Temporal Effects in Simultaneous Masking and Loudness

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Abstract
The intention of the research described was twofold. One purpose was to investigate the difference between threshold curves for tones masked by bands of noise and the corresponding displacement curves obtained from models of the basilar membrane. The second object of investigation was the behavior of a strange masking transient which indicates that masking of a short signal pulse by a longer masker burst is stronger at the beginning of the masker burst than later under certain circumstances, but that under other conditions masking remains constant during the total duration of the masker. The threshold of signal pulses masked by masker bursts was measured as a function of different variables such as bandwidth and center frequency of masker, delay between onset of masker and onset of signal, duration of signal, and spectrum shape of masker. The results, especially those obtained when white noise with a frequency gap was the masker, lead to the hypothesis that the masking excitation appears almost instantaneously. This hypothesis was tested and accepted on the basis of loudness judgments comparing equally long tone pulses and white-noise pulses of very short and long duration. The conclusion that excitation occurs almost instantaneously, taken together with the known relationship between the masking effect of white noise and that of narrow-band noise, is construed to mean that a complex spatial inhibition in the nervous system may not be responsible for the narrow sensitivity curve; in fact, a sharp mechanical filter could account for the findings.

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