Age-related decline of online visuomotor adaptation: a combined effect of deteriorations of motor anticipation and execution

Abstract

The literature has established that the capability of visuomotor adaptation decreases with aging. However, the underlying mechanisms of this decline are yet to be fully understood. The current study addressed this issue by examining how aging affected visuomotor adaptation in a continuous manual tracking task with delayed visual feedback. To distinguish separate contributions of the declined capability of motor anticipation and deterioration of motor execution to this age-related decline, we recorded and analyzed participants' manual tracking performances and their eye movements during tracking. Twenty-nine older people and twenty-three young adults (control group) participated in this experiment. The results showed that the age-related decline of visuomotor adaptation was strongly linked to degraded performance in predictive pursuit eye movement, indicating that declined capability motor anticipation with aging had critical influences on the age-related decline of visuomotor adaptation. Additionally, deterioration of motor execution, measured by random error after controlling for the lag between target and cursor, was found to have an independent contribution to the decline of visuomotor adaptation. Taking these findings together, we see a picture that the age-related decline of visuomotor adaptation is a joint effect of the declined capability of motor anticipation and the deterioration of motor execution with aging.

Keywords: aging; eye movement; manual tracking; online control; visuomotor adaptation.

Figure 1

The illustration of the experiment setting.

Figure 2

(A) illustrates stimuli used in the experiment, including the red point that indexes the position of the cursor (C) and the white circular target (T). Black solid curves are target movement trajectories that are visible to participants; the dashed line (invisible for participants) represents the distance between the cursor and the target. The left panel illustrates a trial without delay perturbation, in which the hand position (H) and C position are matched. In contrast, the right panel illustrates a trial with delay perturbation, in which the C position was behind the H position. (B) illustrates the procedures of a sample trial without delay perturbation (first) and a sample trial with (second), respectively. (C) illustrates the experiment design for each participant, including the first 4 baseline trials, 12 delay adaptation trials, and 3 post-test trials. Delay perturbation was an additional 200 ms artificial feedback delay in reference to the actual hand movement direction in the delay adaptation phase.

Figure 3

The left panels show dynamics of target, hand, cursor, saccade, and eye movement positions in two sample trials at (A) the baseline phase and (C) the adaptation phase from a young participant, and two sample trials at (B) at the baseline phase and (D) the adaptation phase from an older participant, respectively. (E–H) The right panels show the time series of target-hand errors, target-cursor errors, and target-eye errors of the same trials at the baseline phase and the adaptation phase from the same participants, respectively.

Figure 4

(A, B) illustrate the means of RMSE and (C, D) illustrate the mean lag between target and cursor as a function of trial number for the groups of young and older participants, respectively. Positive lag represents that the cursor lags behind the target. Error bars depict ±1 standard errors of means.

Figure 5

Mean frequencies of saccades per second during the baseline, adaptation, and post-test phases for the two groups, respectively. Error bars depict ±1 standard errors of means.

Figure 6

(A) illustrates the mean lags between eye and cursor and (B) illustrates the mean lags between eye and target as a function of trial number for young participants (white circle) and older participants (black diamond). Error bars depict ±1 standard errors of means.

Figure 7

Scatter plots of lags between target and cursor in the adaptation phase for (A) older participants and (B) young participants. Trials in the same order are marked using a unique color. The solid lines represent simple linear regression model fits.

Figure 8

The means of RMSE between target and cursor after controlling for the lag effect as functions of trial order of young adults (white circle) and older people (black diamond). Positive lags represent that the cursor lags behind the target. Error bars depict ±1 standard errors of means.

Figure 9

Scatter plots of RMSE between target and cursor after controlling for the lag effect in the adaptation phase for (A) older participants and (B) young participants. Trials in the same order are marked using a unique color. The solid lines represent simple linear regression model fits.