A generation ago, when the poetry of PEnnsylvania and BUtterfield was about to give way to telephone numbers in unpoetic strings, a critical question arose: Would people be able to remember all seven digits long enough to dial them?

And when, not long afterward, the dial gave way to push buttons, new questions arose: round buttons, or square? How big should they be? Most crucially, how should they be arrayed? In a circle? A rectangle? An arc?

For decades after World War II, these questions were studied by a group of social scientists and engineers in New Jersey led by one man, a Bell Labs industrial psychologist named John Karlin.

By all accounts a modest man despite his variegated accomplishments (he had a doctorate in mathematical psychology, was trained in electrical engineering and had been a professional violinist), Karlin, who died Jan. 28, at 94, was virtually unknown to the general public. But his research quietly yet emphatically defined the experience of using the telephone in the mid-20th century and afterward.

“He was the one who introduced the notion that behavioral sciences could answer some questions about telephone design,” said Ed Israelski, an engineer who worked under Karlin at Bell Labs in the 1970s.

In 2013, the 50th anniversary of the introduction of the touch-tone phone, the answers to those questions remain palpable at the press of a button. The rectangular design of the keypad, the shape of its buttons and the position of the numbers all sprang from empirical research conducted or overseen by Karlin. The legacy of that research now extends far beyond the telephone: the keypad design Karlin shepherded into being has become the international standard on objects as diverse as ATMs, gas pumps, door locks, vending machines and medical equipment.

Karlin, associated from 1945 until his retirement in 1977 with Bell Labs, headquartered in Murray Hill, N.J., was widely considered the father of human-factors engineering in U.S. industry. A branch of industrial psychology that combines experimentation, engineering and product design, human-factors engineering is concerned with easing the often ill-considered marriage between man and machine.

Karlin later said he realized that the dynamics of using a telephone involved far more than speaking and hearing. In 1947 he persuaded Bell Labs to create a unit to study these larger questions; Karlin became its head in 1951.

By the late 1950s, when touch-tone dialing — much faster than rotary — seemed an inevitability, Karlin’s group began to study what form the phone of the future should take. Today’s omnipresent 12-button keypad, with star and pound keys flanking the zero, grew directly from the victorious design.