A SURVEY OF THE SENSES
Psychophysics allows us to specify the correspondence between physical stimuli and psychological experiences, but this is just the first step of our inquiry. We also want to understand why this correspondence is as it is. Let’s say, for example, that we’ve learned from psychophysics that placing a particular molecule on the tongue leads someone to say, “Yeah, I can detect a taste—and it’s sweet. It’s chocolate!” What are the steps that bring us from the molecule to this recognition? As our first question, we might ask how the molecule manages to trigger a response in the nervous system at all. We’d also want to ask why the molecule leads to a sensation of sweet, while some other molecule might lead to a sensation of salty. And once the molecule has triggered a response in the nerv-ous system, how does this response lead to the conscious experience of tasting a deli-cious bit of chocolate?
To answer questions like these, notice that we need to begin with the physics of the stimulus. From there we’ll move to electrochemistry, to examine how physical inputs trigger events in our bodies. Next we need to ask how the nervous system analyzes and then recognizes these incoming signals. Then, finally, we can zero in on our ultimate target—an explanation of the conscious experience of the “chocolate” sensation; or, with a different stimulus, the conscious experience of seeing a beautiful shade of blue.
Let’s pause to appreciate the extraordinary ambition of this project. We’re seeking to build a bridge from events that are microscopic and objective to events that are large scale and entirely subjective. We’re trying to specify the connections that will let us move seamlessly from a discussion of physics at one end of the process to comments about conscious experience at the other end. Seems ambitious, doesn’t it? Maybe so, but we’ve made enormous progress on this project.