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Kevin Smith, Joshua Davis, Benjamin Bergen, Edward Vul; Similarities and differences in forward and reverse motion extrapolation. Journal of Vision 2015;15(12):288. doi: https://doi.org/10.1167/15.12.288.
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© ARVO (1962-2015); The Authors (2016-present)
We often must not only extrapolate the future trajectory of objects (where will a thrown rock go?) but also extrapolate backwards in time (where did the rock flying by your head come from?). We matched forward and reverse extrapolation in two experiments to investigate similarities and differences between extrapolation directions. Forward and reverse extrapolation share biases and response time patterns across various trajectories, but reverse extrapolation is noisier. This suggests both forms of extrapolation share cognitive processes, and opens up further avenues of investigation into why reverse extrapolation is noisier. In Experiment 1, participants observed a ball moving either towards (forward) or away from (reverse) a semi-circular occluder, then a mark appeared on the outside of the semi-circle and participants indicated whether the ball would travel (forward) or came from (reverse) above or below this mark. 85% accuracy was maintained by dynamically adjusting the mark for each condition. Participants were slightly slower to respond when the occluder was larger (F(2,32)=4.8, p=0.015), but speed was unaffected by extrapolation type (F(1,16)=0.4, p=0.56). Reverse extrapolation was harder (greater offset thresholds: F(1,16)=5.4, p=0.034), though difficulty increased at the same rate over distance (no interaction: F(2,32)=0.04, p=0.96). These results suggest shared processing underlies both extrapolation directions, but do not differentiate whether reverse extrapolation is more biased or simply more variable. In Experiment 2, participants observed a ball in motion and indicated where on a line it would next cross (forward) or last came from (reverse). Each forward trial had a matched reverse trial with mirrored motion, so the line crossing would be identical. Systematic biases were nearly identical across extrapolation directions (r=0.96) but people were on average 30% more variable on reverse trials. This suggests that reverse extrapolation and forward extrapolation share biases, and that greater variability caused the increased difficulty in Experiment 1.
Meeting abstract presented at VSS 2015
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