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Abstract:
Abstract: Spatial neglect following brain damage is organized
in multiple reference frames, some of which are environmental.
Although neglect can occur on one side of an object's primary
vertical axis, the handedness (right/left sides) of most objects is
not coded intrinsically. Instead, right/left must be determined
with respect to a frame external to the object. In the case of
letters, previous work has shown that handedness judgments utilize
an environmental (scene-based) frame. We used a spatial performance
asymmetry (rightward advantage) in normal participants to assess
whether the origin of the horizontal axis of this frame is
determined by the locus of fixation or of attention. In each trial,
one of three crosses (left, center, right) was cued. The letter
target appeared to the left or right of the cued cross, and whether
it was normally oriented or reflected was reported via a right or
left keypress. Central fixation was assured via eye-tracking, and
feedback for fixation breaks was provided. Holding the spatial
location of the target constant, both a strong rightward advantage
and a Simon effect were obtained with respect to the cued location.
A smaller rightward advantage, but no Simon effect, appeared around
fixation. These findings converge with others using very different
paradigms to suggest that environmental reference frames can be
attention-centered, and that spatial performance asymmetries can
occur in multiple frames.
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