Abstract
Purpose: :
Naturalistic stimuli differ from random stimuli since they are strongly correlated in space, time and wavelength (Van Hateren, 1993), and have a large range of intensities and contrasts. Early retinal processing stages are largely concerned with reducing these correlations and compressing the intensity and contrast ranges. While often argued that these early processing steps are essentially linear we find this assumption is incorrect for naturalistic stimuli (Endeman and Kamermans, 2010). To continue our work towards a fully validated model of the outer retina’s spatiotemporal and dynamic properties we quantified 1) the performance of M and L cones and mono- and biphasic horizontal cells (MHC and BHC) to a naturalistic chromatic time series of intensities and 2) the filter properties of cones, HCs and feedback from HCs to cone (FB) using classical white light sinusoidal stimuli.
Methods: :
Cone, HC, and FB responses to aforesaid stimuli were recorded by single cell electrophysiological methods in the goldfish retina. Filter properties were determined and the performance of the retina at these stages was expressed as expected coherence and expected coherence rates.
Results: :
Cones, HC and FB all displayed low pass filter characteristics. FB had the lowest cutoff frequency illustrating the slow nature of FB. The performance of MHC and BHCs was similar. Their expected coherence rate was about 120 bits/sec. This information rate was approx. 4 times greater than that of cones experiencing the same visual stimuli.
Conclusions: :
1) Naturalistic stimuli contain less chromatic than luminosity information. If chromatic and luminosity information is carried separately by MHCs and BHCs then their information rates should differ. As this was not the case, it implies luminosity and chromatic information is distributed across MHCs and BHCs. 2) The greater performance of HC, compared to that of cones, suggests that convergence of many cones to a single HC and HC-HC coupling acts to amplify signal strength while simultaneously reducing the noise component.
Keywords: horizontal cells • photoreceptors • retinal connections, networks, circuitry