Biomedical subjects
P Emmerson
Publications and source records attributed to P Emmerson.
Are nurse practitioners merely substitute doctors?
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The nature of sensorimotor adaptation to altered G-levels: evidence from mass discrimination.
Mass discrimination is impaired under zero G compared to 1 G. This is partly due to loss of weight information (a reduction in z-axis pressure stimulation), and probably also to incomplete adaptation to the reduced G-level. Maladaptation to an increased G-level postflight causes objects to feel too heavy and weight discrimination to be impaired. Video tapes of hand movements while shaking test objects were made before, during, and after the D-1 Spacelab mission. Movements were faster inflight than preflight, slowed down postflight and returned to baseline by about the third day. Corresponding changes in movement amplitude also occurred. Errors of weight or mass perception during the maladaptation phase may be due to both inadequate monitoring of command signals and to inappropriate scaling of afferent signals. High-acceleration shaking was found to improve mass discrimination but impair weight discrimination.
Mass discrimination in weightlessness improves with arm movements of higher acceleration.
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Colour constancy with change of viewing distance under water.
Colour constancy is commonly considered to be the product both of high-order (cognitive) and of lower-order (retinal) mechanisms. A study is reported of colour appearance in situations where the spectral radiance of an object changes significantly with viewing distance. Subjects were instructed to match the colour appearance of a number of coloured tiles in air and at various viewing distances in different types of water. Colour-constancy ratios were calculated by comparing the visual data with simultaneously obtained spectroradiometric and photometric data. The obtained constancy ratios were attributed to the role of distance estimation in the determination of colour appearance, an effect that is presumably masked under normal viewing conditions, where long viewpaths are necessary to produce significant radiance changes. A similarity to the size-distance invariance hypothesis is noted.