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Abstract:
In our subjective experience, there is a tight link between covert visual attention and egocentric
spatial attention. One key difference is that the latter can extend beyond the visual
field, providing us with an acurate mental representation of an object’s location relative to
our body position. A neural link between visual and ego-centric spatial attention is suggested
by lesions in parietal cortex, that lead not only to deficits in covert visual attention, but
frequently also to a disorder of ego-centric spatial awareness, known as hemi-spatial neglect.
While parietal involvement in covert visual spatial attention has been much studied, relatively
little is known about mental representations of the unseen space around. In the present study
we examined whether also unseen spatial locations beyond the visual field are represented
in parietal activity, and how they are related to retinotopic representations. We employed a
novel virtual reality (VR) paradigm during functional magnetic resonance imaging (fMRI),
whereby observers were prompted to draw their spatial attention to the position of one of
eight possible objects located around them in an octagonal room. By changing the observers’
facing direction every few trials, the ego-centric location of objects was disentangled from their
absolute position and from the objectsâ identity. Thus, mental representations of egocentric
space surrounding the observer were sampled eight-fold. Decoding results of a multivariate
pattern analysis classifier (MVPA), but not univariate results, showed that egocentric spatial
directions were specifically represented in parietal cortex. These representations overlapped
only partly with visually driven retinotopic activity. Our results thus show that parietal cortex
codes not only for retinotopic and visually accessible space, but also for ego-centric locations
of the three-dimensional space surrounding us, including unseen space.
