I am running reaching and grasping experiments using tools and have always found reliable scaling of grip as object sizes increased in the past and performance has always been directly comparable to performance when grasping with the hand. However in my latest study I have found little to no grip scaling (a slope of 0.2, compared to the earlier 0.7/0.8 slopes) and I am wondering if anyone knows any literature that might account for this?
We had a much smaller stimulus range in this study, does anyone well-versed in reaching and grasping literature know if stimulus range has an effect on grip scaling? I am completely at a loss!
The 0.8 slope is generally found (Smeets & Brenner, 1999). Several factors are known to have a slight effect on the slope, such as object shape (steeper slope for a block than a cylinder; Verheij et al., 2012). But these variations are very minor. The very low slopes you report remind me of the values Thomas Schenk found with patient DF in situations without haptic feedback (Schenk, 2012).
Hope this helps, Jeroen
Schenk, T. (2012). No Dissociation between Perception and Action in Patient DF When Haptic Feedback is Withdrawn. Journal of Neuroscience, 32(6), 2013-2017.
Smeets, J. B. J., & Brenner, E. (1999). A new view on grasping. Motor Control, 3(3), 237-271.
Verheij, R., Brenner, E., & Smeets, J. B. J. (2012). Grasping Kinematics from the Perspective of the Individual Digits: A Modelling Study. PLoS ONE, 7(3), e33150.
Thank you for your answer, this confirms my original thought that something certainly went wrong in this study! The same tools and protocol were used in this study as in previous ones so I cannot think that haptic feedback could be the culprit here, but your answer is nonetheless helpful with avenues I should investigate. Thank you for taking the time to reply.
I find this curious, esp the comparison of the results of DF, thus I wonder what is the tool being used, and does it somehow perturb haptic feedback?
Hello Daniel, they are similar to a pair of tongs, I would certainly say that the tools lessen haptic feedback to some extent, however in previous studies ran with the same tools we did not find the same lack of scaling and instead had normal slopes of 0.7/0.8 so I think that this finding cannot be solely down to the tools.
Yes, stimulus range can have an effect on grip scaling, but yours is lower than most. It could also depend if the tongs are spring loaded to return to a set aperture (like tweezers) or more scissor-like. Haptic feedback being absent could contribute too.
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