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Zusammenfassung:
Parkinson’s disease (PD) is a progressive, neurological dis-
order caused by the loss of dopaminergic cells in the basal
ganglia, which is involved in motor control. This leads to the
cardinal motor symptoms of PD: tremor, bradykinesia (slow-
ness of movement), rigidity and postural instability. PD also
leads to general cognitive impairment (executive function,
memory, visuospatial abilities), and language impairments;
PD patients perform worse at language tasks such as provid-
ing word definitions and naming objects, generating lists of
verbs, and naming actions. Thus, there seems to be a par-
ticular impairment for action-language. Despite the fact that
action and language are both impaired in PD, little research
has explored if and how co-speech gestures, which embody
a link between these two domains, are affected. The Ges-
ture as Simulated Action hypothesis argues that gestures arise
from cognitive representations or simulations of actions. It
has been argued that people with PD may be less able to cog-
nitively represent, simulate and imagine actions, which could
account for their action-language impairment and may also
mean that gestures are affected. Recently, it has been shown
that while there is not a straightforward reduction in gesture
use in PD, patients’ gestures which described actions are less
precise/informative than those of controls. However, partici-
pants only described two actions, and to a knowing addressee
(so the task was not communicative).
The present study extended this by asking participants to
describe a wide range of actions in an apparently commu-
nicative task, and compared viewpoint as well as precision
between the two groups. Gesture viewpoint was examined
in order to provide a window into the cognitive representa-
tions underlying gesture, by demonstrating whether or not
the speaker has placed themselves as the agent within the ac-
tion (character viewpoint), requiring a cognitive simulation
of the action. Overall, studying gestures in PD has clinical
relevance, and will provide insight into the cognitive basis of
gestures in healthy people.
25 PD patients and 25 age-matched controls viewed 10
pictures and 10 videos depicting a range of actions and de-
scribed them to help an addressee identify the correct stimu-
lus. No difference in the rate of gesture production between
the two groups was found. However, the precision of ges-
tures describing actions was found to be significantly lower
in the PD group. Furthermore, the proportion of gestures
produced from character viewpoint was found to differ be-
tween the groups, with PD patients producing significantly
less C-VPT gestures. This suggests that the cognitive repre-
sentations underlying the gestures have changed in PD, and
that people with PD are less able to imagine themselves as
the agent of the action. This supports the GSA hypothesis by
demonstrating that gesture production changes when the abil-
ity to perform and to cognitively simulate actions is impaired.
Our next study will assess the relationships between cognitive
factors affected in PD and gesture, and motor imagery ability
and gesture. The study will also examine gestures produced
by people with PD when describing a wide range of semantic
content in various communicative situations.
