Summary: A newly developed eye movement measurement test sheds light on inhibitory control and brain aging.
Source: University of Liverpool
A new study, published in PeerJ, shows how University of Liverpool researchers have used a newly developed eye movement test to improve the understanding of how parts of the brain work.
Healthy, older adults are widely reported to experience cognitive decline, including impairments in inhibitory control (the ability to stop ourselves thinking or doing things). However, because aging effects on inhibitory control are highly variable between individuals, vary depending on tests used, and are sometimes not distinguished from general age-related slowing, this general view is a matter of debate.
Inhibitory control is also important in conditions like schizophrenia, ADHD and forms of Parkinson’s disease; patients can become jumpy, distractible or have problems with unwanted thoughts.
Researchers from the University’s Department of Eye and Vision Science, led by Dr Paul Knox, developed a new test, using measurements of eye movements, to provide an improved method of investigating inhibitory control, and have applied to study the effects of aging on this ability.
In the study two cohorts of healthy people were recruited from two different age groups, 19 to 27 years old and 50 to 72 years old. Participants viewed a dot in the centre of a computer a screen and then had to to look at a second dot that appeared to the left or right not when it appeared, but when it disappeared. As people instinctively look at things when they appear, this requires the inhibition of a normal automatic eye movement. Eye movements were measured precisely using an infrared eye tracker, revealing how often they looked too early.
The results showed that older participants were much more likely to look at the dot when it appeared (not when it diapered) and were slower compared to younger participants.
Dr Paul Knox, said: “We are designed to react to things appearing in our visual world. It is something we do automatically. However, we also have the ability to stop ourselves responding and this prevents us becoming slaves to our sensory environment.
“This new test allows us to measure inhibitory behaviour precisely. It is clear that older participants found it more difficult to inhibit their actions, even once we had accounted for the general slowing that occurs with aging.
“This confirms that a decline in inhibitory control is a part of normal aging. We are doing experiments to refine the test, and then we hope to use it to study inhibitory control in a range of important diseases.”
University of Liverpool
Simon Wood – University of Liverpool
The image is in the public domain.
Original Research: Open access
“Age-related alterations in inhibitory control investigated using the minimally delayed oculomotor response task”. Paul C. Knox, Nikitha Pasunuru.
Age-related alterations in inhibitory control investigated using the minimally delayed oculomotor response task
Healthy, older adults are widely reported to experience cognitive decline, including impairments in inhibitory control. However, this general proposition has recently come under scrutiny because ageing effects are highly variable between individuals, are task dependent, and are sometimes not distinguished from general age-related slowing. We recently developed the minimally delayed oculomotor response (MDOR) task in which participants are presented with a simple visual target step, and instructed to saccade not to the target when it appears (a prosaccade response), but when it disappears (i.e. on target offset). Varying the target display duration (TDD) prevents offset timing being predictable from the time of target onset, and saccades prior to the offset are counted as errors. A comparison of MDOR task performance in a group of 22 older adults (mean age 62 years, range 50–72 years) with that in a group of 39 younger adults (22 years, range 19–27 years) demonstrated that MDOR latency was significantly increased in the older group by 34–68 ms depending on TDD. However, when MDOR latencies were corrected by subtracting the latency observed in a standard prosaccade task, the latency difference between groups was abolished. There was a larger latency modulation with TDD in the older group which was observed even when their generally longer latencies were taken into account. Error rates were significantly increased in the older group. An analysis of the timing distribution of errors demonstrated that most errors were failures to inhibit responses to target onsets. When error distributions were used to isolate clear inhibition failures from other types of error, the older group still exhibited significantly higher error rates as well as a higher residual error rate. Although MDOR latency in older participants may largely reflect a general slowing in the oculomotor system with age, both the latency modulation and error rate results are consistent with an age-related inhibitory control deficit. How this relates to performance on other inhibitory control tasks remains to be investigated.