The time it takes the human brain to recognize a picture may be as brief as one fourth of a second.
Researchers at Johns Hopkins University School of Medicine in Baltimore, Md, arrived at the elusive calculation with the help of a 22-year-old patient who was being prepared for surgery to control intractable seizures from epilepsy that he had experienced for more than a decade.
With a grid of 174 electrodes temporarily implanted on the surface of his brain, the patient participated in a series of language experiments. While asking him to name and categorize various pictures and words, the researchers monitored his brain activity through the electrode grid or by applying a mild electrical current through 2 of the electrodes. The current temporarily disables areas of the brain to which it is applied, but causes no permanent adverse effect.
Voelker R. Measuring the Speed of Thought. JAMA. 1998;279(24):1939. doi:10.1001/jama.279.24.1939