Visual Fixation in NBA Free-Throws and the Relationship to On-Court Performance

Purpose Although hitting a baseball is often described as the most difficult task in all of sports, shooting baskets during a game likely ranks a close second. Previous studies have described the role of vision in basketball and more specifically a concept termed the “quiet eye” is related to basketball performance. How a shooter visualizes the target, how consistent their visual fixation is, and how long they maintain that fixation has been correlated to shooting success. Although the majority of previous reports have included non-professional basketball shooters, we evaluated NBA (National Basketball Association) players to determine if this skill was significant at the professional level. Materials and Methods We evaluated 16 professional NBA players before to the 2018-2019 NBA season. All players shot 30 consecutive free-throws while wearing Tobii Pro eye-tracking glasses. Following the completion of the task, several metrics were calculated including shooting success rate, as well as four measures of the position and duration of ocular fixation just prior to, during, and immediately after ball release for each shot of each player. Additionally, player performance statistics from the 2018-2019 season were recorded and compared to the visual fixation data. Descriptive statistics, as well as correlations between the visual fixation metrics and on-court performance metrics, were calculated. Results NBA shooters averaged a 79% success rate in free throw (FT%) shooting (SD = 14%, min = 56%, max=100%) during the study. Moderate statistically significant correlations were found between the percentage of successful free throws and the four measures of visual fixation (r=0.539 to 0.687). In addition, visual fixation measures were found to be correlated with on-court metrics suggesting that shooters who had more frequent, as well as longer, fixations on the rim were more likely to have lower Usage Percentage Laby_173419. indd 1 12/31/19 7:15 PM J Sports Perf Vis Vol 2(1):1-7; January 6, 2020. This article is distributed under the terms of the Creative Commons Attribution-Non Commercial 4.0 International License. ©Laby. Visual Fixation in NBA free-throws and the Relationship to On-Court Performance e2 (USG%), and Offensive Rebound Percentage (ORB%) as well as higher Three-Point Field Goal Percentage (FG3%). The percentage of successful shots in the study was compared to the on-court FT% and found to be moderately correlated (r=0.536). Conclusions The need to maintain ocular fixation on the rim while shooting seems elementary, but varies greatly among NBA players, as noted in these results. Our data suggest that players who visually fixate longer and more frequently on the rim are more likely to be successful in free throws, as well as more successful in 3-point goals, but less successful in offensive rebounds. The reduced offensive rebound percentage is possibly related to their being more distant from the basket when attempting 3-point goals. This data set appears to describe basketball guards in contrast to forwards/centers and supports previous research on non-professional basketball players. Almost 25 years ago, Prof. Joan Vickers described the differences between basketball free-throw success and the length of time, as well as when, the shooter visually fixated on the target. This work, as well as many subsequent publications, have termed this ability the quiet eye (technically the length of the final fixation just before the task’s motor final movement) and have highlighted the importance of visual fixation in sporting success. Subsequent research has further described the intricate relationship between stationary shooting (i.e., free throws) and dynamic shooting (i.e. jump shots) as well as shooting style. For example, Oudejans et al. differentiated jump shots from other static shooting tasks. In their report they describe different shooting styles (high vs low) and at what point during the task visual information is critical. Using ocular occlusion, they created four different shooting scenarios. The scenarios provided the shooter full vision while taking the shot, no vision while taking the shot, the initial vision (up to 350 ms before taking the shot), and late vision (the final 350 ms of vision before taking the shot). The authors found that for shooters with a high shooting style, vision in the final 350 ms before the shot was critical to success. The authors further concluded that “shooting style and visual control develop in close correspondence. ” More recently, Zwierko et al noted similar differences as reported by Oudejans et al in free throw vs jump shots. In their study, the shooters performed a shooting task following a 60-second fatigue protocol. They found more frequent fixations and longer fixations in free throws as compared to jump shots as well more frequent fixations in free throws and more variable fixations in jump shots following exertion and fatigue. Wilson et al 4 found similar results with a 19% decrease in performance and a 45% decrease in quiet eye following acute, severe intensity exercise (cycling). Additionally, not only are there differences in visual fixation between static and dynamic tasks, as well as with exertion, but other factors such as contested shots, and age also play a role in the quiet eye and shooting success. In a 2018 report, Klostermann et al 5 described the effect of shooting in a defended vs non-defended scenario for intermediate and highly skilled basketball shooters. Their report describes the beneficial effect of longer quiet eye durations in defended, but not in the undefended, the scenario on shooting performance. They also noted that the onset of the quiet eye as well as the offset of the quiet eye was related to shooting success. They conclude that not only is the quiet eye duration important, but its timing relative to the task is important as well. Interestingly, Fischer et al compared free throw shooting ability and quiet eye duration in younger vs. older shooters. As might be expected, they found a reduction in shooting accuracy in the older cohort. But somewhat surprisingly, they found that the quiet eye duration remained unchanged in the older population as compared to the younger population. They concluded that although motor performance is reduced with age, perceptual motor skills appear to be maintained with advanced age. Fortunately, the quiet eye can be trained with resulting in improved basketball shooting ability and success. Several reports comparing trained, untrained, as well as Laby_173419. indd 2 12/31/19 7:15 PM J Sports Perf Vis Vol 2(1):1-7; January 6, 2020. This article is distributed under the terms of the Creative Commons Attribution-Non Commercial 4.0 International License. ©Laby. Visual Fixation in NBA free-throws and the Relationship to On-Court Performance e3 sham quiet eye training groups suggest that at least in an uncontested situation, quiet eye trained shooters are more successful than non-quiet eye trained subjects. In some reports, this increased ability does not seem to transfer to situations involving contested shots and defensive pressure. The consensus though, does suggest a benefit to specific quiet eye training in basketball shooting. This project is intended to further describe the quiet eye, in a cohort of professional NBA (National Basketball Association) athletes, and its relationship to on-court performance metrics. Many previous reports have described the quiet eye in novice, near expert and expert athletes at many levels; this report describes the phenomenon, and its relationship to on-court performance, in high elite professional NBA athletes who would be expected to be the most expert in this ability. MATERIALS AND METHODS Participants Sixteen professional basketball players were included in this report. Athletes were evaluated during routine evaluation in the 2018 pre-season training camp of a single NBA (National Basketball Association) team. Thirteen of the 16 players were available for analysis as two players did not have 2018 on-court season performance data and one player’s data was removed after reporting that he purposely did not try to make the free throw shots during the testing session. All the players were male. This retrospective review was conducted in accordance with the US Department of Health and Human Services “Regulatory consideration regarding classification of projects involving real-world data” and was exempt from regulation per 45 CFR §46.104(d)(4). All data was utilized without the inclusion of any protected health information and informed consent as it is classified as secondary research. Testing was conducted with the Tobii Pro 2 eye tracking system (Tobii Technology, Inc, Falls Church, VA). Once testing was completed, raw data were analyzed with the Tobii Pro Lab software on a Microsoft Windows Surface Pro computer. Testing Procedure Each player was instructed to take 30 consecutive free-throw shots following a player determined number FIG. 1 Area of basketball rim, and backboard, used to determine optimal visual fixation during free-throw shots. of “warm-up” shots. Testing was conducted on the team’s practice court using NBA regulation distances and rim/backboard dimensions. While taking the 30 free throws, the Tobii Pro 2 glasses were worn, and each shot was recorded using the built-in software. Following the completion of shooting for all of the subjects, the data files were transferred to the Tobii Pro Lab software and analyzed. The data analysis software allows the calculation of several visual fixation metrics resulting from the thirty free-throws. After specifying an area of interest, in this case, the rim and surrounding backboard (Figure 1), it was possible to calculate the number of times the shooter visually fixated on a location within the area of interest (fixation count), the number of times his fixation left and re-entered the area of interest (visit count), and th