Task conditions | Response observed | Perturbations and numbers of trials†|
---|---|---|
Familiarisation: Stance, unconstrained arm and foot motion (instructed to react naturally) | not applicable | 4 medium translations‡ (F,B,L,R) 4 large translations‡ (F,B,L,R) 4 waist pulls (F,B,L,R) Total = 12 trials |
Trial block #1: Stance, arm motion restricted, instructed to react naturally but minimise number of steps | Compensatory stepping main focus: multiple-step responses (a-p perturbations) | 5 backward translations 3 forward translations 2 lateral translations (L,R)§ 4 translations, 2nd waveform (F,B,L,R)# 5 forward waist pulls 3 backward waist pulls 2 lateral waist pulls (L,R)§ Total = 24 trials |
Trial block #2: Walking in-place, arm motion restricted, instructed to react naturally but minimise number of steps | Compensatory stepping main focus: foot collisions (lateral perturbations) | 5 leftward translations 3 rightward translations 2 a-p translations (F,B)§ 4 translations, 2nd waveform (F,B,L,R)# 5 rightward waist pulls 3 leftward waist pulls 2 a-p waist pulls (F,B)§ Total = 24 trials |
Trial block #3: Stance, foot motion restricted, instructed to recover balance by grasping handrail (at right of subject) | Compensatory grasping main focus: speed of grasping (a-p perturbations) | 5 forward translations 4 backward translations§ 4 forward waist pulls§ 5 backward waist pulls Total = 18 trials |