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Laboratory experiments were undertaken to develop improved aural detection criteria for light aircraft. Specifically two series of psychoacoustic judgment tests were conducted to determine the applicability of the psychophysical Theory of Signal Detectability (TSD) to prediction of the aural detectability of light aircraft noise signatures in jungle noise backgrounds. The first series of tests produced data supporting development of a simplified graphical prediction method based on TSD. The second testing program validated the precision and accuracy of the prediction method under quasi-realistic listening conditions. Predicted levels of performance were typically within one or two dB of the data averaged for all observers.

A previous test exposed chinchillas for seven days to an octave band of noise centered at 500 Hz and at 95 dB SPL to produce temporary shifts of behavioral auditory thresholds which required 4-7 days to recover to normal. In the present study physiological potentials were measured about 5, 24, and 48 hours after exposures to the same noise for 2 or 3 days. Cochlear microphonoic responses and dc endocochlear potentials were measured in each of the three cochlear turns. Input-output functions for whole-nerve action potential responses to clicks and visual detection levels for early averaged evoked responses arising in the brain stem were also measured.