Motion Induced Blindness
You probably noticed that the yellow dots seem to wink in and out -- most people see this effect. It works best in dim lighting.
This illustration is not traumatic, but -- at least metaphorically -- it illustrates a dissociative process of intermittently not knowing whether a traumatic event "really happened".
The Motion Induced Blindness illusion was discovered by Yoram Bonneh. Work by Jack Pettigrew at University of Queensland suggests that this illusion results from a rivalry for dominance between the left and right hemispheres at the parietal lobe. When the right hemisphere is dominant, you see the yellow dots; when left hemisphere gains dominance, the yellow dots disappear. Please try an improved example of the MIB illusion, if you initially had difficulty seeing this effect.
On the other hand, this illusion may work similarly to some dissociative experiences. Our right hemisphere sees the world more as it really is. The left hemisphere suppresses sensory information that conflicts with what it believes "ought" to be. Paul Valent discusses this issue, and its implications for trauma therapy, in a presentation on the right brain as a substrate for reforging psychoanalytic and trauma therapies.
Bonneh, Y. S. et al. (2001). Motion-induced blindness in normal observers. Nature, 411, 798-801. (Letters).
Funk & Pettigrew (2003). Does interhemispheric competition mediate motion-induced blindness? A transcranial magnetic stimulation study. Perception, 32, 1328-1338.
Valent, P. (2001). The right brain as a substrate for reforging psychoanalytic and trauma therapies. Presented at the ASTSS/NCPTSD Annual Conference, Canberra, Australia. March 2001.