Grip Force Paradigm

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Grip Force paradigm is the measurement of the pressure applied on a small sensor held in hands in Newton. In this paradigm, we are looking for the unconscious micro variations of this force which is in millinewton. The sensor evaluates grip force through electrical measurements. Additionally, since we are looking for micro-variations, the electrical noise of the experimental setup also needs to be evaluated.

Characterise the noise

For the cell - TIPPA

Recording force variations in the order of millinewtons requires meticulous attention to both protocol design and sensor calibration. Numerous sensor models exist, and they can be customised by research teams, such as with aluminium plates, as in our study, or with plastic or metal alternatives, potentially altering measurements. Therefore, it is crucial to characterise the sensors used in studies to accurately document the experimental setup and ensure replicability. However, it is impractical to analyse every sensor’s surface adhesion properties, ease of grip, or individual characteristics such as skin texture and sweat levels. In this study, we introduce TIPPA, a methodological contribution aimed at optimising signal quality and facilitating study replicability. During the preparation of this study, we asked ten participants (laboratory colleagues) to hold the grip force sensor between their fingers (see Figure 2a) and then release it as gradually as possible over a box filled with foam cubes until it falls. This operation was repeated ten times. We obtained a signal with a relatively consistent dynamic (resembling a droplet shape, or "tippa" in Finnish, see Figure 2b), from which we extracted several characteristics: peak height, grasp dynamics, average duration of the first phase (first release), the second relaxation phase (slow release), and finally, drop value. We believe these characteristics (detailed on Table 2c) complement those typically presented in the literature ([45]) to construct the "physical signature" of our sensor. We encourage future Grip Force research projects to adopt similar practices to cross-analyse the impact of sensor configuration on the type of measurements obtained.

(Capra & Berthaut, Submitted)

TIPS

• The use of a laptop to record Grip Force can add some noise to the recording. It's better to use a desktop computer to get a cleaner signal.