The incorporation of level and level-invariant cues for the detection of a tone added to noise.
The potential contribution of level-dependent and level-invariant cues for the detection of a tone added to narrow bands of noise was assessed in two experiments. In the first experiment, three masker bandwidths, 40, 120, and 360 Hz, and three center frequencies, 600, 1800, and 5400 Hz were tested. For the tone-in-noise detection task, the signal to be detected was a tone with a frequency equal to the center frequency of the noise masker. The level of the added tone was adjusted so as to generate d' scores of approximately 2 in a two-alternative, forced-choice procedure. Then, the distributions of across-interval changes in level were measured. The distribution of differences in level was applied to either the noise-alone or the tone-plus-noise stimuli, allowing the measurement of sensitivity to changes in level for a two-interval, forced-choice intensity discrimination task. For one of the four observers, there was a good correspondence between the d' values obtained in the tone-in-noise task and the d' values obtained in the intensity discrimination task. For the other three observers, the discriminability of changes in intensity could not account for the detection of a tone added to noise. In order to estimate sensitivity to level-invariant cues, the noise-alone and tone-plus-noise waveforms were scaled so as to present no reliable differences in level, and observers again detected which stimulus contained the added tone. Normalization led to d' scores smaller than those obtained in the initial tone-in-noise discrimination task, but performance levels did not fall to chance. For three of the four observers, the detection of a tone added to noise appeared to depend on both level and level-invariant cues. In a second experiment, psychometric functions were obtained for the detection of a tone added to noise, for the detection of changes in level associated with the noise-alone and the tone-plus-noise stimuli, and for the detection of a tone added to noise using noise-alone and tone-plus-noise waveforms with no reliable differences in level. The maskers were centered at 1800 Hz, and bandwidths of 40 and 100 Hz were tested. Individual differences in detection strategy were obtained. Two observers appeared to rely on changes in level, one observer appeared to rely on level-invariant cues, and the remaining four observers appeared to adopt a decision strategy that integrated level and level-invariant cues.(ABSTRACT TRUNCATED AT 400 WORDS)
Richards
V M
VM
Department of Psychology, University of Pennsylvania, Philadelphia 19104.
Nekrich
R D
RD
D000161:Acoustic Stimulation; D000465:Algorithms; D001307:Auditory Perception; D005260:Female; D006801:Humans; D008297:Male; D009622:Noise; D010775:Photic Stimulation; D011594:Psychometrics