A technique that measures tiny movements of the eyes may help better understand and eventually improve diagnosis of ADHD, scientists say. Emerging evidence shows that small involuntary eye movements are a promising new tool for shedding light on the hidden workings of mental processes like attention and anticipation, cognitive processes that are often impaired in individuals with Attention-deficit/hyperactivity disorder (ADHD).
A study suggests that carefully tracking eye movements offers a new method for empirically monitoring temporal expectation in people with ADHD. “The eye is restless and eye movements occur constantly, even when observers try to avoid them. Our study shows that this continuous stream of eye movements is temporarily paused before an anticipated visual event,” said Shlomit Yuval-Greenberg, assistant professor at Tel Aviv University in Israel.
“This attenuation in eye movements can be used as an estimate for whether and when the occurrence of regular events was indeed predicted,” said Yuval-Greenberg. Researchers found that individuals without a diagnosis of ADHD tended to have different patterns of eye movements compared with individuals who had an ADHD diagnosis. The findings indicate that careful analysis of eye movements may offer an objective measure to complement other tools used for diagnosis and assessing treatment efficacy.
For the study, researchers collected data from a group of 20 ADHD patients and a group of 20 controls. On two different days, the participants came into the lab where they were shown a series of coloured shapes on a screen while their eye movements were monitored. The participants were instructed to press a key whenever they saw a red square, which appeared around 25 per cent of the time.
On one day, participants were shown the shapes at predictable intervals: Every two seconds the next shape would appear. On the other day, the time between shapes varied from 1 to 2.5 seconds. Participants were not told that the timing would be different between the two sessions. When the stimulus appeared at regular, predictable intervals, people in the control group responded more quickly than when it appeared at varied intervals.
However, the reaction times of those with ADHD did not improve under predictable conditions. The researchers also found that those in the control group tended to have fewer eye movements immediately before a predicted event. In contrast, those in the ADHD group did not show the same eye movement slow down in preparation for an upcoming stimulus. The research was published in the journal Psychological Science.