That's a very cool fact of which I had been unaware. I'm posting this just to let our readers know about it. As to your question, I don't really have anything much to say.
We can always spectrum-analyze an optical signal and make five outputs corresponding to the pigeons' five different types of cone cell. Maybe we could code three of the signals as colors and two as fast and slow modulations in intensity, or some other perceptible thing. Then we could at least see what patterns the pigeons see. I wonder if an infant raised on that sort of image would develop the brain circuitry to form the equivalent of a five-color sense.
Generally, it's more or less impossible to imagine what it would be like subjectively to experience with additional senses, like bat sonar, platypus electrical senses, etc. It sure would be fun though.
p.s. Discussions with my more neuro-scientifically literate son bring up some more points. There are some women who are quadrochromatic, but since they have two rather similar red receptors the subjective difference isn't big. More importantly, he points out that the conventional view is that our brain is not
pre-wired to know that there are three types of color receptors. It's more likely that the detailed neural structure forms in response to the actual inputs. Therefore if one were to add genes for a couple of different cone cells to a developing infant (the dreaded human-pigeon hybrid) you could probably raise people who would see pentachromatically. Maybe my artificial modified input scheme would have the same neural effect.
It's still hard to subjectively imagine a different sensory world. You might try talking to a color-blind friend (common among males) about what they're subjectively missing, then try changing the sign of what they say.
(published on 07/21/11)