Pressure and particle motion detection thresholds in fish: A re-examination of salient auditory cues in teleosts

The auditory evoked potential technique has been used for the past 30years to evaluate the hearing ability of fish. The resulting audiograms are typically presented in terms of sound pressure (dB re. 1Pa) with the particle motion (dB re. 1ms–2) component largely ignored until recently. When audiograms have been presented in terms of particle acceleration, one of two approaches has been used for stimulus characterisation: measuring the pressure gradient between two hydrophones or using accelerometers. With rare exceptions these values are presented from experiments using a speaker as the stimulus, thus making it impossible to truly separate the contribution of direct particle motion and pressure detection in the response. Here, we compared the particle acceleration and pressure auditory thresholds of three species of fish with differing hearing specialisations, goldfish (Carassius auratus, weberian ossicles), bigeye (Pempheris adspersus, ligamentous hearing specialisation) and a third species with no swim bladder, the common triplefin (Forstergyian lappillum), using three different methods of determining particle acceleration. In terms of particle acceleration, all three fish species have similar hearing thresholds, but when expressed as pressure thresholds goldfish are the most sensitive, followed by bigeye, with triplefin the least sensitive. It is suggested here that all fish have a similar ability to detect the particle motion component of the sound field and it is their ability to transduce the pressure component of the sound field to the inner ear via ancillary hearing structures that provides the differences in hearing ability. Therefore, care is needed in stimuli presentation and measurement when determining hearing ability of fish and when interpreting comparative hearing abilities between species

The use of airphoto interpretation as an aid to prospecting for road building materials in South West Africa

Two introductory chapters have been used to give the necessary background to the main subject-matter of the thesis. The first of these chronologizes the significant steps in the development of aerial photographic interpretation from the first recorded aerial photograph to the present day respected position of the art in both military and civilian professional circles. The second introductory chapter deals with the fundamental principles involved in airphoto interpretation and of their specific application to soil engineering mapping for road projects in Southern Africa. This is followed by the major theme of the thesis, which concerns the direct location by aerial photographic interpretation of the various classes of material used in the construction of a modern day road. Although aerial photographs have been employed in recent years for direct interpretation and interpolation of certain specific road building materials, their use in this manner has been limited to a few special cases. This thesis sets out to show that under certain conditions, which pertain in many regions of the world, airphoto interpretation can be used for the direct location of 1materials possessing particular engineering characteristics. Further, it sets out to show, that this can be done for the full range of engineering properties required of materials for all the significant layers of construction, despite the fact that the materials involved may be of widely differing composition and geological origin. The actual interpretation is based on the fundamental recognition of the elements of form, tone, and texture making up the total photographic pattern. Similar features reflected on photographs are shown to be comprised of similar materials, not merely geologically speaking, but more especially in respect of their significant engineering characteristics; it is still further demonstrated that this is applicable even when such features are situated some considerable distance apart. Variations of notable engineering importance within one and the same geological occurrence, are also shown to be identifiable on the aerial photographs. For major road projects in areas subjected to certain environmental conditions, these possibilities form the basis of a new prospecting technique, which incorporates the full use of the science or art of interpretation. The basic concept governing the applicability of this technique and the steps necessary to ensure the development of the full potential of aerial photography in its application, are discussed and illustrated by detailed accounts of a number of specific projects. These projects incorporate both materials appraisals of wide strips of country for route location purposes and intensive prospecting along chosen routes. The techniques thus developed, constitute a new approach to materials investigations for major road projects and in this respect contribute to knowledge in this field. Finally, conclusions are drawn on the relative merits of materials investigation methods in current use in South West Africa and on how these methods affect the different organisations involved in the planning and construction of major road projects. The use made of airphoto interpretation for similar engineering works in other countries, as well as the possible future scope for the application of the particular method of materials investigation described in this thesis, are also covered

Biol Letters Data

File contains all raw data from auditory evoked potentials as well as all worksheet files compiled in TDT BioSig from all Pempheris adspersa manipulations and controls