Modelling the effects of a negative feedback circuit from horizontal cells to cones on the impulse responses of cones and horizontal cells in the catfish retina

Abstract

A model of the cone-L-HC circuit for the catfish retina is presented with the following features: the outer segment consists of a compression factor and 7 low-pass filters in tandem; the cone pedicle consists of an internal negative feedback circuit in series with a low-pass filter; and the L-HC consists of a low-pass filter and forms a negative feedback circuit with the cone pedicle. By proper adjustment of the various time constants of the low-pass filters and the gain factors, the impulse responses for cones and L-HCs of the catfish retina (and turtle) can be duplicated. The negative feedback gain increases with increasing levels of mean illuminance which causes the monophasic impulse responses to become faster, biphasic and decrease in amplitude, i.e. in gain. This is an expression of the Weber-Fechner law.

Color Perception of Aperture Colors Using a Computational Model of the Human Visual System

“…where cp is a compression factor with total = intensity of the stimulus as determined by (1b) and ␣ = 0.2; fdb is the feedback with n 1 = 1, k 5 = 5, and k 4 = 0.2 are the feedforward and feedback gains of the 'internal' negative feedback circuit involving the cone [30,31,42,43]. The original model contained an 'internal' and an 'external' feedback circuit, which involved feedback from the L-HC to the cones.…”

Simulated bipolar cells in fovea of human retina

“…A tenet of the present model of the human retinal fovea is that the retina up to the ganglion cell level is piecewise linear [36,[39][40][41][42], i.e. for a given steady-state illumination level the output is a linear function of input.…”

“…There are automatic gain control systems whereby gains of individual cones are inversely proportional to steady-state illumination level [39,42]. The Weber relationship between steady illumination levels and responses is a result of automatic gain control in the cone [31,36,49].…”

“…There is an additional negative feedback circuit between cones and horizontal cells [5,33], but this system appears to be negligible in human fovea at normal and moderate illumination levels [21]: therefore the present model does not include this "external" negative feedback circuit. If present, 499 electrical coupling between cones and between horizontal cells [ 15,31] in human central fovea are negligible as compared to the effects of the point spread functions [38][39][40]; therefore electrical coupling are not included in the working model.…”

“…Receptive field centers are formed by direct cone-hyperpolarizing or -depolarizing inputs, while antagonistic surrounds are formed by horizontal ceils acting as voltage inverters [33,[39][40][41][42]46,48]. Two basic BC types are possible as to polarization changes; (H-type) hyperpolarizing-center/depolarizing-surround, and (Dtype) depolarizing-center/hyperpolarizing-surround [30].…”