Psychology
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Browsing Psychology by Author "Langridge, Ryan W."
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- ItemOpen AccessEye-hand Coordination in Reaching and Grasping Vertically Translating Targets(2019) Thulasiram, Matsya R; Langridge, Ryan W; Abbas, Hana H; Marotta, Jonathan JPrevious research in our lab has revealed a strong visual bias toward the eventual index finger contact location when grasping stationary or horizontally moving targets. However, the unique properties of the thumb may have an increased role when grasping vertically moving targets. Using their index finger and thumb, right-handed individuals reached for and grasped 2-D rectangular targets moving upward or downward on a vertically oriented computer screen. It was expected that fixations would be directed toward the index finger when grasping upward moving targets, and to the thumb when grasping downward moving targets. In trials involving upward moving targets, initial fixations were positioned well above the target, in anticipation of the eventual movement, and remained above the target even after the target started to move. Gaze shifted to the leading (upper) edge of the target when participants initiated their reaching movement, suggesting that participants were primarily attending to the eventual contact location of the index finger. Initial fixations toward downward moving targets were positioned well below its bottom edge, once again anticipating eventual movement. When the targets started to move, gaze shifted upward to a position just below the target’s centre of mass (COM) and remained there during reach onset. Final fixations for both upward and downward moving targets were positioned slightly above the target’s COM, a location that would allow the monitoring of both index and thumb when grasping. These results suggest that while index finger placement is prioritized when grasping upward moving targets, visual attention is directed toward more central locations when grasping downward moving targets, thus allowing both contact points to be monitored simultaneously. This is suggestive of an increased importance of the thumb, in addition to the index finger placement, not shown previously when grasping stationary or horizontally translating targets.
- ItemOpen AccessGrasping 2-D Targets in Motion: The Influence of a Preferable Central Grasp Location on Eye-Hand Coordination(2019) Langridge, Ryan W.; Marotta, Jonathan J.When using a precision grip to grasp a rectangular object (index finger on top and thumb on the bottom of the object), digit placement is usually close to the object’s horizontal center, ensuring stability. An object’s position will also influence convenient digit placement (e.g. the left side of a rightward positioned object). This research investigated the direction of gaze and index finger placement while visually pursing and grasping moving targets that either allowed for or discouraged a central placement of the index finger and thumb when grasping. Right-handed participants’ eye and hand movements were recorded while they reached for and ‘grasped’ 2-D computer generated targets translating horizontally across a computer screen. Reaches were cued at early, middle, and late stages of target travel. Control targets appeared as a 4 x 4 cm square. Experimental targets resembled Control targets, however the middle portion of the top and bottom edges were removed. At onset of target movement, gaze was directed toward its leading edge. During the reach itself, including at the time of contact, gaze and grasp positions shifted toward the trailing edge. This was especially true for grasps occurring at later stages of target travel, where deviations behind the midline were the largest. In general, gaze deviated further behind the Experimental targets’ midline compared to the Control targets. Overall, horizontal gaze and index finger placement were closer to the target’s midline when grasping Leftward moving targets. Though a misplaced grasp has no consequence when grasping 2-D targets, these results suggest participants favoured a safe, mechanically comfortable movement. In the absence of a preferable central grasp location, participants avoided the front of the object, potentially minimizing the risk of a collision with the leading edge. Increased accuracy when grasping leftward moving targets may reflect a compensatory strategy for cross-body reaching.