A
code-theoretic note on object handedness
Emanuel L. J. Leeuwenberg, Peter A. van der
Helm
Abstract. This study
is a theoretical exercise dealing with discrimination between
images and mirror-images. It focuses on the way codes of shapes
represent their handedness. We compare two code systems with different
reference frames. These frames determine the specific sensitivity of
each system. One system uses an asymmetric reference frame. It is
called the H-system and was inspired by an idea of Corballis (1988
Psychological Review 95 115 - 123). The other system, being our
proposal, uses a symmetric reference frame and we have named
it the M-system. We demonstrate the following. A code of the H-system
provides
a cue for the handedness of a shape, but not for rotation, ie no cue
for
the appropriate kind of code rotation which should be tested in case
images
and mirror-images are discerned by mental rotation. The M-system is the
converse
in both respects. A code of this system does not provide a handedness
cue
but, instead, a rotation cue. Thus, for handedness discrimination, the
H-system
neither needs nor guides mental rotation, whereas the M-system does
both.
This M-system generates object-centred structural codes enriched with
viewpoint
information. Various visual experiments reported in the literature
favour
the M-system over the H-system, implying that perception does not make
use
of an asymmetric but of a symmetric reference frame.
Peter
A. van der Helm 