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Joseph E. Barton, Theodore E. Cohn; Size Modulation Sensitivity for a Two-Dimensional Shape. Journal of Vision 2004;4(8):616. doi: 10.1167/4.8.616.
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Collision avoidance requires that an observer accurately and continuously track an approaching object's distance (range) and closing speed (range rate). To investigate the dynamic characteristics of the visual system in this task, experiments have been performed in which a circle (representing the outline of a looming object) was presented on an x-y driven CRT, and its radius modulated sinusoidally. The circle subtended a visual angle of approximately 4° and was written at 30 kHz. Three observers (all having normal vision) were tested, at each of nine different frequencies between 0.05 Hz to 20 Hz. Their task was to detect modulation in the radius of the circle. For each observer, threshold modulation amplitude as a function of frequency was obtained using the adaptive staircase algorithm of Watson and Pelli (Percept Psychophys, 1983). All three observers exhibited a bandpass characteristic for this detection task. Under the assumption that the underlying visual processes involved are approximately linear, these data have been used to derive an impulse response function, employing the techniques of Stork and Falk (J Opt Soc Am A, 1987). The results of this experiment will be compared to predictions obtained from an analytically/experimentally derived, three-stage detection model.
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