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Murthy V. Bhavaraju, Ennio Mingolla; Perception of speed across variations in spatiotemporal frequency. Journal of Vision 2004;4(8):84. https://doi.org/10.1167/4.8.84.
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© ARVO (1962-2015); The Authors (2016-present)
Many pairs of spatial and temporal frequencies in a motion display can result in the same stimulus speed for a moving object, but nonetheless these different pairs of spatial and temporal frequencies can produce different speed percepts. In the present experiment a small square or disk object (subtending approximately 0.5 to 2.9 degrees) moves intermittently; i.e., it is always present on the screen (unlike flicker) but moves by a small amount at fixed temporal intervals. The spatial movement of these objects varied from approximately 1.5 minutes to 2.2 degrees, at temporal intervals ranging from 10 milliseconds to a second. (The subjects' heads were not fixed; all calculations assume a nominal viewing distance of 60 cm.) Using the method of paired comparisons, the observer is asked to choose which of two objects is moving faster over its linear trajectory. Each object has a different combination of spatial and temporal frequencies that result in the same overall speed as the other object. Results for four observers indicate that the subjective perception of the speed of an object depends on the spatiotemporal frequency of the moving pattern. This estimated speed varies as an inverted U-shaped function, peaking at a specific spatial and temporal frequency combination and decreasing as one moves away from it. While individual differences are found, the location of this peak is dependent on the size of the object that is being tracked, but not on its shape. As the size of the object increases, the peak tends to shift to lower spatial (i.e. large displacements) and lower temporal frequencies (that result in the same stimulus speed). The presence of sharp rather than blurred object boundaries and the shape of the object did not have a noticeable effect on the perceived speed. In conclusion, the perceived speed of an object varies systematically across combinations of spatiotemporal frequency that produce equivalent stimulus speeds.
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