But the fact that we can scientifically test and prove that individuals experience the world differently raises the peculiar question: do you and I experience the same world? On the surface "no", but deep down, we share so much experience with enough overlap that for all practical purposes "yes the world is 'objective' and we share it".
Here is a bit from a blog entry on the ScienceBlogs web site written by a molecular and developmental neurobiologist:
Subjective experience poses a major problem for neuroscientists and philosphers alike, and the relationship between them and brain function is particularly puzzling. How can I know that my perception of the colour red is the same as yours, when my experience of the colour occupies a private mental world to which nobody else has access? How is the sensory information from an object transformed into an experience that enters conscious awareness? The neural mechanisms involved are like a black box, whose inner workings are a complete mystery.Go read the whole article. If you are not aware of synesthesia, then this article will open your mind to a whole world that you -- and I -- are missing because we aren't wired in the necessary way. These synesthetes have different wiring in the brain (while colour blindness comes from defective molecules in the cone cell receptors of the retina). I watched my mother struggle with problems after brain surgery because she had left neglect syndrome and cognitive problems with recognizing people (something like prosopagnosia, but I'm safer to simply call it a type of agnosia).
In synaesthesia, the information entering one sensory system gives rise to sensations in another sensory modality. Letters can evoke colours, for example, and movements can evoke sounds. These extraordinary additional sensations therefore offer a unique opportunity to investigate how the subjective experiences of healthy people are related to brain function. Dutch psychologists now report that different types of synaesthetic experiences are associated with different brain mechanisms, providing a rare glimpse into the workings of the black box.
One of the best characterized forms of synaesthesia is grapheme-colour synaesthesia, in which seeing or hearing a particular letter or number evokes the experience of a particular colour. One well-known grapheme-colour synaesthete is the Nobel Prize-winning physicist Richard Feynman, who said, "When I see equations, I see the letters in colours." Feynman was a "projector" synaesthete - he automatically perceived the evoked colours in the external space, or "outside world". The quality of the synaesthetic experience can, however, differ markedly between individuals: in "associator" synaesthetes, the evoked colour is perceived internally, or "in the mind's eye".
Romke Rouwe and H. Steven Scholte of the University of Amsterdam now report that these different synaesthetic experiences are associated with distinct underlying brain mechanisms, and that there also are structural differences between the brains of projector and associator synaesthetes.
One of my favourite books about this synesthesia is The Man Who Tasted Shapes by Dr. Richard Cytowic. Another interesting book is Born on a Blue Day by the synesthete and mnemonist and autistic savant Daniel Tammet.
My favourite book about prosopagnosia is Oliver Sacks' book The Man Who Mistook his Wife for a Hat.
The world is stranger than we would believe. The wonderful thing about science is that it opens us up to the richness of the real world. I get so tired of religious fanatics who pound on a two thousand year old book and claim that "all truth" is bound in the pages of that book. What a sad, blighted, narrow-minded view of the wonders of the world.