Contribution of Chromatic Aberration to Responses of Parvocellular Pathway Neurones

Abstract

Abstract: : Purpose: To compare the spatial transfer characteristics for chromatic and luminance signals in parvocellular pathway (PC) cells of dichromatic and trichromatic marmosets. Methods: Extracellular recordings of visually–evoked activity in individual PC cells were made in Sufentanil–anaesthetised marmosets (Callithrix Jacchus). Stimuli were drifting sine gratings, with red (R) and green (G) phospor intensity of the display adjusted to produce defined ratios of activation in the M and L class photoreceptors. Response amplitude and phase (fundamental Fourier component) were measured. The colour vision genotype of each animal was diagnosed using PCR amplification of cone opsin–encoding genes. Results: Responses of PC cells in trichromatic marmosets showed, as expected, low–pass transfer characteristic for RG modulation. In dichromatic marmosets, RG gratings which at low spatial frequencies produced no modulation in the single (M or L) cone class providing input to the PC cell receptive field (n=20), nevertheless yielded neuronal responses at frequencies near the cell's acuity limit. Analysis of response phase and amplitude for the R and G components presented in isolation (in 17 PC cells) showed intrusion of both transverse and longitudinal aberrations at spatial frequencies near the cell's resolution limit. Conclusions: Transmission of high–acuity spatial signals by PC cells may be constrained by chromatic aberrations.

Keywords: color vision • electrophysiology: non-clinical • thalamus/lateral geniculate nucleus