| To study the human postural control, 2-Alternative-Forced-Choice (2-AFC) experiments were conducted to determine a subject's psychophysical detection thresholds for short anterior-posterior perturbations of a platform on which a blindfolded subject stood. These tests eliminated visual contributions to perturbation detection. However, with the inputs of both vestibular and somatosensory systems, these experiments could not discriminate one sensory contribution from the other. To study how visual, vestibular and somatosensory systems contributed to perturbation detection, new 2-AFC experiments were processed with a subject either standing or sitting on a moving platform, during which the subject was blindfolded or vision restricted to a scene. Our blindfolded standing tests revealed similar results as found from previous research—that there was a negative power law trade relationship between platform move displacements and subject acceleration detection thresholds. A relatively weak positive power law trade was observed between the move lengths and acceleration thresholds for the same subjects while subjects were blindfolded and sitting on a chair, which was mounted to the moving platform. With vision restricted to a visual scene (moving towards a subject), most subjects reached their minimum thresholds at a longer move length.;In standing 2-AFC tests, blindfolded subjects showed more significant lower limb EMG activities (TA and GS) for longer platform moves compared to hardly observed EMG responses for shorter platform perturbations. The TKEO process was applied to the EMG data to check the EMG onset time. For 16mm standing tests, in supra-threshold trials, more than half of TA-EMGs were on before test accelerations reaching thresholds during platform moves. Higher thresholds for a subject indicated a higher minimum acceleration needed to trigger TA activation. |
