Point-and-Click Psychophysics

Poster sessions at scientific meetings are a strange ritual. The idea is simple enough: the presenter pins a poster describing his work to a big easel and stands there for a few hours talking about it to whomever stops by and displays (even an iota of) interest. The posters themselves look a lot better than they did when I was in grad school; they are laser printed in color on a single piece of glossy paper. Back in the day they were literally cut-and-paste jobs that required a lot of stick pins.

One thing that hasn’t changed is the social awkwardness of the poster session. Big name presenters are mobbed; the unknown post-doc with a hot result might get some attention; an incremental advance in a fringe area will attract maybe three people in an entire morning. Call it a sympathy viewing.

Negotiating the poster session floor is hazardous. Pause too long in front of one and you may trigger an unsolicited offer to “talk you through” the poster. A one-minute once-over is welcome; one can always ask for more information. But watch out for the obsessive (or novice) presenter for whom each detail is precious and for whom time has no meaning. It’s not easy to politely extract oneself from the minutiae geek. 

At the AChemS meeting I work the floor with a list of posters I want to see. New findings are the currency of the realm, but I’m also looking for new experimental techniques: ways of observing or quantifying perception that are easy to use and give robust results.

I found one at Barry Green’s poster “Measuring referral of retronasal odors: The effect of taste.” Barry was once a colleague of mine at the Monell Chemical Senses Center; he now works at the John B. Pierce Laboratory at Yale. He’s a hard-core psychophysicist devoted to measuring sensation and perception in various sensory modalities. His poster grabbed my attention because it involved the interaction of smell and taste. (Retronasal olfaction is odor perceived from food or drink in the mouth; things smelled from within rather than from without.)

In the study, each subject held 5 ml of liquid in his mouth for three seconds then spit it out. He spent the next five seconds paying attention to where in his mouth and/or nose he smelled an odor. (The solutions contained various combinations and concentrations of salt, sugar, citral and vanillin.) A computer screen displayed an anatomical cartoon of a human head with nose, mouth, tongue and palate. The volunteer’s task was to color in the location of the odor using a mouse and Microsoft Paint.

That alone is so cool—an intuitive way for people to tell you where they are experiencing a retronasal smell. No vocabulary (soft palate, nasopharynx, etc.); no number scales; just “show me.” Easier than Etch A Sketch.

So what did Barry find? In a nutshell, odors presented in a water solution are localized equally often to the nose and mouth. When the solution is sweetened with sucrose, the odor is perceived closer to the tongue. Adding salt to the solution doesn’t produce this effect. This adds to our recently expanding knowledge of smell and taste interactions, but to my mind the innovation in measurement technique is the best part.