ELECTRORETINOGRAM PATTERNS OF WHITE-EYED BLOWFLY IN REGION OF FLICKER FUSION FREQUENCY

The white eyes of flies respond to stimuli of 80 Hz (flickers per second, at 20° C) with potentials of constant amplitude. Between 80 and 180 Hz an alternating pattern is produced with one potential high and the next low. Beyond 180 Hz each stimulus is responded to with a response of constant amplitude. The amplitude of the alternatingly high and low potentials shows a marked dependence on frequency. At c. 80 Hz the responses are almost the same (13.5 mV). At c. 120 Hz the larger potential increases by about 14% (to 15.4 mV); whereas the smaller potential decreases to 6 mV. With increasing frequency the larger potential then decreases so that at 180 Hz alternating responses have the same amplitude (3.4 mV). The frequency range at which the potentials display an alternating pattern also depends on temperature. At 7° the pattern appears between 34 and 91 Hz; at 31° between 103 and 238 Hz. The potential pattern appears only after long exposure to flicker frequency. The longer the eye is adapted to dark, the longer the time required for the pattern to develop. At the onset of the flickering the flashes produce potentials of the same height. Their amplitude then sinks to a critical value, at which one begins to increase and the following to decrease. The increase of the one is precisely correlated with the decrease of the other. From this observation it is deduced that the pattern of potentials can develop only in a definite physiological state (of adaptation). Periodical flicker patterns produce specific response patterns. When a single bright flash periodically follows an odd number of less intense flashes (so that the total number of flashes per period is even), the ratio of period duration between stimulus and response is 1:1. When the total number of flashes per period is odd, the ratio of periods duration between stimulus and response is 1:2. By increasing the intensity of the background light during flickering the alternating pattern of potential gradually yields to potentials of equal height. All these empirical phenomena (the development of the pattern of potentials, the dependence of the pattern on flicker frequency, and the behaviour of the potential pattern during periodic flicker patterns) can be explained by a simple statistical model. The model supposes that the amplitudes of the potentials of alternating height are produced by a different number of equivalent nervous elements. The model permits the theoretical construction of all empirical results. © 1969 Springer-Verlag.