Dr Mikko Juusola: Naturalistic Stimulation

Our initial work with Drosophila photoreceptors was conducted using pseudorandomly modulated light or current stimuli that, although they provide a rigorous mathematical characterisation of the system, they cannot reveal features of the coding present during natural stimuli. This is particularly important when examining the contributions of ion channels to specific aspects of visual coding. For example, the rapid intensity changes occurring in natural stimuli appears to interact with the activation/inactivation properties of the ion channels leading to non-additive noise (Juusola & de Polavieja, 2003).

We have, therefore, recently started experimenting with natural contrast time series (kindly donated by Hans van Hateren) and designed a new mathematical analysis for estimating the information rate Drosophila photoreceptor and LMC voltage responses, which are both non-Gaussian and non-linear at such stimulus conditions (Juusola & de Polavieja, 2003). The findings suggest that the coding precisions of the visual neurones depends heavily on the stimulus statistics, which themselves change continuously in time and space, not only because objects in the outside world may move but also because the eyes are moving themselves (Juusola & de Polavieja, 2003; Niven et al., 2004; Zheng et al., 2006)