Abstract
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.
Highlights
In order to address some of these issues we developed the minimally delayed oculomotor response (MDOR) task (Knox, Heming De-Allie & Wolohan, 2018; Wolohan & Knox, 2014)
We demonstrated that saccade latency in the MDOR task was much longer than is consistent with simple prosaccade responses to target onsets, and that it is modulated by target display duration (TDD)
We have shown previously that both the AS and MDOR tasks involve the inhibition of reflexive prosaccades, the error rates in the two tasks do not correlate when compared in the same participants (Wolohan & Knox, 2014)
Summary
The observation that as we age the performance of many tasks becomes more difficult, leads to the narrative of inevitable age-related decline. While there is debate about how they are best classified, one approach views them as being separable into three broad domains of task or set shifting, working memory functions and inhibition, based on performance across a range of tasks (Miyake & Friedman, 2012; Miyake et al, 2000). In this and other accounts, inhibition or inhibitory control is a key domain (Verbruggen et al, 2014). The hypothesis of a general inhibitory control deficit in older age, once age-related changes in processing speed have been accounted for, is matter of ongoing debate (Rey-Mermet & Gade, 2018; Rey-Mermet, Gade & Oberauer, 2018; Verhaeghen, 2011, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
