Eye-hand synergy and intermittent behaviors during target-directed tracking with visual and non-visual information

Abstract

Visual feedback and non-visual information play different roles in tracking of an external target. This study explored the respective roles of the visual and non-visual information in eleven healthy volunteers who coupled the manual cursor to a rhythmically moving target of 0.5 Hz under three sensorimotor conditions: eye-alone tracking (EA), eye-hand tracking with visual feedback of manual outputs (EH tracking), and the same tracking without such feedback (EHM tracking). Tracking error, kinematic variables, and movement intermittency (saccade and speed pulse) were contrasted among tracking conditions. The results showed that EHM tracking exhibited larger pursuit gain, less tracking error, and less movement intermittency for the ocular plant than EA tracking. With the vision of manual cursor, EH tracking achieved superior tracking congruency of the ocular and manual effectors with smaller movement intermittency than EHM tracking, except that the rate precision of manual action was similar for both types of tracking. The present study demonstrated that visibility of manual consequences altered mutual relationships between movement intermittency and tracking error. The speed pulse metrics of manual output were linked to ocular tracking error, and saccade events were time-locked to the positional error of manual tracking during EH tracking. In conclusion, peripheral non-visual information is critical to smooth pursuit characteristics and rate control of rhythmic manual tracking. Visual information adds to eye-hand synchrony, underlying improved amplitude control and elaborate error interpretation during oculo-manual tracking.

Figure 1. Experimental setup and conditions.

(A) A schematic drawing of the experimental setup and the equipment. (B) Diagrammatic representations of the experimental conditions: EA, EHM, and EH tracking. Subjects tracked the target signal (black solid line) visually and/or manually (see the text for details). Timely visual feedback of the manual force output (blue solid line) was available during EH tracking, but was masked during EHM tracking.

Figure 2. Raw data plots.

Central 10 seconds of data of finger action and eye movement from a typical subject under the three tracking conditions. (A) Displacement traces, (B) velocity traces.

Figure 3. Ocular and manual tracking errors and eye-hand trajectory mismatches for three tracking conditions.

(Significant difference, ^**: P<0.01).

Figure 4. Contrasts of characteristics for composite eye movements under the three tracking conditions.

(A) Incidences of saccade and pursuit movements (*: P<0.05; ⁺: P<0.05), (B) peak saccade velocity, and (C) pursuit velocity gain. (Significant difference, ^*: P<0.05; ^**: P<0.01; ^***: P<0.001).

Figure 5. Comparison of manual tracking variables between EH and EHM tracking.

(A) Displacement gain; (B) peak frequency, together with a representative amplitude spectrum. (Significant difference, ^***: P<0.001).

Figure 6. Contrasts of submovement characteristics between EH and EHM tracking.

(A) Representative examples of speed pulse traces, with a box showing the measures of pulse amplitude and duration; (B) amplitude, (C) duration, (D) frequency of speed pulses (Significant difference, ^***: P<0.001).

Figure 7. Scatter plots and regression lines of ocular tracking error versus speed pulse metrics.

(A) amplitude, (B) duration, and (C) frequency of speed pulses under the EHM (•) and EH (○) conditions. The symbol x in the equations represents ocular tracking error, and the symbol y represents speed pulse metrics in each plot of (A)-(C). (Significant regression slope: ^*: P<0.05, ^**: P<0.01).

Figure 8. Temporal dispersion and regressive slope for manual positional and velocity errors in the defined window.

(A) Positional errors, and (B) velocity errors in the EHM condition; (C) positional errors, and (D) velocity errors in the EH condition. For each plot of (A)–(D), individual (thin line) and mean (thick line) temporal error dispersions are displayed in the left panel. The shadowed area (from time point Ta to Tb) represents an occurrence of a saccade event. The box-plots in the right panel of (A)–(D) show the median (central line), lower and upper quartile (lower and upper lines), and the mean value (circle) for regressive slope of manual tracking errors before and after the saccade event. The lines extending from each end of the box represent the minimum and maximum observations. Asterisks in the box-plots denote significant differences of the regression slope from zero. (^*: P<0.05; ^**: P<0.01; ^**: P<0.01).