A random dot pattern that moved within an invisible aperture was used to present two motions contiguously in time. The motions differed slightly either in speed (Experiments 1 and 3) or in direction (Experiments 2 and 4) and the subject had to discriminate the sign of the change (e.g. increment or decrement). The same discrimination task was performed when the two motions were temporally separated by 1 s. In Experiments 1 and 2 discrimination thresholds were measured with motion durations of 0.125, 0.25, 0.5 and 1.0 s and mean speeds of 2, 4, 8, and 16 degrees/s. In Experiments 3 and 4 thresholds were measured with aperture widths of 5 and 20 cm. The discrimination of contiguous motions progressively deteriorated with decreasing duration and mean speed of motion. For the lowest value of duration the Weber fraction for contiguous speeds was more than three times as the Weber fractions for separate speeds. For the same low value of duration the thresholds for discrimination of direction of contiguous motions were only about 50% higher than the thresholds for separate motions. The Weber fraction for contiguous speeds was ca. three times higher with the smaller aperture than with the larger one, provided the ratio 'aperture width mean speed' (i.e. the lifetime of the moving dots) was less than 0.3 s. Aperture width did not affect the discrimination of direction of contiguous motions. The discrimination of contiguous motions is discussed together with the known data for detection of changes in speed and direction. It is suggested that both, detection of changes in speed and discrimination of the sign of speed changes, may be performed by a common visual mechanism.
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http://dx.doi.org/10.1016/s0042-6989(99)00185-6 | DOI Listing |
Med Phys
November 2024
CNRS, CRMSB, UMR 5536, IHU Liryc, University of Bordeaux, Bordeaux, France.
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November 2024
Department of Neurosurgery, Cleveland Clinic Foundation, Cleveland, Ohio, USA.
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View Article and Find Full Text PDFMil Med
August 2024
Department of Industrial, Manufacturing, and Systems Engineering, Texas Tech University, Lubbock, TX 79409-3061, USA.
Introduction: The cervical spine, pivotal for mobility and overall body function, can be affected by cervical spondylosis, a major contributor to neural disorders. Prevalent in both general and military populations, especially among pilots, cervical spondylosis induces pain and limits spinal capabilities. Anterior Cervical Discectomy and Fusion (ACDF) surgery, proposed by Cloward in the 1950s, is a promising solution for restoring natural cervical curvature.
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June 2024
Cardiology, University of Michigan Hospitals, Ann Arbor, USA.
Med Phys
September 2024
Dept. of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada.
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