Sonar properties of the lower jaw of the Atlantic bottlenose dolphin (Tursiops truncatus)

The primary function of this research project has been to investigate the physical properties of the lower jaw of the Atlantic Bottlenose Dolphin (Tursiops truneatus). This has been achieved through numerical modelling techniques, established physical measurements and modem Laser Doppler Velocity Measurements. During the course of this work some interesting characteristics of the dolphin jaw structure have been discovered. Sound speeds and attenuation levels of the jawbone have been determined and the implications assessed. The geometric array formed by the dolphin teeth of the lower jaw can be used to form an end-fire array which produces a beam pattern similar to those of the dolphin. The geometric array has also been analysed for its passive acoustical properties, in particular its ability to form acoustic stop bands within the audible range of the dolphin. The results of this research show that the directivity of the dolphin can be reproduced using the morphological features of the lower jaw.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Investigating the build-up of precedence effect using reflection masking

The auditory processing level involved in the build‐up of precedence [Freyman et al., J. Acoust. Soc. Am. 90, 874–884 (1991)] has been investigated here by employing reflection masked threshold (RMT) techniques. Given that RMT techniques are generally assumed to address lower levels of the auditory signal processing, such an approach represents a bottom‐up approach to the buildup of precedence. Three conditioner configurations measuring a possible buildup of reflection suppression were compared to the baseline RMT for four reflection delays ranging from 2.5–15 ms. No buildup of reflection suppression was observed for any of the conditioner configurations. Buildup of template (decrease in RMT for two of the conditioners), on the other hand, was found to be delay dependent. For five of six listeners, with reflection delay=2.5 and 15 ms, RMT decreased relative to the baseline. For 5‐ and 10‐ms delay, no change in threshold was observed. It is concluded that the low‐level auditory processing involved in RMT is not sufficient to realize a buildup of reflection suppression. This confirms suggestions that higher level processing is involved in PE buildup. The observed enhancement of reflection detection (RMT) may contribute to active suppression at higher processing levels