dc.description.abstract
One of the most useful tools in the service of communication is language. However,
the neuro-cognitive basis of language has often been studied outside of its natural
niche and in isolation from its communicative function. This thesis examines the
neuro-cognitive processes that are at the basis of processing communicative intention
conveyed by language by employing a range of psycho- and neurolinguistic methods.
In particular, the present work focuses on two pragmatic phenomena: speech acts
and indirect speech acts. The following questions are asked: (1) Can the differences
in neural signatures of speech acts previously observed in the comprehension modality
also be found in speech production? (2) Is the right temporo-parietal junction,
an important node of the ToM network, causally involved in the comprehension of
indirect speech acts? (3) Do indirect speech acts systematically differ from direct
ones in psycholinguistic properties, whose processing is known to be reflected in
different neural processes? The general methodological approach taken here is to
use identical words or sentences but alter their pragmatic-communicative roles by
embedding them in different dialogic or situational contexts. This way, the communicative
function can be examined independently from the linguistic form used to
carry it out.
In a first study, the neural representations of naming and request actions were
examined. These were performed using the same utterance during speech production,
while subjects participated in an interactive communicative task and while
participants neural activity was recorded by electroencephalography. The aim was
to compare these findings to previous findings in the comprehension modalities.
We find that uttering the same words with different speech act functions (naming
and request) is associated with different electrophysiological signatures. These differences
are similar to those found when comparing the same two speech acts in
the comprehension modality. In particular, requests are associated with activations
of the motor system, supporting the idea that their intrinsic link to action is also
encoded in the brain.
The second study tested whether the comprehension of indirect speech acts relies
on the right-temporoparietal junction, a brain region thought to contribute to
Theory of Mind processes. To do so, activity in these brain regions was altered by means of (non-invasive) transcranial magnetic stimulation. Subjects were then
exposed to indirect speech acts and their matched direct controls, and their comprehension
processes were behaviorally monitored. The finding that comprehending
indirect speech acts is more costly than comprehending direct ones was replicated.
Applying TMS to the right-temporoparietal junction did not affect the processing
of indirect speech acts when these were matched to their direct controls in terms of
communicative function. However, the speed of comprehension of indirect speech
acts was altered relative to the direct controls when they were not matched for
communicative function.
In a third study, subjects were asked to provide ratings of several psycholinguistic
dimensions for both direct and indirect speech acts to assess the differences between
them. Compared to their direct counterparts, indirect speech acts were found to be
less predictable, less coherent with their context, less semantically related to their
context, and understood with less certainty. Notably, these properties were tightly
related to the in/directness of the stimuli.
In summary, it could be shown that (i) communicative function can be encoded in
the brain in ways that are similar between comprehension and production modality,
(ii) specificities of the neural representations of speech acts can be related to their use
in communication, (iii) there was no evidence of the right-temporoparietal junction
processing indirect speech acts when compared to well-matched controls, and (iv)
contrasting direct and indirect speech acts revealed several differences unrelated
to ToM that suggest the (additional) contribution of other brain systems in the
comprehension of indirect speech acts. Overall, it was demonstrated that when
identical utterances are used with different communicative functions—whether direct
or indirect—are associated with different neurocognitive processes. These findings
add to the growing literature examining the communicative function of language
and argue for greater inclusion of pragmatics in neurocognitive models of language
function.
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