Probing oculomotor inhibition with the minimally delayed oculomotor response task

Abstract

The ability to not execute (i.e. to inhibit) actions is important for behavioural flexibility and frees us from being slaves to our immediate sensory environment. The antisaccade task is one of several used to investigate behavioural inhibitory control. However, antisaccades involve a number of important processes besides inhibition such as attention and working memory. In the minimally delayed oculomotor response (MDOR) task, participants are presented with a simple target step, but 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 prevents offset timing being predictable from the time of target onset, and saccades prior to the offset are counted as errors. Antisaccade error rate and latency are modified by alterations in fixation conditions produced by inserting a gap between fixation target offset and stimulus onset (the gap paradigm; error rate increases, latency decreases) or by leaving the fixation target on when the target appears (overlap paradigm; error rate decreases, latency increases). We investigated the effect of gaps and overlaps on performance in the MDOR task. In Experiment 1 we confirmed that, compared to a control condition in which participants responded to target onsets, in the MDOR task saccade latency was considerably increased (increases of 122–272 ms depending on target display duration and experimental condition). However, there was no difference in error rate or saccade latency between gap and synchronous (fixation target offset followed immediately by saccade target onset) conditions. In Experiment 2, in a different group of participants, we compared overlap and synchronous conditions and again found no statistically significant differences in error rate and saccade latency. The timing distribution of errors suggested that most were responses to target onsets, which we take to be evidence of inhibition failure. We conclude that the MDOR task evokes behaviour that is consistent across different groups of participants. Because it is free of the non-inhibitory processes operative in the antisaccade task, it provides a useful means of investigating behavioural inhibition.

Peer Review #2 of "Age-related alterations in inhibitory control investigated using the minimally delayed oculomotor response task (v0.1)"

“…149 150 All of the experiments we have conducted with the MDOR task so far have been on younger 151 participants. Across multiple groups of younger participants, we have observed performance to 152 be similar and consistent, noticeably so for error rate (Knox et al 2018). To explore the MDOR 153 task further, and given the prominence of saccade tasks in both the ageing and inhibitory 154 control literatures, our aim in the current study was to investigate MDOR performance in older 155 healthy participants, and to compare it to that in younger participants.…”

“…168 Apparatus and Stimuli 169 We used the same apparatus and stimuli as in earlier experiments (Knox et al 2018;Wolohan & 170 Knox 2014). Briefly, stimuli were presented on a 21" monitor (1024×768 spatial resolution, 100 171 Hz temporal resolution) driven by a VSG2/5 card (Cambridge Research Systems, Rochester, UK), 172 positioned on the fronto-parallel plane 57 cm from the participant's eye.…”

“…Oculomotor data was stored for off-line, trial-by-trial analysis using 176 custom software. 177 We used the synchronous version of the MDOR task (Knox et al, 2018; Fig 1) in which a central 178 fixation target (0.2° black square; 11cd/m 2 ) was presented on a light background (56cd/m 2 ; 179 contrast 79%) for a randomised period of 0.5-1.5s. Immediately when it was extinguished, the 180 saccade target (a 0.2° black square) appeared 5° to the left or to the right of fixation 181 (randomised and with equal frequency) and was displayed for either 200ms or 1000ms 182 (randomised from trial to trial).…”

“…The calibration task was not simply a repetition of the MDOR task without 397 inhibition, as is the MDOR control task. 398 399 Increased latency in the MDOR task is indicative of the requirement to inhibit the reflexive 400 response to target onset (discussed in detail in Knox et al 2018). The modulation in latency 401 with TDD is consistent with higher levels of inhibition if the target offset (the go signal) occurs 402 soon after target onset (as in the 200ms condition), with the level of inhibition declining the 403 longer the target is displayed.…”

“…0% error rates) in control 431 groups. However, this option is not available with the MDOR task (Knox et al 2018). But 432 investigating other stimulus and task features (e.g.…”