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The complex visual search involved in baggage screening requires operators to determine quickly whether a bag contains threatening objects that are embedded in a high degree of visual clutter. Methods for calculating visual clutter have been developed, and research has demonstrated the negative impact of clutter on search performance. The current study examined whether leveraging visual clutter information on the display during search could improve baggage screening performance above and beyond the conventional screening process. Ninety undergraduates searched x-ray images of bags for weapon items in a low fidelity baggage screening simulation; two clutter-based preview conditions displayed a limited portion of the bag to the participant before the entire bag was displayed. Eye movement data confirmed that the preview process guided the participant's attention to the corresponding previewed region. However, analysis of the baggage screening performance data showed there were no significant benefits associated with either clutter-based preview conditions compared with a control condition in which the entire bag was displayed for the duration of the trial. Thus, the results suggest that using clutter-based preview to guide visual attention does not substantially improve weapon detection performance. Despite this null effect, the current study provides additional evidence regarding the impact of visual clutter on complex search performance by demonstrating significant reductions in weapon detection accuracy and search efficiency due to increasing levels of visual clutter. Further research should explore methods for improving complex visual search by considering the negative impacts of visual clutter and ensuring that both attention guidance and object recognition processes are facilitated during search.

Undergraduate honors paper--Mount Holyoke College, 2006. Program in Neuroscience and Behavior. / Includes bibliographical references (leaves 58-60).

Thesis (doctoral)--University of Bath, 2001. / BLDSC reference no.: DX217256.

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Tesis para optar al grado de Magister en Comunicación Política / El presente estudio pretende indagar, en un sentido, en el poder de las imágenes y las imágenes del poder. Parece una frase arreglada para que suene bien, ingeniosa, pero a pesar de que puede ser un recurso retórico, estas dos frases guardan en su relación una profunda verdad. Pues a ningún miembro de nuestras sociedades occidentales modernas le causará problema aceptar el poderoso papel que cumplen las imágenes en nuestro día a día: articulan nuestros deseos, guían y ordenan la importancia de la realidad, le otorgan un grado de sentido a un mundo que es, finamente, caos, y a través de su (cada vez más fácil) reproducción han llegado a transformarse en un lenguaje propio, difícil de describir y dominar teóricamente, pero que fluye con naturalidad en la cotidianeidad. Tal vez no podamos describirlo con facilidad, pero lo intuimos: las imágenes no son poderosas: son poder, poseen los argumentos y la fuerza para movernos. La inescapable relación con la imagen tenía para esta iglesia temprana una dimensión peculiar, vinculada con las prohibiciones iconográficas heredadas del judaísmo, pero es lícito extrapolar la experiencia a cualquier institución social moderna. En parte porque hemos heredado esa tradición cultural de conflicto con la imagen y porque una institución como el Estado moderno, que nos ocupa en esta investigación, posee un nivel de importancia asimilable. Somos una sociedad abandonada a las fuerzas tectónicas de las imágenes y hemos construido nuestras relaciones sociales con escaza o nula capacidad de relación con ellas, y ciertamente, sin mucha reflexión. Este desconocimiento no ha detenido a los encargados de manejar el poder: se busca siempre tener una medida de control sobre las imágenes, pero ¿Qué medida de control podría pretender ordenar una avalancha? La reproductibilidad técnica ha alcanzado niveles impensables antes de la explosión digital, una situación que ni los más teóricos más visionarios podrían haber previsto, donde la producción digital borronea la distinción de original.

D.Phil. (Optometry) / The measurement of Contrast Visual Acuities (contrast VA) is recognised in various studies as an important psychophysical measure of visual function, and contrast VA is often used to understand visual limitations or functional disability. Contrast VA is also useful for monitoring the effects of disease modifying therapies. High and medium contrast levels are generally used in studies to evaluate contact lens performance, the outcomes of surgical procedures and for assessing activities of daily living. Measurement of stimuli with low contrast levels are also sometimes applied in diagnosing, monitoring and evaluating disease processes and their management, especially where high contrast visual acuity remains intact. This is believed to be the first study that comprehensively investigates the reliability (or repeatability) of four contrast levels using the computerized Thomson Test Chart 2000 XPert. (A similar study with four contrast levels and both univariate and multivariate analysis as applied in this thesis has not been performed elsewhere). Although the main emphasis of this study was to explore various issues relating to short-term repeatability of contrast VA, both within and across individuals, both univariate and multivariate statistical analyses were also used in this thesis to investigate age and gender related changes in measurements of contrast VA. Together the results from this thesis provide test and re-test contrast VA reliability measures and some basic or preliminary statistical normative contrast VA values, which should aid clinicians to confidently detect abnormal measurements which, in turn, promotes good clinical practice. For this thesis and within a clinical environment to investigate inter-subject variation in contrast VA, two measurements of contrast VA at four specified contrast levels (100%, 10%, 5% and 2.5%) at a 6 metre distance were obtained for the right eyes only of 155 healthy participants. Thus, at each contrast level 155 test and re-test contrast VA measurements were determined using the computerized Thomson Test Chart 2000 XPert. All measurements were determined through the optimal refractive compensation for each right eye of the 155 participants concerned. In a subset of ten subjects or participants, samples of thirty consecutive measurements of contrast VA at each of the four contrast levels were also obtained to explore short-term intra-subject variation in contrast VA. A simple questionnaire was administered to all subjects to obtain biographical, general and ocular health histories. Visual assessment included II subjective clinical refraction, stereopsis, colour vision, direct ophthalmoscopy and biomicroscopy to understand the eyes of the participants and exclude possible factors that could cause ocular or neurological changes in the retina or in vision thereby influencing contrast VA in a detrimental fashion...

A dissertation submitted to the Faculty of Health Sciences, School of Therapeutic Sciences, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Occupational Therapy. Johannesburg, 2017 / Occupational therapists routinely make use of the Test of Visual Perceptual Skills - Third Edition (TVPS-3), the Developmental Test of Visual Perception - Third Edition (DTVP-3) and the Developmental Test of Visual-Motor integration - Six Edition (Beery VMI-6) to determine visual perception and visual-motor integration (VMI) dysfunction. This study aimed to determine the validity and reliability of the TVPS-3, DTVP-3 and Beery VMI-6, on a sample of six to nine year old South African children. The scores for the typical children attending a mainstream school fell within the norms reported for children in the USA for all three tests. The DTVP-3, TVPS-3 and Beery VMI-6 were found to discriminate between children with and without a specific learning disability. All three assessments were found to have low levels of sensitivity, however were found to exhibit adequate levels of reliability. With the exception of the visual closure subtest on the TVPS-3 and DTVP-3, the tests cannot be used interchangeably but are all suitable for use with South African children from middle socio-economic backgrounds and can be used to identify visual perceptual and VMI dysfunction. This study was limited by a few factors such as that not all learners with a specific learning disability had visual perceptual problems, the participants used in this study only represented one region of Johannesburg and one province and lastly only learners aged six to nine years were included in this study. Further research on a more representative sample of South African learners is recommended as socio-economic status and environmental conditions have been shown to affect the performance on these tests. / MT2017

O estudo da acuidade Vernier (VRN) revela a capacidade do sistema visual humano em detectar deslocamentos espaciais de poucos arcos de segundos, menores que a distância entre dois cones foveais adjacentes. Tal fato desperta interesse teórico sobre o tema, além de futuras aplicações na área clínica. A acuidade VRN pode ser medida tanto psicofisicamente quanto eletrofisiologicamente. Para a detecção de quebras de colinearidade (acuidade VRN), alguns autores hipotetizam que as células ganglionares (CGs) M da retina provêem sinal adequado da retina ao córtex, e dão suporte ao desempenho psicofísico da tarefa VRN. Em condições de estímulos semelhantes, as células ganglionares magnocelulares (M) em primatas parecem ter precisão espacial com razão sinal-ruído mais alta do que as células parvocelulares (P) . A dependência ao contraste (C) das células M na precisão espacial, frequência espacial, frequência temporal e velocidade do estímulo é mais similar ao desempenho psicofísico em humanos do que comparados aos dados das células P (Rüttiger et al., 2002; Sun et al., 2004). Nós utilizamos o Potencial Provocado Cortical Visual de Varredura (sVEP) para avaliar esta hipótese no nível de processamento intermediário entre as respostas de célula única na retina e a detecção psicofísica. Nós medimos os limiares corticais VRN em função do contraste (14 participantes, média de 28,21 ± 2,8) e lacunas (9 participantes, média de 29,7 ± 5,9). As quebras verticais VRN na colinearidade foram introduzidas em uma grade de onda quadrada horizontal. O estímulo VRN alternou entre um estado alinhado (grades sem quebras) e desalinhado (grades com quebras) a 6 Hz. Durante cada uma das 10 tentativas, o deslocamento aumentou em passos logarítmicos iguais de 0,5 a 7,5. O limiar VRN foi definido no momento do deslocamento em que a extrapolação linear da média vetorial das respostas em 1F atinge zero uV. Os contrastes testados foram: 4, 8, 16, 32, 64, 80%. Os resultados mostram que (1) aos limiares VRN em Log, medidos com sVEP, com o C em Log, diminuíram de forma linear (com uma inclinação de -0,5), similiares às células ganglionares M mas não P (Sun et al., 2004) e próximo às medidas psicofísicas (Sun et al., 2004; Wehrhahn e Westheimer, 1990); (2) Para C 16% obtivemos limiares de hiperacuidade (menor que 1 arcmin). Em altos contrastes a média do limiar foi de 0,37(erro padrão de 0,06 unidades logarítmicas); (3) Os limiares para o 2F tiveram uma dependência para o contraste diferente, com poucos efeitos para contraste abaixo de 16%. (4) As inclinações das linhas de extrapolação dos sVEP para o 1F1 foram 2 a 3 vezes maiores que as inclinações para 2F; (5) No protocolo controle, deslocamentos bidirecionais e simétricos geraram somente respostas no 2F. Os resultados 3 a 5 implicam que os componentes 1F e 2F derivam de neurônios distintos e fundamentam que respostas no 2F refletem respostas de movimento cortical simétrico. A dependência dos limiares de contraste do sVEP VRN (1F) é similiar aos estudos prévios psicofísicos (Sun et al., 2004; Wehrhahn e Westheimer, 1990), e repete a dependência ao contraste das células M (Sun et al., 2004). Estes resultados fundamentam a hipótese que o córtex extrai informações da posição relativa com precisão de hiperacuidade dos sinais advindos das células M / The human visual system is able to detect spatial displacements of a few arcsec, much smaller than the distance between two adjacent foveal cones. Hyperacuity tasks such as Vernier (VRN) have both theoretical importance as well as clinical application. VRN can be measured psychophysically and with sVEP. Some authors hypothesize that M ganglion cells provide the retinal signal to cortex adequate to support Vernier performance. Under stimulus conditions analogous to detection of Vernier offsets, primate magnocellular (M) ganglion cells appear to have more precise spatial localization (with higher Signal to Noise Ratio) than parvocellular (P) cells, and the dependence of M cell spatial precision on contrast (C), spatial frequency, temporal frequency and stimulus velocity is more similar to human psychophysical performance than comparable data from P cells (Ruttiger et al, 2002; Sun et al., 2003, 2004) (Rüttiger et al., 2002; Sun et al., 2004). We measured the C-dependence of cortical VRN thresholds (thd) using the Sweep VEP (sVEP) to help evaluate this hypothesis at a processing level intermediate between single-cell retinal responses and psychophysical detection. We measured Vernier thds using sVEP as function of constrast (12 young adults, age means 28.21 yrs ± 2.8) and Gaps (9 participants, 29.7 ± 5.9) with normal vision. Vertical VRN breaks in colinearity were introduced to a horizontal squarewave grating. The VRN stimulus alternated between aligned (grating w/o breaks) and misaligned (w/breaks) states at 6 (or 10) Hz. During each of ten, 10-s trials, displacement (D) was increased in equal logarithmic steps from 0.5 to 7.5. Vernier thd was defined as the D at which the rising slope of the vector averaged 1F response extrapolated to zero V. The Cs tested were: 4, 8, 16, 32, 64, 80%. We Found: (1) Log Vernier thd measuered with sVEP decreased linearly with log C similar to M- (but not P-) ganglion cells (Sun et al., 2004) with a slope of -0.5, close to that measured psychophysically (Rüttiger et al., 2002; Sun et al., 2004); (2) For C 16% , thds were true hyperacuities (less than 1). At high C, mean thd was 0.37(S.E = 0.06 log units); (3) Thds for 2F had a different C dependence, with little effect of C below 16 %. Thds for 2F were < 1F thds below 16 % C, but were 1F thds beyond 16 %; (4) The slopes of the sVEP extrapolation lines for 1F were 2-3 times > 2F slopes; (5) In a control protocol, symmetric, bidirectional displacements only generated 2F responses. Results 3-5 imply that the 1F and 2F components derive from distinct neurons, and support the notion that 2F responses reflect symmetric cortical motion responses. The C-dependence of sVEP Vernier (1F) thresholds is similar to prior psychophysics (Sun et al., 2004; Wehrhahn e Westheimer, 1990), and recapitulates Mcell C-dependence (Sun et al., 2004). This results support the hypothesis that cortex extracts relative position information with hyperacuity precision preferentially from M cell signals