Eyes wide shut: Tripping in the dark


Q. Press lightly with fingertips on closed eyelids, and you may see brilliant flashes of light and color, called phosphenes. Why the free show? –T. Leary

A. Pressure stimulation of the optic nerves accounts for these "inner" sight sensations. In other cases, lack of stimulation will trigger them: People confined to dark cells report seeing phosphenes ("prisoners' cinema"), as do truck drivers after staring for long periods at snow-covered roads, says Cleveland State University's Jearl Walker in Flying Circus of Physics.

Back in Ben Franklin's day, it was fashionable to hold phosphene parties (Franklin himself attended one) at which guests would join hands in a large circle, then receive a high-voltage shock from an electrostatic charge generator. Switching currents on and off somehow unleashed colorful phosphenes in the participants (don't try this!).

In experiments by Paul Tobias and J. P. Meehan, reported in Scientific American, blindfolded volunteers who were spun in a centrifuge saw phosphene arrays of blue spots and stars. At 3.6 G's (3.6 times gravity), these inner visions became "golden worms," then at 4.5 G's the worms transformed into brilliant orange geometric patterns that began to pulsate. Following the centrifuge ride, subjects described phosphene afterimages lasting a minute or more, weird donut-like shapes or appearances of a solar eclipse against a dark background.

Given the acceleration-phosphene connection, pilots and astronauts are also apt to experience these images, as are rapidly spinning amusement park riders– providing, adds Walker, they're not too white-knuckled to notice the show.

Q. Can gustatory science tell us... What makes your favorite food or drink taste so darn good? –E. Lagasse

A. Something like 800 odorants exist, with a few or a few dozen combining into hundreds of unique experiences, says Cornell food scientist Terry Acree. Certain flavorants turn up again and again, such as cis-roseoxide, a component of flowers used in perfumes and that gives Lychee fruit a recognizable smell and Gewurztraminer wine a unique "Lychee note."

Chemoreceptors on the tongue produce perceptions of salt, sour, sweet and savory, responding to many fewer chemicals than the nose. Perceptions of hot, cool, astringent, pain and texture also are part of flavor, called "chemesthesis."

"Taken together, about 1000 chemicals go into flavor, that then combine with those for smell to create the singular food and drink experience," Acree says.

And more: Flavor perceptions are modified by memory and emotion–"Hum, this smells like salmon. But it doesn't taste like fresh salmon. It tastes spoiled. Yak! Spit!"

Oddly, it is entirely possible to have something smell great and taste terrible, as was often the case with wild fruits and vegetables before people bred them for better taste, says Acree.

"Other foods, such as the tropical fruit Durian– banned from hotels and airlines– may smell horrible but taste good," adds Cornell biochemist Karl Siebert. And according to Washington State University's Charles G. Edwards, "there are even molecules that you can't smell (tannins) that are so astringent you would really pucker up even though the food smelled good."

Q. Teratogens are environmental agents that can cause harm to a human embryo or fetus– alcohol, tobacco, aspirin, etc. As the list of these continues to grow, Moms-and-Dads- to-be grow increasingly concerned. In fact, what fraction of babies are born healthy, without abnormalities? a) 76 percent b) 86 percent c) 96 percent. –B. Spock

 A. Thanks to the marvels of human biology, only 4 percent (c) of babies are born with abnormalities, and most of these are so slight as to have minimal impact on daily function, say V. Gregory Payne and Larry D. Isaacs in Human Motor Development: A Lifespan Approach. In the battle against these problems is a growing array of diagnostic prenatal tools– ultrasound, amniocentesis, chorionic villus sampling, the alpha-fetoprotein test, and the triple-marker screening blood test– not cures, of course, but welcome aids in alerting expectant parents and health-care professionals.

Send Strange questions to brothers Bill and Rich at strangetrue@compuserve.com.