Frequency-Doubling Technology and Parasol Cells

Abstract

Swanson et al. 1 have reported an excellent study of the responses of macaque retinal ganglion cells (RGCs) to Goldmann size III stimuli and contrast-modulated grating stimuli. They estimated the contrast gain of the initial rising phase of the contrast response function of the cells. From the physiology shown, the extracellular recorded RGCs are parasol and midget RGCs and are referred to in terms of their lateral geniculate nucleus (LGN) targets as M- and P-cells, respectively. The ratios of the gains for the two RGC types indicated that size III stimuli have higher relative gain for M-cells than the grating stimuli. Given that the gratings are described as displaying the frequencydoubling (FD) illusion, this may be taken to mean that the stimuli of the FDT perimeter do not preferentially stimulate a pathway that is useful for glaucoma diagnosis. The original idea of FD stimuli was that they might stimulate nonlinear Y-cells. 2 Such cells had been reported from extracellular recordings of the M-layers of the primate LGN and so were dubbed My-cells. No anatomic substrate was known. The concept was that if humans were like all other mammals, Y-like cells should be larger and less densely overlapping than their X-like (parasol cell) partners. Cell losses could be more easily detected if the lower densities meant few of these Y-cells saw each point in visual space. 2–3 Recently, anatomic substrates for primate Y-cells have been reported: the smooth monostratified