Erroneous decision? Blame noisy information, not your brain

April 17, 2013

Rat auditory task: poke the left or right port to indicate which side played more clicks (credit: B. W. Brunton et al./Science)

Princeton University researchers have found that making an erroneous decision is caused by errors, or “noise,” in the information coming into your brain, rather than errors in how your brain accumulates or processes that information.

The researchers separated sensory inputs from the internal mental process. ”To our great surprise, the internal mental process was perfectly noiseless. All of the imperfections came from noise in the sensory processes,” said senior investigator Carlos Brody, a Princeton associate professor of molecular biology and the Princeton Neuroscience Institute (PNI), and a Howard Hughes Medical Institute Investigator.

The experiment

The research subjects — four college-age volunteers and 19 laboratory rats — listened to streams of randomly timed clicks coming into both the left ear and the right ear. After listening to a stream, the subjects had to choose the side from which more clicks originated. (The rats had been trained to turn their noses in the direction from which more clicks originated.)

The test subjects mostly chose the correct side but occasionally made errors. By comparing various patterns of clicks with the volunteers’ responses, researchers found that all of the errors arose when two clicks overlapped, and not from any observable noise in the brain system that tallied the clicks. This was true in experiment after experiment, utilizing different click patterns, in humans and rats.

The researchers used the timing of the clicks and the decision-making behavior of the test subjects to create computer models, used to indicate what happens in the brain during decision-making. The models provide a clear window into the brain during the “mulling over” period of decision-making, the time when a person is accumulating information but has yet to choose, Brody said.

“Before we conducted this study, we did not have a way of looking at this process without inserting electrodes into the brain,” Brody said. “Now thanks to our model, we have an estimation of what is going on at each moment in time during the formation of the decision.”

Implications

The study suggests that information represented and processed in the brain’s neurons must be robust to noise, Brody said.

“The new work from the Brody lab is important for a few reasons,” said Anne Churchland, an assistant professor of biological sciences at Cold Spring Harbor Laboratory who studies decision-making and was not involved in the study. “First, the work was very innovative because the researchers were able to study carefully controlled decision-making behavior in rodents. This is surprising in that one might have guessed rodents were incapable of producing stable, reliable decisions that are based on complex sensory stimuli.

“This work exposed some unexpected features of why animals, including humans, sometimes make incorrect decisions,” Churchland said. “Specifically, the researchers found that errors are mostly driven by the inability to accurately encode sensory information. Alternative possibilities, which the authors ruled out, included noise associated with holding the stimulus in mind, or memory noise, and noise associated with a bias toward one alternative or the other.”

The work was funded by the Howard Hughes Medical Institute, Princeton University, and National Institutes of Health training grants.

This has interesting implications for education, work, and driving. —Editor