Article Figures & Data
Figures
- Figure 1.
Experimental design and SLRs. A, B, General display and configuration of targets (A) and corresponding hand and eye start positions, potential targets, go cues, and SFs used for each of the experiments (B; see Materials and Methods for more details). C, Trial-by-trial recruitment of right PEC for an example subject (s30, from experiment 2) generating left or right reaches. Each row is a different trial, with color conveying degree of recruitment. Trials sorted by RT (white boxes), and aligned to stimulus onset. The SLR (highlighted in gray vertical box) appears as a vertical banding of increased or decreased recruitment aligned to left or right stimulus presentation, respectively, rather than movement onset. D, E, Mean EMG activity (±SE; D) and time-series ROC analysis (E) for data shown in C. Horizontal dashed lines in E shows the 0.6 or 0.4 level which constitutes discrimination threshold.
- Figure 2.
RTs and detection of SLRs. A, Cumulative RT distributions in all experiments, pooled across all participants and directions and segregated by SF. B, Slope of the relationship between discrimination time and average RT for early and late RT groups, for all experiments. Each data point represents a unique subject for a particular SF. Slopes are capped at 90°. Results are grouped into those who exhibiting an SLR in at least one condition (SLR+) or not (SLR–), given a slope threshold of 67.5° (horizontal dashed line).
- Figure 3.
Example results from experiment 1a. A, Muscle recruitment from an example subject (s14) from experiment 1a, segregated by movement direction and SF. Same format as Figure 1C. Trials were separated into early (red) or late (blue) RT groups based on the median RT. B, Time-series ROC plot analysis from early (red) or late (blue) RT groups for data in A. Vertical colored solid lines depict discrimination time. C, Plot of the average RT versus discrimination time for early and late groups. The data were deemed to exhibit an SLR if the slope of the line exceeded 67.5°, which indicated that the initiation of EMG recruitment was more locked to stimulus rather than movement onset.
- Figure 4.
Example results from the same participant (s20) in experiments 1b (A–C) and 2 (D–F). Same format as Figure 3.
- Figure 5.
Effect of SF on latency and prevalence of the SLR, across all experiments (Experiments 1a, 1b, and 2 in A, B, and C respectively) and participants. In each column, the top row conveys SLR prevalence (the percentage of SLR+ participants across the sample) as a function of SF, and the bottom row conveys SLR latency as a function of SF. Error bars in lower row show SEM. Asterisks depict differences significant at the p < 0.05 level (for details, see Results).
- Figure 6.
Example results from all experiments for trials matched by RTs. Trial-by-trial EMG activity (A, D, G; same format as Fig. 1C), mean EMG activity (B, E, H; same format as Fig. 1D), and time-series ROC analysis (C, F, I; same format as Fig. 1E) for data from experiment 1a (A–C, s14), experiment 1b (D–F, s30), and experiment 2 (G–I, s30). For each experiment, the RTs were matched for individual trials following presentation of a stimulus of a low SF (purple) or high SF (green). The solid boxes around the trial-by-trial plots depict data that exhibits an SLR, even with the reduced number of trials.
- Figure 7.
The influence of SF on SLR characteristics persisted for RT-matched trials (data from Experiments 1a, 1b, and 2 shown in A, B, and C respectively). Same format as Figure 5, using data matched for RT.
- Figure 8.
Discrimination times during on-line reach corrections (experiment 2) plotted as a function of discrimination times for reaches initiated from a static posture (experiment 1b). Discrimination times are derived from the time-series ROC analysis. Each data point depicts data from a unique combination of subject and stimulus SF (see color scheme). A, Data from occurrences with an SLR+ observation in both experiment 1b and experiment 2. B, Data from all participants, with symbols depicting whether SLRs were observed in both experiments (dots, same data as in A, but on a different time scale), whether an SLR was observed in only one experiment (crosses), or whether an SLR was not observed in either experiment (asterisks). Solid diagonal line shows line of unity. The clustering of data below the line of unity means that shorter discrimination times were observed in experiment 2.
- Figure 9.
Characteristics of on-line reach corrections to different SFs in experiment 2. A, Results from a sample participant (s20), depicting the mean lateral distance for on-line reach corrections to displaced stimuli composed of different SFs (colored lines), or to the control condition where the reach target was not displaced (black line). B, Initiation latency of the on-line reach correction as a function of SF, across the sample. The latency was derived from a time-series ROC analysis of lateral distance for left versus right displaced stimuli. C, The time to target, measured as the time from target jump to the time at which the hand attains the jumped target, also varies as a function of SF. D, The SF of the jumped target influenced magnitude of the on-line reach correction over the 400 ms after the target jump (measured as the area between the left and right trajectories over this 400-ms interval, normalized to the maximum within each participant). E, In contrast, the dispersion of the horizontal component between left and right on-line reach correction, measured from the initiation of the correction to the point at which the vertical component has progressed a further 4 cm, did not vary with SF (in E, data from two participants were excluded since many corrections were initiated <4 cm along the y component from the central target in at least one condition). Error bars represent SEM. Asterisks depict differences significant at the p 0.05 level (for details, see Results).
- Figure 10.
Three-way relationship between EMG discrimination, and the latency and magnitude of the on-line reach correction (as measured in Fig. 9D). Each point represents data from a single participant, color-coded by SF, with the symbol indicating whether an SLR was observed (asterisks) or not (circles).
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