The hard problem was discussed in the December 1995 issue of Scientific American. Here are two excerpts:
David J. Chalmers:
'Researchers use the word 'consciousness' in many different ways.
To clarify the issues, we first have to separate the problems that are
often clustered together under the name. For this purpose, I find it
useful to distinguish between the 'easy problems' of consciousness
and the 'hard problem' of consciousness. The easy problems are by
no means trivial - they are actually as challenging as most in
psychology and biology - but it is with the hard problem that the
central mystery lies.
'The easy problems of consciousness include the following: How can a human subject discriminate sensory stimuli and react to them appropriately? How does the brain integrate information from many different sources and use this information to control behavior? How is it that subjects can verbalize their internal states? Although all these questions are associated with consciousness, they all concern the objective mechanisms of the cognitive system. Consequently, we have every reason to expect that continued work in cognitive psychology and neuroscience will answer them.
'The hard problem, in contrast, is the question of how physical
processes in the brain give rise to subjective experience. This puzzle
involves the inner aspect of thought and perception: the way things
feel for the subject. When we see, for example, we experience visual
sensations, such as that of vivid blue. Or think of the ineffable sound
of a distant oboe, the agony of an intense pain, the sparkle of happiness
or the meditative quality of a moment lost in thought. All are part of
what I am calling consciousness. It is these phenomena that pose the
real mystery of the mind.'
For further study of the nature of the hard problem, please
access Chalmers' 1994 Tucson I paper.
Francis Crick and Christof Koch:
'We believe that at the moment the best approach to the problem of
explaining consciousness is to concentrate on finding what is known
as the neural correlates of consciousness - the processes in the brain
that are most directly responsible for consciousness. By locating the
neurons in the cerebral cortex that correlate best with consciousness,
and figuring out how they link to neurons elsewhere in the brain,
we may come across key insights into what David J. Chalmers calls
the hard problem: a full accounting of the manner in which subjective
experience arises from these cerebral processes.'