Investigating stationary limb localization using psychophysics: Beware of proprioceptive drift


Quantifying the accuracy and variance of hand localization without vision is integral to understand the reliability of the proprioceptive system. Psychophysical methods primarily compare the endpoint position of a passively moved limb to a stationary visual reference (e.g., Sadler & Cressman, 2019). The purpose of the current study was to understand the ability to localize one's stationary, rather than passively moved, limb without vision using psychophysical methods. Participants placed their unseen limb under a half-silvered mirror with their index and ring finger atop of tactors. One finger was stimulated and then a visual mask was presented followed by a briefly flashed comparison dot. Participants then dictated whether the comparison dot was left or right of their stimulated finger position. An adaptive staircase procedure used the participant's response to determine the position of the comparison dot on the next trial. The initial comparison position was either fixed (task 1) or based on the participant's initial perceived finger positions (tasks 2 and 3). Additionally, a proprioceptive cue presented every 5 trials had participants lift their arm, clinch their fist and isometrically flex their wrist and elbow flexors/extensors (task 3; Wann & Ibrahim, 1992). In all three tasks, the perception of participants' finger position drifted in the magnitude of ~3cm, resulting in unreliable psychophysical estimates of perceptual accuracy and variability. The results suggest that when isolating somatosensory cues and not allowing for any visual recalibration, researchers must be aware of and account for large perceptual drifts in one's stationary limb position.

Acknowledgments: University of Toronto, Ontario Research Fund, Canadian Foundation for Innovation, National Sciences and Engineering Council