Children do not recalibrate motor-sensory temporal order after exposure to delayed sensory feedback

Abstract

Prolonged adaptation to delayed sensory feedback to a simple motor act (such as pressing a key) causes recalibration of sensory-motor synchronization, so instantaneous feedback appears to precede the motor act that caused it (Stetson, Cui, Montague & Eagleman, 2006). We investigated whether similar recalibration occurs in school-age children. Although plasticity may be expected to be even greater in children than in adults, we found no evidence of recalibration in children aged 8-11 years. Subjects adapted to delayed feedback for 100 trials, intermittently pressing a key that caused a tone to sound after a 200 ms delay. During the test phase, subjects responded to a visual cue by pressing a key, which triggered a tone to be played at variable intervals before or after the keypress. Subjects judged whether the tone preceded or followed the keypress, yielding psychometric functions estimating the delay when they perceived the tone to be synchronous with the action. The psychometric functions also gave an estimate of the precision of the temporal order judgment. In agreement with previous studies, adaptation caused a shift in perceived synchrony in adults, so the keypress appeared to trail behind the auditory feedback, implying sensory-motor recalibration. However, school children of 8 to 11 years showed no measureable adaptation of perceived simultaneity, even after adaptation with 500 ms lags. Importantly, precision in the simultaneity task also improved with age, and this developmental trend correlated strongly with the magnitude of recalibration. This suggests that lack of recalibration of sensory-motor simultaneity after adaptation in school-age children is related to their poor precision in temporal order judgments. To test this idea we measured recalibration in adult subjects with auditory noise added to the stimuli (which hampered temporal precision). Under these conditions, recalibration was greatly reduced, with the magnitude of recalibration strongly correlating with temporal precision.

Figure 1

(a) Adaptation and test trials. Each block started with 100 trials of adaptation to a synchronous sequence (‘baseline condition’), or to 200 ms or 500 ms delayed sensory feedback (‘delayed feedback condition’). After adaptation, subjects performed a temporal order judgment task, judging whether their own action (a keypress) or an acoustic stimulus appeared first. (b) The button used during the test phase. The force required to press it was 0.2 N, and the distance to contact ~1 mm.

Figure 2

Example psychometric functions for three representative subjects (a–c), and for data averaged over the three age groups (d–f). The curves plot the proportion of trials where the sound appeared to follow the movement as a function of stimulus offset asynchrony of the sound compared with the movement. The black curves and symbols plot data for the baseline condition, and grey the delayed feedback condition. Positive values of PSS mean that the sound occurs after the movement when they appeared to be simultaneous. While adults showed a positive shift in the perceived simultaneity (see grey and black arrows) in the ‘delayed feedback block’, for the 8-year-olds, the 11-year-olds and the adult group in the noise condition the two curves are fully overlapped, revealing no recalibration effect.

Figure 3

Points of perceived simultaneity (PSS) after adaptation to delayed sensory feedback, plotted as a function of PSS in the baseline condition, for the various groups. (a) Adults: standard condition (adaptation at 200 ms delays). (b) Adults: adaptation to 200 ms delays, with auditory noise added to the stimulus (see Methods). (c) 11-year-old group (7.7 ± 0.1 years), standard adaption condition (200 ms adaptation); (d) 8-year-old group (11.3 ± 0.3 years), standard condition (200 ms adaptation); (e) Children group (9 ± 0.2 years) with 500 ms adaptation; (f) Bar graphs summarizing the average recalibration effects (difference in temporal order judgment task for the baseline and adaptation conditions), for the five different groups. Error bars show ±1 SEM.

Figure 4

Average recalibration effect for all groups measured as the differences in the PSS in the two experimental blocks as a function of age. (a) Average thresholds (calculated from the individual standard deviations of each group) as a function of age. (b) The recalibration effect as a function of thresholds, for individual subjects; squares represent adult subjects, circles 11-year-olds and triangles 8-year-olds. Recalibration magnitude correlates strongly with thresholds. The dashed line shows the linear regression (R² = 0.25; p < .001, slope = −0.9).

Figure 5

(a) Average thresholds for the two adult groups in the standard condition (grey) and in the noise condition (red). Black symbols represent individual data. Thresholds are significantly higher in the noise condition (153 ms) compared with the standard condition (76 ms). (b) Average recalibration for the two adult groups in the standard noise conditions (color-coded as a), with symbols showing individual data. The noise causes a reduction of 53 ms in the average calibration. (c) The recalibration effect as a function of thresholds. The grey symbols show data for the standard condition and red symbols the data for the adult noise group. The dashed line shows that the effect of recalibration linearly decreases with the increasing of thresholds (R²= 0.25; p < .005).

Figure 6

(a) The average recalibration effect calculated for each group of subjects separately for the first, second and third 20-trial blocks. Black symbols represent adults in the standard condition, red symbols adults in the noise condition and grey circles and squares represent 11- and 8-year-old children, respectively. There is no difference in the magnitude of recalibration between trial blocks in any of the group of participants. (b) Lapse rate index (essentially the proportion of errors for very large asynchronies) plotted as a function of age. The black symbols represent the baseline condition while the grey symbols represent the adaptation condition. Each symbol represents the average lapse rate for each age group. The index does not change with age or with experimental condition. Bars show ±1 SEM.