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Biomedical subjects

D R Bradley

Publications and source records attributed to D R Bradley.

14 recordsLinked to original sources
PubMed2000

Overestimation of the effectiveness of cardiopulmonary resuscitation as a function of CPR certification level.

67 college students holding three different levels of certification in CPR estimated the survival rates of people given this procedure. Students not certified in CPR estimated the survival rate to be 51.2%, those previously certified estimated 43.8%, and those currently certified estimated 27.0%. Although knowledge of CPR was associated with greater accuracy, all three groups significantly overestimated the actual survival rate of 10%.

Attitude to Health↗
PubMed1985

Perceptual organization and apparent brightness in subjective contour figures.

According to a number of theories subjective contours arise from brightness contrast and/or assimilation. The apparent brightness gradients generated by these effects are assumed to give rise to the perception of contours delineating the gradients. A study is reported in which naive observers were shown a subjective contour display and asked to report what they saw. They were then asked to judge whether the center or the surround of the display appeared brighter. Subjects whose reports indicated that they had seen the subjective contour figure showed an overwhelming preference for the center of the display being brighter than the surround. However, subjects who did not see the subjective contour figure did not differ significantly in their selection of the center over the surround. This finding presents difficulties for any theory which derives subjective contours from the apparent brightness difference.

Color Perception↗
PubMed1984

The effects of illumination level and retinal size on the depth stratification of subjective contour figures.

The apparent stratification in depth of subjective contour figures over their backgrounds was investigated as a function of illumination level, figure size, and viewing distance. Magnitude estimation, with a real contour figure serving as the modulus, was used to measure the stratification in depth of a subjective contour figure over its background. Illumination level and retinal size both had significant effects on the depth stratification of the subjective contour figures. The greatest apparent depth differences were obtained for figures of small retinal size under low levels of illumination. These results paralleled previous findings for judgments of subjective contour strength. Consequently, both contour clarity and depth stratification of subjective contour figures are affected in similar ways by illumination level, figure size, and viewing distance. The implications of this response coupling are discussed in terms of current theories of subjective contours.

Adult↗
PubMed1984

The 'shrinking circle illusion' is a shrinking ellipse.

Twenty-four subjects judged the size of the horizontal and vertical extents of the path traversed by a circularly rotating target. The target was rotated at velocities ranging from 0.18 to 1.13 cycles s-1, and observed with smooth pursuit eye movements or by fixating a point in the center of the path. It was found that underestimation of the target path increased with velocity, and was more pronounced for the horizontal than vertical component of the target path. These effects were quite strong during smooth pursuit, but weak during fixation. In previous research on the 'shrinking circle illusion' the vertical component of the path was not measured. The present findings indicate that the apparent shape of the path is elliptical, and that the eccentricity of this ellipse increases with velocity during smooth pursuit.

Adult↗
PubMed1984

Psychophysical functions for perceived and remembered distance.

Two separate groups of subjects made magnitude estimations of the distances to fifteen objects (from 20 ft to 14.28 miles away) situated in a landscape. On day 1 of the experiment both groups learned the names and locations of the objects while viewing them from the top of a small mountain. On day 2 the perception group (N = 19) judged the distances to the objects while viewing them from the top of the mountain, whereas the memory group (N = 18) judged the distances while visualizing the landscape from memory. The data for both groups were well fit by power functions; the exponent was reliably smaller for the memory group (0.596) than for the perception group (0.811). Both groups drew maps of the landscape (reproduction task) from memory and the exponents were 0.483 and 0.514 for the memory and perception groups, respectively. The results are discussed in light of possible transformations performed on the original stimulus inputs by the sensory/perceptual and the memorial systems.

Distance Perception↗
PubMed1978

Psychophysical functions for perceived and remembered size.

Separate groups of people estimated the sizes of perceived or of remembered objects. In three independent experiments, both sets of data were well fit by power functions, and the exponent was reliably smaller by remembered than for perceived size.

Humans↗
PubMed1977

Organizational determinants of subjective contour: the subjective Necker cube.

With specially arranged inducing elements on a white surface of uniform luminosity, a phenomenally complete Necker cube can be seen in any array where only the 'corners' of the cube are physically represented. The subjectively seen bars of the cube disappear when the inducing 'discs' are seen as 'holes' in an interposing surface, through which the corners of a partially occluded cube are viewed. Illusory brightness effects are also observed in connection with the different organizations of this ambiguous figure.

Cues↗