The shaman's vision became disturbed at the start of the trance; the shaman would see patterned flashes of light. Produced in the brain, these flashes are also known as 'entoptic' images. They are depicted in the seemingly abstract geometric patterns in the rock art.

Geometric patterns surrounding the 'Dancing Kudu'.

The shaman's vision became disturbed at the start of the trance; the shaman would see patterned flashes of light. Produced in the brain, these flashes are also known as 'entoptic' images. They are depicted in the seemingly abstract geometric patterns in the rock art.

Geometric rock art of Twyfelfontein https://t.co/JHDTzqazsX #Namibia #Africa #archaeology pic.twitter.com/5KynK8bIWF

— Bradshaw Foundation (@BradshawFND) May 30, 2017

Meanders, dots, lines, grids, spirals and whorls resemble entoptic or inner-eye images recorded in neurophysiological experiments.

Some geometric engravings are often associated with the broken edges of rock faces. It is thought the edge is integral to the image, possibly reflecting the trance and the edge of consciousness.

Although entoptic images are similar for all people in the world, the associations formed in a state of trance are contextual.
The shaman fuses the hallucinatory visions with images of animals and other potent spiritual symbols. 

It is possible that making the engravings helped to prepare the shaman for a state of trance. The repetitive chipping at the rock and the monotonous sound could have contributed to mental concentration.

http://www.bradshawfoundation.com/news/rock_art.php?id=Rock-Art-of-Namibia