Advances and retreats In laterality research

The pattern of intra-/inter-hemispheric interactions of left and right hemispheres in visual word processing

This study aimed to investigate the intra-/inter-hemispheric interactions during visual word processing, by manipulating stimulus onset asynchrony (SOA) in a primed-lateralized lexical decision task. To assess intra-/inter-hemispheric priming effects, identical prime-target pairs were presented in the same or opposite unilateral visual fields. The study found that the right visual field advantage (RVFA) was observed when Korean words were presented sequentially within hemispheres, indicating that the inherent characteristics of the two hemispheres, rather than differences in memory or linguistic aspects of lexical processing, contributed to the hemispheric asymmetry. Additionally, intra-hemispheric priming effects were symmetrical in both hemispheres, with similar increases in priming for words and nonwords from SOA 120 ms to SOA 600 ms. Furthermore, inter-hemispheric priming effects were asymmetrical, with stronger priming when stimuli were presented in a sequence of LH→RH than in RH→LH. These findings suggest that the intrinsic differences in lexical processing between the two hemispheres may be related to the asymmetric pattern of hemispheric interactions in visual word processing.

Left and right hemisphere contributions to physiognomic and verbal discrimination

The relative contributions of the right- and left-temporal lobes in rapid recognition of faces and letters were studied in patients with anterior right- or left-temporal lobe excisions and a matched control group. On the basis of findings in patients with unilateral and bilateral brain damage, it was hypothesized that left hemisphere damage would not change the reaction time of letters analyzed by the right hemisphere and that right hemisphere damage would not change the reaction time of faces analyzed by the left hemisphere. The hypothesis was supported for letters but not for faces. Patients in the right-temporal group, particularly those with large hippocampal removals, were slow to recognize faces in both visual fields. Two possible explanations for the findings with faces are explored: One holds that right hemisphere mechanisms are involved even when a face is presented to the left hemisphere for rapid recognition; the other holds that specialized encoding is carried out by the right hemisphere during learning, with the encoded template then being used by each hemisphere independently.

Toward a model to explain infant preferences by cerebral emotional asymmetry and hemisphere priming

This paper argues that the rightward preference observed in most infants can be described as the consequence of two characteristics of the human brain: (1) hemispheric asymmetry of processes underlying emotional experience and (2) priming of cerebral function. Ample research evidence supports each of these propositions, and they have gained increasing, though not universal, acceptance. In combination, they provide a sufficient explanation for several preferences which may have human survival value. They also produce several side-effects in human behavior which can be observed, but which appear to have no survival function.

A role for hemispheric asymmetry in human behavioral variability

A model is presented in which functional lateral specialization and selective hemisphere priming combine to provide a mechanism for behavioral variability. The model is tested and supported by two experiments in which lateral attentional priming produces significant reductions in between-subject and within-subject variability. These findings help us to understand the source of behavioral variability, broaden our knowledge of the gross structures and functions of the brain, provide information about the manipulation of perceived control, and offer a technique for increasing statistical power in a wide variety of research settings.