Technical note: contour plot visualization of the light adapted electroretinogram using a generalized additive model

Purpose: To describe a new method to visualize the amplitude profile of light adapted ERGs as a series of contour plots in response to a Flash Strength series.

Methods: Light adapted ERGs from a dataset of n = 88 Autism Spectrum Disorder (ASD) and n = 70 typically developing Control participants were used incorporating 10 flash strengths ranging from 12 to 446 Troland seconds (Td.s). The region chosen for analysis included the baseline, a-wave and ascending limb of the b-wave and included n = 1736 control and n = 1300 ASD waveforms. A Generalized Additive Model (GAM) with complexity penalized tensor product splines was applied to the waveform intervals.

Results: Contour plots derived from the ASD and Control groups revealed a pattern of reduced amplitude in the ascending limb of the b-wave for the ASD group. Representative responses were derived from the GAM model for discrete Flash Strengths to exemplify the changing profile of the ERG waveform. A contour plot of the derived z-scores provided a qualitative evaluation of the differences in the mean amplitudes which was concentrated on the b-wave.

Conclusions: The production of contour plots based on amplitude, time and Flash Strength with minimal a priori assumptions provide an additional approach to analyzing stimulus response data series and may support clinical applications. Additionally, the GAM-based methodology provides a tool for simultaneous investigation of the amplitude changes over time and Flash Strength which can be useful for theoretical purposes.