Navigational strategy used to intercept fly balls under real-world conditions with moving visual background fields

Abstract

This study explored the navigational strategy used to intercept fly balls in a real-world environment under conditions with moving visual background fields. Fielders ran across a gymnasium attempting to catch fly balls that varied in distance and direction. During each trial, the launched balls traveled in front of a moving background texture that was projected onto an entire wall of a gymnasium. The background texture consisted of a field of random dots that moved together, at a constant speed and direction that varied between trials. The fielder route deviation was defined as the signed area swept out between the actual running path and a straightline path to the destination, and these route deviation values were compared as a function of the background motion conditions. The findings confirmed that the moving visual background fields systematically altered the fielder running paths, which curved more forward and then to the side when the background gradient moved laterally with the ball, and curved more to the side and then forward when the background gradient moved opposite the ball. Fielder running paths deviated systematically, in a manner consistent with the use of a geometric optical control strategy that helps guide real-world perception-action tasks of interception, such as catching balls.

Optical angular constancy is maintained as a navigational control strategy when pursuing robots moving along complex pathways

“…Results support that the strategy of maintaining a LOT relative to the background best matches the fielder behavior. This is consistent with past findings of fielders intercepting ballistic airborne baseballs (Aboufadel, 1996;Marken, 2001;McBeath et al, 1995a;Shaffer & McBeath, 2002;Wang et al, 2015), more complex moving airborne targets such as Frisbees and toy helicopters (Shaffer et al, 2004;Shaffer et al, 2008;Shaffer, Marken et al, 2013), as well as ballistic ground balls (Sugar, McBeath, & Wang, 2006), but in the case of groundbased trajectories, fielders maintain a flipped version of the same optical angular control heuristics. Thus, despite the vast differences in forces applied on airborne versus ground-based targets and resultant differences in target behavior, in both cases fielders selected running paths that maintained constancy of optical speed and angle of the target.…”

“…For balls headed within the sagittal plane, directly toward the fielder, the lateral optical movement is eliminated and the optical trajectory converges and simplifies down to just vertical optical constancy specified by OAC. The LOT control strategy has also been confirmed with mobile robots intercepting balls (Sugar & McBeath, 2001;Sugar, McBeath, Suluh et al, 2006), with moving backgrounds (Wang, McBeath, & Sugar, 2015), and a segmented version of the LOT has been found with dogs catching Frisbees that change in direction (Shaffer, Kruchunas, Eddy & McBeath, 2004), and with human fielders chasing randomly moving toy helicopters (Shaffer, Marken et al, 2013).…”

“…Because the control strategies that we compare are based on maintenance of optical angles, there is not a unique optimal running path for each strategy, but rather each specifies a family of running paths, determined by the angular parameters the fielder selects. This may seem to be a disadvantage of such models, but this level of diversity more accurately characterizes actual variance found between running paths in cases in which fielders run to catch fly balls (McBeath et al, 1995a(McBeath et al, , 1995bMcLeod et al, 2006;Shaffer et al, 2008;Wang et al, 2015). This expected variance is particularly notable in circumstances in which either an airborne target is at a very high vertical angle such as infield pop flies or a ground-based target is very distant and near the horizon Sugar, McBeath, Suluh, et al, 2006).…”

“…Realistically, there will be variance between the ongoing value of b and the predicted proportion of a, resulting in offsets from keeping the target moving along a straight optical path. Because the fielder typically continues to foveate on the ball image, retinally the local background scenery moves linearly in the opposite direction (Postma et al, 2014;Wang, McBeath, & Sugar, 2015).…”

“…As shown in Figure 1a, the optical ball trajectory can be compared to that of an imaginary elevator rising from the home plate at a constant velocity and tilted by the amount that fielders run forward or backward (Babler & Dannemiller, 1993;McLeod & Dienes, 1993, 1996McLeod, Reed, & Dienes, 2003, 2006Michaels & Oudejans, 1992). Although some work examining acceleration discrimination has questioned OAC (Brouwer, Brenner, & Smeets, 2002;Zaal, Bongers, Pepping, & Bootsma, 2012), other Citation: Wang, W., McBeath, M. K., & Sugar, T. G. (2015). Optical angular constancy is maintained as a navigational control strategy when pursuing robots moving along complex pathways.…”