Re: Effects of Eye Position on Perception

[P3D Stephen J Hart <sjhart@xxxxxxxxx>]

At <http://www.nature.com> I found *two* relevant abstracts for their 10
April 1997 issue:

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Compression of visual space before saccades

Saccadic eye movements, in which the eye moves rapidly between two resting
positions, shift the position of our retinal images. If our perception of
the world is to remain stable, the visual directions associated with
retinal sites, and others they report to, must be updated to compensate for
changes in the point of gaze. It has long been suspected that this
compensation is achieved by a uniform shift of coordinates driven by an
extra-retinal position signal, although some consider this to be
unnecessary. Considerable effort has been devoted to a search for such a
signal and to measuring its time course and accuracy. Here, by using
multiple as well as single targets under normal viewing conditions, the
authors show that changes in apparent visual direction anticipate saccades
and are not of the same size, or even in the same direction, for all parts
of the visual field. They also show that there is a compression of visual
space sufficient to reduce the spacing and even the apparent number of
pattern elements. The results are in part consistent with
electrophysiological findings of anticipatory shifts in the receptive
fields of neurons in parietal cortex and superior colliculi.

J Ross, M Concetta Morrone & D C Burr Compression of visual space before
saccades (Letter to Nature)

Nature 386, 598 (1997)

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Perceived geometrical relationships affected by eye-movement signals

To determine the location of visual objects relative to the observer, the
visual system must take account not only of the location of the stimulus on
the retina, but also of the direction of gaze. In contrast, the perceived
spatial relationship between visual stimuli is normally assumed to depend
on retinal information alone, and not to require information about eye
position. The authors' now show, however, that the perceived alignment of
three dots---tested by a vernier alignment task,---is systematically
altered in the period immediately preceding a saccade. Thus, information
about eye position can modify not only the perceived relationship of the
entire retinal image to the observer, but also the relations between
elements within the image. The processing of relative position and of
egocentric (observer-centred) position may therefore be less distinct than
previously believed.

R H Cai, A Pouget, M Schlag-Rey & J Schlag

Perceived geometrical relationships affected by eye-movement signals
(Letter to Nature)

Nature 386, 601 (1997)

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