Attention Does Not Modulate the Imitation of Biological Motion Kinematics in Autism Spectrum Disorders

Background: Interpersonal contexts require imitation of biological motion. Such imitation is impaired in autism spectrum disorders (autism) due to top-down processes associated with social modulation and attention orientation, and lower-level visuomotor control processes. This is based on examining biological motion during automatic imitation, or using voluntary imitation and manipulating movement speed. Here, we examined voluntary imitation using a novel methodology that displayed models with the same movement time, but different biological motion. A non-human agent model was used to control social modulation. To investigate the effects of attention we examined imitation under general attention, and selective attention to the biological motion during observation.

Objectives: (1) examine imitation of biological motion kinematics; (2) examine whether the imitation of biological motion is influenced by attentional control.

Methods: Eleven adults with autism, diagnosed by a clinical assessment and ADOS, plus eleven adults (control) participated in a four-phase study, which was approved by the local ethics committee. In a General-Attention phase, participants were instructed to “observe and copy the dot”. In a Selective-Attention phase, participants were instructed to “observe and copy exactly how the dot moves”. There were two biological motion models: atypical and typical velocity. All participants then performed a multiple object tracking task and a biological-motion-perception-task.

Results:  Planned comparisons indicated that although the groups did not differ in the imitation of typical velocity (p > 0.05), the control group imitated atypical velocity more accurately than the autism group (p < 0.001). When attention was directed to the model, the control group more accurately imitated the ­typical velocity compared to general-attention phase. Imitation by the autism group remained the same for atypical and typical velocity irrespective of attentional instruction. The multiple object tracking task showed the control group (96% accurate) was more successful (p = 0.02) at tracking objects than the autism group (84% accurate). The biological-motion-perception-task indicated the autism group (74% accurate) and control group (70% accurate) were similarly successful in judging differences between biological motion models.

Conclusions: Compared to the control group, we showed imitation of biological motion was impaired in autism. When instruction directed attention to the model, imitation performance was not improved in the autism group. It is therefore unlikely that low-fidelity imitation of biological motion in the autism group can be explained by participants not observing the kinematics presented by the model. Moreover, although there was a group difference in general attention ability as evidenced by the multiple-object tracking task, the autism group still performed successfully (84% accurate). Also, the autism group was equally successful as the control group in perceiving and judging differences between two single-point-light dots presenting different forms of atypical velocity. Taking into consideration the effects for attention and perception of kinematics, in a situation where we controlled for social modulation, these findings suggest the deficit in imitating biological motion kinematics in autism is most likely related to the sensory-motor integration and representation of biological motion.