Masking protection in the perception of auditory objects

Three experiments demonstrate the phenomenon of masking protection, where the threshold for identifying a brief masked signal is lowered when that signal is presented in conjunction with other sounds that provide no information about the correct response and which are separated from the distinctive signal by more than a critical band (Gordon, 1997a,b). The ®rst experiment shows that listeners' thresholds for distinguishing a low tone (375 Hz) from a high tone (625 Hz) is lower when those tones are accompanied by a synthetic speech sound that combines with the tones to give percepts of /I/ or /e/, respectively. This e€ect is reliable for individual listeners and involves a change in perceptual sensitivity. The second experiment shows that a similar lowering of identi®cation thresholds is produced when the distinctive signals are combined with high-frequency, acoustic energy that does not prompt a speech percept. The third experiment shows that identi®cation thresholds are elevated when the non-distinctive, high-frequency acoustic energy leads and lags the distinctive signals. The results of the experiments indicate that mechanisms of perceptual object formation that exploit the temporal alignment of energy changes across the spectrum can contribute to the accurate identi®cation of speech and non-speech sounds. Ó 2000 Elsevier Science B.V. All rights