Abstract
In a recent study von Muhlenen and Sunny (2010, Journal of Vision) showed that motion onset capture attention only when motion was jerky (refreshed at 8 or 17 Hertz), but not when it was smooth (33 or 100 Hertz). They also showed that simple flicker (without motion) did not account for this result, ruling out explanations that put capture down to the continuous stream of luminance transients produced by jerky motion. Thus, it remains unclear why the onset of jerky motion captures attention. In this study we build on von Muhlenen, Rempel, and Enns (2005, Psychological Science) and suggest that the lower motion refresh rate delays the perceived motion onset, turning it into a temporally unique event. According to von Muhlenen et al. (2005) any change can capture attention provided that it occurs during a period of temporal calm, where no other display changes happen. Experiment 1 used the same paradigm and refresh rate manipulation as von Muhlenen and Sunny (2010), except that one item was now continuously moving from the beginning of the trial. The results showed no capture for continuous motion irrespective of whether motion was jerky or smooth. This means, attention is not captured by jerky motion per se, but by the onset of jerky motion. Experiment 2 used again motion onset as in von Muhlenen and Sunny's study. However after the first displacement, which occurred either after 120, 60, 30, or 10 ms (equivalent to the 8, 17, 33 or 100 Hz motion refresh rates previously used), all moving stimuli continued with smooth 100-Hz motion. The results showed essentially the same pattern as in von Muhlenen and Sunny's experiment, with significant capture only in the delayed (120 and 60 ms) displacement conditions. Both experiments support von Muhlenen et al. (2005) unique-event account.