The target as an obstacle: Grasping an object at different heights

Area of Science:

• Neuroscience
• Biomechanics
• Human motor control

Background:

• Human grasping involves stereotypical movement patterns.
• The underlying cause of these patterns is not fully understood.
• One hypothesis suggests objects are perceived as obstacles beyond intended grasp points.

Purpose of the Study:

• To investigate if the perception of an object as an obstacle influences grasping behavior.
• To test the hypothesis that increased collision risk leads to larger maximum grip aperture.
• To examine the relationship between grasp height, object dimensions, and grip aperture.

Main Methods:

• Participants grasped vertically oriented cuboids of varying heights and grip positions.
• Maximum grip aperture was measured during the reaching and grasping movement.
• Experimental data were compared against predictions derived from the obstacle hypothesis.

Main Results:

• Maximum grip aperture decreased when grasping taller cuboids at higher positions.
• Maximum grip aperture increased when grasping cuboids whose height varied with grip height.
• Both experimental findings supported the predictions based on the obstacle hypothesis.

Conclusions:

• The perception of a target object as an obstacle at non-goal positions influences stereotypical grasping movements.
• Goal positions for digits impact maximum grip aperture, even when the distance between them remains constant.
• This finding provides insight into the neural mechanisms underlying human prehension.