From "ear" to there: a review of biorobotic models of auditory processing in lizards.

The peripheral auditory system of lizards has been extensively studied, because of its remarkable directionality. In this paper, we review the research that has been performed on this system using a biorobotic approach. The various robotic implementations developed to date, both wheeled and legged, of the auditory model exhibit strong phonotactic performance for two types of steering mechanisms-a simple threshold decision model and Braitenberg sensorimotor cross-couplings. The Braitenberg approach removed the need for a decision model, but produced relatively inefficient robot trajectories. Introducing various asymmetries in the auditory model reduced the efficiency of the robot trajectories, but successful phonotaxis was maintained. Relatively loud noise distractors degraded the trajectory efficiency and above-threshold noise resulted in unsuccessful phonotaxis. Machine learning techniques were applied to successfully compensate for asymmetries as well as noise distractors. Such techniques were also successfully used to construct a representation of auditory space, which is crucial for sound localisation while remaining stationary as opposed to phonotaxis-based localisation. The peripheral auditory model was furthermore found to adhere to an auditory scaling law governing the variation in frequency response with respect to physical ear separation. Overall, the research to date paves the way towards investigating the more fundamental topic of auditory metres versus auditory maps, and the existing robotic implementations can act as tools to compare the two approaches.