Originally posted by humy
Arr thanks for that.
That seems to answer at least one of my questions: assuming birds have the same red cone sensitivity of light as humans, there really is two local maxs to that response curve! And the lower max to the left explains why we see violet light as not blue but violet light!
I'm wary of this conclusion, the apparent double peak could easily be noise. You might want to look at the paper that this graph is taken from , which you can read for free online. The eye came from a patient at Moorfields Eye Hospital who had a malignant tumour. The eye was removed at 10:30 am and dissection started at 2:30 pm at Sussex University. Whether healthy eyes in the body will behave like this is an unresolvable question. However, the real problem for your statement about multiple local maxima is to do with the baseline behaviour of the microspectrograph. The central figure and the shape of the peak around it are good (i.e. well clear of the baseline behaviour of the instrument), but you should see the graphs on page 504 (the article starts on p.501 of the journal), the signal to noise ratio is getting pretty small and is not far from the baseline response of the instrument. The baseline behaviour of the instrument also shows this upswing
. So the apparent upswing looks to me like an artifact of the equipment and nothing to do with the actual behaviour of the rods and cones.
This link takes you straight to the page where the raw data is plotted, the graphs Wiki copied are on p 505.