Philosophers have long agonized over the fact that one person cannot enter the mind of another. He cannot think the other's thoughts. He cannot feel the other's pain. And he cannot hear the sounds in the other's head.

A piece of technological wizardry known as the cochlear implant revives that ancient problem. We call it an artificial ear, but it isn't. We think of it as a miracle that can allow the deaf to hear, but it can't.

It does something else.

Public television's look at the cochlear implant, the first of four segments of tonight's "Discover" program (8 p.m. on Channel 26, closed-captioned), underscores the limitations of medical technology while celebrating the promise.

We meet Dennis Dale, a cheery father of three who works as a newspaper printer and, 29 years ago at age 9, went deaf from spinal meningitis. He is profoundly deaf, which means he hears nothing at all.

His advantage, though, is that his auditory nerves, leading from his ears to his brain, are intact. They would send sound messages to the brain if only they were activated. Normally, the nerves would be activated by tiny hair cells in the inner ear's seashell-shaped cochlea, vibrating in response to sound waves. But Dale's hair cells were destroyed by the meningitis in 1956.

The cochlear implant -- a string of 22 electrodes attached to an outside receiver -- replaces those hair cells.

The program follows Dale from shortly before he receives his implant through his struggle to try to make sense of the strange sounds suddenly entering his head. We listen to him wonder about the sounds of his sons' voices and then "hear" those voices for the first time.

The show gives what feels like a true sense of Dale's personality, but it tells little of his history. In a bylined article in the Staten Island Advance, the newspaper for which he works, Dale recalled his last moments of hearing:

"I got sick on the train. We were near my grandmother's, so we went there . . . I was feeling worse and worse. I talked to my mother on the phone. She wanted to know if she should come down or not. She didn't know how sick I was. I said, 'Come down.'

"That was the last time I used a phone."

The next time, 29 years later, is when he again tries to talk to his mother by phone, one of the most moving moments of the show. Sounds are there, buzzes and beeps, but no meaning. "All static," he says at one point.

He has to learn to hear again.

Dale's early frustrations are contrasted to the remarkable success of an Austrian woman who has worn a similar implant for four years. With a Mozart horn concerto providing the background music, Sonja is shown taking part in normal conversations and doing well in a hearing test.

"Sonja is lucky," narrator Peter Graves says, "a real star in the world of cochlear implant patients."

Her implant, made by 3M, uses a different speech-processing computer than Dale's, although that does not explain her success. The technology is too new for doctors to be able to predict when an implant will succeed and when it will fail.

A study in the journal Medical Progress Through Technology concludes that "it is possible to reestablish some understanding of open speech through the use of the cochlear implant without additional lipreading."

How much understanding? Cochlear Corp., maker of Dale's implant, puts it this way in a warning it distributes with promotional material: ". . . it is important to realize that the sounds heard will not be the same as those with normal hearing."

Dale puts it this way: "Being deaf for 29 years, I was getting used to it. Since I've been wearing this, I can't go without it."

And the "Discover" program puts it another way. At one point, through an eerie rendering of the nursery rhyme "Hickory Dickory Dock," the program tries to approximate what Dale hears with his implant. The simulation is almost amusing, sounding like a rhyme set to weird music. It is a reminder that what Dale really hears will always be a mystery. Resources

For more information on cochlear implants:

Alexander Graham Bell Association for the Deaf, 3417 Volta Pl. NW, Washington, D.C. 20007, (337-5220, voice or TTY).

Cochlear Corp., 61 Inverness Dr. East, Englewood, Colo., 80112 (800-523-5798).

3M Otologic Products, Bldg. 225-5N-03, St. Paul, Minn., 55144 (800-328-1684; TTY 612-736-4608).

Symbion Inc., 825 N. 300 West, Salt Lake City, Utah 84103. (800-654-7400; TTY 801-359-1656).