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Abstract:
Background
Behavioural studies of children and adults show that goal-directedness is an important cue for the attribution of
animacy to elements of the environment. In monkey and human, the cortex surrounding the superior temporal
sulcus (STS) and gyrus (STG) is known to respond to biological motion and to intentional actions [1], and could
thus participate in the detection of animate entities [2]. A growing number of neuroimaging studies also indicate
that the STS appears to be involved in the representation of mental states. We reasoned that if the STS and STG
are sensitive to intentional motion, activation in these structures would vary with the amount of perceived
goal-directed motion. Further, if the STS is involved in the attribution of mental states, this structure might
respond more when an observed goal-directed behaviour is directed by a representation of the target’s goal rather
than a representation of the target’s position. Also, previous studies revealed attention effects on activation of the
STS during processing of biological motion and of socially relevant characteristics of a face. Which level of
processing in the STS is affected by attention is not yet clear.
Methods
We devised two fMRI experiments to study the response of the STS and of other brain regions to
goal-directedness and the role of attention on this process. We presented healthy adult volunteers with animations
of two round shapes moving in a seemingly animate way. In experiment 1, we parametrically varied the amount
of goal-directed motion of the two abstract moving objects. Subjects had either to rate the amount of interaction
between the moving objects or their speed, which was manipulated independently. In experiment 2, we
manipulated the strategy used to reach the goal: agents either seemed to use knowledge of the goals attributed to
the target object or to follow the target object. Stimuli were controlled for speed and quantity of movement, and
eye movements were monitored in experiment 1.
Results
Increase in goal-directed behaviour parametrically increased activation in STS/STG and also in the medial
occipital cortex and fusiform gyrus, even when subjects performed an incidental task. In experiment 2, watching
agents trying to reach targets by using knowledge about the goals of the target object increased activation in the
STS/STG, but only when subjects payed attention to the chaser’s strategy and not to the outcome of the chase.
Conclusion
We conclude that 1) the cortex in the STS/STG region responds to goal-directed behaviour independently of the
task performed by the subject, and 2) it reponds more when a chase appears to be directed by a representation of
the target’s goal rather than the target’s position, but only when subjects explicitly look for strategies of the
chaser. This suggests that only higher levels of processing of socially relevant characteristics are under the
influence of attention.
