Autism spectrum condition (ASC) is a neurodevelopmental disorder characterized by impaired social skills, restrictive and repetitive behaviors, and sensorimotor atypicalities. To better understand the source of the sensorimotor atypicalities (such as difficulty with synchronizing movements to external events), we investigated two opposing theories. The first theory suggests that the sensorimotor deficiency in ASC arises from reduced online correction of synchronization error (the “slow update” theory), while the second theory suggests that it arises from noisy internal representations (the “elevated internal noise” theory).
To test sensorimotor deficiency, we administered a finger tapping task to ASC individuals and typically developing (TD) individuals. In the task, participants were instructed to synchronize their tapping with a metronome, which occasionally had tempo changes of different lengths and at other times maintained a consistent tempo, and then continue tapping alone at the same tempo they last heard after the metronome stopped.
Since in the continuation part, the participants rely only on their internal representations, the slow update theory would predict that individuals with ASC will have no difficulty with this part, so their performances in this part will not be different compared to the TDs’ performances. On the other hand, the elevated noise theory would predict difficulties of the ASC group in this part compared to the TD group.
Our results showed that individuals with ASC do not differ from typically developing (TD) individuals in their ability to keep the metronome’s tempo after it stops when given several seconds of updating. These results suggest that the impairment in synchronizing with external beats in individuals with ASC is due to slow update theory than elevated internal noise levels. The findings imply that individuals with ASC are capable of accurately estimating environmental statistics but exhibit slower speed in updating internal priors compared to TD individuals.
Figure 1- Isochronous trials: ITIs with the metronome (synchronization) and without the metronome (continuation) – stopping the metronome has a larger effect on the ASCs’ standard deviation. Mean and SD of ITI of each group, a: During the synchronization phase. b: During the continuation phase. Participants of both groups manage to reliably keep the mean metronome tempo, and mean ITI is similar in the two groups in both phases. However, SD is significantly larger in the ASC group during the synchronization phase, whereas during the continuation phase the variability is similar in the two groups. c: The difference in participants’ SD between the synchronization and continuation phases. In both groups SD is larger in the synchronization phase, where errors are corrected both for mean ITI and for synchronization with the metronome. The reduction of SD is significantly larger in the ASC group, which corrects less during synchronization. Each dot represents the performance of one participant. The median of each group is denoted as a black horizontal bar; error bars around this median denote the interquartile range.
Figure 2- tempo change trials: The mean (absolute) steady-state distance from the required ITI in the continuation phase. a: In the short sequences, the distance between the actual and the required ITI marginally differed between the groups. b: In the long sequences there is no group difference. c: The difference between the short and long sequences is positive for both groups. Namely, the distance from the required interval is smaller in the long sequences. Yet, the ASC group benefitted significantly more from this extended window of updating. The y-axis represents the mean distance of participants’ ITIs from the required response, calculated separately for each tap, and then averaged within, then across participants. Colors represent the groups, blue – TD and green – ASC. The medians are denoted as horizontal black bars; error bars around this median denote the cross participants’ interquartile range.
