Behavioral thresholds to binaural cues

Abstract

Objectives: There is recent interest in bilateral cochlear implantation to obtain the benefits of binaural hearing. This interest necessitates development of animal models to examine the effects of bilateral implants on the binaural system. Our goal is to develop the unanesthetized rabbit as a model to study behavior and physiology with bilateral implants. This species was chosen because of the wealth of the physiological data from normal animals. However, there is no comparable behavioral data in rabbits. Thus, for this study we behaviorally tested the ability of rabbits to discriminate interaural time differences (ITDs). Methods: Normal hearing Dutch-belted rabbits were trained to discriminate ITDs using conditioned avoidance. A tracking method was used to determine the threshold interaural time difference (ITD) that was discriminable between a reference ITD and a warning ITD. Results: The minimum perceptual threshold was 78 μs at a reference ITD of 100 μs. At 0 μs reference ITD the threshold was 109 μs, increasing to 245 μs at reference ITD of 300 μs. Conclusion: Compared to human beings, the most sensitive region for ITD detection in rabbits is lateralized (100 μs instead of 0 μs) and thresholds are higher (78 μs instead of ∼15 μs). Surprisingly, the rabbit behavioral thresholds are worse than those calculated from physiological responses in neurons, which are comparable to human behavioral thresholds. This study advances the goal of using rabbits as a model system for bilateral cochlear implants.