Halving and doubling isometric force: evidence for a decelerating psychophysical function consistent with an...

Area of Science:

• Psychophysics
• Motor Control
• Biomechanics

Background:

• Previous research indicated accelerating psychophysical functions for perceived force, with exponents around 1.7.
• This contradicts the common understanding of sensory perception and force estimation.

Purpose of the Study:

• To investigate the psychophysical function of perceived force using halving and doubling experiments.
• To reconcile conflicting results between previous studies and current findings.
• To explore the role of motor commands versus sensory feedback in force perception.

Main Methods:

• Experiment 1: Subjects performed force halving and doubling judgments using instrumented cylinders.
• Experiment 2: Replicated previous study's paradigm using handgrip force judgments with a dynamometer.
• Experiment 3: Measured hand mechanical compliance to validate the proposed motor control model.

Main Results:

• Both experiments yielded decelerating psychophysical functions for perceived force, with exponents between 0.58 and 0.80.
• Results contradict earlier findings of accelerating functions.
• A motor control model explaining these results assumes adjustments in central motor commands, not direct force sensation.

Conclusions:

• Perceived force is likely mediated by the central motor command, not solely by sensory feedback.
• The hand's mechanical compliance plays a crucial role in shaping the perceived force function.
• This study proposes a new framework for understanding force perception and motor control.