Author:
TROY J.B.,BOHNSACK D.L.,DILLER L.C.
Abstract
Our objective with this study was to provide a
near complete characterization of how mean light level
changes the spatial receptive-field properties of X-cells.
Single X-cells were recorded extracellularly either from
cell bodies in the retina or from their axons in the optic
tract. Frequency responses of the cells at 2 Hz were measured
for a set of gratings of different spatial frequencies
and for a stimulus designed to probe the spatial properties
of the receptive-field surround. Predicted frequency responses
of a Gaussian center-surround model for the receptive field
were fit simultaneously to both sets of measurements and
the parameters of the model that best fit the data used
to characterize the spatial properties of the receptive
field. Measurements were made at a number of mean light
levels for each cell and changes in receptive-field properties
were characterized by changes in the parameters of the
Gaussian center-surround model. The range of illuminances
studied covered the bulk of the range encountered by a
cat naturally and three distinct functional ranges appeared
to express themselves in the data. One range corresponded
to the cat's photopic range of vision. The other two
ranges were where signals originating in rods dominate
X-cell responses. We argue that one corresponds to the
range that rod signals pass predominantly through rod bipolars
en route to the X-cell, while the other is where
rod signals flow predominantly through cones via
gap junctions and then follow the path of cone signals
to the X-cell. Among the major findings are that Weber's
Law is followed throughout the photopic but not the scotopic
range, that center radius expands under scotopic conditions,
and that the surround is present even at the lowest scotopic
levels we studied.
Publisher
Cambridge University Press (CUP)
Subject
Sensory Systems,Physiology
Cited by
31 articles.
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