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George Sperling, Son-Hee Lyu; Motion Standstill in Luminance-Modulated and Texture-Contrast-Modulated Gratings. Journal of Vision 2011;11(11):753. doi: 10.1167/11.11.753.
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© ARVO (1962-2015); The Authors (2016-present)
Motion standstill is a phenomenon in which a rapidly moving stimulus appears to be standing still. It occurs when the spatiotemporal resolution of the shape and texture perception systems exceeds that of the motion perception systems. Motion standstill has been incidentally observed in previous visual investigations but it has been studied parametrically only with isoluminant chromatic gratings and dynamic-random-dot stereo gratings—stimuli that exclusively stimulate the third-order motion system. Here we test luminance-modulated (LM) and texture-contrast-modulated (CM) gratings. LM stimuli stimulate primarily the first-order and CM stimuli primarily the second-order motion systems, although lower spatial and temporal frequencies of the CM stimuli also excite the third-order motion system. Method: High-contrast linearly moving LM and CM sinusoidal gratings were viewed over full ranges of spatial and temporal frequencies. The gratings were oriented +45 or −45 deg and appeared either as a 1.9 deg disk in the fovea or an 8–10 deg annulus in the periphery. Observers reported the speed, slant and motion direction of the moving grating on each trial. Results: For LM stimuli, motion standstill reliably occurred in both fovea and periphery: that is, motion-direction judgments were at chance, slant judgments were virtually perfect, and the grating speed was judged as zero. For CM stimuli, standstill judgments were extremely rare. The range of reliable motion standstill for foveal LM was typically 16–22 cpd, for peripheral, LM 10–13 cpd, both over the full test range of temporal frequencies (3–19 Hz). Conclusion: Motion standstill occurs in moving LM gratings that fall within the spatial resolution of the shape-object system but exceed the spatial resolution of the first-order motion system. The shape system extracts a single, representative stationary image from the moving display to present to consciousness.
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