Human Eye Unknowingly Distracted By Irrelevant Objects, Study Finds

When such an unexpected object appears, the eye takes an average of one-tenth of a second to check it out before returning to an intended location, according to researchers at the University of Illinois and the TNO Human Factors Research Institute in the Netherlands.

"The immediate effects of distraction are rather small if viewed individually," said Arthur F. Kramer, a professor of psychology and affiliate of the U. of I. Beckman Institute for Advanced Science and Technology. "However, when you consider the number of eye movements we make in a day ­ about three per second ­ the effects can add up quickly both in terms of lost time and missed information from relevant environmental events when the eyes go to where you did not intend them to go."

The research -- funded by the U.S. Army -- was reported in the September issue of Psychological Science and involved two studies that measured both human performance and eye movements.

In one study, subjects viewed six gray circles equally spaced around an imaginary circle. All but one of the circles turned red and showed letters inside them; the subjects were told to move their eyes as quickly as possible to the gray circle and indicate which direction the letter inside was facing. In half of the trials, a seventh red circle, irrelevant to the subjects' task, was added as a distraction. Their eyes often went reflexively to the new object, stopped briefly and then went on to the uniquely colored target. In half of the cases, the new circle disrupted the planning and execution of eye movements.

"Surprisingly," Kramer said, "the subjects were almost always unaware that they had looked at the new object. This is interesting since they did look at it frequently and then always moved their eyes to the target. This suggests that environmental factors can capture our attention without our awareness."

In the second study, visual cues were given as to where the target would appear when color changes occurred. A distracting object appeared in half of the trials. In this case, the visual cues worked to virtually eliminate the capture of the eyes and attention by the distracting object. Combined with the data of the first study, this finding suggests that eye-scan patterns are most susceptible to distractions when someone is searching for something in the visual field, Kramer said. Once a person has located a desired object, eye-movement capture does not appear to occur.

The studies, Kramer said, also suggest something informative about the coordination between the two areas of the brain that guide eye movement -- the goal-directed system in the frontal lobes of the brain and the reflexive system in the midbrain. "Our data suggest that two brain systems that drive eye movements are capable of programming multiple eye movements in parallel. Otherwise, it would be impossible to move the eyes as quickly as subjects did from the wrong to the right object."