Spatiotemporal summation of perimetric stimuli in healthy observers

Giovanni Montesano, Pádraig J Mulholland, David F Garway-Heath, Josephine Evans, Giovanni Ometto, David P Crabb

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)
19 Downloads (Pure)


Spatial summation of perimetric stimuli has been used to derive conclusions about the spatial extent of retinal-cortical convergence, mostly from the size of the critical area of summation (Ricco's area, RA) and critical number of retinal ganglion cells (RGCs). However, spatial summation is known to change dynamically with stimulus duration. Conversely, temporal summation and critical duration also vary with stimulus size. Such an important and often neglected spatiotemporal interaction has important implications for modeling perimetric sensitivity in healthy observers and for formulating hypotheses for changes measured in disease. In this work, we performed experiments on visually heathy observers confirming the interaction of stimulus size and duration in determining summation responses in photopic conditions. We then propose a simplified computational model that captures these aspects of perimetric sensitivity by modelling the total retinal input, the combined effect of stimulus size, duration, and retinal cones-to-RGC ratio. We additionally show that, in the macula, the enlargement of RA with eccentricity might not correspond to a constant critical number of RGCs, as often reported, but to a constant critical total retinal input. We finally compare our results with previous literature and show possible implications for modeling disease, especially glaucoma.

Original languageEnglish
Article number2
Pages (from-to)1-25
Number of pages25
JournalJournal of Vision
Issue number4
Publication statusPublished (in print/issue) - 3 Apr 2023

Bibliographical note

Funding Information:
GM, PM and DGH receive financial support from the NIHR BRC based at Moorfields Eye Hospital (MEH) NHS Foundation Trust and UCL Institute of Ophthalmology.

Publisher Copyright:
© Copyright 2023 The Authors


  • spatial summation
  • temporal summation
  • perimetry
  • spatiotemporal summation


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