Seeing with sound: Investigating the behavioural applications and neural correlates of human echolocation

Some blind humans use the reflected echoes from self-produced signals to perceive their silent surroundings. Although the use of echolocation is well documented in animals such as bats and dolphins, comparatively little is known about human echolocation. The overarching goal of the work presented in this thesis was to shed light on some of the basic functions of human echolocation, including the perception of the shape, size, and material. I addressed these aspects of echolocation using behavioural psychophysics and neuroimaging. In Chapter 2 I show that blind echolocators were able to accurately identify the shape of 2D objects, but that their ability to do so was dependent on the use of head and body movements to ‘scan’ the objects’ edges. I suggest that these scanning movements may be similar to the many saccades made by sighted individuals when visually surveying an object or scene. In Chapter 3 I addressed the possibility that object size perception via echolocation shows size constancy – a perceptual phenomenon associated with vision. The results revealed that an expert echolocator accurately perceived the true physical size of objects independent of their distance, even though changes to distance directly affect size-related echo information. The results of this study highlight the ‘visual’ nature of echolocation, and suggest further parallels between the two modalities than previously known or theorized. Chapter 4 presents the results of a functional neuroimaging study aimed at uncovering the neural correlates of material processing via echolocation. By having echolocators listen to recordings of echoes reflected from surfaces of different materials, I show not only that they can determine the material properties of objects, but also that the neural processing underlying this ability may make use of a visual- and auditory-material processing area in the parahippocampal cortex. Taken together, the work presented in the current thesis describes some of the recent contributions to our understanding of human echolocation, with a particular emphasis on its apparent parallels with vision and visual processing. The results of this work show that accurate and reliable information can be extracted from echoes, thus supporting echolocation as a viable resource for the blind

INVESTIGATING THE EFFECTS OF OBJECT CONNECTEDNESS ON RAPID VISUALLY-GUIDED REACHING TOWARD MULTIPLE GOALS

We developed a rapid reaching paradigm in which we require participants to make speeded reaches toward ambiguous target displays, with a goal target filling-in only after movement onset. In our previous work, we have found that initial reaches extend toward the averaged spatial location of the presented targets. Our aim for the current study was to determine if object connectedness - a strong perceptual illusion in which two connected objects appear as one - could influence the strategic reaching behaviour. Even though there was a powerful effect of the illusion on perception, the visuomotor system was able to utilize the true target information and continue to plan reaches based on the number and distribution of targets presented. These results resonate with the idea of a division of labour between vision-for-perception and vision-for-action - but extend this dissociation (with respect to the action system) into the realm of motor planning

Multi-Epoch Spectropolarimetry for a Sample of Type IIn Supernovae: Persistent Asymmetry in Dusty Circumstellar Material

We present multi-epoch spectropolarimetry and spectra for a sample of 14 Type IIn supernovae (SNe IIn). We find that after correcting for likely interstellar polarization, SNe IIn commonly show intrinsic continuum polarization of 1--3% at the time of peak optical luminosity, although a few show weaker or negligible polarization. While some SNe IIn have even stronger polarization at early times, their polarization tends to drop smoothly over several hundred days after peak. We find a tendency for the intrinsic polarization to be stronger at bluer wavelengths, especially at early times. While polarization from an electron scattering region is expected to be grey, scattering of SN light by dusty circumstellar material (CSM) may induce such a wavelength-dependent polarization. For most SNe IIn, changes in polarization degree and wavelength dependence are not accompanied by changes in the position angle, requiring that asymmetric pre-SN mass loss had a persistent geometry. While 2--3% polarization is typical, about 30% of SNe IIn have very low or undetected polarization. Under the simplifying assumption that all SN IIn progenitors have axisymmetric CSM (i.e. disk/torus/bipolar), then the distribution of polarization values we observe is consistent with similarly asymmetric CSM seen from a distribution of random viewing angles. This asymmetry has very important implications for understanding the origin of pre-SN mass loss in SNe IIn, suggesting that it was shaped by binary interaction.Comment: 76 pages, 54 figures (13 in main text, 41 in appendix A

The Health and Economic Costs of Violence against Women and Girls on Survivors, Their Families, and Communities in Ghana

Violence against women and girls (VAWG) is a worldwide phenomenon. Globally, 35% of women have experienced physical or sexual intimate partner violence (IPV) or non-partner sexual violence in their lives. VAWG is estimated to cost the global economy about US$ eight trillion. Most studies on violence in Ghana discuss domestic violence or some forms of sexual violence but lack a comprehensive view of VAWG and its costs and impacts on communities, businesses, and the national economy. Our international consortium undertook a mixed-methods study to estimate the economic and non-economic losses caused by VAWG. We surveyed 2002 women and 805 male and female employees and conducted 24 in-depth interviews (IDIs) and 8 focus group discussions (FGDs). The study finds that costs of VAWG are high and multi-fold. It estimates costs to health, social relationships, and productivity for individuals, their families, and communities. Individual well-being and capabilities are impacted through absenteeism or missed care work and mental health issues. VAWG deepens household poverty by out-of-pocket expenditures that arise to address medical and legal issues that result from violence. Additionally, VAWG affects the vibrancy of communities as women’s participation and leadership decline. These costs accumulate to have profound effects on the Ghanaian economy and society

SN2012ab: A Peculiar Type IIn Supernova with Aspherical Circumstellar Material

We present photometry, spectra, and spectropolarimetry of supernova (SN) 2012ab, mostly obtained over the course of $\sim 300$ days after discovery. SN 2012ab was a Type IIn (SN IIn) event discovered near the nucleus of spiral galaxy 2MASXJ12224762+0536247. While its light curve resembles that of SN 1998S, its spectral evolution does not. We see indications of CSM interaction in the strong intermediate-width emission features, the high luminosity (peak at absolute magnitude $M=-19.5$), and the lack of broad absorption features in the spectrum. The H$\alpha$ emission undergoes a peculiar transition. At early times it shows a broad blue emission wing out to $-14{,}000$ km $\mathrm{s^{-1}}$ and a truncated red wing. Then at late times ($>$ 100$\,$days) it shows a truncated blue wing and a very broad red emission wing out to roughly $+20{,}000$ km $\mathrm{s^{-1}}$. This late-time broad red wing probably arises in the reverse shock. Spectra also show an asymmetric intermediate-width H$\alpha$ component with stronger emission on the red side at late times. The evolution of the asymmetric profiles requires a density structure in the distant CSM that is highly aspherical. Our spectropolarimetric data also suggest asphericity with a strong continuum polarization of $\sim 1-3$% and depolarization in the H$\alpha$ line, indicating asphericity in the CSM at a level comparable to that in other SNe IIn. We estimate a mass-loss rate of $\dot{M} = 0.050\, {\rm M}_{\odot}\,\mathrm{yr^{-1}}$ for $v_{\rm pre} = 100$$\,$km$\,$$\mathrm{s^{-1}}$ extending back at least 75$\,$yr prior to the SN. The strong departure from axisymmetry in the CSM of SN 2012ab may suggest that the progenitor was an eccentric binary system undergoing eruptive mass loss.Comment: 18 pages, 12 figure

Counting on the motor system: Rapid action planning reveals the format- and magnitude-dependent extraction of numerical quantity

Symbolic numbers (e.g., 2 ) acquire their meaning by becoming linked to the core nonsymbolic quantities they represent (e.g., two items). However, the extent to which symbolic and nonsymbolic information converges onto the same internal core representations of quantity remains a point of considerable debate. As nearly all previous work on this topic has employed perceptual tasks requiring the conscious reporting of numerical magnitudes, here we question the extent to which numerical processing via the visual-motor system might shed further light on the fundamental basis of how different number formats are encoded.We show, using a rapid reaching task and a detailed analysis of initial arm trajectories, that there are key differences in how the quantity information extracted from symbolic Arabic numerals and nonsymbolic collections of discrete items are used to guide action planning. In particular, we found that the magnitude derived from discrete dots resulted in movements being biased by an amount directly proportional to the actual quantities presented whereasthe magnitude derived from numerals resulted in movements being biased only by the relative (e.g., larger than) quantities presented. In addition, we found that initial motor plans were more sensitive to changes in numerical quantity within small (1-3) than large (5-15) number ranges, irrespective of their format (dots or numerals). In light of previous work, our visual-motor results clearly show that the processing of numerical quantity information is both format and magnitude dependent. © 2014 ARVO

SN2013fs and SN2013fr: Exploring the circumstellar-material diversity in Type II supernovae

We present photometry and spectroscopy of SN2013fs and SN2013fr in the first 100 days post-explosion. Both objects showed transient, relatively narrow H$\alpha$ emission lines characteristic of SNeIIn, but later resembled normal SNeII-P or SNeII-L, indicative of fleeting interaction with circumstellar material (CSM). SN2013fs was discovered within 8hr of explosion. Its light curve exhibits a plateau, with spectra revealing strong CSM interaction at early times. It is a less luminous version of the transitional SNIIn PTF11iqb, further demonstrating a continuum of CSM interaction intensity between SNeII-P and IIn. It requires dense CSM within 6.5$\times$10$^{14}$~cm of the progenitor, from a phase of advanced pre-SN mass loss shortly before explosion. Spectropolarimetry of SN2013fs shows little continuum polarization, but noticeable line polarization during the plateau phase. SN2013fr morphed from a SNIIn at early times to a SNII-L. After the first epoch its narrow lines probably arose from host-galaxy emission, but the bright, narrow H$\alpha$ emission at early times may be intrinsic. As for SN2013fs, this would point to a short-lived phase of strong CSM interaction if proven to be intrinsic, suggesting a continuum between SNeIIn and II-L. It is a low-velocity SNII-L, like SN2009kr but more luminous. SN2013fr also developed an IR excess at later times, due to warm CSM dust that require a more sustained phase of strong pre-SN mass loss.Comment: MNRAS accepted. 28 pages, 23 figures, 8 table