Subjective evaluation of an emerging theory of low-frequency sound source localization in closed acoustic spaces

An earlier reported theory of low-frequency sound-source localization within closed acoustic spaces proposed that virtual image acuity is strongly dependent on sufficient inter-arrival time between a direct sound and its first reflection. This current study aims to test the theory’s predictions by subjective experiment where participants are required to indicate perceived sound source direction, but without knowledge of loudspeaker location. Test signals of frequencies 40 Hz to 115 Hz take the form of either windowed sine or square waves. Results confirm broad agreement with theoretical expectations and support the conjecture, contrary to common expectation, that low-frequency sound localization within the context of closed acoustic spaces is possible, although strongly dependent on system configuration and size of a listening space

Low-frequency sound source localization as a function of closed acoustic spaces

Further development of an emerging generalized theory of low-frequency sound localization in closed listening spaces is presented that aims to resolve the ambiguities inherent in previous research. The approach takes a robust set of equations based on source/listener location, reverberation time and room dimensions and tests them against a set of evaluation procedures to explore image location against theoretical expectations. Phantom imaging is germane to the methodology and its match within the theoretical framework is investigated. Binaural recordings are used to inspect a range of closed environments for localization clues each with a range of source-listener placements. A complementary series of small-scale listening tests are included for perceptual validation

A Functional Ecological Comparison of three Sponge Species from the Lower Florida Keys

The shallow, tidal flats off the islands of the lower Florida Keys represent a harsh environment for sessile marine invertebrates. This habitat is home to three taxonomically distinct sponge species that share similar rope morphologies: Cliona varians forma varians, Ircinia variabilis, and Neopetrosia subtriangularis. Despite sharing a habitat, these three species differ in their symbiont regime, with C. varians hosting dinoflagellate photosymbionts, and I. variabilis and N. subtriangularis hosting cyanobacterial photosymbionts. We conducted experiments to measure other ecological differences between these species. The sponges were all assayed for pumping rates using dye-video analysis and tissue samples were taken to compare the composition and functional genes of their microbiomes. The results indicated that N. subtriangularis had a significantly higher pumping rate than the other species. The microbiomes of the species varied, and the microbiome functional gene screening provided evidence that C. varians forma varians hosts nitrogen fixing bacteria, that I. variabilis hosts methane metabolizing bacteria, and that N. subtriangularis hosts nitric oxide reducing bacteria. More work is currently underway to examine the metabolism of these sponges, giving us insight into the unique ecology of this harsh habitat

Voting at 16 – lessons for the future from the Scottish Referendum

The 2014 Referendum on Scottish independence raised many issues about the future of Scotland. It also produced an innovation as regards the electoral process by making 16 years the minimum age of participation. This article examines issues surrounding the voting age and draws on a schools-based study, which shed light on teacher and pupil opinion about this lower than usual threshold for voting. It is also concerned with how schools cover the teaching of politics and prepared students for the Referendum debate within a context of expected neutrality on a highly divisive matter. Some implications of extending the lower voting age for future elections are discussed

Morphological Plasticity in the Tropical Sponge Anthosigmella Varians: Responses to Predators and Wave Energy.

The goal of the research presented here was to examine phenotypic plasticity exhibited by three morphotypes of the common Caribbean sponge Anthosigmella varians (Duchassaing & Michelotti). We were interested in examining the biotic (and, to a lesser extent, abiotic) factors responsible for branch production in this species. We also tested the hypothesis that the skeleton may serve an antipredator function in this sponge, focusing on vertebrate fish predators (i.e., angelfish) in this work. In transplant and caging experiments, unprotected forma varians replicates were immediately consumed by angelfish, while caged replicates persisted on the reef for several months. These findings support the hypothesis that predators (and not wave energy) restrict forma varians to lagoonal habitats. Branch production was not observed in A. varians forma incrustans when sponges were protected from predators or placed in predator-free, low-wave-energy environments. It is not clear from our work whether forma incrustans is capable of producing branches (i.e., whether branch production is a plastic trait in this morph). Additional field experiments demonstrated that A. varians forma varians increased spicule concentrations, compared to uninjured sponges, in response to artificial predation events, and A. varians forma rigida reduced spicule concentrations, compared to uncaged controls, when protected from predators. These findings indicate that spicule concentration is a plastic morphological trait that can be induced by damage, and that A. varians may be able to reduce spicule concentrations when environmental conditions change (e.g., in the absence of predators). The potential significance of inducible defenses and structural anti-predator defenses in sponges is discussed in relation to recent work on sponge chemical defenses

Towards a generalized theory of low-frequency sound source localization

Low-frequency sound source localization generates considerable amount of disagreement between audio/acoustics researchers, with some arguing that below a certain frequency humans cannot localize a source with others insisting that in certain cases localization is possible, even down to the lowest audible of frequencies. Nearly all previous work in this area depends on subjective evaluations to formulate theorems for low-frequency localization. This, of course, opens the argument of data reliability, a critical factor that may go some way to explain the reported ambiguities with regard to low-frequency localization. The resulting proposal stipulates that low-frequency source localization is highly dependent on room dimensions, source/listener location and absorptive properties. In some cases, a source can be accurately localized down to the lowest audible of frequencies, while in other situations it cannot. This is relevant as the standard procedure in live sound reinforcement, cinema sound and home-theater surround sound is to have a single mono channel for the low-frequency content, based on the assumption that human’s cannot determine direction in this band. This work takes the first steps towards showing that this may not be a universally valid simplification and that certain sound reproduction systems may actually benefit from directional low-frequency content