Lloyd Alexander Jeffress (November 15, 1900 – April 2, 1986)[1] was an acoustical scientist, a professor of experimental psychology at the University of Texas at Austin,[1] and a developer of mine-hunting models for the US Navy during World War II and after,[2] Jeffress was known to psychologists for his pioneering research on auditory masking in psychoacoustics, his stimulus-oriented approach to signal-detection theory in psychophysics, and his "ingenious" electronic and mathematical models of the auditory process.

[6] The next year, he transferred to the University of California at Berkeley as a physics major, but, while completing that degree, he became increasingly interested in the newly expanding field of experimental psychology.

[2] Jeffress was accepted as a graduate student in psychology at the only school to which he applied, UC Berkeley, in 1922, and soon associated himself with Warner Brown.

[1] While he was at Berkeley in 1925, his knowledge of physics and love of gadgets led him to develop a self-recording maze that gained him a publication—his first—with one of the best-known cognitive psychologists of his time, E.C Tolman.

It was only after he began his long association with UT's Defense Research Laboratory (DRL) in 1950 that he had assistants capable of, and interested in, doing all the menial work necessary to implement and run the experiments he said he had been thinking about all along.

[10] Beginning about 1940, Jeffress' primary research interest was the auditory system, especially the mechanisms underlying sound localization.

[2] In 1947 and 1948, he worked as the Hixon visiting professor at the California Institute of Technology, where he brought together many premiere scientists of his day to examine the state of knowledge about human behavior and the brain.

[6] The participants in the 1948 Hixon Symposium on neural mechanisms were noted academics from a number of disciplines: Pauling (chemistry), Heinrich Klüver (cybernetics), John von Neumann (cellular automata), Karl Lashley (behavior and learning), Ogden Lindsley (precision teaching), Rafael Lorente de Nó (neuroanatomy/neurophysiology), Warren McCulloch (neural network modeling), and W.C. Halstead (neuropsychological assessment).

[15] Many of the papers collected in Cerebral Mechanisms in Behavior: The Hixon Symposium, with Jeffress as editor, became classics cited in thousands of scientific articles.

The Science magazine review of the book said: "The Hixon Symposium has significance for anyone concerned with the theory of human behavior and contraptions man himself has built—namely, computing and cybernetic machinery.

Upon his return after the war, Boner became director of the Defense Research Laboratory (DRL) at the University of Texas,[17] and Jeffress eventually became head of the Psychoacoustics Division.

[17] Jeffress' first project at DRL was to determine whether the improvement humans show when detecting binaural rather than monaural signals could be adapted to Navy sonars.

Jeffress designed and built an experimental binaural sonar that he and his students tested at Austin's Lake Travis.

While this project was unsuccessful, it initiated a program at DRL on masking and binaural hearing that endured, and was highly productive, for more than 20 years.

These data, which were in the form of photographic and magnetic tape recordings, had to be analyzed in detail to provide quantitative measures of target detection probability, location errors, etc., as a function of a number of variables.

This document, together with other reports he wrote, remained the standard works on mine hunting and were still to be found on every mine-hunting craft in the US Fleet at Jeffress' death.

[2] Jeffress made many contributions to the science of mine countermeasures, especially in the areas of precise radio and acoustic navigation systems.

Hirsh on what later came to be called masking-level differences caught Jeffress' attention and began him on a two-decade research program in which he and his students documented various aspects of the binaural system's performance in signal-detection tasks.

[2] Upon his death, the American Journal of Psychology (AJP) called Jeffress the "acknowledged authority" on auditory masking and masking-level differences.

Jeffress' approach to understanding sensory and perceptual behavior was to examine the physical stimulus carefully first to attempt to isolate those aspects of it that appeared to be critical.

[1] In a series of papers published in the Journal of the Acoustical Society of America in the 1960s, Jeffress developed what he called a "stimulus-oriented" view of human detection performance.