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Abstract:
In order to communicate efficiently, speakers have to
take into account which information they share with their
addressee (common ground) and which information
they do not share (privileged ground). Two views
have emerged about how and when common ground
influences language production. In one view, speakers
take common ground into account early on during
utterance planning (e.g., Brennan & Hanna, 2009).
Alternatively, it has been proposed that speakers’ initial
utterance plans are egocentric, but that they monitor
their plans and revise them if needed (Horton & Keysar,
1996). In an fMRI study, we investigated which neural
mechanisms support speakers’ ability to take into account
common ground, and at what stage during speech
planning these mechanisms come into play. We tested
22 pairs of native Dutch speakers (20 pairs retained in
the analysis), who were assigned to the roles of speaker
or listener for the course of the experiment. The speaker
performed the experiment in the MRI scanner, while the
listener sat behind a computer in the MRI control room.
The speaker performed a communicative and a noncommunicative
task in the scanner. The communicative
task was a referential communication game in which
the speaker described objects in an array to the listener.
The listener could hear the speaker’s descriptions over
headphones and tried to select the intended object on
her screen using a mouse. We manipulated common
ground within the communicative task. In the privileged
ground condition, the speaker saw additional competitor
objects that were occluded from the listener’s point of
view. In order to communicate efficiently, the speaker
had to ignore the occluded competitor objects. In the
control conditions, all relevant objects were in common
ground. The non-communicative task was identical to
the communicative task, except that the speaker was
instructed to describe the objects without the listener
listening. When comparing the BOLD response during
speech planning in the communicative and the noncommunicative
tasks, we found activations in the right
medial prefrontal cortex and bilateral insula, brain areas
involved in mentalizing and empathy. These results
confirm previous neuroimaging research that found that
speaking in a communicative context as compared to a
non-communicative context activates brain areas that
are involved in mentalizing (Sassa et al., 2007; Willems
et al., 2010). We also contrasted brain activity in the
privileged ground and control conditions within the
communicative task to tap into the neural mechanisms
that allow speakers to take common ground into account.
We again found activity in brain regions involved in
mentalizing and visual perspective-taking (the bilateral
temporo-parietal junction and medial prefrontal cortex).
In addition, we found a cluster in the dorsolateral
prefrontal cortex, a brain area that has previously been
proposed to support the inhibition of task-irrelevant
perspectives (Ramsey et al., 2013). Interestingly, these
clusters are located outside the traditional language
network. Our results suggest that speakers engage in
mentalizing and visual perspective-taking during speech
planning in order to compute common ground rather
than monitoring and adjusting their initial egocentric
utterance plans.
