Performance Deficits in a Voluntary Saccade Task in Chinese ‘‘Express Saccade Makers’’ Paul C. Knox1*, Nabin Amatya2, Xiaoyu Jiang2, Qyong Gong2 1 Eye and Vision Science, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, United Kingdom, 2 Department of Radiology, Centre for Medical Imaging, Huaxi MR Research Centre, West China Hospital, Sichuan University, Chengdu, China Abstract Differences in behaviour and cognition have been observed in different human populations. It has been reported that in various types of complex visual task, eye movement patterns differ systematically between Chinese and non-Chinese participants, an observation that has been related to differences in culture between groups. However, we confirm here that, in healthy, na¨ıve adult Chinese participants, a far higher proportion (22%) than expected (1–5%) exhibit a pattern of reflexive eye movement behaviour (high numbers of low latency express saccades) in circumstances designed to inhibit such responses (prosaccade overlap tasks). These participants are defined as ‘‘express saccade makers’’ (ESMs). We then show using the antisaccade paradigm, which requires the inhibition of reflexive responses and the programming and execution of voluntary saccades, that the performance of ESMs is compromised; they have higher antisaccade directional error rates, and the latency distributions of their error saccades again exhibit a higher proportion of low latency express saccade errors consistent with a reduced ability to inhibit reflexive responses. These results are difficult to reconcile with a cultural explanation as they relate to important and specific performance differences within a particular population. They suggest a potential unexpected confound relevant to those studies of Chinese versus other groups which have investigated group differences using oculomotor measures, and explained them in terms of culture. The confirmation of higher numbers of ESMs among Chinese participants provides new opportunities for examining oculomotor control. Citation: Knox PC, Amatya N, Jiang X, Gong Q (2012) Performance Deficits in a Voluntary Saccade Task in Chinese ‘‘Express Saccade Makers’’. PLoS ONE 7(10): e47688. doi:10.1371/journal.pone.0047688 Editor: Markus Lappe, University of Muenster, Germany Received May 28, 2012; Accepted September 17, 2012; Published October 16, 2012 Copyright: 2012 Knox et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was supported by the National Natural Science Foundation of China (Grant No. 81030027) and a UK Royal Society International Joint Project grant (Grant No. 30711130226). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: pcknox@liv.ac.uk Introduction Over the last decade, cognitive and behavioural differences between human populations have been reported in a wide range of studies [1,2,3,4,5,6]. It has recently also been argued that most of what is currently known about human cognition is based on data from a strikingly unrepresentative sample of the global human population [7]. So on the one hand the literature is dominated by data generated from this narrow participant base, while on the other when different populations are examined it appears that brain and behaviour vary systematically for reasons that remain a matter of debate [8,9]. A useful contrast might be drawn between differences in cognition (eg in processes such as memory and attention) and differences in reflexive behaviours. We recently demonstrated a difference between groups of Chinese and (white) UK participants in a reflexive saccade task [10]. Express saccades (ES) are low latency visually-guided saccades that have a distinct neurophysiological origin [11,12,13]. Although saccade latency is modified by many factors, and is dependent on task design, saccades with latency in the range of 80 ms to 130 ms can reasonably be considered to be ES [10,14]. In circumstances which greatly decrease the occurrence of express saccades – prosaccade overlap tasks in which a central fixation target remains present when the saccade target appears - we found that 29% of Chinese participants persisted in producing high numbers of ES compared to only 3% of the UK group. This phenomenon has been reported previously [15,16], giving rise to the concept of the ‘‘express saccade maker’’ (ESM), a na¨ıve participant who in the absence of any pathology exhibits a high proportion (.30%) of ES in overlap conditions. A previous informal estimate suggested that ESMs are encountered rarely (comprising 1% to 5% of the adult population [15]); this is consistent with a number of relatively large saccade studies that did not observe any ESMs [17,18]. Confirmation of high numbers of ESMs among Chinese participants would provide a new avenue for the investigation of population differences as well as a means of investigating ESMs in greater numbers than previously possible. It would also imply a possible confound in experiments which have found differences in eye movement patterns between Chinese and non-Chinese groups and attributed them to culture [19,20]. Where dependant variables such as fixation time or saccade number have been the focus of analysis, altered low-level oculomotor performance in the Chinese group might explain part or all of the group differences in performance. What we do not yet know is whether the saccade performance differences in Chinese participants generalise to tasks beyond the simple reflexive tasks that we used previously. The links between saccade behavioural measurements and their underlying neurophysiology are well understood. Therefore, saccades provide a behavioural means of investigating specific neural circuits [21]. If in ESMs there is an important general PLOS ONE | www.plosone.org 1 October 2012 | Volume 7 | Issue 10 | e47688