The contrast gain control of the cat retina (original) (raw)

How the contrast gain control modifies the frequency responses of cat retinal ganglion cells

The Journal of physiology, 1981

1. A model is proposed for the effect of contrast on the first-order frequency responses of cat retinal ganglion cells. The model consists of several cascaded low pass filters ('leaky integrators') followed by a single stage of negative feed-back. 2. Values of time constants and gain of the components in this model were chosen to approximate (with least-squared deviation) experimentally measured first-order frequency responses. In the experiments used for the analysis, the visual stimulus was a sine grating modulated by a sum of sinusoids. 3. For both X cells and Y cells, the over-all gain and the time constants of the cascade of low pass filters were insensitive to contrast. 4. In all cells, the gain-bandwidth product of the negative feed-back loop was markedly increased with increasing contrast. 5. The effect of stimulation in the periphery of the receptive fields on the first-order frequency response to a centrally placed spot was identical to the effect of increasing con...

The effect of contrast on the transfer properties of cat retinal ganglion cells

The Journal of physiology, 1978

1. Variation in stimulus contrast produces a marked effect on the dynamics of the cat retina. This contrast effect was investigated by measurement of the responses of X and Y ganglion cells. The stimuli were sine gratings or rectangular spots modulated by a temporal signal which was a sum of sinusoids. Fourier analysis of the neural response to such a stimulus allowed us to calculate first order and second order frequency kernels. 2. The first order frequency kernel of both X and Y ganglion cells became more sharply tuned at higher contrasts. The peak amplitude also shifted to higher temporal frequency at higher contrasts. Responses to low frequencies of modulation (less than 1 Hz) grew less than proportionally with contrast. However, response amplitudes at higher modulation frequencies (greater than 4 Hz) scaled approximately proportionally with contrast. Also, there was a marked phase advance in these latter components as contrast increased. 3. The contrast effect was significantl...

Nonlinear analysis of cat retinal ganglion cells in the frequency domain

Proceedings of the National Academy of Sciences, 1977

We have analyzed the responses of cat retinal ganglion cells to luminosity gratings that are modulated in time by a sum of sinusoids. A judicious choice of the component temporal frequencies permits a separation of the linear and second-order nonlinear components. Y cell responses show harmonic generation and intermodulation distortion over a wide frequency range. These nonlinear components predominate over the linear components for certain types of spatial stimuli. Nonlinear components in X cells are greatly diminished in comparison. The character of the nonlinear responses provides strong constraints on prospective models for the nonlinear pathway of the Y cell. The visual pathway of the cat has been studied intensively in order to discover the stages in which the visual image undergoes neural transformation. Analyses of responses in retinal ganglion cells have led to the discovery of parallel processing in the cat retina (1). Distinct classes of ganglion cells, named X cells and Y cells, combine light-evoked signals from the receptors in different ways.

The effect of contrast on the non-linear response of the Y cell

The Journal of physiology, 1980

1. Second-order frequency responses were obtained from cat retinal ganglion cells of the Y type. The cells were stimulated by a spatial sine grating whose contrast was modulated in time by a sum of eight sinusoids. 2. Second-order frequency responses obtained at higher contrasts have a peak amplitude at higher input temporal frequency, and phase shifts, compared to their low-contrast counterparts. 3. This change in shape of the second-order frequency response is a departure from the prediction of the linear/static non-linear/linear sandwich model of the non-linear pathway in the cat retina. The departure is analysed by means of the hypothesis that the two filters of the sandwich model are parametric in contrast. 4. Most of the change in shape of the second-order frequency response with contrast is accounted for in terms of the sandwich model by changes in the transfer characteristics of the filter preceding the static non-linearity. 5. The effect of contrast on the second-order resp...

Spatiotemporal frequency responses of cat retinal ganglion cells

The Journal of General Physiology, 1987

Spatiotemporal frequency responses were measured at different levels of light adaptation for cat X and Y retinal ganglion cells. Stationary sinusoidal luminance gratings whose contrast was modulated sinusoidally in time or drifting gratings were used as stimuli . Under photopic illumination, when the spatial frequency was held constant at or above its optimum value, an X cell's responsivity was essentially constant as the temporal frequency was changed from 1 .5 to 30 Hz. At lower temporal frequencies, responsivity rolled off gradually, and at higher ones it rolled off rapidly. In contrast, when the spatial frequency was held constant at a low value, an X cell's responsivity increased continuously with temporal frequency from a very low value at 0.1 Hz to substantial values at temporal frequencies higher than 30 Hz, from which responsivity rolled off again . Thus, 0 cycles -deg' became the optimal spatial frequency above 30 Hz. For Y cells under photopic illumination, the spatiotemporal interaction was even more complex. When the spatial frequency was held constant at or above its optimal value, the temporal frequency range over which responsivity was constant was shorter than that of X cells . At lower spatial frequencies, this range was not appreciably different . As for X cells, 0 cycles deg ' was the optimal spatial frequency above 30 Hz . Temporal resolution (defined as the high temporal frequency at which responsivity had fallen to 10 impulses -s') for a uniform field was^-95 Hz for X cells and^-120 Hz for Y cells under photopic illumination . Temporal resolution was lower at lower adaptation levels. The results were interpreted in terms of a Gaussian centersurround model . For X cells, the surround and center strengths were nearly equal at low and moderate temporal frequencies, but the surround strength exceeded the center strength above 30 Hz . Thus, the response to a spatially uniform stimulus at high temporal frequencies was dominated by the surround. In addition, at temporal frequencies above 30 Hz, the center radius increased .

Receptive field mechanisms of cat X and Y retinal ganglion cells

The Journal of General Physiology, 1979

A B S T R A C: T We investigated receptive field properties of cat retinal ganglion cells with visual stimuli which were sinusoidal spatial gratings amplitude modulated in time by a sum of sinusoids. Neural responses were analyzed into the Fourier components at the input frequencies and the components at sum and difference frequencies. The first-order frequency response of X cells had a marked spatial phase and spatial frequency dependence which could be explained in terms of linear interactions between center and surround mechanisms in the receptive field. The second-order frequency response of X cells was much smaller than the first-order frequency response at all spatial frequencies. The spatial phase and spatial frequency dependence of the first-order frequency response in Y cells in some ways resembled that of X cells. However, the Y firstorder response declined to zero at a much lower spatial frequency than in X cells. Furthermore, the second-order frequency response was larger in Y cells; the second-order frequency components became the dominant part of the response for patterns of high spatial frequency. This implies that the receptive field center and surround mechanisms are physiologically quite different in Y cells from those in X cells, and that the Y cells also receive excitatory drive from an additional nonlinear receptive field mechanism.

Retinal bipolar cells: Contrast encoding for sinusoidal modulation and steps of luminance contrast

Visual Neuroscience, 2004

Contrast encoding for sinusoidal modulations of luminance contrast was investigated by intracellular recording in the intact salamander retina. In what appears to be the first study of this kind for vertebrate bipolar cells, responses of the central receptive-field mechanism of cone-driven cells to modulation of 3 Hz were analyzed quantitatively via both signal averaging and a Fast Fourier Transform (FFT) while the retina was light adapted to 20 cd0m 2. Depolarizing and hyperpolarizing bipolar cells showed very similar encoding. Both responded with sinusoidal waveforms whose amplitude varied linearly with modulation depths ranging up to 7-8%. The slope of the modulation0response curve was very steep in this range. Thus, the contrast gain was high, reaching values of 6-7, and the half-maximal response was achieved at modulations of 9% or less. At modulations above ;15%, the responses typically showed strong compressive nonlinearity and the waveform was increasingly distorted. At maximum modulation, the higher harmonics of the FFT constituted about 30% of the amplitude of the fundamental. Measurements were also made for cones and horizontal cells. Both cell types showed predominantly linear responses and low contrast gain, in marked contrast to bipolar cells. These results suggest that the high contrast gain and strong nonlinearity of bipolar cells largely arise postsynaptic to cone transmitter release. Further experiments were performed to compare responses to contrast steps versus those to sinusoidal modulation. In the linear range, we show that the contrast gains of cones and horizontal cells are low and virtually identical for both steps and sinusoidal modulations. In bipolar cells, on the other hand, the contrast gain is about two times greater for steps than that for the 3-Hz sine waves. These results suggest that mechanisms intrinsic to bipolar cells act like a high-pass filter with a short time constant to selectively emphasize contrast transients over slower changes in contrast.

Bimodal receptive fields of cat retinal ganglion cells

Vision research, 1983

Receptive fields of cat retinal ganglion cells were stimulated by a drifting, sinusoidal luminance pattern of fixed contrast. The amplitudes and phases of the harmonic components in the response were determined as a function of spatial frequency. For most cells, the graphs of response vs spatial frequency (when plotted on linear scales) were unimodal and skewed towards zero frequency for all stimulus orientations. However, some cells had bimodal frequency response functions when the stimulus was in the non-preferred orientation. These unusual cells also exhibited a sudden phase-reversal of pi radians which occurred at the frequency of the changeover between the two modes. Calculations based on the experimental data predicted two distinctly separate regions of high sensitivity within the receptive centres of such cells. A narrow bar stimulus was used to confirm that the receptive fields had, in effect, double centres.

Responses to pulses and sinusoids in macaque ganglion cells

1994

The goal of the study was to compare pulse respomx~ with sinusoidal temporal responsivity. The response of macaque ganglion eetls was measured to brief luminance and chromatic pulses and to fuminance or chromatic sin~oidal m~u~ation. To make both positive and negative lobes of the pulse response visible, responses to pulses of opposite polarity were combined to yield a linearized pulse response. Tests of superposition were used to evaluate the linearized pulse response to different combinations of pulse duration and Weber contrast. A prediction of the pulse response was derived using sinusoidal responsivity functions and Fourier synthesis. For ganglion ceils of the parvocellular (PC) pathway, shape and absolute amplitude of linearized pulse respomes corresponded weif to the predicted responses over a range of pulse durations at 0.5 and 1.0 Weber contrast for both tumiuance and chromatic modulation.

Nonlinear spatial summation and the contrast gain control of cat retinal ganglion cells

The Journal of physiology, 1979

1. We studied how responses to visual stimuli at spatially separated locations were combined by cat retinal ganglion cells. 2. The temporal signal which modulated the stimuli was a sum of sinusoids. Fourier analysis of the ganglion cell impulse train yielded first order responses at the modulation frequencies, and second order responses at sums and differences of the input frequencies. 3. Spatial stimuli were spots in the centre and periphery of the cell's receptive field. Four conditions of stimulation were used: centre alone, periphery alone, centre and periphery in phase, centre and periphery out of phase. 4. The effective first order response of the centre was defined as the response due to centre stimulation in the presence of periphery stimulation, but independent of the relative phases of the two regions. Likewise, the effective first order response of the periphery was defined as the response due to periphery in the presence of centre stimulation, but independent of the ...