Chapter 6. The value of left and right

Around 90% of humans prefer their right hand for unimanual actions and are left-hemisphere dominant for language functions; a pattern far from negligible. The phenomena of handedness and cerebral lateralization for language are presented along with the different theories that attempt to explain the presence of these functional asymmetries. The focus is on the adaptive advantages both on the individual and the population level. Most importantly, the intriguing question of why humans are right-handed and left-brained and not the other way around is tackled; a number of evolutionary, cultural, and genetic accounts are presented, along with theories that explain the observed pattern of asymmetries by means of the different properties of the two cerebral hemispheres.

Journal of Experimental Psychology: General, 2009

Polemikos, N. & Papaeliou, C. (2000). Sidedness preference as an index of organization of laterality. Perceptual & Motor Skills, 91 (3 Pt 2), 1083-1090., 2000

A rightward bias to all forms of sidedness seems to be particularly human and perhaps characteristic of every human society. However, this phenomenon has been studied mainly in relation to lateralization of handedness and language. This study investigated the consistency of right- and nonright-handed individuals in prefer ring the same side for foot, eye, and ear using Coren's Lateral Preference Inventory. The sample of 194 students, 91 boys and 103 girls, ranging in age from 11.5-14.5 years (M age 13.2 yr.) was recruited from public junior high schools in a rural area in Greece on the island of Rhodes. Despite the dominance of the right side observed in handedness, footedness, eyedness, and earedness, this tendency was not equally strong in all four indexes of lateral preference, with handedness showing comparatively the strongest tendency and earedness showing comparatively the weakest tendency. Moreover, the strength of preference for the same side for foot, eye, and ear was significantly weaker in nonright-handed individuals compared to right handed individuals. These results agree with the hypothesis that nonright-handers may have reduced rather than reversed asymmetry.

Emotion Review, 2011

Rutherford and Lindell (2011) review an extensive literature on lateralization of emotion. As they note, an important issue surrounding this question is the nature of emotion, which bears on what, precisely, is lateralized. The present comments are intended to broaden the context of the review, by considering lateralization from the standpoint of a bivariate model of evaluative processes and a neuroevolutionary perspective.

Cortex

The visual half-field technique has been shown to be a reliable and valid neuropsychological measurement of language lateralisation, typically showing higher accuracy and faster correct responses for linguistic stimuli presented in the right visual field (RVF) than left visual field (LVF). The RVF advantage corresponds to the well-known dominance of the left hemisphere (LH) in processing language(s). However, clinical and experimental neuroscientists around the globe use different variations of the visual half-field paradigm, making direct comparisons difficult. The current study used a word/non-word visual half-field paradigm with translingual stimuli. In total, 496 participants from seven European countries were investigated: Belgium (64), England (49), Germany (85), Italy (34), The Netherlands (87), Norway (51), and Switzerland (126), covering six international languages (Dutch, English, French, German, Italian, Norwegian). All language groups revealed a significant RVF/LH advantage in accuracy and reaction times that accounted for up to 26.1% of the total variance in performance. We found some variation in the degree of the RVF/LH advantage across language groups, accounting for a maximum of 3.7% of the total variance in performance. The RVF/LH advantage did not differ between subsamples speaking English, French or German as first or second languages or between monolingual and early/late bi/multilinguals. The findings suggest that the translingual lexical decision task (TLDT) is a simple but reliable measurement of language lateralisation that can be applied clinically and experimentally across linguistic and national boundaries.

NeuroImage, 2005

The nature of cerebral asymmetry of the language function is still not fully understood. Two main views are that laterality is best explained (1) by left cortical specialization for the processing of spectrally rich and rapidly changing sounds, and (2) by a predisposition of one hemisphere to develop a module for phonemes. We tested both of these views by investigating magnetic brain responses to the same brief acoustic stimulus, placed in contexts where it was perceived either as a noise burst with no resemblance of speech, or as a native language sound being part of a meaningless pseudoword. In further experiments, the same acoustic element was placed in the context of words. We found reliable left hemispheric dominance only when the sound was placed in word context. These results, obtained in a passive odd-ball paradigm, suggest that neither physical properties nor phoneme status of a sound are sufficient for laterality. In order to elicit left lateralized cortical activation in normal right-handed individuals, a rapidly changing spectrally rich sound with phoneme status needs to be placed in the context of frequently encountered larger language elements, such as words. This demonstrates that language laterality is bound to the processing of sounds as units of frequently occurring meaningful items and can thus be linked to the processes of learning and memory trace formation for such items rather than to their physical or phonological properties.

Neuropsychologia, 2003

In dichotic listening, a right ear advantage for linguistic tasks reflects left hemisphere specialization, and a left ear advantage for prosodic tasks reflects right hemisphere specialization. Three experiments used a response hand manipulation with a dichotic listening task to distinguish between direct access (relative specialization) and callosal relay (absolute specialization) explanations of perceptual asymmetries for linguistic and prosodic processing. Experiment 1 found evidence for direct access in linguistic processing and callosal relay in prosodic processing. Direct access for linguistic processing was found to depend on lexical status (Experiment 2) and affective prosody (Experiment 3). Results are interpreted in terms of a dynamic model of hemispheric specialization in which right hemisphere contributions to linguistic processing emerge when stimuli are words, and when they are spoken with affective prosody.

Cortex, 1991

Behavioral Lateralization in Vertebrates, 2012

Investigations of human laterality suggest motor preference is not arbitrary, but rather represents an evolutionary bias stemming from the asymmetric organization of underlying neural function for skilled action. The most prominent manifestation of lateralized motor behavior in humans is right-handedness. While human right-handedness provides a highly reliable marker for the brain organization of left hemisphere language function, the causal evolutionary link between the two remains highly controversial. Once considered a unique hallmark of human evolution, structural neuroanatomical investigations have now revealed homologous asymmetric language regions (larger left hemisphere) in great apes, providing evidence for a common mechanism underlying communication processes in humans and apes. However, whether this translates into a handedness bias in great apes remains highly controversial. This chapter discusses the unique characteristics of human and non-human primate handedness within an evolutionary framework and explores new manual laterality findings, celebrating the emergence of multimodal, quantitative methodologies aimed at bridging the gap between studies of brain and behavior.