Predictions of future sensory states shape perception and action. On moving limbs, the tactile signals are down-weighted likely due to sensory predictions matching the actual sensory feedback. When tactile feedback processing demands are high, e.g. when grasping a slippery object, predictive weights decrease to favor sensory sampling. Contrary to these results, we recently found hampered sensory processing in standing than sitting, i.e. in situations with high feedback processing demands. To explore the role of feedback processing demands on tactile perception, we investigated how postural demands modulate tactile perception on the lower limb and how these effects change in old age when reliance on predictions increases.
The participant’s task was to detect a brief vibrotactile stimulus (50 ms) of different intensities on their calf while fixating a visual target on the wall. They performed three conditions: sitting (baseline), standing, and standing on foam. For the latter two conditions, participants stood on a force plate which was used to quantify their center of pressure behavior indicating postural demands. We estimated detection thresholds via psychometric function fitting and normalized the two standing conditions to their perceptual results in the sitting condition.
Our preliminary results show that posture was less stable and tactile perception poorer when standing on unstable than stable surfaces, independent of age. Additionally, older compared to young adults showed generally poorer tactile perception in all conditions. Overall, tactile feedback signals are down-weighted when postural demands increase in stance retention, probably due to shifting processing capacities to the more important task.