How do you have an unconscious visual experience?
Vision is so important to us that it tends to dominate research on consciousness. To get at the heart of a conscious experience, we need to compare the brain’s response to consciously and unconsciously perceived stimuli. But how do you have an unconscious visual experience?
The usual trick is to apply backward masking – a visual stimulus is shown to a subject very briefly and is then replaced by a strong second stimulus. This dominates the conscious visual response, ‘masking’ the original stimulus. Subjects cannot say, or even guess, what it is they were shown.
However, psychological tests and brain imaging show that they have registered the image. If it was an angry face, they react much more strongly when shown it again than if they were seeing it for the first time – even though they do not ‘know’ they have seen it before.Lead image:
Illustration © Glen McBeth