ABSTRACT
Duration of activation at the Temporo-parietal junction and its correlation with
angle of mental transformation as a demarcating measure of Presence in
Upright and Inverted bodies.
Tej.Tadi,
Leila Overney
Olaf Blanke
Lab. of Cognitive Neuroscience
Lab.of Cognitive Neuroscience
Lab.of Cognitive Neuroscience
Brain Mind Institute, EPFL
Brain Mind Institute, EPFL
Brain Mind Institute, EPFL
Lausanne, Switzerland
Lausanne, Switzerland
Lausanne, Switzerland
tej.tadi@epfl.ch
leila.overney@epfl.ch
olaf.blanke@epfl.ch
Introduction
Mental rotation is the ability to imagine the rotation of an object in space and is essential in
spatial reasoning and problem solving. It has been shown that reaction times increase linearly
with the angle of rotation (Petit & Harris, 2005), which is referred to as the mental rotation
function. When imagining spatial transformations of one’s own body the time required to
mentally simulate a movement from a given position to another body position also correlates
with the time taken to actually perform the displacement physically (Parsons, 1987). Blanke et
al. (2005) have shown that these mental own body transformations activate the temporoparietal junction (TPJ) at 330-400 ms after stimulus onset. As only few different angles of
rotation were tested in this previous study no mental rotation function could be calculated.
Here, we designed new stimuli and searched for behavioral and neural correlates of the mental
rotation function in own body transformations.
Methods
12 healthy participants (12 male; mean age 22) made right-left judgements after imagining
themselves in the position of a three-dimensional humanoid .The orientation of the humanoid
differed systematically from the participants’ orientation along the vertical axis. Eight
different angles of rotation were tested (body position: from 0° to 360°; steps of 45°). In
addition, mental own body transformations were tested showing the human body in the
upright and inverted position (body position). Behavioural data (reaction times; error rates)
and electrophysiological data (200-channel evoked potential mapping; EP mapping) were
recorded (Blanke at al., 2005).
Results
For upright body positions, analysis of reaction times revealed a mental rotation function
(reaction times increased with increasing angle of rotation of the human body). This was not
the case for inverted bodies. EP mapping and application of a linear inverse solution showed
the selective activation of the temporo-parietal junction (TPJ) at 300-400 ms. This activation
was only found for upright (but not inverted) body positions and not found for earlier or later
brain activations.
Discussion
These data reveal a mental rotation function for mental own body transformations along the
vertical body axis for upright body postion. Whereas mental rotation of objects has been
shown to implicate right parietal cortex, these data show that mental own transformations
with human bodies rely on bilateral, but mainly right hemispheric activation, of the TPJ at
300-400 ms.
Presence:
We hypothesize that subjects experience higher levels of immersion and presence for upright
body positions (the subjects identify their physical body position to the upright stimulus
relatively easily as compared to the inverted body stimuli). The Mental rotation function can
help decode the trend in presence the subjects experience through different angles around the
body axis for different body positions.