CoSAC

Comparisons of Saccades Across Cultures - This project began as a study of particular individuals, “express saccade makers” (ESMs), who produce high proportions of low latency “express saccades”, even in conditions that are designed to discourage this (overlap trials, in which a central fixation target remains illuminated when a saccade target appears).  ESMs were thought to be relatively rare; they were suggested to make up 1%-5% of the healthy adult population.  However, completely by accident, we discovered that ESMs made up 30% of a group of healthy Chinese participants, tested in China (compared to 1/44 Caucasian participants tested in the UK; Amatya et al, 2011).  We subsequently confirmed this surprising result it in a different group of 77 Chinese participants, 17 of whom  turned out to be ESMs. We also went on to demonstrate that the performance of the ESMs was compromised on a voluntary saccade task called the antisaccade task. When ESMs had to do antisaccades, they generated more errors than non-ESM participants, and many of these error saccades were very low latency. 

Why is there a difference in eye movement performance between Chinese and Caucasian participants? The CoSAC project was set up to investigate this, and was funded by the Leverhulme Trust. We recruited and tested a group of Chinese participants who were born and educated in the UK compared to a large group of Chinese overseas students studying in Liverpool. If the high proportion of ESMs was the product of “culture” then we would expect these two groups to be different in terms of their eye movement control, and they should have very different proportions of ESMs. In fact while we were able to show that culturally the two Chinese groups were different, in terms of their eye movements they were identical; in both Chinese groups there were more ESMs than expected, and in general their saccade latencies were lower than the Caucasian group (Knox & Wolohan, 2014). 

Now we were able to work with large groups of ESMs we were able to investigate the relationship between oculomotor performance and other aspects of processing such as behavioural inhibition and attention. Our results demostrated that in general ESMs do not have a problem with inhibiting eye movement responses, as might be argued from our antisaccade results. Using a new task (the minimally delayed oculomotor response, MDOR, task) we showed that error rates were very similar between ESM and non-ESMs. (As an aside, the MDOR experiments led to an interest in oculomotor inhibition that we're following up in the LICS project).  ESM errors, when they occurred, tended to be a very low latency (Wolohan & Knox, 2014). We also demonstrated that these patterns of behaviour were very stable over time, as was the classification of participants into ESM and non-ESM groups. And it wasn't possible to “train” normal participants to respond like ESMs  (Knox & Wolohan, 2015). 

Retuning to the culture theme, in colaboration with Mai Helmy in the University of Menoufia in Egypt, we obtained saccade data from a large group of Egyptian participants (Knox et al, 2017). We found 14% of the group were ESMs. The Egyptian dataset contained other features suggesting that performance was intermediate between that of Chinese and Caucasian participants, although it could still be that it is the Chinese population that is the outlier.

So, ESMs are not as rare as once thought (at least in certain populations), and this pattern of of eye movement behaviour is stable, and relatively uninfluenced by culture or environment (including training). It appears to represent a distinct, stable oculomotor phenotype. There are still large gaps in out knowledge of course.  When all is said and done we've still only tested a very small part of the whole human population and only from three geographical locations. Where would other populations fit into the patterns we've seen? And if culture and environment don't explain the difference in saccade behaviour between populations, what could? Perhaps the underlying neurogenetics? 

We have tested saccades in other locations too. As part of a larger study into the effects of cerebral malaria (CM), we recently reported longitudinal results on Malawian children (see Knox et al, 2016).  Using saccade analysis, we followed the development of a group of children who had suffered CM versus a group who had not. Using antisaccades we found the the error rates were very high in the CM group. The problem for us is that the error rates were also much higher than expected in the "healthy" control group.  We interpret this result as showing that there are other factors affecting childrens' develop in this part of Africa. This could be diseases other than malaria, as well as environmental factors (like smoke from cooking fires).  We're hoping to continue these studies in the future to find out what's going on.