My Masters thesis is titled Using art therapy with children diagnosed with autism spectrum disorder to increase engagement with the external world. The research involved six individual art therapy sessions with six clients. All were under twelve. Five were within the moderate range of the autistic spectrum (of which two were non verbal) and one had mild autism.
In the first session all five within the moderate range spent most of the session using the brush to transfer one colour of paint (mostly yellow) from the palette which they then stirred into the water.
This reflects the experience many autistic people of being overwhelmed by the external environment, of the senses being inundated and input being out of control. As a result many people on the autistic spectrum withdraw and/or make repetitive movements or sounds to block out external input. Stirring the paint into the water contained the fluid media which can flow and spill. It was a way to control the input. The children were also fascinated to see the water change colour and to watch lumps of paint mix into the whirlpool of stirred water.
It took a few sessions to encourage each client to brush the paint onto the paper. All were timid at first and made only tiny movements resulting in small marks. Over the remaining sessions however, all expanded their range of movement and increasingly filled the paper, reflecting a lessened need to control. In the supported environment all clients had increased their level of engagement with the art materials and had positive experiences of engaging with the external world. They were able to control and interact with input and showed interest, even excitement in the unpredictable effects of colour change and the flow of marks. As they became increasingly engaged in painting clients also ceased repetitive movements or sounds. One non verbal client made sounds in response as he watched watched the effects of painting.
You can read more about my thesis and research at https://www.researchgate.net/profile/Anita_Bragge/contributions.