The dependence of
RF
onh on
r and
frequency
(Figs. 4B and 5) is similar to that observed for the magno-
and parvo-cellular retinal ganglion cells activity
7 and
for the pattern electroretinogram (PERG), a response correlated with
ganglion cell activity.
9 10 17 18 By recording the
responses of magno- and parvocellular ganglion cells to luminance and
R–G equiluminance flicker modulation in monkeys, it was
found that, at high frequency, response sensitivity of magnocellular
ganglion cells was substantially weaker for the equiluminance than for
the luminance flicker.
7 By contrast, at low frequency, the
response sensitivity of parvocellular ganglion cells to chromatic
equiluminance was stronger than the corresponding responses to
luminance flicker. Recordings of the steady state PERGs at relatively
high temporal frequencies (≥6 Hz) as a function of
r of
R–G patterns revealed that the response amplitude decreased
significantly when
r was changed from luminance to mixed
luminance and chromatic contrast modulation.
9 18 10 Furthermore, in both humans and monkeys the PERG amplitude showed a
local maximum at equiluminance.
9 10 By decreasing stimulus
temporal frequency, this maximum was relatively more pronounced,
compared to the responses to patterns of pure luminance
contrast.
9 These similarities suggest a correlation
between the observed
RF
onh behavior and the
physiological responses of retinal ganglion cells to respectively
high-frequency luminance flicker modulation and low-frequency
equiluminance flicker chromatic modulation. Although the neural
responses to luminance flicker may have a contribution of both magno-
and parvocellular systems,
9 18 it may be suggested that
the responses to equiluminance flicker reflect, selectively or
prevalently, the activity of the parvo system.
7 8 It
should be noted, however, that the neural parvo-response might change
depending on the type of stimulus. It is indeed known, from single
cells studies
7 that the temporal response function of the
parvo-system is low-pass with chromatic, but band-pass with luminance
modulation.