Article Figures & Data
Figures
- Figure 1.
Experimental setup. A shows the object (frontal plane) used for our reach-to-grasp task, the location of the reflective markers, and the slots where a mass was added to change object CM location. Object rolls toward the thumb and finger sides were defined as negative and positive angles, respectively, relative to the vertical (y) in the gravitational frame of reference. For the verbal cue experiment (B), subjects were told on each trial where the mass was added but were not allowed to view the location of the added mass (dashed lines denote CM placement, not visible to subjects). In contrast, for the visual cue experiment (C), subjects were allowed to see the location of the added mass but received no verbal cue. Note that the view of the object in A–C are depicted from the subject's perspective. D shows the approximate location of the cameras and the workspace used for motion capture (top view; figure is not to scale). The photo shows start hand posture together with marker placement on the hand and wrist.
- Figure 2.
Individual fingertip contact points. Fingertip vertical location relative to the base of the cylinder is shown for each digit as a function of CM location. Data from the no cue (Lukos et al., 2007), verbal cue, and visual cue experiments are shown on the left, middle, and right columns, respectively. Data from blocked (filled squares) and random (open triangles) conditions are shown for each experiment. The range of the vertical axes is the same for all plots to allow comparison across digits. Data are means ± SEs of all subjects; asterisks represent significant differences (p < 0.05) confirmed by post hoc analyses.
- Figure 3.
Linear covariation between fingertip contact points. The magnitude of the correlation coefficient (Pearson's r) computed on the vertical location of the contact points of each digit pair is shown for the no cue (Lukos et al., 2007), verbal cue, and visual cue experiments (left, middle, and right polar plot, respectively). The r values shown in each polar plot were averaged across all subjects. Black and white dots denote blocked and random conditions, respectively. T, I, M, R, and L denote thumb, index, middle, ring, and little fingers, respectively. The r values were z-normalized before averaging across subjects (r values closer to 0 indicate greater independence between finger contact point pairs).
- Figure 4.
Peak object roll as a function of trial. Each panel shows peak object roll measured for each trial for subjects 1–12 (s1–s12). Data on the left, middle, and right columns denote experimental sessions that started with the visual cue, verbal cue, and no cue experiment, respectively (labeled as Visual, Verbal, and No). For each experiment, trials from blocked and random conditions are indicated by gray and white boxes, respectively. Red, black, and blue symbols denote peak object roll for left, center, and right CM location trials, respectively. Note that the order of experiments, predictability conditions, and CM blocks (blocked condition) was counterbalanced across all subjects.
- Figure 5.
Object roll minimization. A shows the time course of object roll for one representative subject (#8) for each experiment [no cue (Lukos et al., 2007), verbal cue, and visual cue; top, middle, and bottom rows, respectively]. Data from blocked and random CM presentation are shown on left and right columns, respectively. Dashed and solid vertical lines denote object lift onset and average end of lift, respectively (for details, see Lukos et al., 2007). Data are aligned with respect to object lift onset. Positive and negative values denote object rolls toward the subject's fingers and thumb, respectively (see Fig. 1A). B shows peak object roll averaged across all subjects (± SE) for each predictability condition and experiment. **p < 0.001, significant main effect of predictability condition.
- Figure 6.
Distributions of peak object roll as a function of object CM location. The trial distributions of peak object roll for no cue (Lukos et al., 2007), verbal cue, and visual cue experiments (top, middle, and bottom rows, respectively) were pooled across all subjects and binned at 4° intervals. Note, however, that statistical analysis was performed on the peak roll distributions from each subject. The vertical line (0°) denotes gravitational vertical (the bin labeled 0° represents the number of trials characterized by peak object rolls of ±2°). Negative and positive object rolls indicate rolls to the left (thumb side) and right (finger side), respectively (Fig. 1A).
- Figure 7.
Variance of peak object roll and minimization within ±2° object rolls. A shows the variance of the peak object roll distributions from individual subjects (each symbol denotes data from one subject) and the mean variance averaged across all subjects (bars) for the no cue (Lukos et al., 2007), verbal cue, and visual cue (first, second, and third columns, respectively) for each predictability condition. B shows the number of trials characterized by object rolls that were within ±2° from the vertical averaged across all subjects (± SE). **p < 0.01.
- Figure 8.
Object roll minimization on practice trial and first experimental trial. Row A shows peak object roll during the blocked condition measured on the practice trial versus the first experimental trial for the no cue, verbal cue, and visual cue experiments (Pno vs 1stno, Pverbal vs 1stverbal, and Pvisual vs 1stvisual, respectively). Row B shows peak object roll during the blocked condition measured on the practice trial of the no cue experiment plotted against the practice trial of verbal cue and visual cue experiments (Pno vs Pverbal and Pno vs Pvisual, respectively). Row C shows peak object roll during the blocked condition on the practice trial of the verbal cue and visual cue experiments plotted against peak object roll measured on the first experimental trial of the no cue experiment (Pverbal vs 1stno and Pvisual vs 1stno, respectively). Each point represents individual trial data from each subject and CM location. The diagonal line shown in each plot is the unity line (shown in the inset as y = x) denoting equal peak object roll for trials across different conditions and/or experiments. Shaded regions in the inset denote areas in the plots associated with adaptation of peak object roll (i.e., ability to minimize object rolls) occurring from practice trial to first experimental trial (row A), on practice trial without versus with cues (row B), and on the practice trial with cues versus first experimental trial of the no cue experiment (row C).
