Spike-Triggered Covariance Analysis Reveals Phenomenological Diversity of Contrast Adaptation in the Retina
Fig 6
Analysis of contrast-dependent filter changes in Type II cells after separation of On and Off pathways.
(A) Separation of spike-triggered stimuli into On and Off pathway shown for a sample cell of Type II. Left: Scatter plot of spike-triggered stimuli for high-contrast stimulation, projected onto k1 and k2. Red and blue data points mark the clusters corresponding to the On and Off pathways, respectively. Center: Filters kON and kOFF, obtained by computing the STAs for the two clusters separately, as well as the full STA, obtained from all spikes. Right: Nonlinearities obtained from the separated On and Off clusters (red and blue, respectively) as well as for the entire set of spikes (thick line). (B) Same as (A), but for low-contrast stimulation. (C) STA fits with the kON and kOFF features, obtained under high contrast. Fit of high-contrast STA (i) and low-contrast STA (ii) for the sample cell as well as coefficients of determination (iii) and corresponding weights obtained for the two features (iv) for all recorded cells of Type II. Note that, in contrast to k1 and k2, kON and kOFF are generally not orthogonal to each other. Thus, the sum of squared weights obtained from the fit is not bounded by unity. The inset in (i) shows kON and kOFF. The green data points in (iii) and (iv) mark the sample cell. (D) Same as (C), but using only spikes from the Off-pathway cluster and their features k1 and k2, derived from the high-contrast STC analysis. The insets in (i) show the corresponding eigenvalue spectrum as well as k1 and k2.