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A procedure for transmitting the letters of the alphabet by tone-coded signals was examined in quiet and against a noise background. The procedure employed successive selections, each from among a small number of alternatives, in order to transmit a target vocabulary of 25 letters. Four stimulus variables: tonal frequency, sound level, location, and duration were examined, one at a time. Successive selections were made among two, three, and five alternatives per variable. The highest reception rate was obtained with a three-alternative frequency-coded display. Reception of tone-coded signals in noise was nearly equivalent to that in the quiet, when the tonal signals were about 3 db above masked threshold.

No abstract

A procedure for transmitting the letters of the alphabet by tone-coded signals was examined in quiet and against a noise background. The procedure employed successive selections, each from among a small number of alternatives, in order to transmit a target-vocabulary of 25 letters. Four stimulus variables: tonal frequency, sound level, location, and duration were examined, one at a time. Successive selections were made among two, three, and five alternatives per variable. With less than 1 min of practice at slow rates of presentation with the two-alternative frequency code, naive listeners were able to receive the entire vocabulary with insignificant error. The highest transmission rate was obtained with a three-alternative, frequency-coded display, at only about 1.5 bits per sec. Transmission of tone-coded signals in noise was nearly equivalent to that in the quiet, when the tonal signals were about 3 db above masked threshold.