Biology Reference
In-Depth Information
degrees of mutual modifications were obtained when different zones
within the receptive field were activated simultaneously by the two
test lights.
Furthermore, Kuffler found that the ratio of regions dominated
by 'on' or 'off' differed in
different
receptive fields.
To explain his results, Kuffler suggested that specific small areas
within a receptive field of a ganglion cell gave rise to predominantly
inhibitory or excitatory impulses and that the discharge pattern
of larger areas of the field depended on the summed effect of the
pathways converging on the given ganglion cell.
The important question of whether the receptive field organi-
zation of a ganglion cell was the same for the rod and cone receptor
systems was pursued by Barlow, Fitzhugh and Kuffler (
1957
). In the light-
adapted state, they found, in accord with Kuffler (
1953
), the receptive
field of ganglion cells of the cat retina to be arranged so that the central
and peripheral regions of the field were mutually antagonistic, evoking
electrical potentials of opposite sign regardless of whether the ganglion
cell explored was an 'on'- or 'off'-centre unit. In the dark-adapted state,
on the other hand, they did not find this antagonistic interaction,
suggesting that the receptive field organization of the rod and cone
systems, in fact, was based on quite different principles.
Further investigation, however, revealed that the mutually
antagonistic interaction between the central and peripheral parts of
the receptive field could be obtained under conditions where only
cones and only rods were test stimulated. Hence, it was concluded
that dark adaptation, not a change in the receptor system, reduced
the antagonistic interactions of the receptive field.
To explain the lateral inhibition found, the authors pointed to
several possibilities: horizontal, amacrine or bipolar cells could all be
responsible.
They also suggested that lateral inhibition could play a role
in the simultaneous contrast effects observed psychophysically and
also explain the well-known psychophysical fact stressed by Lythgoe
(
1940
, p. 40) that summation of the light stimulus was more marked
