EFFECT OF TEMPORAL FREQUENCY AND CONTRAST ON PERIPHERAL GRATING RESOLUTION

We measured resolution at 10 degrees in the inferior temporal retina using horizontal and vertical gratings of different contrasts which modulated in time at temporal frequencies from 0 to 40 Hz. Since peripheral grating resolution is directly related to the sampling density of retinal ganglion cells this allowed us to observe changes in responding ganglion cell density as the stimulus properties changed to selectively stimulate magnocellular pathway cells (M cells) instead of parvocellular pathway cells (P cells). At all contrasts there was no decline in resolution performance up to 10 Hz, after which resolution deteriorated significantly, this effect being greater at lower contrasts. The predicted psychophysical resolution limit for M cells calculated from the anatomical data of Dacey indicates that resolution for high temporal frequency (30 Hz) or low contrast (5%) stimuli is too good to be mediated by M cells alone and there is still significant P cell stimulation by these stimuli.