Retinal adaptation and invariance to changes in higher-order stimulus statistics

TL;DR

This study investigates how retinal ganglion cells adapt to changes in stimulus contrast and higher-order statistics, revealing adaptation to contrast but invariance to skew and kurtosis, which do not significantly impact information encoding.

Contribution

The paper demonstrates that retinal ganglion cells adapt to contrast but remain invariant to higher-order stimulus statistics, supported by experimental data and theoretical analysis.

Findings

Retinal ganglion cells adapt to contrast changes.

Ganglion cells show invariance to skew and kurtosis.

High information rate maintained without adaptation to higher-order moments.

Abstract

Adaptation in the retina is thought to optimize the encoding of natural light signals into sequences of spikes sent to the brain. However, adaptation also entails computational costs: adaptive code is intrinsically ambiguous, because output symbols cannot be trivially mapped back to the stimuli without the knowledge of the adaptive state of the encoding neuron. It is thus important to learn which statistical changes in the input do, and which do not, invoke adaptive responses, and ask about the reasons for potential limits to adaptation. We measured the ganglion cell responses in the tiger salamander retina to controlled changes in the second (contrast), third (skew) and fourth (kurtosis) moments of the light intensity distribution of spatially uniform temporally independent stimuli. The skew and kurtosis of the stimuli were chosen to cover the range observed in natural scenes. We quantified adaptation in ganglion cells by studying two-dimensional linear-nonlinear models that capture well the retinal encoding properties across all stimuli. We found that the retinal ganglion cells adapt to contrast, but exhibit remarkably invariant behavior to changes in higher-order statistics. Finally, by theoretically analyzing optimal coding in LN-type models, we showed that the neural code can maintain a high information rate without dynamic adaptation despite changes in stimulus skew and kurtosis.