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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
411

Audiovisual time perception is spatially specific

Heron, James, Roach, N.W., Hanson, James Vincent Michael, McGraw, Paul V., Whitaker, David J. January 2012 (has links)
No / Our sensory systems face a daily barrage of auditory and visual signals whose arrival times form a wide range of audiovisual asynchronies. These temporal relationships constitute an important metric for the nervous system when surmising which signals originate from common external events. Internal consistency is known to be aided by sensory adaptation: repeated exposure to consistent asynchrony brings perceived arrival times closer to simultaneity. However, given the diverse nature of our audiovisual environment, functionally useful adaptation would need to be constrained to signals that were generated together. In the current study, we investigate the role of two potential constraining factors: spatial and contextual correspondence. By employing an experimental design that allows independent control of both factors, we show that observers are able to simultaneously adapt to two opposing temporal relationships, provided they are segregated in space. No such recalibration was observed when spatial segregation was replaced by contextual stimulus features (in this case, pitch and spatial frequency). These effects provide support for dedicated asynchrony mechanisms that interact with spatially selective mechanisms early in visual and auditory sensory pathways.
412

Duration channels mediate human time perception

Heron, James, Aaen-Stockdale, Craig, Hotchkiss, John, Roach, N.W., McGraw, Paul V., Whitaker, David J. January 2012 (has links)
No / The task of deciding how long sensory events seem to last is one that the human nervous system appears to perform rapidly and, for sub-second intervals, seemingly without conscious effort. That these estimates can be performed within and between multiple sensory and motor domains suggest time perception forms one of the core, fundamental processes of our perception of the world around us. Given this significance, the current paucity in our understanding of how this process operates is surprising. One candidate mechanism for duration perception posits that duration may be mediated via a system of duration-selective 'channels', which are differentially activated depending on the match between afferent duration information and the channels' 'preferred' duration. However, this model awaits experimental validation. In the current study, we use the technique of sensory adaptation, and we present data that are well described by banks of duration channels that are limited in their bandwidth, sensory-specific, and appear to operate at a relatively early stage of visual and auditory sensory processing. Our results suggest that many of the computational principles the nervous system applies to coding visual spatial and auditory spectral information are common to its processing of temporal extent.
413

The chromatic selectivity of visual crowding

Kennedy, Graeme J., Whitaker, David J. January 2010 (has links)
No / Precortical vision is mediated by three opponent mechanisms that combine receptoral outputs to form a luminance channel (L + M) and two chromatic channels, red-green (L/M) and blue-yellow (S/L + M). Here we ask the extent to which these basic color opponent mechanisms interact in the phenomenon of crowding, where nearby targets interfere with the processing of a central test target. The task was to identify the orientation of a Gabor patch while an annular plaid surrounded the patch. The radius of the annulus was varied in order to produce different separations of the test and flanker. The chromatic content of the Gabor and the annulus could be varied independently along the (L + M), (L/M), and (S/L + M) cardinal axes. For all targets, when the target and flanker shared the same chromaticity, performance decreased with decreasing separation of the target and annulus, i.e., a typical crowding effect was seen. When the test and flanker isolated different chromatic mechanisms, very little crowding was observed, even at the minimum separation of test target and annulus. In addition to this, intermediate chromaticities were found to produce intermediate levels of crowding. Finally, crowding effects using "half-wave rectified" stimuli suggest a locus for crowding effects beyond the level of color opponent mechanisms.
414

Intermediate hair follicles: a new more clinically relevant model for hair growth investigations

Miranda, Benjamin H., Tobin, Desmond J., Sharpe, David T., Randall, Valerie A. January 2010 (has links)
No / BACKGROUND: Alopecia causes widespread psychological distress, but is relatively poorly controlled. The development of new treatments is hampered by the lack of suitable human hair follicle models. Although intermediate and vellus hair follicles are the main clinical targets for pharmacological therapy, terminal hair follicles are more frequently studied as smaller hair follicles are more difficult to obtain. OBJECTIVES: This investigation was designed to quantify in vivo morphological and in vitro behavioural differences in organ culture between matched intermediate and terminal hair follicles, in order to develop a new clinically relevant model system. METHODS: Microdissected terminal and intermediate hair follicles, from the same individuals, were analysed morphometrically (250 follicles; five individuals), or observed and measured over 9 days of organ culture (210 follicles; six individuals). RESULTS: Intermediate hair follicles were less pigmented and smaller, penetrating less below the skin surface (mean +/- SEM) (2.59 +/- 0.07 vs. 3.52 +/- 0.10 mm; P = 0.02), with smaller fibre (0.03 +/- 0.002 vs. 0.07 +/- 0.002 mm), connective tissue sheath (0.24 +/- 0.01 mm vs. 0.33 +/- 0.01 mm), bulb (0.19 +/- 0.01 vs. 0.31 +/- 0.01 mm) and dermal papilla (0.06 +/- 0.002 vs. 0.12 +/- 0.01 mm) diameters (P < 0.001). Intermediate hair follicle bulbs appeared 'tubular', unlike their 'bulbous' terminal follicle counterparts. In organ culture they also grew more slowly (0.044 +/- 0.002 vs. 0.067 +/- 0.003 mm per day; P < 0.001), remained in anagen longer (84 +/- 0.03% vs. 74 +/- 0.03% at day 9; P = 0.012) and produced less hair fibre (0.36 +/- 0.02 vs. 0.50 +/- 0.03 mm; P < 0.001) than terminal follicles. CONCLUSIONS: Smaller intermediate hair follicles showed major morphological differences from terminal follicles in vivo and retained significant, biologically relevant differences in vitro in organ culture. Therefore, intermediate hair follicles offer a novel, exciting, more clinically relevant, albeit technically difficult, model for future investigations into hair growth. This should be particularly important for developing new therapies.
415

Simultaneous chromatic and luminance human electroretinogram responses

Parry, Neil R.A., Murray, I.J., Panorgias, A., McKeefry, Declan J., Lee, B.B., Kremers, Jan January 2012 (has links)
No / The parallel processing of information forms an important organisational principle of the primate visual system. Here we describe experiments which use a novel chromatic-achromatic temporal compound stimulus to simultaneously identify colour and luminance specific signals in the human electroretinogram (ERG). Luminance and chromatic components are separated in the stimulus; the luminance modulation has twice the temporal frequency of the chromatic modulation. ERGs were recorded from four trichromatic and two dichromatic subjects (1 deuteranope and 1 protanope). At isoluminance, the fundamental (first harmonic) response was elicited by the chromatic component in the stimulus. The trichromatic ERGs possessed low-pass temporal tuning characteristics, reflecting the activity of parvocellular post-receptoral mechanisms. There was very little first harmonic response in the dichromats' ERGs. The second harmonic response was elicited by the luminance modulation in the compound stimulus and showed, in all subjects, band-pass temporal tuning characteristic of magnocellular activity. Thus it is possible to concurrently elicit ERG responses from the human retina which reflect processing in both chromatic and luminance pathways. As well as providing a clear demonstration of the parallel nature of chromatic and luminance processing in the human retina, the differences that exist between ERGs from trichromatic and dichromatic subjects point to the existence of interactions between afferent post-receptoral pathways that are in operation from the earliest stages of visual processing.
416

The acoustic and visual factors influencing the construction of tranquil space in urban and rural environments tranquil spaces-quiet places?

Pheasant, Robert J., Horoshenkov, Kirill V., Watts, Gregory R., Barrett, Brendan T. January 2008 (has links)
No / Prior to this work no structured mechanism existed in the UK to evaluate the tranquillity of open spaces with respect to the characteristics of both acoustic and visual stimuli. This is largely due to the fact that within the context of "tranquil" environments, little is known about the interaction of the audio-visual modalities and how they combine to lead to the perception of tranquillity. This paper presents the findings of a study in which visual and acoustic data, captured from 11 English rural and urban landscapes, were used by 44 volunteers to make subjective assessments of both their perceived tranquillity of a location, and the loudness of five generic soundscape components. The results were then analyzed alongside objective measurements taken in the laboratory. It was found that the maximum sound pressure level (L(Amax)) and the percentage of natural features present at a location were the key factors influencing tranquillity. Engineering formulas for the tranquillity as a function of the noise level and proportion of the natural features are proposed.
417

Asynchrony adaptation reveals neural population code for audio-visual timing

Roach, N.W., Heron, James, Whitaker, David J., McGraw, Paul V. January 2011 (has links)
No / The relative timing of auditory and visual stimuli is a critical cue for determining whether sensory signals relate to a common source and for making inferences about causality. However, the way in which the brain represents temporal relationships remains poorly understood. Recent studies indicate that our perception of multisensory timing is flexible--adaptation to a regular inter-modal delay alters the point at which subsequent stimuli are judged to be simultaneous. Here, we measure the effect of audio-visual asynchrony adaptation on the perception of a wide range of sub-second temporal relationships. We find distinctive patterns of induced biases that are inconsistent with the previous explanations based on changes in perceptual latency. Instead, our results can be well accounted for by a neural population coding model in which: (i) relative audio-visual timing is represented by the distributed activity across a relatively small number of neurons tuned to different delays; (ii) the algorithm for reading out this population code is efficient, but subject to biases owing to under-sampling; and (iii) the effect of adaptation is to modify neuronal response gain. These results suggest that multisensory timing information is represented by a dedicated population code and that shifts in perceived simultaneity following asynchrony adaptation arise from analogous neural processes to well-known perceptual after-effects.
418

Development, validation and application of a patient satisfaction scale for a community pharmacy medicines-management service

Tinelli, M., Blenkinsopp, Alison, Bond, C. January 2011 (has links)
No / OBJECTIVE: To develop, validate and apply a scale to measure patient satisfaction in a randomised controlled trial of community pharmacy service. METHODS: Published scales were reviewed to inform development of the patient satisfaction scale. Questionnaires were sent to patients in the control (n=500) and intervention (n=941) groups of a randomised controlled trial of community pharmacy-led management of coronary heart disease at baseline and 12-month follow-up. Any underlying main factors were assessed with exploratory factor analysis. Reliability and construct validity were tested. The 15-item scale was used to compare patient satisfaction across arms with their most recent pharmacy visit. RESULTS: Response rates were 92% (461/500) for control and 96% (903/941) for intervention groups at baseline and 85% control (399/472) and intervention (810/941) at follow-up. At baseline satisfaction was very similar in the intervention and control groups (median scores of 42). At follow-up mean satisfaction had significantly improved for the intervention compared with the control (median scores of 46 compared with 43; P<0.01); intervention females were more likely to be satisfied with the service than males (49 compared with 44; P<0.01). Three main factors explained the majority of the data variance. Cronbach's alpha was 0.7-0.9 for both groups over time for all factors and total scale. An increase in the overall satisfaction corresponding to a decrease in subjects wanting that particular service to be provided during their next visit indicated construct validity of the scale. CONCLUSION: A new scale of patient satisfaction with community pharmacy services was developed and shown to be reliable and valid. Its application showed increased satisfaction in the intervention group receiving a new pharmacy service.
419

Dystroglycan function is a novel determinant of tumor growth and behavior in prostate cancer

Mitchell, Andrew, Mathew, G., Jiang, T., Hamdy, F.C., Cross, S.S., Eaton, C., Winder, S.J. January 2013 (has links)
No / Dystroglycan is a ubiquitously expressed cell adhesion molecule frequently found to be altered or reduced in adenocarcinomas, however the mechanisms or consequences of dystroglycan loss have not been studied extensively. We examined the consequence of overexpression or RNAi depletion of dystroglycan on properties of in vitro growth migration and invasion of LNCaP, PC3, and DU145 prostate cancer cell lines. RESULTS: Using LNCaP cells we observed cell density-dependent changes in beta-dystroglycan with the appearance of several lower molecular weight species ranging in size from 43 to 26 kDa. The bands of 31 and 26 kDa were attributed to proteolysis, whereas bands between 43 and 38 kDa were a consequence of mis-glycosylation. The localization of beta-dystroglycan in LNCaP colonies in culture also varied, cells with a mesenchymal appearance at the periphery of the colony had more pronounced membrane localization of dystroglycan. Whereas some cells demonstrated nuclear dystroglycan. Increased dystroglycan levels were inhibitory to growth in soft agar but promoted Matrigel invasion, whereas reduced dystroglycan levels promoted growth in soft agar but inhibited invasion. Similar results were also obtained for PC3 and DU145 cells. This study suggests that changes in beta-dystroglycan distribution within the cell and/or the loss of dystroglycan during tumorigenesis, through a combination of proteolysis and altered glycosylation, leads to an increased ability to grow in an anchorage independent manner, however dystroglycan may need to be re-expressed for cell invasion and metastasis to occur.
420

Aldehyde dehydrogenases in cancer: an opportunity for biomarker and drug development?

Pors, Klaus, Moreb, J.S. 12 1900 (has links)
No / Aldehyde dehydrogenases (ALDHs) belong to a superfamily of 19 isozymes that are known to participate in many physiologically important biosynthetic processes including detoxification of specific endogenous and exogenous aldehyde substrates. The high expression levels of an emerging number of ALDHs in various cancer tissues suggest that these enzymes have pivotal roles in cancer cell survival and progression. Mapping out the heterogeneity of tumours and their cancer stem cell (CSC) component will be key to successful design of strategies involving therapeutics that are targeted against specific ALDH isozymes. This review summarises recent progress in ALDH-focused cancer research and discovery of small-molecule-based inhibitors.

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