The pantomime of mental rotation: Left-handers are less lateralized.

INTRODUCTION: The conceptualization of skilled hand movements (praxis) may be grounded in hemispherically specialized functions. However, a left-hemispherical advantage of (tool-use) pantomime gestures and a right-hemispherical advantage of spatial gestures may be more prominent in right-handed than left-handed individuals. We therefore investigated the hypothesis that right-handed but not left-handed individuals show a superiority of the left hemisphere (/right-hand preference) for the execution of pantomime (rotation of an object) gestures as well as a right-hemispherical superiority (/left-hand preference) for gestures that depict spatial information (/positioning of an object). METHODS: 20 right- and 20 left-handed participants were asked in two experiments to demonstrate with their two hands how to move tachistoscopically (in the left (LVF) or right visual hemifields (RVF)) presented geometric objects of different rotations into an identical final position. Two independent blind raters evaluated the videotaped hand gestures employing the Neuropsychological Gesture (NEUROGES) Coding System. RESULTS: In contrast to left-handed individuals, right-handed individuals present increased pantomime - rotation gestures with the right hand and pantomime - position gestures with the left hand during stimuli presentation in either visual field. Left-handers showed significantly increased left-hand pantomime - rotation gestures during stimulus presentation within the LVF (only). DISCUSSION: Right-handed individuals increase their pantomime - rotation gestures with the right hand to depict motion but use their left hand for pantomime - position gestures to describe spatial relations of the objects. Left-handers do not show a clear lateralization of the right and left hand with regards to either handedness or hemispherically lateralized motor functions. The hemispherical lateralization of praxis functions is therefore more pronounced in right-handed than left-handed individuals.

Hemispheric specialization for nonverbal gestures depicting motion and space.

INTRODUCTION: The right hemispheric specialisation for mental rotation suggests a left hand preference for nonverbal gestures that depict spatial information. We therefore hypothesized that nonverbal depictions of spatial information are preferentially demonstrated by the left hand, i.e., are grounded in right hemispheric functions. METHODS: Right-handed participants were asked in two experiments to nonverbally demonstrate how to move tachistoscopically presented (in the left or right visual hemifields) geometric objects of different rotations into an identical final position. Two independent blind raters evaluated the videotaped hand gestures employing the Neuropsychological Gesture (NEUROGES) Coding System. RESULTS: Pantomime gestures increase in order to rotate gravitationally unstable objects whereas spatial relation presentation gestures increase when to nonverbally demonstrate a gravitationally stable object. Individuals preferred the right hand for pantomime gestures but the left hand for spatial relation presentation gestures. DISCUSSION: Individuals increase their pantomime gestures to nonverbally depict motion particularly with the right hand, i.e. the left hemisphere. In contrast, increased left hand spatial relation presentations gestures indicate that those gestures are of right hemispheric origin. Thus, the hemispherical lateralization of nonverbal gestures seems to depend on the hands' functional depiction.