Mechanisms of masking.

Some of the strategies which an observer might use in detecting a tone presented against a background of noise are discussed. In Experiment I thresholds for tones in noise were measured under a number of different conditions, using flat−spectrum and notch−filtered noises, in a two−interval forced−choice task. Threshold did not correspond to a constant difference in critical−band levels on the two halves of the trial. Performance at the highest frequency used (6.1 kHz) was worse than at lower frequencies (1055 and 4080 Hz), and, in contrast to them, was not independent of overall level. This is contrary to the classical data, and indicates that the critical ratio is not a constant fraction of the critical band. In Experiment II the intensity discrimination of 1/3−octave bands of noise was studied. The noises were presented alone or in a wide−band noise background. For noise bands presented alone, performance is roughly independent of overall level, and improves slightly with increasing center frequency. Fo...