Function of Brain Lateralization

1
supervisors E. Hogervorst, W. Sellersexternal
supervisor C. Blois-Heulin
Amandine Chapelain
Department of Human Sciences, Loughborough
University, LE11 3TU, England
a.s.chapelain_at_lboro.ac.uk
Laterality in social behaviour and handedness in
social manual actions and gestures in bonobos
Method
Laterality in social behaviour
19 bonobos from 2 zoos (Twycross, UK Apenheul,
Holland) 155 days of observations. direct
observation, ad libitum sampling, observe
spontaneous social interactions. Data collected
identity of individuals, side of approach,
reaction of the approached individual,
interaction following the approach, relative
position during the interaction
Function of Brain Lateralization Advantages at
the individual-level improves brain efficiency
allows simultaneous processing of different
processes, avoids hemispheric competition, avoids
replication of functions, and may improve
cognitive skills and behavioural
efficiency. Advantages of population-level
laterality social ? The direction of
asymmetries is often the same in most individuals
of a population. Based on evidences from low
vertebrates, a new theory proposes that
population-level laterality may have been
selected to improve the ability to interact with
conspecifics, on the ground that if most
individuals display the same laterality this may
create a certain predictability in behaviour and
facilitate social interactions. It predicts that
social related functions would be lateralized and
that laterality would be present in social
behaviour.
Results
Analysis in progress, we present here data from
the one month pilot study (9 bonobos, Twycross)

• Approach before the interaction
• - Bokela and Banya preferred to approach others
  from their left visual field, Cheka from their
  right visual field. No group-level bias to
  approach others from one visual field.
• - Banya was approached more often from its left
  visual field. No group-level bias to be
  approached from one visual field more often.
• - Dyad-level the preferences of the approaching
  individuals may depend on the approached
  individual identity. i.e. the dominant male
  seemed to induce preferences in the approach.
• Approached individuals reacted by accept
  more often when approached in the left visual
  field.

Support for the social related hypothesis Chicks
the hierarchy is maintained better when the
individuals are lateralized. Fishes social
species show population-level laterality,
non-social species tend to show only
individual-level laterality. Primates baboons
prefer to use the Left visual field to monitor
the congener. Preferences to place themselves
relative to the congener may indicate a visual
field preference to monitor the congener.

• During the interaction
• - approaching individuals Bokela and Luo
  preferred to have the conspecific in the left
  visual field. Group-level bias to have the
  approached individual in the left visual field
  (especially for positive interactions).
• approached individuals Bokela was more often
  located in the left visual field of approached
  individuals. Banya had approaching individuals
  more often in her left visual field.
• No group-level bias, but trend for the
  individuals to be located more often in the left
  visual field of the approached individual
  (especially for neutral interactions).
• - Approached individuals acted by accept more
  often when the approaching individual was located
  in the left visual field.

Conclusion
Social related Hypothesis Does laterality exist
in social interactions in bonobos ? 1. Is there
a preferred side to approach a congener ? 2.
Does the reaction of the approached subject
depend on the side of approach ? 3. Is there a
side preference to place itself relative to the
congener during dyadic interactions ? 4. Do
lateral preferences depend on interaction type,
relative social status, age/sex class ? 5. Does
the interaction depend on the side of approach or
relative position during interaction ?
Evidences of asymmetries in approach and relative
placement during social interactions individual
and group-level biases, mostly left sided. The
presence of asymmetries in social behaviour and
the possible effect of the interaction type and
of the specific relationship between the
individuals involved would support the hypothesis.
Handedness in social manual actions and gestures
Along with the social related hypothesis,
group-level biases in social hand use would be
expected, to facilitate social interactions.
Laterality in social manual actions can also be
related to the discussion on the origins of
language and of its lateralization. The
hypothesis of the gestural origin of language
states that the left hemisphere may have
controlled intentional gestures prior to the
emergence of speech, and may have led to a left
hemisphere control of language. There are
evidences of right hand preference for gesturing
in chimpanzees (work of Hopkins et al.), which
would indicate a left cerebral control of
gestures and support the hypothesis. Despite its
outstanding linguistics skills, few data have
been collected in bonobos.
Methods 35 bonobos. 3 zoos (Twycross, UK
Stuttgart, Germany Apenheul, Holland). March to
October 2006. direct observation, ad libitum
sampling. Data collected manual actions that
occurred in the social context, including
spontaneous social interactions between the
bonobos, and spontaneous gestures directed to the
keeper. Results Analysis is in progress, we
present here preliminary data for 12 bonobos. We
found individual hand preferences for the
following behaviours see table.
Conclusion Evidences of individual preferences.
no group-level bias. Slight trend for
preferential use of the right hand in accordance
with the hypothesis, but small sample size of
subjects and data points per subject.
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