The Effect of Recruitment on Speech Perception—A Simulation for Normal Listeners
Edgar Villchur · The Journal of the Acoustical Society of America · 1974
It has been suggested that one cause of the loss of intelligibility in perceptive deafness is the radical change, brought about by recruitment, in the normal loudness relationships among the acoustical elements of speech. This hypothesis is explored through an analogy in which deaf-subject loudness relationships are transposed to the normal span of hearing. The limiting frequency/amplitude coordinates of amplified speech are plotted relative to the average measured hearing span of five deaf subjects (the span between threshold and an equal-loudness contour at preferred speech level), and are projected to proportionate positions relative to the corresponding normal span. The loudness distortion of these deaf subjects can be represented by the response of an electronic model, a bank of fast-acting expanders with frequency-dependent expansion ratios, followed by a treble attenuator. Speech with and without interference has been processed by such a model, to simulate deaf-subject loudness relationships for normal listeners, and will be demonstrated. Experimental hearing-aid processing will also be demonstrated. The model predicts that frequency-dependent amplitude compression followed by frequency equalization will benefit intelligibility much more than would be indicated by the limited benefit of either process used separately.