What they see and what they draw
WESTBOROUGH, MA November 3, 2014 Visual processing is a key component to living a healthy and independent life. Visual perception refers to the sensory processing of visual information including language i.e. reading and abstraction i.e. shapes and designs. Visual spatial deficits are common after traumatic brain injury, stroke, or tumor. Stroke that impacts the right side of the brain can result in sometimes profound visual perceptual deficits. The right middle cerebral artery supplies much needed blood to a large distribution of the right side of the brain – usually in the parietal lobe. When sensory receptors are damaged they are no longer available to process information using visual pathways. The right side of the brain controls the left side of the body. The negative impact of lesions in this region can be dramatic when it comes to vision, processing abstract stimuli, and and visual perception.
Perhaps the most profound thing we do as humans that requires rapid visual processing is to operate a motor vehicle. Driving requires fluid visual processing that quickly adapts to whatever circumstance it encounters – like potholes, other cars, and people walking. Without the use of the right hemisphere one might not efficiently process all aspects of the visual information being seen. In fact, there is a high likelihood that some individuals fail to look to the left often missing large bits of visual information.
Neuropsychological aspects of the right middle cerebral artery
This is the drawing made by a patient who was shown the complex figure above. The brain is called upon to see and interpret the figure. As it does this it becomes organized in some manner depending upon the cognitive style of person who is copying it. As you can see from the figure on the left there is a loss of appreciation of the outer configuration as well as a paucity of detail.
The right hemisphere is thought to play a role in processing non-linguistic information, abstract stimuli and attention. But there are many other things that can go wrong when someone suffers a stroke in the right side of their brain – like appreciation for music, expressing emotion in speech, and initiating a plan. It is not uncommon that I am asked to consult on a case of right hemisphere CVA that is suddenly always crying or even laughing! This is called pseudobulbar affect. It is a common occurrence after stroke and often a sign of emotional “release” due to decreased emotional control following stroke. It can be a bit unnerving if you have not worked with it before. Another common problem found after stoke affecting the right side of the brain is called perseveration. This refers to the tendency to keep producing the same response even when you are told that the task has changed or you have moved on to something different. I have seen this is someone’s writing. For example someone might be writing a sentence like “Baseball players are tough”. They produce perseverative responses like “baseball ball ball players are tufffff.” You can see the perseveration in what is produced in the written language.
Visual illusions – not hallucinations
Some patients experience changes in how they interpret visual information making them appear quite idiosyncratic – sometimes like a psychiatric patient to an untrained observer. The right hemisphere syndrome sometimes results in visual illusions as a result of the misidentification of a complex visual array. Remember a book written by Oliver Sacks, M.D. entitled The man who mistook his wife for a hat” – now 30 years old? It is largely about visual misidentification or agnosia – an inability to identify common objects. “The world can become a complex and dangerous place when visual perception is corrupt due to stroke or some other affliction” according to Michael Sefton, Ph.D.. “More than a few times I have been asked to consult on a patient having hallucinations when in fact the patient has misidentified objects in his visual field and called it something else that it could not be” according to Sefton. For example, a patient with a prominent left neglect had been doing much better undergoing physical rehabilitation. Some bed linens had been placed on the bedside table on his left. In the periphery of his vision he sensed that something was there but could not spontaneously look to the left and identify what it was. He became quite anxious and suspicious that someone was standing to his left watching him. He mistook the pile of linen for a small person who was silently standing and felt threatened. By moving the extra stuff in his room and lighting the environment we were able to lessen the disruptive anxiety he exhibited. It takes time to assess the systems of the brain especially a complex system that is interconnected with attention, language, and spatial relations.
Michael Sefton – Whittier Rehabilitation Hospital
Capruso, D. et al. (2009) Clinical Evaluation of Visual Perception and Construction Ability. In Clinical Neuropsychology, Second Edition. Snyder, P. (Ed). APA.