Psychology and telephone design →

Bell Labs engineer John Karlin helped pioneer the use of behavioral testing in industrial design. His New York Times obituary offers this nugget:

Mr. Karlin also introduced the white dot inside each finger hole that was a fixture of rotary phones in later years. After the phone was redesigned at midcentury, with the letters and numbers moved outside the finger holes, users, to AT&T’s bewilderment, could no longer dial as quickly.

With blank space at the center of the holes, Mr. Karlin found, callers no longer had a target at which to aim their fingers. The dot restored the speed.

Karlin, the Times reports, “stud[ied] the psychological capabilities and limitations of ordinary people” to identify telephone designs that maximized usability.

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