Measuring the apparent width of auditory sources in normal and impaired hearing.

It is often assumed that single sources of sound are perceived as being punctate, but this cannot be guaranteed, especially for hearing-impaired listeners. Any impairment that gives a reduction at the periphery in the accuracy of coding fine-scale temporal information must give a slight interaural jitter in the temporal information passed to higher centres, and so would be expected to lead to an effective reduction in the interaural coherence (IC) of any stimulus. This would lead to deficits in locating sounds, but deficits of imprecision, not inaccuracy. In turn, this implies that older hearing-impaired individuals should have a diminished perception of auditory space, affecting their abilities to perceive clear, concise, punctate spatial impressions or to separate sounds by location. The current work tested this hypothesis by using two separate visual-analogy methods to measure auditory source width for broadband sounds. In one method, the listener sketched the auditory image, a visual-description task, and for the other, the listener selected the closest one of a set of pre-drawn visual sketches (note that the first is an open-set experiment, whereas the second is a closed-set experiment). We found that older hearing-impaired listeners had increased difficulty in judging changes in interaural coherence, showing a corresponding insensitivity to auditory source width in the visual-analogy tasks.