Selective Reaching to Grasp: Evidence for Distractor Interference Effects

Abstract

Transport and grasp kinematics were examined in a task in which subjects selectively reached to grasp a target object in the presence of non-target objects. In a variety of experiments significant interference effects were observed in temporal parameters, such as movement time, and spatial parameters, such as path. In general, the presence of non-targets slowed down the reach. Furthermore, reach paths were affected such that the hand veered away from near non-targets in reaches for far targets, even though the non-targets were not physical obstacles to the reaching hand. In contrast, the hand veered towards far non-targets in near reaches. We conclude that non-targets evoke competing responses, and the inhibitory mechanisms that resolve this competition are revealed in the reach path.

Selective reaching: Evidence for multiple frames of reference.

“…This analysis too yielded a highly significant Target-Distractor Separation ϫ Target Location interaction, F(2, 60) ϭ 6.27, p Ͻ .01. Howard, & Jackson, 1997). According to the visuomotor processing hypothesis, this occurs because advance information regarding the position of the target allows selection of the motor representation of the target and inhibition of the motor representation of the competing distractor before observable behavior begins.…”

“…This spatial repulsion effect-first reported by Fischer and Adam (2001)-adds to previous reports showing hand path deviations caused by the presence of distractors (e.g., . Interestingly, however, hand paths may veer either away or toward distractors (e.g., Tipper et al, 1997;Welsh, Elliott, & Weeks, 1999). Tipper and colleagues postulated a tentative neurophysiological model to explain hand path deviations Tipper, Howard, & Houghton, 2000;Tipper et al, 1997).…”

“…Interestingly, however, hand paths may veer either away or toward distractors (e.g., Tipper et al, 1997;Welsh, Elliott, & Weeks, 1999). Tipper and colleagues postulated a tentative neurophysiological model to explain hand path deviations Tipper, Howard, & Houghton, 2000;Tipper et al, 1997). In essence, their model is based on the idea of population coding in the human cortex (e.g., Georgopoulos, 1990), and path interference effects are explained in terms of a selection process from overlapping population codes-activated by the target and distractor-through inhibitory mechanisms.…”

“…The visuomotor processing hypothesis can explain both the proximity-to-hand and ipsilateral effects by assuming that near or ipsilateral locations are associated with shorter reaction or move-1 Distractor interference effects in selective action are sometimes (e.g., Fischer & Adam, 2001;Meegan & Tipper, 1998;Pratt & Abrams, 1994), but not always (e.g., Castiello, 1996;Jackson, Jackson, & Rosicky, 1995), replicated. For a discussion of methodological factors possibly contributing to these conflicting results, see Tipper, Howard, and Jackson (1997). ment times (MTs) than far or contralateral locations, respectively (see also Meegan & Tipper, 1998).…”

Non-obstructing 3D depth cues influence reach-to-grasp kinematics

“…Specifically, various studies have demonstrated that the brain not only identifies and encodes information about the target object, but that the neural architecture also takes into account the presence of non-target objects located within the surrounding area (Rice et al 2006;Tipper, Howard & Jackson, 1997;Tresilian, 1998). For example, Tipper, et al, (1997) demonstrated that hand trajectories were affected by the presence of non-target objects, even when such non-target objects did not physically obstruct the path of the hand to the target object. When these items were present in the workspace, the trajectory paths of the reaching hand significantly deviated away from the perceived obstruction.…”