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Stephen R. Gabbard, Scott N. J. Watamaniuk; The flash-lag effect (FLE) as a biasing factor for offside determination in soccer. Journal of Vision 2011;11(11):759. doi: 10.1167/11.11.759.
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Leading theories of the FLE, differential neural latency and postdiction (temporally weighted spatial average), posit that a moving object's perceived position lags a temporal marker by tens of ms. Baldo (2002) suggested that the FLE might be operational on a soccer field as the Assistant Referee (AR) determines the position of a moving attacker relative to a defender, typically also moving. The temporal marker would be the observation, extrapolated anticipation, or sound of the ball being kicked by a teammate of the attacker, usually outside the foveal vision of the AR as s/he attends to the possibly offside attacker. In a study designed to simulate some of the dynamics of the offside call, four soccer referees and three non-referees judged the position of a moving blue rectangle relative to either a stationary or moving red reference rectangle at a time identified by a tone (object positions at the time of the tone were varied systematically). Trials lasted from 500 to 2000 ms and objects moved at a range of soccer-appropriate speeds. There was no fixation point and observers were free (as referees are) to pursue objects as they saw fit. Data from 30 conditions, presented randomly over several sessions, were fit with logistic functions. A 2-way repeated measures ANOVA (speed x participant group) showed significant main effects only (approach speed - F(2,95) = 9.93, p < .0001; participant group - F(1,95) = 1301, p < .0005). Non-referees perceived the blue target rectangle to have moved further than referees. However, the effect was smaller than predicted by the typical FLE, suggesting that the FLE is unlikely to be operating on the soccer field. However, even the small position error observed would produce a robust offside call bias in soccer, which may be an adaptation to compensate for the perceptual complexity of the offside call.
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