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Para Kang, Steven Shevell; Binding the features of a continuously changing visual stimulus. Journal of Vision 2011;11(11):853. doi: 10.1167/11.11.853.
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© ARVO (1962-2015); The Authors (2016-present)
Consider a disk that is changing along a continuum of color over two seconds, from red to green. If the disk is yellow after one second, and at this same instant a second yellow disk is presented as a brief pulse, the color of the continuously changing disk is perceived to be ahead on the color continuum (say, greenish yellow) compared to the pulsed disk (Sheth, Nijhawan, & Shimojo, 2000). Chromaticities of both disks are identical when the pulse is presented but the two disks are perceived to be different. Similar results hold for luminance, spatial frequency and pattern entropy but the lead times vary for different features (for example, longer for color than spatial frequency). How is our percept affected by the combination of features that have different lead times? METHOD: A circular window (diameter 2.6 deg) with a 1.3 cpd square-wave grating appeared on one side of a fixation point. The color of the grating changed continuously, either from green to red or from red to green; simultaneously, the grating rotated either clockwise or counter-clockwise. Exactly halfway through the presentation, a second stimulus was briefly presented (79 msec) on the other side of the fixation point. The color and orientation of the pulsed grating were the same as the continuously changing grating at that instant. At the end of each presentation, the observer compared the pulsed stimulus to the continuous one in (1) only color, (2) only orientation or (3) both. RESULTS & CONCLUSIONS: When color or orientation was matched alone, color showed longer lead times than orientation. When observers matched both color and orientation simultaneously, the lead times for color were still substantially longer than for orientation. This implies that observers perceived the continuously changing stimulus to have a combination of orientation and color that was never actually presented to the eye!
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