Effects of processing speed on cerebral asymmetry for left- and right-oriented faces

What Affects Facing Direction in Human Facial Profile Drawing? A Meta-Analytic Inquiry

Two meta-analyses were conducted to examine two potential sources of spatial orientation biases in human profile drawings by brain-intact individuals. The first examined profile facing direction as function of hand used to draw. The second examined profile facing direction in relation to directional scanning biases related to reading/writing habits. Results of the first meta-analysis, based on 27 study samples with 4171 participants, showed that leftward facing of profiles (from the viewer's perspective) was significantly associated with using the right hand to draw. The reading/writing direction meta-analysis, based on 10 study samples with 1552 participants, suggested a modest relationship between leftward profile facing and primary use of a left-to-right reading/writing direction. These findings suggest that biomechanical and cultural factors jointly influence hand movement preferences and in turn the direction of facing of human profile drawings.

The Lateralizer: a tool for students to explore the divided brain

Despite a profusion of popular misinformation about the left brain and right brain, there are functional differences between the left and right cerebral hemispheres in humans. Evidence from split-brain patients, individuals with unilateral brain damage, and neuroimaging studies suggest that each hemisphere may be specialized for certain cognitive processes. One way to easily explore these hemispheric asymmetries is with the divided visual field technique, where visual stimuli are presented on either the left or right side of the visual field and task performance is compared between these two conditions; any behavioral differences between the left and right visual fields may be interpreted as evidence for functional asymmetries between the left and right cerebral hemispheres. We developed a simple software package that implements the divided visual field technique, called the Lateralizer, and introduced this experimental approach as a problem-based learning module in a lower-division research methods course. Second-year undergraduate students used the Lateralizer to experimentally challenge and explore theories of the differences between the left and right cerebral hemispheres. Measured learning outcomes after active exploration with the Lateralizer, including new knowledge of brain anatomy and connectivity, were on par with those observed in an upper-division lecture course. Moreover, the project added to the students' research skill sets and seemed to foster an appreciation of the link between brain anatomy and function.

Perceptual asymmetry for chimeric stimuli in children with early unilateral brain damage

The present study used a chimeric stimuli task to assess the magnitude of the left-hemispace bias in children with congenital unilateral brain damage (n = 46) as compared to typically developing matched controls (n = 46). As would be expected, controls exhibited a significant left-hemispace bias. In the presence of left hemisphere (LH) damage, the left-hemispace preference was found to be present, but attenuated, whereas right hemisphere (RH) damage resulted in a less lateralized process. Examination of lesion severity revealed that large lesions in the RH were associated with a reversal of the typical left-hemispace bias, while small lesions resulted in a left bias approximating that of controls. In contrast, the left-hemispace preference in children with LH damage was similar across lesion size. We conclude that damage to either hemisphere early in brain development may alter hemispheric preference for processing of nonverbal stimuli, and that at least in the case of RH damage, alteration of the normal perceptual asymmetry may depend on the interaction between lesion side and severity.

Valence, gender, and lateralization of functional brain anatomy in emotion: a meta-analysis of findings from neuroimaging

We performed quantitative meta-analyses on 65 neuroimaging studies of emotion. In an earlier report (NeuroImage 16 (2002), 331). we examined the effects of induction method, specific emotions, and cognitive demand in emotional tasks. This paper focuses on the effects of emotional valence (positive vs negative and approach vs withdrawal) and gender on regional brain activations, with particular emphasis on hypotheses concerning lateralization of brain function in emotion. Overall, we found no support for the hypothesis of overall right-lateralization of emotional function, and limited support for valence-specific lateralization of emotional activity in frontal cortex. In addition, we found that males showed more lateralization of emotional activity, and females showed more brainstem activation in affective paradigms. The study provides evidence that lateralization of emotional activity is more complex and region-specific than predicted by previous theories of emotion and the brain.

Correlated auditory asymmetries in lexical and nonlexical tasks

Two experiments address the question of whether different auditory verbal tasks produce correlated asymmetries. The first shows that ear asymmetries from dichotic word and syllable tasks do in fact correlate, but not to asymmetry from a visual face processing task. The second replicates the correlation between word and syllable asymmetries and shows that this significant relationship does not extend to another dichotic task involving the recognition of emotional tones of voice. The results are viewed as consistent with a left-hemisphere based "auditory linguistic" process involved in recognizing both lexical and nonlexical materials.

The Benton-Van Allen faces: a lateralized tachistoscopic study

The Benton-Van Allen Facial Recognition Test (FRT) was adapted to a lateralized same-different task. The lateralized same targets were either physically identical to the central upright faces or had the same face identity but were transformed (3/4-views or shadowed faces). Faces were also modified to include or exclude external features. There was a left hemifield (right hemisphere) advantage only for the most difficult, shadowed faces. The absence of a left hemifield advantage for the matching of upright faces to identical or 3/4-view faces shows bilateral competence for face processing, both by physical and by face identity, and confirms previous observations that the FRT does not discriminate left from right hemisphere-damaged patients. Removal of external features affected performance in the right but not the left visual field, suggesting that the left hemisphere uses a less feature-dependent mechanism than the right hemisphere. This effect was only present in females, who were more lateralized than males.

Visual field differences for clockwise and counterclockwise mental rotation

Geometric line drawings were presented to normal subjects in the left visual field (LVF) or right visual field (RVF) at various degrees of rotation from a centrally presented vertical standard. The task of the subject was to indicate with a reaction time (RT) response whether the laterally presented stimulus could be rotated into the vertical standard or if it was a rotated mirror image of the standard. In Study 1, an overall right hemisphere superiority was found for RT and accuracy on match trials. Most interestingly, interactions between Visual Field and Rotation Angle for the match accuracy data and between Visual Field and Direction of Rotation (clockwise or counterclockwise) for the match RT slopes were found. These interactions suggested that clockwise rotations were more readily performed in the LVF and counterclockwise rotations in the RVF, consistent with other literature for mental rotation. The purpose of Study 2 was to replicate this finding of visual field differences for rotation direction using a design in which direction and degree of rotation were varied orthogonally. No main effect of Visual Field was found. However, significant interactions between Visual Field and Rotation Angle were found for both RT and accuracy, confirming the presence of visual field differences for rotation direction in a new sample of subjects. These differences were discussed in terms of the possibly greater relevance of medially directed stimuli and a possible hemispheric bias for rotation direction, and in terms of interhemispheric transmission factors.