[By.Jove (Jove)]

I’m sure an experiment can be devised analogous to a hearing test and I can recall doing something similar with an optician many years ago regarding my own vision anomalies.

What I would suggest is this:

1. Take a broad-spectrum source, and set up a slit and spectroscope so a person looking into an eyepiece sees a nice big patch of 1 colour. You need a spectroscope that has some sort of calibrated dial so you can determine what colour they are being shown; and you want to do this remotely so that cannot tell when you changed the colour - or not. These devices exist but not cheap.

2. You will also want a means to dim the light source too; the slit width/length would probably do.

3. Put a shutter in the path, electrically operated that you can operate remotely, so you can turn the light on, at will, randomly.

4. Give the test person a button to press each time they see a coloured patch in the eyepiece.

Now, the way this works is that each time the person sees a colour patch, they press the button. This has to correlate with the moment you opened the shutter. You start with orange, move into red, and continue through the spectrum…

If they don’t press the button when you opened the shutter, or pressed the button with the shutter closed that’s a false response.

If they’re scoring above say 95% correlation, obviously they are seeing what you show them. As you change the frequency (colour) this correlation will change if they aren’t seeing the patch of colour.

The question is, at what level are they not seeing anything reliably ? 80% ? 75% ? 50% ? This is standard statistics and confidence-interval stuff for the mathematically inclined.