Bollocks.
Bertie sees a green thing. Green light impinges on his eyes, which creates electrochemical reactions in his nervous system, and, eventually, his brain. There is never any green thing in Bertie's brain, there are communication patterns. And they are eminently physical and material.
These patterns give rise to others, some of which are patterns of recall of either knowledge or emotion, cascading communications, none of which are green, sad, or have to do with the colour of the jacket in which his father was buried, e.g. (I'm making all of this paragraph up for illustrative purposes.)
Bertie recalls a green thing. Using mechanisms we are only now beginning to understand, Bertie causes those patterns to repeat, triggering many of the same reactions elsewhere in his brain. Again, none of the things in his brain are green, sad, a jacket, a funeral, etc., but all of these things are physical, material, measurable.
We just don't know how to measure them at fine enough detail, but we have reliable hypotheses backed by apparently valid conceptual theories, etc., to make us believe we are on the right track.
I find it very hard to leave this whopper of an error aside and continue with the article.
If someone else is less lazy and more forgiving than me, please tl;dr! Thanks.
The argument talks about the experience of "greenness" as the after-image of a red object:
Suppose Bertie is experiencing a green after-image
as a result of seeing a red flash bulb go off;
the greenness of the after-image is the quale.
Indeed, there is no green object outside or inside of Bertie. The light bulb was red, the memories or patterns in the brain are not green. Sensory qualities pose a serious problem for materialist
theories of the mind. For where, ontologically speaking,
are they located?
The argument is about materialist theories of the mind.
After the argument, which seems to me a valid argument against oldschool hardcore materialism (a material location for the greenness is needed), the following paragraph mentions a more modern development, namely the modern representational theory of sensory qualities, sometimes as an attempt to resolve the foregoing dilemma compatibly with materialism.