Familiar trajectories facilitate the interpretation of physical forces when intercepting a moving target

Abstract

Familiarity with the visual environment affects our expectations about the objects in a scene, aiding in recognition and interaction. Here we tested whether the familiarity with the specific trajectory followed by a moving target facilitates the interpretation of the effects of underlying physical forces. Participants intercepted a target sliding down either an inclined plane or a tautochrone. Gravity accelerated the target by the same amount in both cases, but the inclined plane represented a familiar trajectory whereas the tautochrone was unfamiliar to the participants. In separate sessions, the gravity field was consistent with either natural gravity or artificial reversed gravity. Target motion was occluded from view over the last segment. We found that the responses in the session with unnatural forces were systematically delayed relative to those with natural forces, but only for the inclined plane. The time shift is consistent with a bias for natural gravity, in so far as it reflects an a priori expectation that a target not affected by natural forces will arrive later than one accelerated downwards by gravity. Instead, we did not find any significant time shift with unnatural forces in the case of the tautochrone. We argue that interception of a moving target relies on the integration of the high-level cue of trajectory familiarity with low-level cues related to target kinematics.

Filling gaps in visual motion for target capture

“…In these experiments, the gravity field could be congruent with either natural gravity or reversed gravity and the target motion could be occluded from view for variable time intervals before interception. Time shifts consistent with a-priori assumptions of natural gravity between the interceptive responses to natural and non-natural targets were found only for the familiar condition of the inclined plane but not for the tautochrone (see Figure 6B ), suggesting that target motion extrapolation depends on integration of high-level cues about trajectory familiarity with lower-level target kinematics information (Mijatović et al, 2014 ).…”

“…For example, time-to-contact estimates of approaching objects may be affected greatly by identity/familiarity information about the object, in addition to the retinal image expansion rates (Hosking and Crassini, 2010 ). Experiments in which participants intercepted targets sliding down either an inclined plane or a tautochrone (i.e., the cycloid curve along which a point mass slides to the bottom under gravity in the same time regardless of the starting position) examined this possibility more in depth (Mijatović et al, 2014 ). Although gravity acceleration affected the targets similarly in both cases, the inclined plane represented a familiar situation, whereas the tautochrone did not (Figure 6A ).…”

“… Manual interception of familiar and unfamiliar trajectories . (A) Visual scenes displayed during the experiments of Mijatović et al ( 2014 ). Top and bottom rows show the inclined planes (familiar situation) and the tautochrones (unfamiliar situation).…”

Gravity as a Strong Prior: Implications for Perception and Action

“…), another physical variable came into focus: (earth) gravity. Gravitational biases have been reported for free falling targets (McIntyre et al, 2001; Zago et al, 2005, 2008, 2010, 2011) as well as for parabolic trajectories (Bosco et al, 2012; Diaz et al, 2013; Delle Monache et al, 2014; de la Malla and López-Moliner, 2015; Lacquaniti et al, 2015, validated a gravity based model for parabolic interception brought forward in Gómez and López-Moliner, 2013), objects on ramps (Mijatović et al, 2014), and even for objects that move horizontally (De Sá Teixeira et al, 2013; De Sá Teixeira, 2016). Interestingly, there seem to be certain constraints as to when computations can access the internal representation of gravity; when the so called “idiotropic vector” along the vertical body axis, for example, is not aligned with the direction of gravity, the contribution of the internal representation of gravity decreases (De Sá Teixeira, 2014; De Sá Teixeira and Hecht, 2014).…”

“…Here, results are seemingly contradictory: some studies report the use of a gravity prior, as for example Mijatović et al (2014) who found that participants were judging time of arrival correctly for balls rolling down familiar geometrical shapes (an inclined plane) under 1g conditions, but overestimated time of arrival for −1g conditions, that is, when the ball was rolling up the plane. Similarly, Zago et al (2010) found that performance for targets on a partially occluded, vertical trajectory was consistently better for 1g than for 0g or −1g; likewise, for partially occluded parabolic trajectories, arrival of the ball was spatially and temporally underestimated for 0g, judged correctly for 1g and overestimated for 2g (Bosco et al, 2012).…”