Brain, Vol 121, Issue 6 1065-1072, Copyright © 1998 by Oxford University Press
L Weiskrantz, A Cowey and C Le Mare
The pupil of the normal human subject constricts in response not only to
average increases in light energy, but also selectively to the spatial
structure of a visual stimulus even when there are no energy changes. This
enables one to measure visual acuity and sensitivity as a function of
spatial frequency. It is known that pupillometric measures of acuity
correlate well with those determined psychophysically for normal human
observers. The purpose of the present study was to measure pupillary
changes with stimuli delivered to the 'blind' hemifields of monkeys with
unilateral V1 removal, and also with stimulation of a human subject (G.Y.)
with putative V1 destruction. The results show that there are small but
reliable pupillary changes to flux-equated gratings in the blind fields
both in monkeys and human. The response profile in both species is very
similar: it is narrowly tuned, with a peak at approximately 1 cycle/degree
and a cut-off acuity of approximately 7 or 8 cycles/degree, a significant
reduction compared with the intact hemifield. The result also maps well
onto the psychophysically determined spatiotemporal response profile to
gratings in the blind field, as determined independently for G.Y. Thus,
there is a narrowly tuned spatial visual channel that does not require the
integrity of V1 in monkey or human. There was no evidence under these
particular conditions in either monkeys or subject G.Y. of a pupillary
response to an equiluminant change from white to green or red in the
hemianopic field. The pupil holds promise as a non-verbal, indirect method
for determining the spatial profile, sensitivity and other properties of
residual visual capacity, both in animals and humans.
ARTICLES
Learning from the pupil: a spatial visual channel in the absence of V1 in monkey and human
Department of Experimental Psychology, University of Oxford, UK.
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