By Roger Segelken
Watch some wine-tasters contemplate their choice and you might think flavors take forever to register in the brain. In fact, humans can make taste-dependent decisions after as little as 50 milliseconds (50 thousandths of a second) of tasting, research here is showing.
That's a good thing, says sensory physiologist Bruce P. Halpern. For awhile it looked like even rats made up their minds faster than humans.
"Rats need only 125 milliseconds to make a taste-dependent decision, but for years it was thought that humans require 700 to 1,000 milliseconds," said Halpern, chair of the Department of Psychology, professor of neurobiology and behavior and the recently named Susan Linn Sage Professor of Psychology. "Taste," he said, "was always described as the 'unusually slow sensory system' in humans."
Granted, rats have a life-or-death reason to make up their minds quickly about taste -- especially tastes that may be poison. Rats drink by rapid licking, and they can't vomit away their mistakes, Halpern said. Humans are suction drinkers and ca hold liquids in the mouth for several seconds before swallowing or spitting out. But could rats really be nearly 10 times faster at tasting?
Halpern designed a series of experiments that eventually demonstrated that humans are both fast and flexible tasters. In one test, volunteers were asked to spit out a "target" flavor and swallow any others while throat microphones and lip electrodes measured events for computer analysis. The target flavor was very reliably spit, even when -- a few minutes before -- it had not been the target flavor and had been consistently swallowed instead.
"The spit test was never popular," he said. "Volunteers didn't mind, but lab assistants hated it."
Now that the sensory physiologist has humans registering taste in the 50-millisecondsrange, Halpern has moved on to more complex questions of interest not only to physiologists and psychologists but to the food-and-beverage industry. For example, how long does a taste sensation take to peak in intensity, change or disappear? Sweetener makers don't want the taste to rise too slowly or leave an aftertaste, he noted. But beer makers may want to provide a slowly increasing perception of bitterness.
His efforts at time-intensity tracking required redesigned experiments, and one, he said, "is similar to something that Cornell students apparently have a lot of experience with -- video games." Students use a joystick to draw pictures of changing taste intensities as they experience them. Another test, time-quality tracking, requires a little more training: learning keyboard codes for 24 taste descriptions, such as "fruity," "bouillon" and "yuck."
Halpern, a member of the Cornell faculty since 1966, is the seventh psychologist to hold a Sage Professorship. (Terence H. Irwin is the Susan Linn Sage Professor of Philosophy and Humane Letters.) The chair was named for the late wife of Henry W. Sage when he endowed and established the Susan Linn Sage School of Philosophy in 1891.
Eleanor J. Gibson served as Sage Professor of Psychology from 1972 until her retirement in 1979 and is now the Sage Professor of Psychology Emeritus. The psychology professorship was most recently held by Ulric Neisser, who left Cornell for Emory University in 1983; Neisser will return to Cornell this year for a professorial appointment.
At Cornell, Halpern teaches Chemosensory Perception, Sensory Function, and Effects of Aging on Sensory and Perception Systems.
Research in sensory physiology also has clinical applications, potentially improving the diagnosis and treatment of chemosensory (smell and taste) disorders, Halpern said.