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Harold E. Bedell, Lan K. Nguyen, Saumil S. Patel; The relationship between visual frame-of-reference effects for perceived size and speed. Journal of Vision 2004;4(8):574. doi: 10.1167/4.8.574.
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© 2017 Association for Research in Vision and Ophthalmology.
Purpose: Previous studies showed that a visual reference frame influences perceived target size or speed, with substantial variability among observers. We evaluated the influence of a visual frame on perceived size and speed in the same observers, to determine if the frame affects different perceptual attributes similarly within individual observers. Methods: The stimuli were a stationary spot (size: 0.4 – 1.8 deg) or a moving dot or field of limited-lifetime dots (speed: 2.8 – 12.4 deg/s) presented for 2 s within one of 3 square frames (2.7, 5.4, 10.9 deg). In different experiments, the moving dots were either scaled or unscaled to the size of the frame. Observers (12 – 16 per experiment) adjusted a target in a standard 5.4-deg reference frame to match the perceived size or speed of the previously viewed stimulus. Stimuli were presented binocularly in a totally dark room on a computer screen at 1 m. Frame effects were quantified as the percentage increase in matched size or speed of a target when presented in the largest vs. the smallest frame. Results: Increasing frame size from 2.7 to 10.9 deg produced, on average, a 13% increase in matched target size. The increase in matched speed with frame size depended on the moving targets: 70% when unscaled dots moved one at a time through the frame, 175% when size-scaled dots moved one at a time through the frame, 5% when the spatial interval between moving dots was scaled to the size of the frame, 23% when the targets were unscaled random dots, and 300% when the targets were size-scaled random dots. Across motion conditions, the highest correlation between the frame-size effect on perceived size and perceived speed was 0.07. Conclusions: The effect of a reference frame on perceived speed depends on whether (1) the moving targets are scaled to the size of the frame and (2) the target temporal frequency covaries with speed. Our results show that a visual frame exerts independent effects on the perception of size and speed.
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