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It's All Done with Mirrors: Proof of Non-Existence

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Abstract

Mirrors can show us to be absent (with minimal cognitive damage) and also can show imaginary lines to be unreal (again with little or no effect on the adjoining percept). The processes that create the subjective lines are immune to the optic information that the lines do not exist.
Perception, 1985, volume 14, pages 513-514
It's all done with mirrors: Proof of non-existence
John
M
Kennedy
Scarborough College, West
Hill,
Ontario M1C 1A4, Canada
Received 24 January 1985, in revised form 3 March 1985
Abstract. Mirrors can show us to be absent (with minimal cognitive damage) and also can show
imaginary lines to be unreal (again with little or no effect on the adjoining percept). The processes that
create the subjective lines are immune to the optic information that the lines do not exist.
Mirrors are of considerable interest to perceptual psychologists. They present problems
for ecological optics—J J Gibson's basis for naive realism. Is a plane textureless surface
with perfect reflectivity acceptable as part of the 'ecological' environment in Gibson's
sense? Mirror surfaces lack texture. The absence of texture creates problems for Gibson's
analysis in which texture provides optical information for surfaces (Gibson 1966). On a
calm day the surface of a lake can approach a perfect mirror, so that one cannot simply
set mirrors aside as 'unecclogical' in the way that Gibsonians have disposed of some
other problems (Kennedy 1974). The ecological indicator of the presence of a mirror is
an axis of symmetry between a sample of the optic array and a reflection of that sample.
There are many puzzles created by mirrors. Here, three puzzles of existence will be
described.
With monocular gaze many three-dimensional surfaces reverse, for example, a cup
may 'reverse' to look as though it is a dome instead of a hollow. This effect can be used to
suggest one's own absence in the following way. Take a slightly convex piece of smooth
reflecting material, for example, a lens from commercial sun glasses. If the glass is set at
45° to the horizontal to reflect the ceiling, and one then perceptually 'reverses' it, it
appears slightly concave. It should then reflect the viewer, were it truly concave. But it
does not do so. There is optical information that one does not exist.
Alternatively, take a trapezoidal plane mirror that resembles a square drawn in
perspective, two converging sides, and two parallels. Place the larger of the parallel sides
uppermost and tilt the mirror back until it projects a square image. If one looks at this
mirror and perceives it as square and upright, which is fairly easy to do, one would expect
to see one's reflection. However, if it is tilted back sufficiently, no trace of the viewer is
seen. This is a most disquieting upshot, suggesting one is elsewhere, or a phantom that
has no reflection.
Another interesting display can be arranged with a three-dimensional object in which a
subjective wire appears to join the tips of rods (Ware and Kennedy 1977). A large
version of this can be constructed (ours is 2 ft by 9 in). If a small mirror is placed behind
the imaginary line joining the tips of the rods there will be no reflection of the imaginary
line.
Hence, here is optical information for the nonexistence of the subjective wire-infor-
mation that the wire is at best a phantom. Similarly, the wire does not cast a shadow on a
small card held behind it. The perceiver nevertheless continues to see the subjective wire.
The optical information which disconfirms the hypothesis that the wire is present is not
enough to destroy its perception. We may conclude that whatever part of the visual
system creates the subjective wire takes no account of the absence of expected reflec-
tions.
The 'cognitive' information provided by the mirror is dealt with independently of
the visual processes that create the apparent visual divisions.
514 J M Kennedy
The Imaginary wire' demonstration is a neat complement of the 'absent self demon-
stration. In one, the mirror shows that a wire is imaginary, but it does not disappear. In
the other, the mirror shows us to be unreal, but
we
do not,
I
hope,
vanish.
References
Gibson J J, 1966 The Senses
Considered
as
Perceptual
Systems (Boston, MA: Houghton-Mifflin)
Kennedy J M, 1974 A
Psychology
of
Picture Perception
(San Francisco, CA: Jossey-Bass)
Ware C, Kennedy J M, 1977 "Illusory line linking solid rods" Perception 6 601-602
p © 1985 a Pion publication printed in Great Britain
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A solid object--a frame enclosing rods--can be seen as having an illusory 'line' joining the tips of the rods.