Ecological validity of manual grasping movements in an everyday-like grocery shopping task

In our earlier research, kinematic and kinetic parameters of grasping differed significantly when participants grasped the same object once in a traditional laboratory paradigm, and once as part of a captivating computer game. We attributed this finding to the fact that grasping movements in the laboratory were repetitive and meaningless, while those in the computer game were embedded in complex behavior and served a meaningful purpose. In that work, we argued that grasping in the computer game is more characteristic of everyday life behavior; however, this conclusion has been criticized on the grounds that a computer game is not a typical everyday activity. The present study therefore compares grasping in a traditional laboratory paradigm to that in an indisputably everyday context: grocery shopping. Thirty-three young adults executed externally triggered arm movements to grasp nondescript objects (laboratory task, L) and place them on a tablet, or they walked through a fictitious grocery store towards a shelf to grasp grocery products and placed them into a shopping basket (everyday-like task, E). Size, shape, weight and location of to-be-grasped objects were identical in both tasks. We found that of the analyzed 16 kinematic parameters, 13 differed significantly between tasks. Specifically, grip apertures were larger, movements were slower and grip-transport coupling was more variable in E compared to L. We conclude that kinematic differences between both persist even if task is more realistic than in our earlier research. Our findings are compatible with the notion that movement planning is less stringent in E than in L.