Proefschrift - Utrecht. / Summary in English and Dutch.

Proefschrift - Utrecht. / Summary in English and Dutch.

Francis Edward Mitchell. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 80-81 (2nd gp.)). / Acknowledgments --- p.iii / Summary --- p.iv / Introduction --- p.1 / Sharpness and contrast --- p.2 / Causes of unsharpness --- p.3 / Chapter i) --- Photographic unsharpness --- p.3 / Chapter ii) --- Movement unsharpness --- p.6 / Chapter iii) --- Geometric unsharpness --- p.8 / Chapter iv) --- Exposure unsharpness --- p.12 / Contrast factors --- p.15 / Chapter i) --- Subject/object contrast --- p.15 / Chapter ii) --- Radiation --- p.16 / Chapter iii) --- Film and screen --- p.18 / Chapter iv) --- Subjective --- p.20 / "How do we see ""Sharpness & Contrast"" ？" --- p.21 / Factors in perception --- p.26 / Chapter i) --- The individuals eyesight (and age) --- p.26 / Chapter ii) --- Light intensity --- p.26 / Chapter iii) --- Colour --- p.27 / Chapter iv) --- Pupil diameter --- p.27 / Chapter v) --- Size and shape of the object --- p.28 / Chapter vi) --- Eccentricity --- p.28 / Chapter vii) --- Edge enhancement --- p.29 / Chapter viii) --- Background luminance --- p.30 / Chapter ix) --- Maximising information retrieval from an image --- p.30 / Experiment I - Production of an image with controlled sharpness and contrast --- p.31 / Chapter i) --- Choice of film & cassette --- p.31 / Chapter ii) --- Prevention of movement unsharpness --- p.34 / Chapter iii) --- Prevention of parallax --- p.34 / Chapter iv) --- Control of penumbra --- p.35 / Chapter v) --- Verification of image unsharpness --- p.40 / Control of contrast --- p.46 / Radiography of test objects --- p.48 / Experiment II - Perception of sharpness at different contrast levels --- p.53 / Chapter i) --- Experiment --- p.53 / Chapter ii) --- "Viewing the data in terms of ""sharpness""" --- p.56 / Chapter iii) --- Viewing the data in terms of contrast levels --- p.61 / Analysis of data from an expanded group size (N=55) --- p.66 / Experiment III - Effect of room lighting conditions on the perception of sharpness --- p.69 / Overall conclusions --- p.78 / Bibliography --- p.79 / References --- p.80 / Appendix A (VBV calculation) --- p.82 / Appendix B (Line-pair test-tool) --- p.83 / Appendix C (Scattered radiation) --- p.85 / Photo-electric --- p.85 / Compton --- p.85 / Pair-production --- p.85 / Net result --- p.86 / Appendix D (Metal discs) --- p.87 / "Appendix E (OFD, magnification and penumbra)" --- p.88 / Appendix F (Processor developer temperature) --- p.90 / Appendix G (Viewing contrast-sharpness data) --- p.91 / Appendix H (Viewing conditions) --- p.92 / Appendix I (Comparison of data - light and dark viewing conditions) --- p.94 / Appendix J (Curix film & screens) --- p.97

Thesis (M.Sc.). / Written for the School of Physical and Occupational Therapy. Title from title page of PDF (viewed 2009/06/25). Includes bibliographical references.

Thesis--Utrecht. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 107-117).

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 104-110).

Thesis--Utrecht. / Vita. Includes bibliographical references.

Thesis--Utrecht. / Vita. Includes bibliographical references.

BACKGROUND: Descending kerbs during locomotion involves the regulation of appropriate foot placement before the kerb-edge and foot clearance over it. It also involves the modulation of gait output to ensure the body-mass is safely and smoothly lowered to the new level. Previous research has shown that vision is used in such adaptive gait tasks for feedforward planning, with vision from the lower visual field (lvf) used for online updating. The present study determined when lvf information is used to control/update locomotion when stepping from a kerb. METHODOLOGY/PRINCIPAL FINDINGS: 12 young adults stepped down a kerb during ongoing gait. Force sensitive resistors (attached to participants' feet) interfaced with an high-speed PDLC 'smart glass' sheet, allowed the lvf to be unpredictably occluded at either heel-contact of the penultimate or final step before the kerb-edge up to contact with the lower level. Analysis focussed on determining changes in foot placement distance before the kerb-edge, clearance over it, and in kinematic measures of the step down. Lvf occlusion from the instant of final step contact had no significant effect on any dependant variable (p>0.09). Occlusion of the lvf from the instant of penultimate step contact had a significant effect on foot clearance and on several kinematic measures, with findings consistent with participants becoming uncertain regarding relative horizontal location of the kerb-edge. CONCLUSION/SIGNIFICANCE: These findings suggest concurrent feedback of the lower limb, kerb-edge, and/or floor area immediately in front/below the kerb is not used when stepping from a kerb during ongoing gait. Instead heel-clearance and pre-landing-kinematic parameters are determined/planned using lvf information acquired in the penultimate step during the approach to the kerb-edge, with information related to foot placement before the kerb-edge being the most salient.