Capitalizing on an opportunity presented by a patient scheduled for tests using electrodes surgically placed on his brain, Johns Hopkins scientists have clocked the speed of thought, measuring the time the patient took to understand what everyday objects are in pictures.
The Hopkins team, led by neurologist John Hart, M.D., discovered that it took their volunteer patient about 250 to 300 milliseconds, or a fourth of a second, to begin to understand a pictured object, and another 250 to 450 milliseconds to fully comprehend what the object was. He appeared to complete the process more quickly when the object shown was familiar to him, Hart notes.
"The data, obtained within a single stage at a single site in the brain, are further evidence that information accumulates gradually in the brain, rather than in a strictly all-or-none fashion," Hart says.
Understanding the individual steps that cause this accumulation, and how they relate to each other functionally and temporally, could help scientists better understand comprehension and word loss from disorders like stroke or Alzheimer's disease, he notes.
In an article describing the unusual experiment in the May 25 Proceedings of the National Academy of the Sciences, Hart and Hopkins specialists in epilepsy, biomedical engineering, neurosurgery, neuropsychology and cognitive science said knowing the time sequence and speed of language processing and other "cognitive operations" is "critical for building theories of higher mental activity."
"This information has been difficult to acquire," Hart notes, "even with different combinations of behavioral tests, electrical recordings and imaging studies such as PET scans."
Their task was somewhat simplified by an adult epilepsy patient
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Contact: Michael Purdy
mpurdy@welchlink.welch.jhu.edu
(410)955-8725
Johns Hopkins Medical Institutions
26-May-1998