TRANSDUCTION

transduction—how do activities at one level turn into influences at another? A classical example is sensory transduction. We know a fair bit about how light turns into the colors, shapes, and movements we see: light enters the eye, where it triggers a complex computational cascade among a network of highly organized cells in the retina. This generates highly structured nerve impulses that then travel through the brainstem and then into the cerebral cortex through processing stations that make progressively more complex connections, first just with this visual information and then taking account of more and more other information as well. We can tell a similar story about how we hear: vibrations in the air are transduced into what we experience as sound by going through the eardrum into the middle ear, which excites the tiny pitch-sensitive hairs of the cochlea, gets its initial processing in the brainstem, and then gets further sorted out in the primary and associational auditory areas of the cerebral cortex."