Spatial and non-spatial multisensory cueing in unilateral cochlear implant users

In the present study we examined the integrity of spatial and non-spatial multisensory cueing (MSC) mechanisms in unilateral CI users. We tested 17 unilateral CI users and 17 age-matched normal hearing (NH) controls in an elevation-discrimination task for visual targets delivered at peripheral locations. Visual targets were presented alone (visual-only condition) or together with abrupt sounds that matched or did not match the location of the visual targets (audio-visual conditions). All participants were also tested in simple pointing to free-field sounds task, to obtain a basic measure of their spatial hearing ability in the naturalistic environment in which the experiment was conducted. Hearing controls were tested both in binaural and monaural conditions. NH controls showed spatial MSC benefits (i.e., faster discrimination for visual targets that matched sound cues) both in the binaural and in the monaural hearing conditions. In addition, they showed non-spatial MSC benefits (i.e., faster discrimination responses in audio-visual conditions compared to visual-only conditions, regardless of sound cue location) in the monaural condition. Monaural CI users showed no spatial MSC benefits, but retained non-spatial MSC benefits comparable to that observed in NH controls tested monaurally. The absence of spatial MSC in CI users likely reflects the poor spatial hearing ability measured in these participants. These findings reveal the importance of studying the impact of CI re-afferentation beyond auditory processing alone, addressing in particular the fundamental mechanisms that serves orienting of multisensory attention in the environment.