Abstract
Human referential communication is often adjusted to the
presumed knowledge and characteristics of addressees
(“audience design”; Clark, 1996). For instance, utterances
directed towards children show systematic verbal and
gestural adjustments (Snow and Ferguson, 1977; Campisi
and Ozyurek, 2013). However, it remains unclear which
neurobiological mechanisms drive communicators to
implement those adjustments, and alter them on the
basis of the ongoing communicative behaviour. Here
we explore whether oxytocin, a neuropeptide known to
promote prosocial behaviours and to sharpen processing
of socially-relevant information (Bartz et al., 2011),
biases communicative adjustments towards prosocial
beliefs or towards the information acquired during an
interaction. Fifty-eight healthy male adults participated
in a randomized, double-blind, placebo controlled
experiment involving the intranasal administration
of oxytocin (24 IU). Participants communicated to an
addressee the location of a token in a 3x3 grid (visible
only to the communicator) by means of their movements
on the grid (visible to both communicator and addressee).
Participants spontaneously marked the token’s position
by waiting longer on that location as compared to
other locations visited during their movements on the
grid (“TimeOnTarget” effect). Crucially, participants
were made to believe that they interacted with a child
and with another adult, in alternation. In fact, an adult
confederate performed the role of both addressees,
while remaining blind to which one of the two roles
she was performing in any given trial. Accordingly,
both performance and response times of the two
presumed addressees were matched. This feature of this
previously validated protocol (Newman-Norlund et al.,
2009; Stolk et al., 2013) allowed us to test how oxytocin
modulates communicative adjustments driven by the
mere belief of interacting with addressees with different
abilities, while matching their behaviour. If oxytocin
up-regulates prosocial behaviours, then intranasal
oxytocin should enhance belief-driven communicative
adjustments, increasing audience design effects when
compared to placebo administration. Alternatively, if
oxytocin sharpens the perception and saliency of social
information, then intranasal oxytocin should enhance
behaviour-related communicative adjustments, reducing
audience design effects when compared to placebo
administration. Participants believed they interacted with
different addressees, attributing to them different age and
cognitive abilities. Communication was effective (69%
correct, chance-level: 6.6%), with participants spending
longer time on the field containing the target. Participants
receiving placebo showed a larger TimeOnTarget
effect when they thought they were communicating
with a child. Crucially, participants receiving oxytocin
did not show a differential TimeOnTarget effect
between the two addressees. Further exploration of the
temporal dynamics of this between-group difference in
communicative adjustments revealed that, at the onset of
the communicative game, participants receiving oxytocin
had a longer TimeOnTarget when addressing a presumed
child. This effect disappeared over the course of the
experiment. Participants that received placebo showed
the opposite pattern. These findings shed light on a
neurobiological mechanism that modulates the balance
between two elements of audience design: belief-driven
and behaviour-driven adjustments. Oxytocin drives
interlocutors to adjust their communicative utterances
towards the actual behaviour experienced in addressees,
and away from their beliefs on the abilities of those
addressees.
