PT  - JOURNAL ARTICLE
AU  - William S. Tuten
AU  - Robert F. Cooper
AU  - Pavan Tiruveedhula
AU  - Alfredo Dubra
AU  - Austin Roorda
AU  - Nicolas P. Cottaris
AU  - David H. Brainard
AU  - Jessica I.W. Morgan
TI  - Spatial summation in the human fovea: the effect of optical aberrations and fixational eye movements
AID  - 10.1101/283119
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 283119
4099  - http://biorxiv.org/content/early/2018/03/15/283119.short
4100  - http://biorxiv.org/content/early/2018/03/15/283119.full
AB  - Psychophysical inferences about the neural mechanisms supporting spatial vision can be undermined by uncertainties introduced by optical aberrations and fixational eye movements, particularly in fovea where the neuronal grain of the visual system is fine. We examined the effect of these pre-neural factors on photopic spatial summation in the human fovea using a custom adaptive optics scanning light ophthalmoscope that provided control over optical aberrations and retinal stimulus motion. Consistent with previous results, Ricco’s area of complete summation encompassed multiple photoreceptors when measured with ordinary amounts of ocular aberrations and retinal stimulus motion. When both factors were minimized experimentally, summation areas were essentially unchanged, suggesting that foveal spatial summation is limited by post-receptoral neural pooling. We compared our behavioral data to predictions generated with a physiologically-inspired front-end model of the visual system, and were able to capture the shape of the summation curves obtained with and without pre-retinal factors using a single post-receptoral summing filter of fixed spatial extent. Given our data and modeling, neurons in the magnocellular visual pathway, such as parasol ganglion cells, provide a candidate neural correlate of Ricco’s area in the central fovea.