Abstract
Behavioral studies suggest that humans intercept moving targets by maintaining a constant bearing angle (CBA). The purely feedback-driven CBA strategy has been contrasted with the strategy of predicting the eventual time and location of the future interception point. This study considers an intermediate anticipatory strategy of moving so as to produce a CBA a short duration into the future. Subjects controlled their speed of self-motion along a linear path through a simulated environment to intercept a moving target. When targets changed speed midway through the trial in Experiment 1, subjects abandoned an ineffective CBA strategy in favor of a strategy of anticipating the most likely change in target speed. In Experiment 2, targets followed paths of varying curvature. Behavior was inconsistent with both the CBA and the purely predictive strategy. To investigate the intermediate anticipatory strategy, human performance was compared with a model of interceptive behavior that, at each time-step t, produced the velocity adjustment that would minimize the change in bearing angle at time t + ∆t, taking into account the target’s behavior during that interval. Values of ∆t at which the model best fit the human data for practiced subjects varied between 0.5 and 3.5 s, suggesting that actors adopt an anticipatory strategy to keep the bearing angle constant a short time into the future.
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Notes
Fajen and Warren (2007) presented simulations to show that the bearing angle whose change must be nulled is defined in an exocentric reference frame. When simulated agents keep the target at a constant egocentric (rather than exocentric) direction, the resulting trajectory spirals behind the moving target for some initial conditions. By comparison, human subjects follow a straight path ahead of the target (Fajen and Warren 2004).
Although it is common to apply Bonferroni tests and thus to decrease alpha to compensate for the greater family-wise probability of a type 1 error when performing multiple t tests, our strategy of maintaining an alpha of 0.05 was the more conservative approach in that it increased the odds of rejecting the null hypothesis when we should not have rejected it.
For each combination of radius/direction, initial target speed, and target approach angle, the model was then used to produce one simulated speed profile for each possible combination of ∆t, β, and ω 0.
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Acknowledgment
This research was supported by grants from the National Science Foundation (BCS 0545141 and BCS 0236734)
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Diaz, G.J., Phillips, F. & Fajen, B.R. Intercepting moving targets: a little foresight helps a lot. Exp Brain Res 195, 345–360 (2009). https://doi.org/10.1007/s00221-009-1794-5
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DOI: https://doi.org/10.1007/s00221-009-1794-5