Three-dimensional acoustic localisation via directed movements of a two-dimensional model of the lizard peripheral auditory system

Three-dimensional acoustic localisation is relevant in personal and social robot platforms. Conventional approaches extract interaural time difference cues via impractically large stationary two-dimensional multi-microphone grids with at least four microphones or spectral cues via head-related transfer functions of stationary KEMAR dummy heads equipped with two microphones. We present a preliminary approach using two sound sensors, whose directed movements resolve the location of a stationary acoustic target in three dimensions. A model of the peripheral auditory system of lizards provides sound direction information in a single plane which by itself is insufficient to localise the acoustic target in three dimensions. Two spatial orientations of this plane by rotating the sound sensors by −45° and +45° along the sagittal axis generate a pair of measurements, each encoding the location of the acoustic target with respect to one plane of rotation. A multi-layer perceptron neural network is trained via supervised learning to translate the combination of the two measurements into an estimate of the relative location of the acoustic target in terms of its azimuth and elevation. The acoustic localisation performance of the system is evaluated in simulation for noiseless as well as noisy sinusoidal auditory signals with a 20 dB signal-to-noise ratio for four different sound frequencies of 1450 Hz, 1650 Hz, 1850 Hz and 2050 Hz that span the response frequency range of the peripheral auditory model. Three different neural networks with respectively one hidden layer with ten neurons, one hidden layer with twenty neurons and two hidden layers with ten neurons are comparatively evaluated. The neural networks are evaluated for varying locations of the acoustic target on the surface of the frontal spherical section in space defined by an azimuth and elevation range of [−90°, +90°] with a resolution of 1° in both planes.