(Amphithéâtre)
Kita, Sotaro
(Dept. of Experimental Psychology, University of Bristol)
Lausberg, Hedda
(Dept. of Neurology, Free University of Berlin)
Left-hand preference for co-speech gestures in
patients with complete callosal disconnection
The finding that right-handers with left hemisphere language dominance
prefer the right hand for co-speech gestures is a fundamental
argument for neuropsychological, psycholinguistic and recent evolutionary
theories on language and gesture that propose a close association
between speech and co-speech gesture production. However,
several studies have reported an equally frequent use of the right
and left hands in co-speech gestures, thus underlining the need to
establish an alternative hypothesis to explain this association.
The hand preference for spontaneous co-speech gestures during two
personal interviews was investigated in three right-handed patients
with complete callosotomy, one left-handed patient with complete
callosal infarction, and as control groups, fi ve right-handed patients
with partial callosotomy and ten right-handed healthy subjects.
Three of the four patients with complete callosal disconnection, all
with left hemisphere speech and motor dominance, exhibited a reliable
left-hand preference for co-speech gestures despite their left
hand agraphia and apraxia. The fourth patient with presumed bilateral
language production revealed a reliable right-hand preference
for co-speech gestures. No signifi cant right hand preference was
found in the two right-handed control groups but reliable individual
patterns, ranging from right hand preference to left hand preference
were observed.
It is concluded that the patterns of hand preference cannot be
explained by speech lateralisation nor by handedness. Co-speech
gestures can be generated in the right hemisphere, independently
from speech production, and may directly express different right
hemispheric functions such as emotional processes. In contrast to the traditional neuropsychological and psycholinguistic theories on
co-speech gesture production, the present fi ndings suggest a separability
of speech and gestural systems.
