Assume that a human being is a communication channel, taking input and generating output, with the overlap being the amount of transmitted information.
For each perceptual domain (visual, auditory, olfactory, ...) identify perceptual primitives (such as line orientation in the visual domain, pitch in the auditory, and salinity in he olfactory), and measure the number of distinct levels that the average participant can identify with a high degree of accuracy.
The amount of information will follow an asymptotic behavior.
Label this level the channel capacity for information transfer by the human and measure it in bits.
Ignore results from ``specialists'' (experts in the domain of image interpretation) and limit the training given to participants.
Don't include noisy data or context (for now, but this will be important).