The dynamics of adaptation in the fly early visual system

In this dissertation, the adaptive properties of photoreceptors and their post-synaptic large monopolar cells (LMCs) in the fly's compound eyes are studied. Visual stimuli consisting of time varying square wave and natural light intensities with large modulations in the mean light intensity and small fluctuations around the mean were presented in a single LED to the fly. In the square wave experiment, the light intensity is switched between two levels. The effect of changing intensity levels and switching frequency of transition on photoreceptor and LMC's response is discussed. Time varying light intensities recorded from a natural environment were used in the natural light experiment. The light sequence was displayed respectively at three different speeds; a factor of two faster, equal and a factor of two slower relative to the original speed. The effect of the spatiotemporal correlation and large modulations in the natural light intensities on adaptation is discussed. In addition, experiments with seven LEDs were conducted to determine whether lateral connections from neighboring LMCs change the adaptation state. The frequency analysis of response however breaks down at large intensity modulations, because the system is driven away from its stationary state. In this regime, the response of the system is characterized using the method of generalized eigenvalues, which allows for time domain analysis of non-stationary systems. Before apply this method to the non-stationary system, it was applied to stationary system and compared with frequency analysis to verify the effectiveness of this method. Further, relevant parameters such as effective photon rate and information rate that characterize the different states of adaptation of the non-stationary system were calculated by generalized eigenvalues