Spatial summation in human cone mechanisms from 0° to 20° in the superior retina

Vicki J. Volbrecht, Erin E. Shrago, Brooke E. Schefrin, John S Werner

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


The maximum area of complete spatial summation (i.e., Ricco's area) for human short-wavelength-sensitive(S-) and long-wavelength-sensitive- (L-) cone mechanisms was measured psychophysically at the fovea and at 1.5°, 4°, 8°, and 20° along the vertical meridian in the superior retina. Increment thresholds were measured for three observers by a temporal two-alternative forced-choice procedure. Test stimuli ranging from -0.36 to 4.61 log area (min2) were presented on concentric 12.3° adapting and auxiliary fields, which isolated either an S- or an L-cone mechanism on the plateau of its respective threshold versus intensity function. Test flash durations were 50 and 10 ms for the S- and L-cone mechanisms, respectively. The data indicate that, from 0° to 20°, Ricco's area increases monotonically for the L-cone mechanism, is variable for the S-cone mechanism, and is larger for the S-cone mechanism than for the L-cone mechanism for essentially all retinal locations. This pattern of results most likely reflects differences in ganglion cell density and changes in neural convergence with retinal eccentricity.

Original languageEnglish (US)
Pages (from-to)641-650
Number of pages10
JournalJournal of the Optical Society of America A: Optics and Image Science, and Vision
Issue number3
StatePublished - 2000
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Computer Vision and Pattern Recognition


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