shows the results from all assessments used in this study. As expected, there were significant differences between groups on the motor and sensory scales.
Participants with ASD demonstrated motor impairments relative to controls. shows that the ASD group was more impaired than controls on all categories of the PANESS. Participants with ASD performed worse overall (p < 0.01, ) and also performed worse in the over-flow movements, gait/stances, and timed movements subcategories (all p < 0.01, ).
Fig. 2 Group performance on motor and sensory assessments. a The ASD group averaged higher total PANESS scores than did the control group, denoting worse performance (p < 0.001). b The ASD group averaged lower movement “sensory seeking” (more ...)
The Adolescent/Adult Sensory Profile showed that participants with ASD were different from controls across a number of sensory categories (). The ASD group had higher “low registration” scores within visual processing (p = 0.02) and activity level (p = 0.05), suggesting higher neurological thresholds (i.e., hyposensitivity) and more passive behavior. Within taste/smell processing, the ASD group had higher “sensory avoiding” scores (p = 0.02), suggesting lower neurological thresholds (i.e., hypersensitivity) and more active behavior. In a category termed “movement processing,” the ASD group was hypersensitive to proprioceptive and vestibular stimuli and demonstrate more passive behaviors based on lower “sensory seeking” scores (p = 0.01, ) and lower high neurological threshold scores (p = 0.03).
Elbow Angle Accuracy
A repeated measures ANOVA (2 groups × 3 tasks × 4 elbow angles × 2 shoulder angles) was performed for elbow angle estimate error. Collapsing across tasks and arm configurations, there was no effect of group (p = 0.35). Because our collapsed data revealed no differences between groups, we checked for more subtle and specific differences. To confirm that there were no differences between groups in any individual task or configuration, we took the additional step of breaking out elbow angle estimate errors for each of the 24 possible cases (3 tasks, 8 elbow-shoulder configurations). These configuration and task specific errors were compared between control and ASD groups with two-tailed Student t-tests. No group differences were found for 23 of the 24 comparisons (accuracy only differed for the 75° shoulder, 30° elbow configuration in the active elbow angle task, p = 0.04). Thus, we think that the lack of a difference between control and ASD groups is robust.
Repeated measures ANOVA did, however, show a strong trend for task (p = 0.06). This task effect was driven by differences between the passive and active elbow angle tasks, such that estimates in the active task were more biased toward extension than in the passive task (planned comparison, p = 0.01) ().
Fig. 3 Group performance across proprioceptive tasks. a There was no group difference for accuracy (p = 0.35). Estimates were more extended in the active versus passive elbow angle task (p = 0.009, planned comparison). b There was also no group difference for (more ...)
There were also significant effects for shoulder angle (p < 0.01) and elbow angle (p < 0.01). This suggests that arm configuration influences elbow angle estimate accuracy. Indeed, within each task a pattern in accuracy was observed across space: subjects were most accurate when the joints were at intermediate angles and the hand was in the middle of the workspace, and estimates became biased toward or away from the body (i.e., overly flexed or extended) as the hand moved closer or father from the middle of the workspace (i.e., as joint angles became more flexed or extended, respectively). shows average group accuracy for each configuration: consistent across groups and tasks, biases depend on true elbow and shoulder angle.
Fig. 4 Accuracy across joint space. The bar graphs show group errors (top row, controls; bottom row, ASDs) for each arm configuration tested, for each task (error bars represent standard errors). Both groups demonstrated the same accuracy pattern across joint (more ...)
For none of the three tasks did absolute accuracy of elbow angle estimates correlate with PANESS scores or with Sensory Profile neurological threshold scores for touch or movement (all p > 0.2).
Elbow Angle Precision
As with accuracy, a repeated measures ANOVA for standard deviation (i.e., precision) of elbow angle estimates (2 groups × 3 tasks × 4 elbow angles × 2 shoulder angles) found no effect of group (p = 0.48). Here again we took the additional step of breaking out errors for the 24 possible cases (3 tasks, 8 elbow-shoulder configurations) to confirm that there were no specific differences between groups. Two-tailed Student t-tests of group precision for each arm configuration for each task revealed no difference for 23 of the 24 comparisons (precision only differed for the 75° shoulder, 75° elbow configuration in the passive elbow angle task, p = 0.02). As with accuracy, these data strongly support the finding of comparable precision across groups.
Repeated measures ANOVA showed a strong effect of task on precision (p < 0.01). shows that subjects in both groups were the least precise at identifying their elbow angle when their arms were moved passively and they reported their angle with the visual display (passive elbow angle task). Compared to the passive elbow angle task, subjects were more precise at estimating their elbow angles in the passive fingertip task (planned comparison, p < 0.01) and the active elbow angle task (planned comparison, p < 0.01).
There was also an effect of elbow angle (p < 0.01) and shoulder angle (p < 0.01). Elbow angle estimates were more precise when the elbow was at 75° compared to all other angles (planned comparisons: 30 versus 75°, p < 0.01; 45 versus 75°, p < 0.01; 60 versus 75°, p < 0.01; no other significant comparisons) and when the shoulder was at 90° compared to 75°. Subjects were most precise at estimating elbow angle when their arm was positioned such that the elbow and shoulder were most flexed (i.e., the arm was closest to the body).
Precision on the active elbow angle task correlated with high neurological threshold movement scores on the Sensory Profile, such that subjects with lower scores (i.e., hypersensitivity) were less precise (controls: r = −0.646, p = 0.02; ASD: r = −0.524, p = 0.08; all: r = −0.610, p = 0.002). For no task did precision correlate with PANESS scores (all p > 0.3).
Fingertip Accuracy and Precision
In the fingertip matching task, actual finger endpoint errors could be assessed in addition to the calculated elbow angle errors. A repeated measures ANOVA (2 groups × 4 elbow angles × 2 shoulder angles) for endpoint accuracy (i.e., the absolute distance between subjects’ perceived fingertip endpoints and the actual positions of their index fingertip) revealed no effect of group (p = 0.21). There were, however, effects of elbow angle (p < 0.01), shoulder angle (p < 0.01), and elbow × shoulder angle interaction (p = 0.01) such that fingertip estimates were more accurate at flexed joint configurations (i.e., when the hand was closer to the body).
Similarly, a repeated measures ANOVA for endpoint precision (i.e., the average standard deviation of perceived endpoint positions) revealed no effect of group (p = 0.12) but effects of elbow angle (p = 0.02) and shoulder angle (p = 0.05). In addition to being more accurate at estimating fingertip position at flexed joint configurations, subjects were on average also more precise.
Within the control group only, absolute fingertip accuracy correlated with total PANESS scores (r = 0.64, p = 0.03). Fingertip accuracy did not correlate with Sensory Profile neurological threshold scores for touch or movement (all p > 0.2).