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(defined as the area of the retina which when illuminated may cause
a discharge in the particular ganglion cell, i.e. the retinal region
occupied by photoreceptors whose connections converge upon the
ganglion cell) was maximally sensitive in the centre of the field, and
that the sensitivity gradually fell off with increasing distance from
this centre. Also, when the area of the receptive field illuminated was
increased, the response of the ganglion cell increased, demonstrating
spatial summation in the retina of the frog. Clearly, several retinal
pathways had to converge upon the ganglion cell producing a
combined effect.
7.4 Receptive field organization of rods
and cones: Kuffler's investigation
The investigation of Hartline was followed up by Kuffler (
1953
).
He made an extensive study of the configuration and functional
organization of receptive fields in the retina of cats. Discharge
patterns of single ganglion cells of the cat retina were recorded with
a microelectrode while light stimuli were applied to different areas of
its receptive field. Two small independently controlled light beams
and also a background light field that determined the adaptation level
of the retina were employed.
With this technique, Kuffler (
1953
) obtained several very
interesting results. He showed that the retina contained receptive
fields with central and peripheral areas that had opposite discharge
patterns. Fields with 'on'-centre regions had 'off' surrounds and vice
versa. In intermediary regions between the central and peripheral
areas 'on-off' response patterns could be recorded. Both transient and
maintained discharge patterns were found.
The boundaries and extent of the receptive fields were found
to vary with light and dark adaptation. With high background
illumination the receptive fields tended to shrink, while they tended
to expand during dark adaptation. He also found that different regions
within a single receptive field tended to interact: 'off'-areas tended
to suppress the discharges from 'on'-areas and vice versa. In fact, all
