Functions of Brain Lateralization :

1
supervisors E. Hogervorst, W. Sellers 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 for
spontaneous daily actions and for an experimental
task in 36 bonobos
Method
Laterality in social behaviour
19 bonobos from 2 zoos (Twycross, UK Apenheul,
Holland). 155 days of observations. direct
observation (dictaphone). ad libitum group
sampling. I observed spontaneous social
interactions. Data collected identity of the
individuals, side of approach, reaction of the
approached individual, interaction following the
approach, relative position during the interaction
Functions of Brain Lateralization Advantages
at the individual-level improves brain
efficiency allows simultaneous processing of
different processes, avoids hemispheric
competition, avoids replication of functions.
improves 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 this
population-level laterality may have been
selected under social pressures, to improve the
ability to interact with conspecifics. If most
individuals display the same laterality this may
create a certain predictability in behaviour and
facilitate social interactions. The theory
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 analysis preferences of the
  approaching individuals could depend on the
  approached individual identity. e.g. the dominant
  male specifically induced 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
preferentially place themselves with the congener
on their left side. Preferences to place itself
relative to the congener would reflect a visual
field preference to monitor the congener, as
evidenced in low vertebrates.

• During the interaction
• - approaching individuals Bokela and Luo
  preferred to have the approached individual in
  the left visual field. Group-level bias to have
  the approached individual in the left visual
  field.
• approached individuals Bokela was more often
  located in the left visual field of approached
  individuals. Banya had approaching individuals
  more often in its left visual field.
• No group-level bias, but trend for the
  approaching individuals to be located more often
  in the left visual field of the approached
  individual.
• - Approached individuals reacted by accept
  more often when the approaching individual was
  located in the left visual field.

Conclusion
Social related Hypothesis Does laterality exist
in social behaviour 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. Does the
interaction depend on the side of approach or
relative position during interaction ? 5. Do
lateral preferences depend on the interaction
type, relative social status, age/sex class ?
Evidences of asymmetries in the approach and the
relative position during interactions
individual and group-level biases, mostly left
sided. The presence of asymmetries in the social
behaviour, and the influence of the specific
relationship between the two individuals
involved, would support the social related
hypothesis.
Handedness in spontaneous actions (non-social and
social) and for an experimental bimanual task
Methods 36 bonobos. 3 zoos (Twycross, UK
Stuttgart, Germany Apenheul, Holland). March to
October 2006 - spontaneous actions direct
observation (dictaphone), ad libitum group
sampling. - experimental task 10 days of tests
per group. videos. focal sampling.
90 of humans are right-handed. Despite an
important database, handedness in non-human
primates is highly controversial hand
preferences are usually weak and individual (no
group-level bias). almost no data in bonobos. We
studied hand use in 36 bonobos, for 3 groups of
behaviours.

• Results
• Spontaneous actions analysis in progress. we
  present preliminary data from a subsample of
  subjects
• non-social actions individual preferences for
  the behaviours reach, eat, pull grass out, cross
  arms, hang, carry object.
• social actions strong individual preferences
  for the behaviours ventral embrace, play, drag,
  grasp, hit, touch, hold hand cradle, pick up
  and carry baby. Gestures display, invite.
• experimental bimanual task (frequency) data for
  29 bonobos. strong individual
• preferences (mean pref. 78). 11 right-handers,
  15 left-handers, 3 not lateralized.

- non-social actions e.g. food related. only 5
studies on hand preference in bonobos and on
small groups (N 15). Evidences of manual
preferences.

• social actions actions occuring in the social
  context. Along with the gestural origin of
  language hypothesis, the left hemisphere may
  have controlled gestures prior to the emergence
  of speech, and may have led to a left hemisphere
  control of language.
• A right hand preference for gesturing has been
  reported in chimpanzees, which suggests a left
  cerebral control of gestures, and would support
  the hypothesis. Few data in the bonobo, despite
  of its outstanding linguistics skills.

Conclusion Evidences of manual preferences for
several actions suggesting brain lateralization
for manual functions

• experimental task the more complex the task is,
  the stronger the preferences are.
• We assessed preferences with a complex task
  requiring a bimanual coordination along with a
  precise action holding a tube while reaching for
  food inside with the other hand. This tube
  task has revealed strong preferences in other
  species, and right-handedness in chimpanzees.
  Bonobos had never been tested.

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