According to the World Health Organization, individuals with low vision to total blindness are too impaired to conduct a normal life, needing all sorts of support mechanisms to make up for their lack of visual perception. This view of the blind has been held for centuries, but research and new findings are emerging, challenging the most conventional sciences with this question: Is it possible for blind people to be able to respond to visual stimuli that they do not consciously see?
Dr. Beatrice de Gelder, a cognitive and affective neuroscientist based in the Netherlands, has conducted extensive research on the phenomenon known as “blindsight.” This refers to visual abilities in persons with cortical blindness. Formerly a senior scientist at the Martinos Center for Biomedical Imaging at Harvard Medical School and a professor of cognitive neuroscience at Tilburg University, de Gelder is currently director of the Cognitive and Affective Neuroscience Laboratory at Maastricht University. In addition to her work in blindsight, she has also studied face-recognition perception and its deficits, emotional body expressions and social interaction. Her research includes both neurologically intact subjects as well as patients with focal brain lesions, prosopagnosia (face blindness), and neuropsychiatric patients suffering from such mental disorders as schizophrenia and autism. De Gelder has also published several books and publications, among them “Out of Mind: Varieties of Unconscious Processes.” Her latest book is “Emotions and the Body.”
De Gelder gives insight into blindsight by explaining that most patients who are cortically blind due to lesions in their visual cortex are able to avoid obstacles, and are also able to perceive some emotional signals, such as emotions on other people’s faces, without being consciously aware of seeing the face. In 2003, an experiment was conducted wherein a man who was blind in both eyes was asked to walk along a hall without his cane. Surprisingly, he was able to flawlessly navigate around all obstacles. In the same way, de Gelder has also explored how cortically blind people react to emotional stimuli. By using a partition in a computer, she displayed various emotions only to the blindsight of a unilaterally blind patient. This resulted in the person imitating the emotion shown on the screen, completely without being aware of it.
Here, Dr. de Gelder talks to Brain World about the phenomenon of blindsight, how her findings are being used to treat cortically blind patients, and how her neuropsychology studies can contribute to creating a healthier, happier, and more peaceful society.
Brain World: What led you to do research on blindsight?
Beatrice de Gelder: The opportunity presented itself as an adventure. I was working with people who conducted research on mainstream perceptions, and I believe that new things always derive from a crossroads of different lines of interests. The topic of blindsight had already been around for 20 to 30 years when I got involved in it. The researchers were always questioning the basic properties of the visual system, such as orientation and movement.
However, I was more interested in scientific questions about the visual system of those people who were cortically blind. My idea was to understand certain properties of the visual system in relation to the evolution of the brain in a natural context. We do not walk around seeing squares and triangles; so somehow, lines, squares, and triangles are more complex for the natural brain than faces and their emotional expressions. So I thought: What about checking whether these people also have blindsight for affective and emotional signals? That turned out to be the case, and the finding was later replicated in other cases. That is how a whole new line of research started.
BW: How is it possible for people to respond to visual stimuli that they do not consciously see?
BDG: What I tend to bring to people’s attention when this question arises is that our consciousness, or our introspection, are not setting the boundaries of what we can see or not see. If you closely analyze your daily actions, you realize that of course you have conscious vision and that you continuously focus on that, analyze it and reflect upon it; but there are also all sorts of things that you seem to process without ever paying attention to. The brain can support a great number of activities in parallel at the same time, and, luckily, much more than we are aware of.
Last year, I was invited to a small conference on magic organized by two colleagues who are vision scientists. A famous pickpocket attended the meeting, and he could sit, talk to you, and before you realized, you saw your watch or your wallet in his hand and even if you were warned about it in advance, you did not notice what went on till shown the result. You were never aware of it, but you just could not say that it did not happen. The same applies to unconsciously being able to see.