Cite as:
Shi Z, Goldbach M, de'Sperati C, 2006, "Position biases with moving stimuli" Perception 35 ECVP Abstract Supplement

Position biases with moving stimuli

Z Shi, M Goldbach, C de'Sperati

Motion generates illusions such as the flash-lag and the Fröhlich effects. Motion also shifts in its direction the perceived position of stationary stimuli flashed nearby. We mapped position distortions both of moving and of stationary stimuli within the region of space near the moving stimulus. A circular arc revolved at 0.5 cycle s^-1 (4 deg eccentricity), and a spot was flashed at 6 different positions along the motion path, with 3 different eccentricities. At the end of each trial subjects positioned the circular arc at its perceived position at the time of the flash, and then moved the mouse cursor to the perceived flash position. We found: (i) a shift of the perceived flash position in the direction of motion ('push effect', range 9 to 39 min of arc); (ii) a bias in the perceived flash eccentricity, ranging from outward (13 min of arc) to inward (-1 9 min of arc), depending on the objective flash position; (iii) a shift of the perceived position of the arc in the direction of motion ('drag effect', 51 to 104 min of arc), much larger than the flash shift. These results can explain mislocalisation illusions in terms of a systematic distortion of positional information in the presence of motion stimuli.

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