Frequency Doubling
Warning: this phenomenon requires much goodwill on your side…
What to do & observe
Short version. How many black stripes do you see on the right? Probably
four. Now press ‘slow’. How many are there now? – I did not change the number of
stripes, just the speed with which they shift.
Longer version. The grating on the right comes up set to a low spatial
frequency, rapidly phase inverting (=high temporal frequency). To my chagrin the
phase reversal has many hiccups, it stammers (explanation
here). Pick times where phase reversal is regular and ask yourself “how
many vertical black stripes do I see?”. You will probably see four. Now switch to
a low temporal frequency (press ‘slow’) and observe that there are actually only
two vertical black stripes. That’s frequency doubling – you see twice as many stripes
as there are if the following conditions are met (1) temporal frequency is high,
(2) spatial frequency is very low and (3) contrast is high.
Choose a high spatial frequency (press ‘hi’) and then switch the temporal frequencies
between slow and fast – clearly no frequency doubling occurs for such narrow-striped
(=high spatial frequency) gratings.
Comment
The phenomenon was reported by Kelly 1981. The figure on the above depicts visual
sensitivity vs. temporal and spatial frequency (combining the de Lange curve with
the contrast sensitivity function CSF). The striped gray area roughly outlines the
range where frequency doubling occurs.
For explanation, “only a bit of non-linearity” is required.
The frequency doubling phenomenon has made it into a clinical test –not a bad career–
with the following quirks:
1.There was a time (after Quigley 1987) where one thought that in early glaucoma
the magnocellular system is preferentially affected.
2.Ted Maddess looked a frequency doubling using both ERG/PERG and psychophysics
and suggested it be a test of the My subsystem [the cat X/Y-systems do
not map on to the Parvo(Pβ) / Magno (Pα) systems; rather cats don’t have
the Parvo (≈colour) system, and their x/y map into the primates’ Mx/My].
3.From this the spatially resolving Frequency Doubling Test (FDT) was developed
(e.g. Demirel et al. 1999), now commercially available (Humphrey tests at 0.25 cpd
and 25 Hz).
4.The FDT tests the contrast threshold where flicker is just perceived. Ironically,
at low contrast no frequency doubling occurs!
5.It is the current consensus that the magnocellular system is not preferentially
affected in early glaucoma (Johnson 2000, Crawford et al. 2000, Yücel et al. 2001,
2003).
6.Still the FDT performs, to a degree, as does any flicker test in glaucoma…
Sources
Kelly DH (1981) Nonlinear visual responses to flickering sinusoidal gratings. J
Opt Soc Am 71:1051-5
Quigley HA, Sanchez RM, Dunkelberger R, L. LHN, Baginski TA (1987) Chronic glaucoma
selectively damages large optic nerve fibers. Invest Ophthalmol Vis Sci 28:913–920
Maddess T, Goldberg I, Dobinson J, Wine S, Welsh AH, James AC (1999) Testing for
glaucoma with the spatial frequency doubling illusion. 39:4258–4273
Zeppieri & Johnson “Frequency Doubling Technology (FDT) Perimetry”
(at the International Perimetric Socienty)
Crawford ML, Harwerth RS, Smith EL 3rd, Shen F, Carter-Dawson L (2000) Glaucoma
in primates: cytochrome oxidase reactivity in parvo- and magnocellular pathways.
Invest Ophthalmol Vis Sci 41:1791-1802
Yücel YH, Zhang Q, Weinreb RN, Kaufman PL, Gupta N (2001) Atrophy of relay
neurons in magno- and parvocellular layers in the lateral geniculate nucleus in
experimental glaucoma. Invest Ophthalmol Vis Sci 42:3216–3222
Ansari EA, Morgan JE, Snowden RJ (2002) Glaucoma: squaring the psychophysics
and neurobiology. Brit J Ophthal 86:823–826
Yücel YH, Zhang Q, Weinreb RN, Kaufman PL, Gupta N (2003) Effects of retinal
ganglion cell loss on magno-, parvo-, koniocellular pathways in the lateral geniculate
nucleus and visual cortex in glaucoma. Prog Retin Eye Res 22:465–481
Created: 2004-12-21
Last update: 2013-10-04