Eye-tracking methods are widely used in various research domains such as psychology, psychiatry, or sport (Duchowski, 2003). They are popular because eye movement measures are easy to obtain and participants can understand eye movement tasks easily (Noiret et al., 2017). More importantly, eye-tracking methods provide unique means to measure cognitive processes (Thomas et al., 2021). Therefore, eye movement experiments are carried out in different populations in various research domains (Noiret et al., 2018).

Saccade is a rapid eye movement we typically make three times every second (Rayner, 1998). Saccadic eye movements can be characterized by several eye movement measures such as saccade latency (i.e., the time elapsed from the onset of the target to the onset of the first saccade after target onset), saccade velocity (i.e., the velocity of saccade), and saccade amplitude (i.e., the spatial distance between two successive fixations). The prosaccade task is a well-known experimental paradigm that is used to examine saccadic eye movements. In a typical prosaccade task, participants are instructed to fix on a central dot. Then, they have to direct their gaze toward a target dot appearing at the periphery as quickly and as accurately as possible. Research has shown that saccadic eye movements are associated with multiple cognitive processes including processing speed, attention, and inhibitory control (Hutton, 2008; Noiret et al., 2017).

For instance, some previous studies have revealed that the saccade latency needed to trigger a prosaccade in prosaccade tasks varies as a function of the attentional process (Clark, 1999; Pratt et al., 2006; Noiret et al., 2018). Noiret et al. (2017) found that saccade latency is influenced by information processing speed. Moreover, some research on some special populations has suggested that saccade latency variability is a good indicator of attentional fluctuation in saccadic eye movement tasks (Kaufman et al., 2010, 2012). Kaufman et al. (2010) found that patients with Lewy body had greater saccade latency variability than aged controls. Mostofsky et al. (2001) examined the saccadic eye movements of boys with Tourette syndrome. They found that boys with ADHD (i.e., attention deficit hyperactivity disorder) had greater saccade latency variability than boys without ADHD in the prosaccade task. Studies on Alzheimer’s disease have shown that patients with Alzheimer’s disease had longer saccade latency as well as greater saccade latency variability than healthy senior adults.

The purpose of the present study was to use the prosaccade task as a tool to investigate the difference in cognitive processing underlying saccadic eye movements in skilled and less skilled female adolescent soccer players. Soccer is a game that requires players to process a great amount of internal and external information under pressure within a limited time and react to complex and rapidly changing contexts (Vestberg et al., 2012). Soccer players have to distribute their attention over multiple objects (e.g., moving ball, teammates, and opponents) during games (Ando et al., 2001). Therefore, saccadic eye movement is a critical index for soccer players’ performance. Some research has found that eye movement measures vary as a function of skill level in many sports. Ando et al. (2001) revealed that soccer players had shorter visual reaction time than nonathletes when responding to peripheral stimulus, indicating that soccer players had faster visual processing speed. Similarly, Zwierko (2008) found that handball players had shorter response time to peripheral stimulus compared to nonathletes. A recent study showed that cricketers had faster visual reaction times than nonathletes and cricketers’ stability of gaze is associated with faster visual reaction time (Barrett et al., 2020). Moreover, some researchers examined the search behaviors of skilled and less skilled soccer players when viewing film of defensive scenarios in soccer finding that skilled players exhibited more fixations, shorter duration, and more fixation locations than less skilled players (Ward and Williams, 2003; Williams and Ericsson, 2005; Williams, 2009; Roca et al., 2011).

In summary, previous studies have shown that there are differences in eye movement tasks among populations with various skill levels. However, to our knowledge, little work has used the prosaccade task to investigate the differences in saccadic eye movements between skilled and less skilled players. Some studies using the prosaccade task only focus on examining the cognitive changes of players caused by head impact exposure in contact and collision sports (Kiefer et al., 2018; Gallagher et al., 2020).

Therefore, the goal of the present study was to examine the potential differences in cognitive processes underlying saccadic eye movements between skilled and less skilled female adolescent soccer players by using the prosaccade task. Based on previous studies, we predict that skilled players would have higher cognitive ability and would thus perform better than less skilled players in prosaccade task. More specifically, we hypothesized that skilled players will exhibit shorter saccade latency, decreased variability of saccade latency, and higher spatial accuracy of saccade than their less skilled counterparts.

Independent sample t tests were conducted to compare the difference in each index between skilled and less skilled players (Table 2). Skilled players had shorter saccade latency (167.33ms, SD=23.32) than less skilled players (184.43ms, SD=32.02), t(54)=−2.21, p=0.031. Additionally, skilled players had decreased variability of saccade latency (33.89ms, SD=10.46) than less skilled players (45.00ms, SD=24.30), t(54)=−2.57, p=0.013. Skilled players showed higher spatial accuracy of saccade (0.54°, SD=0.11) than less skilled players (0.60°, SD=0.08), t(54)=−2.20, p=0.032. The saccade amplitude, peak velocity, and average velocity of two groups of players were comparable (|t|s<0.91; see Figure 1).

In the current study, we conducted prosaccade task to investigate the difference in saccadic eye movements between skilled and less skilled female adolescent soccer players. As we hypothesized, the results showed that the skilled players, as compared to their less skilled counterparts, were faster to saccade to the target appeared peripherally, exhibited less variability of saccade latency, and more accurate saccade. Hence, our study supports the view that skilled players have higher cognitive ability and would thus perform better than less skilled players in prosaccade task.

The result that skilled players had shorter saccade latency than less skilled players suggests that skilled players had faster information processing speed than less skilled players. This is consistent with previous studies, demonstrating that saccade latency is influenced by information processing speed (Noiret et al., 2017, 2018) and others showing that saccade latency varies as a function of cognitive function (Coors et al., 2021; Thomas et al., 2021). More importantly, this result is also consistent with studies, demonstrating that players’ cognitive capacities vary as a function of their skill levels (Vestberg et al., 2012, 2017; Glavaš, 2020).

Another critical result is that less skilled players exhibited larger variability of saccade latency than skilled players. Kapoula et al. (2010) suggested that variability of saccade latency could be used as a good index of attentional fluctuation in saccadic eye movement tasks. This is due to more attentional lapses caused by more attentional fluctuation in one’s attentional system would contribute more longer reaction times in cognitive tasks (Schmiedek et al., 2007; McVay and Kane, 2012; Unsworth and Robison, 2016). This conclusion was supported by several studies, finding that individuals with inferior attentional system had larger variability of saccade latency than their counterparts with superior attention system (Mostofsky et al., 2001; Jazbec et al., 2006; Yang et al., 2013; Kiefer et al., 2018). Taken together, this result may imply that the attentional system of skilled soccer player is superior which leads to smaller attention fluctuation and less attentional lapse.

The result also suggests that skilled soccer players’ saccades are more accurate than less skilled soccer players. Previous studies have found that the spatial accuracy of prosaccade is mainly influenced by cerebellar (Ettinger et al., 2005; Optican, 2005; Coors et al., 2021), and the cerebellum, particularly the vermis, plays an important role in the spatial accuracy of saccade (Robinson and Fuchs, 2001; Leigh and Kennard, 2004). Hence, this result may imply that the function of cerebellum of skilled soccer player is superior to that of less skilled soccer. Moreover, this result also implies potential structural differences in brain underlying saccadic eye movement between skilled and less skilled soccer players.

No significant differences were observed in saccade amplitude, peak velocity, and average velocity. For saccade amplitude, previous study found that the saccade amplitude was mainly influenced by target eccentricity in prosaccade task (Petrella et al., 2019). On the one hand, the distance between the peripheral target and the position of the onset of saccade (fixation cross) is constant in the present experiment. On the other hand, all participants in this study had normal or corrected-to-normal vision. Therefore, the absent of significant difference between two groups in saccade amplitude is understandable. For saccade velocity, previous research has demonstrated that the peak velocity was relatively stable (Coors et al., 2021). Sparks (2002) suggested that, from the perspective of neurophysiology, peak velocity is subject to the number of spikes and firing rate of saccadic burst cells. Some researcher suggested that as people conduct approximately 200,000 saccades per day, the saccadic burst cells are continuously trained (Pratt and Welsh, 2006). Considering that all players in two groups had not suffered any neurological or psychiatric disorders or traumatic brain injury, their nervous system and oculomotor system should be normal and comparable. Therefore, it is also understandable that skilled and less skilled players did not differ in saccade velocity.

The findings of the present study shed some light on understanding of the relationship between saccadic eye movement and skill level in the field of sport and expertise. Besides, these findings supported the results of previous studies, indicating that cognitive ability differed as a function of skill level (Fontani et al., 2006; Brams et al., 2019; Barrett et al., 2020). Furthermore, the present study implies some practical applications for determining or predicting soccer players’ skill level and cognitive abilities by analyzing their saccadic eye movements during some eye movement tasks. It would be more economical and convenient for coaches and training instructors to determine a player’s skill level using some specific eye movement tasks.

Nevertheless, owing to the restriction of conditions, we should note that the present study has some limitations. For example, the current sample is representative of an adolescent, female, and soccer player sample. It remains unclear whether the results are fully generalizable to adolescent male or adult soccer players’ samples. Likewise, it is also unclear whether the results are fully generalizable to players in other sports. Besides, the relatively small sample was used in the present study as was subject to some objective circumstances. The future studies should include a larger sample to get greater statistical power to detect any differences between groups in cognitive processes on eye movements. Additionally, the current study only explored the differences in saccadic eye movements between skilled and less skilled soccer players using prosaccade task. Yet, growing body of research has shown that antisaccade task is a useful tool to examine the differences in inhibitory control and executive functions among different groups of population (Noiret et al., 2018; Gallagher et al., 2020; Bey et al., 2021; Coors et al., 2021). Therefore, future research should consider combining prosaccade task with antisaccade task when examining the saccadic eye movements of soccer players.

In summary, the results of the current study suggest that skilled soccer players outperform less skilled soccer players on saccadic eye movement in prosaccade task indicating superior cognitive processes underlying saccadic eye movement in skilled soccer players. Overall, the present findings have implications for understanding the relationship between saccadic eye movements and skill level.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.

The studies involving human participants were reviewed and approved by Academic and Ethics Committee of the Fujian Normal University. Written informed consent to participate in this study was provided by the participants’ legal guardian/next of kin.

ZJ contributed to the conception, design of the study, conducted the experiment, performed the statistical analysis, and wrote the first draft of the manuscript.

This research was supported by a grant from the Fujian Social Science Foundation (FJ2018C064), and by a grant from the Planning Project of Fujian Provincial Department of Education (JAS180075).

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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