Transcranial routing of signal (TCROS) was accomplished using completely-in-the-canal (CIC) hearing aids in 5 profoundly unilaterally hearing-impaired individuals. The functional gain realized by the participants far exceeded the gain predicted by measuring the acoustic output and real ear aided response of the hearing aids. The difference between predicted and functional gain increased with signal frequency and was attributed at least in part to mechanical vibration of the hearing aid in the external canal. Implications for fitting unilateral hearing loss using TCROS amplifying systems are discussed.

Bone conduction transmission and head‐shadow effects were determined with transcranial completely‐in‐the‐canal (TCCIC) CROS hearing aids. Five subjects with documented profound unilateral hearing loss and experience with traditional CROS/BICROS fittings (TCROS) were tested with a CIC hearing aid placed in their poorer ear. Peak SPL was measured at the tympanic membrane and ranged from 105–115 dB SPL at 2000 Hz. Pure‐tone crossover thresholds and functional gain tested at frequencies from 250–8000 Hz varied considerably more than the SPL measures. The pure‐tone results indicated that sensitivity in the better ear was moderately associated with functional gain across frequency. Speech recognition was then tested in the sound field in two conditions: direct (noise in the poorer ear, speech in the better ear) and indirect (noise in the better ear, speech in the poorer ear) at S/Ns of −6, 0, +6, +12, and quiet. The TCCIC fittings were more effective than TCROS aids across S/Ns, particularly in the direct condition. In the indirect condition, the two fittings performed similarly. When data were pooled across conditions, the TCCIC aids provided better word recognition than the TCROS aids, particularly for those subjects with greater sensitivity in the better ear.