LICS

The Liverpool Inhibitory Control study - This project grew out of two previous studies. More than 10 years ago we were playing around with tasks in which participants had to keep their eyes pointed at a location for longer rather than shorter periods of time. This made a difference to the timing of their eye movement responses when they had to make a saccade. Actually the purposes of the overall experiment are now quite obscure (perhaps why the paper, Knox 2009, has never been cited). But it got me thinking about how inhibition might be tested using saccades. Then in the CoSAC project, we wanted to test oculomotor inhibition, and began thinking about ways of doing this that might improve on the antisaccade task. The answer was the minimally delayed oculomotor response (MDOR) task.

The basic  idea in MDOR is very simple. In our original version of the task, the stimulus is a small target which jumps a short distance to either left or right and is displayed for either a short (200ms) or long (1s) time. But participants are instructed to respond to the target not when it appears to left or right (this would be a "simple" a reflexive prosaccade response), but when it disappears. This means it's necessary to inhibit the normal reflexive response to the target onset.  We measure performance using the error rate (the proportion of trials in which participants execute a saccade to the target onset) and the latency of correct responses.

So far we know a number of things. The latency of correct responses is related to the time the target is displayed for. If the target goes off very quickly, saccade latencies are very long (at around 400ms up to twice what you'd expect). If the target is on for a longer period of time (we've tested up to 1.2s) latency is still longer than for a normal reflexive response, but lower the greater the target duration (see Expt 1 on this poster; Knox & Abd Razak, 2010).  This is because if the target goes off quickly, the saccade has to executed against a background level of high inhibition - hence the longer latency. We also know that unlike the antisaccade task, fixation conditions (gaps and overlaps) have little influence on performance (see Knox et al, 2018). In older healthy people, latencies are longer for correct responses (although not much longer than you'd expect given their age) but that error rates are also higher - this is consistent with an age-related deficit in inhibitory control (see Knox & Pasunuru 2020). This has been confirmed with a slightly different version of the task with three rather than two target display durations (Knox & Liang 2021).  Recently Brooke Jackson and her colleagues have been using the MDOR task in patients suffering from psychosis, and early results have confirmed that they perform poorly relative to healthy controls. 

Jackson BS, Rodrigue AL, Knox PC, Clementz BA, Mcdowell JE (2021) Probing the Minimally Delayed Ocular-Motor Response task in psychosis. Biological Psychiatry 89, S219.. doi:10.1016/j.biopsych.2021.02.554 (Abstract)

Knox, P.C. (2009) Prior information and oculomotor initiation: the effect of cues in gaps . Exp Brain Res (2009) 192: 75. https://doi.org/10.1007/s00221-008-1556-9

Knox, P.C., Abd Razak, N. (2010) Oculomotor inhibition: Shared or separate mechanisms for saccades and smooth pursuit? Soc. Neuroscience Absts. 676.17

Knox PC, Heming De-Allie E, Wolohan FDA (2018) Probing oculomotor inhibition with the minimally delayed oculomotor response task. Exp. Brain Res 236:2867–2876. https://rdcu.be/3Nno

Knox PC, Liang D (2021) Confirmation of age-related alterations in inhibitory control using a modified minimally delayed oculomotor response (MDOR) task. PeerJ 9:e11610 https://doi.org/10.7717/peerj.11610 

Knox PC, Pasunuru N. 2020. Age-related alterations in inhibitory control investigated using the minimally delayed oculomotor response task. PeerJ 8:e8401 https://peerj.com/articles/8401/