Modeling reaction time in the ankle

We are examining whether robust behavioral laws, initially designed to describe sensorimotor control of the upper extremities, can also describe lower extremity movements. Herein, we present our initial results of our research on measuring ankle reaction time (RT). We show that RT measured in ankle dorsiflexion (DP) and inversion-eversion (IE) of 7 healthy young subjects followed a γ distribution, a typical finding in the upper limb response modalities. We propose that the low-order statistics (mean and variance) of the best-fit γ function can be used to concatenate RT across subjects with similar performance and create super-subjects (SS). We then show that the most widely used model of RT cognitive processes, the Ratcliff diffusion model, is adequate to describe ankle RT in an SS. The combination of experimental data analysis with diffusion modeling of ankle RT proposed that at least two cognitive components of RT are accounted for a difference in mean RT observed between DP and IE, namely the speed of information accumulation and the non-decision time that includes, among others, the time for motor response encoding and execution. These results show a great potential to inform our adaptive assist-as-needed robotic therapy delivered to the lower limbs of children with Cerebral Palsy.