Maintaining a slipping object in hand needs to adjust grip forces. In this study we describe a new method to measure the time-space relation of grip force in a classical conditioning task.

A special grip rod with 200 strange gauges equally distributed on 50 cm^2 was developed. The rod was moved unexpectedly in horizontal direction with different load forces. Subjects were asked to hold the rod in its initial position with a three finger precision grip against varying load forces.

Grip forces were measured as a film containing position and force magnitude of each strange gauge at 150 frames/s. System noise of the strange gauges were calculated separately as a noise frame. Significant data were detected by an image detection algorithm using an advanced Bonferroni test. Therefore each data frame was subtracted by the noise frame and then divided by its own root mean square of the residuals (rRMS). We set as lower limit for rRMS the upper 95% confidence level of rRMS of the noise frame to reduce the number of false positive detection.

Preliminary results show a mean increase of 25% of conditioned grip-forces in respect to the unconditioned trials. Inspection of single finger forces show strong intra- and interindividuel differences of force increase, indicating different strategies to hold the rod.