脑半球功能不对称性研究

本文以视觉的拓扑知觉理论为指导进行大脑半球功能不对称性的研究。全文共有三个实验,考察了辨别扭扑性质差异和其它几何性质差异时大脑半球的功能不对称性．拓扑性质差异包括洞（封闭性）的差异和内外关系的差异．实验结果显示：对于右利手被试,辨别拓扑性质差异时,左半球有优势。辨别距离和朝向等几何性质差异时,右半球有优势或没有统计显著的大脑半球功能不对称性。     

Extinction-like effects in normals: independence of localization and response selection

An extinction-like effect in normal subjects was previously elicited when a low-salience target in the left was simultaneously presented with a highly salient distractor in the right visual hemifield, but not vice versa (Pollmann, 1996). We investigated in four experiments whether this extinction-like effect depends on (a) explicit localization and (b) response competition. It was found that the extinction-like effect could be replicated in the absence of both. In contradistinction to our previous results, low-salience distractors had no effect on pop-out target search. This showed that explicit spatial localization demands lead to low-salience distractor interference on pop-out search.     

Gender differences in salivary alpha-amylase and attentional bias towards negative facial expressions following acute stress induction

This study investigated gender differences in two key processes involved in anxiety, arousal and attentional bias towards threat. Arousal was assessed using salivary alpha-amylase (sAA), a biomarker of noradrenergic arousal and attention bias using a dot-probe task. Twenty-nine women and 27 men completed the dot-probe task and provided saliva samples before and after a stress induction [cold pressor stress (CPS) test]. Women displayed a significant increase in arousal (sAA) following the stressor compared to men, who displayed a significant reduction in arousal. Reaction time data revealed a significant avoidance of threat in women at baseline, but a significant change to an attention bias towards threat following the stressor. Men did not significantly respond to the stressor in terms of attentional bias. These findings suggest that women are more reactive to a stressor than men, and display an initial avoidance response to threat, but an attentional bias towards threat following stress.     

How does reading direction modulate perceptual asymmetry effects?

Left-side bias effects refer to a bias towards the left side of the stimulus/space in perceptual/visuospatial judgments, and are argued to reflect dominance of right hemisphere processing. It remains unclear whether reading direction can also account for the bias effect. Previous studies comparing readers of languages read from left to right with those read from right to left (e.g., French vs. Hebrew) have obtained inconsistent results. As a language that can be read from left to right or from right to left, Chinese provides a unique opportunity for a within-culture examination of reading direction effects. Chinese participants performed a perceptual judgment task (with both face and Chinese character stimuli; Experiment 1) and two visuospatial attention tasks (the greyscales and line bisection tasks; Experiment 2) once before and once after a reading task, in which they read Chinese passages either from left to right or from right to left for about 20 min. After reading from right to left, participants showed significantly reduced left-side bias in Chinese character perceptual judgments but not in the other three tasks. This effect suggests that the role of reading direction on different forms of left-side bias may differ, and its modulation may be stimulus-specific.