Qualia

Perhaps the most difficult biological question of all might be how and why electrochemical neuronal activity in the brain generates subjective conscious experience such as the redness of red or the painfulness of pain. Neuroscientists track how light impinging on the retina is transformed into electrical pulses (neuronal spikes), relayed through the visual thalamus to reach the visual cortex, and finally culminates in activity within speech-related areas causing us to say ‘red’. But how such experience as the redness of red emerges from the processing of sensory information is utterly mysterious. It is also unclear why these experiences possess phenomenal characteristics, which can be directly accessed only from the subject having the experience. This is called the ‘hard problem’ of consciousness as coined by the philosopher David Chalmers. The phenomenal aspect of consciousness or ‘what it is like’ character of subjective experience is called ‘qualia’; the singular form of the word is ‘quale’, from the Latin for ‘what sort’ or ‘what kind’. In this Primer, we provide an overview of the term ‘qualia’ and its conceptual issues, and how neurobiological approaches can contribute to clarify some of these issues.