Linear and non‐linear performance of transducer and pupil in Calliphora retinula cells.

Abstract

SUMMARY1. Intracellular recordings have been made from the blowfly (Calliphora erythrocephala) retinula cell; apart from the transducer mechanism, these cells also feature a pupil mechanism.2. At several mean intensity levels, within the apparently linear range of response, frequency characteristics of amplitude and phase and responses to 'delta '-flashes and 'delta '-flash pairs have been obtained.3. Fourier methods have shown these responses to be mutually compatible, confirming linearity in these circumstances.4. Non-linear behaviour can be made to appear at the lower frequencies when the modulation depth is increased.5. Non-linearities can also appear through application of the superposition test: a low frequency sine wave, modulated so as to elicit an apparently linear response, and a high frequency sine wave which does not give rise to non-linearity even at the highest modulation depths can, when superimposed, yield a greater response to the latter when situated at the minima of the former than at its maxima.6. At frequencies above approximately 1 Hz these superposition nonlinearities are attributed to the transducer mechanism gain control. Below this frequency the pupil mechanism takes part considerably in the retinula cell's total observed gain control: its characteristics remain yet to be cleared up.7. The transducer's linear and non-linear properties fit in closely with those of the Fuortes-Hodgkin model which couples increases in gain and time constants. 8. The Fuortes-Hodgkin model will probably require some quantitative modifications in the originally treated case of LimulUs, on account of its pupil.9. Finally, the merits of Veringa's diffusion model, and the possibility of eventually joining this model with the Fuortes-Hodgkin one are pointed out briefly.

Adaptive strategies in fly vision: On their image-processing qualities

“…This pattern does not move. It is generated with a raster repetition frequency of 180 Hz which is beyond the cutoff frequency of the retina cells [13]. Then, at time Τ = Δ Γ the pattern jumps to a new position which is displaced with respect to its earlier posi tion by Δα deg, as seen from the fly.…”

Contrast gain, signal-to-noise ratio, and linearity in light-adapted blowfly photoreceptors.

“…8 C). Indeed, the improved coherence at high backgrounds indicates that the linearity of Rl-six photoreceptors does not diminish with light adaptation (see also Pinter, 1966Pinter, , 1972Leutscher-Hazelhoff, 1975).…”

“…2 B ;Juusola, 1993;French, Korenberg, J~irvilehto, Kouvalainen, Juusola, and Weckstr6m, 1993). However, if a transient stimulus is superimposed on a slower change in light intensity, the dynamically modulated gain linearises the photoresponses (cf., Leutscher-Hazelhoff, 1975). Thus, the crucial point is the speed of the feed-back; under dynamic stimulation conditions only slow frequencies create nonlinearities, seen as a drop in the coherence at frequencies below 10 Hz.…”

“…This is mostly due to increasing compression (i.e., reduction of the amplitude) of photoresponses to light increments as the adapting background is increased, and differences between the molecular mechanisms behind excitation and deactivation (Laughlin and Hardie, 1978;Howard, Blakeslee, and Laughlin, 1987;Ranganathan, Harris, Stevens, and Zucker, 1991;Hardie and Minke, 1992;Juusola, 1993). Yet, Leutscher-Hazelhoff (1975), using delta-flashes, and experiments with white noise-modulated light stimuli by French (1980b, c) and by Weckstr6m, Kouvalainen, and Jarvilehto (1988) demonstrated that (with small modulation) light adapted fly photoreceptors operate approximately linearly. Recently, Juusola (1993) showed that in blowfly the stimulus-dependent linearity of the photoreceptor dynamics is related to the speed of the response integration.…”

The dynamic behaviour of photoreceptor cells in the fly in response to random (white noise) stimulation at a range of temperatures.

“…For a linear system the response to a short flash of light (impulse response function) and the response to a series of sine wave light intensity fluctuations (frequency response function) theoretically contain identical information and are related to each other by the Fourier transform. A number of authors have used the sine wave method to examine the linear behaviour of photoreceptors (DeVoe, 1966;Pinter, 1966Pinter, , 1972Zettler, 1969; Toyoda Dodge, Shapley & Gemperlein & McCann, 1975; Leutscher-Hazelhoff, 1975 (DeVoe, 1966;Zettler, 1969). However, although a pure delay element might approximate the measured phase lags quite well, it could not explain the reduction in amplitude of the response with increasing frequency, and so some filter elements are essential to any model.…”