Q. Just how sensitive a person are you? We're talking the five senses sensitive.

A. As a typical healthy perceiver, you are able to. . .

- Smell a lone drop of perfume diffused through a three-room apartment (from Charles G. Morris' "Psychology: An Introduction" and other sources)

- Identify something as salty or sweet within .1 second of it touching your tongue

- Gauge a sound's direction based on ..00003-second difference in arrival time from ear to ear

- Feel the weight of a bee's wing falling on your cheek from the height of .4 inch

- On a clear, dark night, see a small candle flame from 30 miles away

- Taste .04 ounce of table salt dissolved in 530 quarts of water (employing a fraction of your 10,000 taste buds)

- Feel a nerve fire when a downy skin hair vibrates .00004 inch

- In balmy youth, hear frequencies from 16 to 20,000 cycles per second (with middle C at 256), a range of more than 10 octaves.

Q. Do you ever find yourself talking to people who aren't there?

A. University of California researcher Ronald K. Siegel, author of "Fire in the Brain: Clinical Tales of Hallucination," tells of a man named Steve whose pregnant wife had died shortly before a daughter was to be born, whom they had already named Star.

Steve lived alone but said he wasn't lonely, because he was in communication with Star's spirit. "She's 3 years old," he said - not "She would have been 3 years old."

He said she was born "on the other side" and could travel at will through time and space, and so visited him often. He saw her now clear as day with sandy hair like her mother, and spoke to her, heard her words. She was the classic bereavement companion, a "typical hallucination suffered by people who mourn a loved one," says Siegel.

Siegel likens it all to an incident in which ventriloquist Edgar Bergen was overheard talking - not rehearsing - alone with his wooden dummy Charlie McCarthy. The two were discussing matters of love and life when they discovered the eavesdropping visitor.

Obviously embarrassed, Bergen explained, "I was talking with Charlie, the wisest person I know." "But it was only your own mind responding," the visitor remarked.

"Well, I guess ultimately it is," allowed Bergen, "but I ask Charlie these questions and he answers, and I haven't the faintest idea of what he's going to say and I'm astounded by his brilliance - so much more than I know."

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

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 physicist Jearl Walker.

In experiments by Paul Tobias and J. P. Meehan, 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 doughnut-like shapes or appearances of a solar eclipse against a dark background.