Low-frequency interaural time differences and available localization cues in the azimuthal plane for listeners with head-worn or body-worn hearing aid(s)

The interaural time differences (ITD), the primary low-frequency localization cues are determined for head-worn and body-worn hearing aids as a function of location and angle of incidence. The ITD's are predicted on the basis of scattering theories for a rigid sphere and cylinder for head-worn and body-worn hearing aids, respectively. The results show that the range of the available localization cues (ITD's) for aided listeners is compressed, yielding a smaller range of cues than that available to unaided listeners. The “apparent angle of incidence” for monaurally aided listeners is shown to be increasingly offset from the true angle of incidence as the hearing aid(s) is worn forward of the earcanal axis. This bivaluedness, which occurs principally when the angle of incidence relative to frontal incidence becomes large or when the hearing aid(s) is located considerably forward of the earcanal axis, yields confusion localization cues. The results also show that body-worn hearing aids can produce ITD's similar to those for unaided listeners if the aids are spaced symmetrically about the median plane of the torso, a distance of ∼22 cm apart. Comparisons of predicted ITD's with published clinical and subjective localization studies for aided listeners are self-consistent and in good agreement.