1 Perceptual and Motor Skills, 2009, 109, Perceptual and Motor Skills 2009 VISUOMOTOR CONTROL OF STRAIGHT AND BREAKING GOLF PUTTS 1 MARK R. WILSON AND RICHARD C. PEARCY University of Exeter Summary. This study assessed golfers gaze behavior in both the preparation (line reading) and execution (ball striking) of putts with different break characteristics. Six golfers completed 25 3-m putts on five different slopes (flat, 0.9 and 1.8 left-to-right, 0.9 and 1.8 right-to-left), while their gaze behavior was analyzed using an Applied Science Laboratories Mobile Eye gaze-registration system. Frameby-frame analyses of 136 putts were performed to assess the number and duration of fixations made during the preparation and execution phases of the putts. Putting performance was significantly poorer for the most severe break (1.8 ) than for other conditions. The only gaze variable to distinguish between successful and unsuccessful putting outcome was the quiet eye period (the final fixation prior to the initiation of the putter movement). Specifically, participants had significantly longer quiet eye periods on successful than on unsuccessful putts. Putting is frequently cited as the most important aspect of the game of golf, contributing an average of 43% of the strokes taken in a round, even at the highest level (Pelz, 2000). The mechanics of the putting stroke have received much attention from a coaching (e.g., Pelz, 2000) and biomechanical (e.g., Delay, Nougier, Orliaguet, & Coello, 1997) standpoint. However, recent research by Karlsen, Smith, and Nilsson (2008) found that the putting stroke itself may have limited influence on the number of putts holed. These authors found that the variability in direction of the putting strokes of elite players was very low and should relate to 95% of 4-m putts being holed (given perfect conditions). However, statistics from the Professional Golf Association (PGA) Tour 2 for 2009 show that the percentage of putts holed from 10 to 15 feet is less than 30%. The findings from Karlsen, et al. s study suggest that an alternative approach, focusing on the control of the entire visuomotor system, is perhaps needed to better understand golfputting performance. Vickers (1992), in the first study to analyze the gaze behaviors of golfers, found that good golfers had a distinct gaze strategy when performing flat putts. During the preparation phase of the putt, these golfers tended to direct two to three fixations to the hole and then to the ball or club face, with distinct saccades linking these fixations. During the execution of the 1 Address correspondence to Dr. Mark Wilson, School of Sport and Health Sciences, University of Exeter, St. Luke s Campus, Exeter EX1 2LU, UK or 2 PGA Tour Putting Statistics. (2009) Retrieved May 24, 2009, from PGA Tour web site: DOI /PMS
2 556 M. R. WILSON & R. C. PEARCY putting stroke, players maintained a steady fixation on the top or the back of the ball. The duration of this fixation on the ball was a significant determinant of both ability (lower handicap golfers had longer fixations than higher handicap golfers) and accuracy (holed putts had longer fixations than missed putts). The importance of this last fixation on a target before the initiation of a motor response (later defined as the quiet eye; Vickers, 1996) has been demonstrated for a variety of aiming tasks (see Vickers, 2007, for a review). Vickers proposed that the quiet eye is a period of time when taskrelevant environmental cues are processed and motor plans are coordinated for the successful completion of an upcoming task. Theoretically, longer quiet eye periods allow performers an extended duration of programming, while minimizing distraction from other environmental cues (Vickers, 1996). However, most putts made on a golf course are not straight and will have some slope which adds difficulty to the putt. First, when putting on a sloped surface, golfers have to judge the amount of break required and hit the ball with the required pace (related to the force with which the ball is struck) to maintain this line. Second, rather than a well-defined target (the hole), the target on a sloped green is abstract and ill-defined, dependent on the pace with which the ball is struck. For this reason it may be important to examine the aiming-gaze strategy, as well as that adopted during the execution phase (i.e., the quiet eye) in sloped putts. To date, there has been no research on breaking putts from a visuomotor-control perspective. The objectives of this research are then to examine how gaze behavior in both the preparation (aiming) and execution (quiet eye) phases of putting may influence performance for putts on different slope characteristics, using the latest generation gaze-registration system. First, it was predicted that there would be greater outcome error for sloped putts than for flat putts. Second, longer quiet eye periods were hypothesized for holed putts than for missed putts (as in Vickers, 1992). Third, while aiming fixations are somewhat exploratory, more fixations would be expected on sloped putts given the difficulty of specifying an abstract target. Method Participants Six university team golfers (mean age 24.0 yr., SD = 4.7) volunteered to participate. All reported normal vision, were right-handed, and were individually tested. Local ethics committee approval and informed consent was obtained before testing.
3 QUIET EYE, AIMING, AND GOLF PUTTING 557 Apparatus A regulation hole (diameter 108 mm) was located centrally and 3.5 m from one end of a rectangular, artificial putting green (4.9 m long and 1.2 m wide), with a stimpmeter value of Two sets of wooden struts could be placed under the left and right edges of the putting green, which raised that edge by a set amount and created either a consistent left-to-right or right-to-left slope along the entire length of the green. Each putt was set up so the ball was located 3 m from the front of the hole (cf. Vickers, 1992) and situated centrally along the width. Each participant was asked to bring the putter they would normally use, and all used Titleist Pro V1 golf balls (Acushnet, Ltd., Massachusetts). Gaze data were captured at 25 Hz using an Applied Science Laboratories (Bedford, Massachusetts) Mobil Eye gaze-registration system. An externally positioned digital video camera (Canon, MD101) was located 3 m behind the hole and perpendicular to the ball-hole line. Procedure Golfers were instructed to try and hole all putts, but to help make selections of a realistic pace, they were asked to try and leave the ball within 1 m of the hole, as would be appropriate if they had to hole out. Each golfer was given five practice putts with the putting green set up for a flat putt and wearing the head unit. This allowed familiarization with both the pace of the surface (coefficient of friction) and the eye-tracking equipment. The head unit was calibrated, and each player performed 25 putts in a randomized order; five on each slope of flat, 0.9 left-to-right and right-to-left (approximately a 13-cm break at optimum speed; Pelz, 1994); and 1.8 leftto-right and right-to-left (approximately a 25-cm break; Pelz, 1994). Measures Performance. Two measures of performance were calculated, reflecting both the outcome (holed or missed) and performance error, indexed by the distance that the ball missed the hole as it passed. Colored circular markers (diameter 7 mm) were placed on either side of the hole, perpendicular to the ball-hole line with a spacing of 4 cm (the approximate width of a golf ball), which allowed a magnitude of the miss to be recorded offline from the external camera video footage. To ensure the reference dots were not used as artificial fixation locations, additional but differently colored markers were randomly placed around them. The colored markers were not clearly identifiable from the golfers viewpoint but could be recorded on the external camera. Number of aiming fixations. A fixation was defined as three or more gaze points to the same location (within 1 of visual angle) that lasted 120 msec. or more (Vickers, 1992, 1996). The location and duration of all aim-
4 558 M. R. WILSON & R. C. PEARCY ing fixations made during the preparation phase (between addressing the ball and initiating the backswing) were calculated by a frame-by-frame analysis of the eye-tracker video, using MotionPro! 6.80 (Cyberaccess123) software. The number of aiming fixations made during the preparation phase for each putt was subsequently recorded. Duration of final aiming fixation. While golfers tend to glance at the hole or abstract targets around the hole more than once during the preparation phase of the putt, the last fixation to a target location around the hole was operationally defined as the final aiming fixation. As this final fixation is likely to reflect the final choice of target (see Vickers, 2007), the duration was calculated to reflect final aiming processing, prior to the attention shift to the ball. Quiet eye. The quiet eye period was operationally defined as the final fixation before the onset of the putting stroke (i.e., first movement of the putter head away from the ball) within 1 visual angle for a minimum of three frames (120 msec.; cf. Vickers, 2007). The location of the quiet eye was either the top or back of the ball, the putter head, or a location adjacent to the ball. Quiet eye durations were calculated using Quiet Eye Solutions Software. 3 Data Analysis Of the total of 150 putts, 136 were analyzed, as some data were lost due to poor pupil capture or the eye-tracker on the participant s head moving slightly. The performance errors were subjected to a three-way analysis of variance (ANOVA; Slope: flat, moderate, severe); Tukey post hoc tests were applied to check significant effects. Given the small number of holed putts in the severe breaking condition (see Table 1), the gaze data for both sloped conditions were combined. The gaze measures were then subjected to a 2 2 (Performance: holed, missed Slope: flat, sloped) ANOVA. Results Performance Error The ANOVA yielded a significant main effect for errors (F 2,122 = 12.33, p <.001), with participants missing the hole by a significantly greater distance in the severe slope condition than in the flat (p <.001) and moderately (p <.001) sloped conditions. Table 1 presents for the putting performance numbers of putts and holed putts and mean magnitude of misses. Quiet Eye This ANOVA also showed a significant effect for performance (F 1,122 = 4.24, p <.05), with participants having significantly shorter quiet eye durations on missed putts (1, msec., SD = ) than on holed putts 3
5 QUIET EYE, AIMING, AND GOLF PUTTING 559 TABLE 1 Means and Standard Deviations For Putting Success and Performance Error (Mean and Standard Deviation of Distance Ball Missed Hole) Slope Type No. of Putts No. of Holed Putts Successful Putts, % Magnitude of Misses, cm Flat Moderate Severe * Total *p <.001. (1, msec., SD = 1,015.15). There was no significant main effect for slope severity (F 1,122 = 2.17, p =.14) and no significant interaction (F 1,122 =.15, p =.70; see Table 2). Number of Aiming Fixations There was a significant main effect for severity of slope (F 1,97 = 4.60, p <.05), with participants using more aiming fixations on sloped putts (7.94 fixations, SD = 3.76) than flat putts (5.93 fixations, SD = 2.09), but none for performance (F 1,97 = 2.65, p =.11) and no significant interaction (F 1,97 =.30, p =.59; see Table 2). Final Aiming Fixation Duration No significant main effects for performance (F 1,114 =.26, p =.61) or slope severity (F 1,114 = 0.04, p =.84) were found, as well as no significant interaction (F 1,114 =.36, p =.55; cf. Table 2). TABLE 2 Gaze: Means and Standard Deviations For Quiet Eye Period, Number of Aiming Fixations, and Final Aiming Fixation Duration For Holed and Missed Putts and Across Sloped and Flat Conditions Gaze Behavior Holed Missed Sloped Flat Sloped Flat M SD M SD M SD M SD Quiet Eye Duration, msec. 1, , , , , No. of Aiming Fixations Final Aiming Fixation Duration, msec Discussion These performance data indicated that golfers found the severely sloped putts more difficult than either the moderately sloped or flat putts. M SD
6 560 M. R. WILSON & R. C. PEARCY First, while 52% of putts were holed from 3 m when they were flat and 41% on a moderate slope, only 11% were holed in the severely sloped condition. Furthermore, error in the putts which were not holed (distance by which the ball missed the hole laterally) was significantly greater for the severely sloped condition than for the other two conditions. These findings suggest that even a consistent side slope of between 0.9 and 1.8 increased the difficulty of the putting task and created more parameters to be processed by the visuomotor system (line, pace, etc.). It seems important, then, that visual processing measures be assessed during the preparation and execution of sloped (as well as flat) putts to further understanding of the mechanisms underlying successful putting performance. Unfortunately, given the low number of holed putts in the severely sloped condition, a collapsed slope measure was estimated for each gaze behavior, combining data for moderately and severely sloped conditions. Durations of the quiet eye support previous research on a variety of aiming tasks, suggesting that this measure reflects a period of critical processing of force and direction components relevant to the task (Vickers, 2007). Successful putts had significantly longer quiet eye periods than unsuccessful putts and these durations were of magnitude similar to those found by Vickers (1992; approximately 2,000 msec. for expert putters). Measures of gaze behavior which indexed the aiming phase of the putt did not distinguish between successful and unsuccessful shots. There were no differences between the number of fixations made while aiming or in the duration of the final aiming fixation for holed or missed putts. Perhaps surprisingly, there were no significant differences in quiet eye periods or in durations of final aiming fixation between flat and sloped putts. Previous research by Williams, Singer, and Frehlich (2002), using a billiards task, showed participants had longer quiet eye periods for more difficult shots than for easier shots. However, in the current study, there was a significant difference between the number of fixations made during the preparation phase of sloped and flat putts. The golfers made more fixations to different target locations in the sloped condition, presumably reflecting their search for the abstract target toward which they would aim. These results suggest that a sufficiently long quiet eye period is the decisive visuomotor measure for ensuring a successful putt and that aiming fixations are not as critical. This is somewhat surprising, as it may be expected that on sloped putts, both the accuracy of the aim and of the strike (as guided by the quiet eye period) would be important. The result might be explained by the uniformly sloped putts in the current study not requiring the same attention as a putt with additional contours and breaks as may occur on an outdoor green. Also, given that participants
7 QUIET EYE, AIMING, AND GOLF PUTTING 561 took five putts in each condition, some familiarity with the slope may have undermined the attention placed on the aiming process for the latter putts in each condition. However, support for the finding that gaze behavior during the preparation phase may not be related to subsequent performance is found in Pelz (1994, 2000). Pelz suggested that most golfers do not actually putt the ball along the line they read but significantly underestimate the amount of borrow required. As Pelz measured green reading by having golfers roll balls down a rail which they lined up to their abstract target, the extent to which these findings are ecologically valid or representative may be questioned. However, he suggested that golfers have to compensate for this under-read during their preparation of the stroke. The quiet eye period may reflect the critical processing required to accomplish this. From a practical point of view, it can be expected that a longer than optimal quiet eye period will not have additional value in terms of preparing the motor response and may indeed be counter-productive. First, there are practical limits to the length of the quiet eye period in most aiming tasks, given postural and attentional fatigue factors (see Behan & Wilson, 2008). Second, by spending too long over a putt, distracting thoughts may intrude and impair the processing of task-relevant information. Research by Wilson, Smith, and Holmes (2007) showed highly anxious golfers took longer over their putts under pressure and had poorer performance than less anxious golfers in a putting task. However, an optimal quiet eye period should actually help protect against intrusive thoughts by directing attention externally (as opposed to internally) to a single taskrelevant location. This process-oriented attention should help golfers focus on what can be controlled: the quality of the ball strike, rather than the outcome of the putt. A final point relating to the golfers gaze behavior is that there were individual differences in the specific gaze-strategies adopted. These differences were evident in the specific locations fixated and the scan paths (the order in which these locations were fixated upon) followed. For example, there were differences in the ways golfers linked fixations to the target area (around the hole) and the ball, either making a rapid saccade between the two targets or travelling back along an imaginary putting line. One golfer checked his feet placement and clubface alignment more regularly than other participants during the aiming phase, and one participant made use of midway target fixations as well as hole-side fixations. Despite these differences, it is evident that the final aiming fixation on the ball, prior to the initiation of the putting stroke (i.e., the quiet eye), distinguished between successful and unsuccessful performance. To conclude, the current research extended the previous work of
8 562 M. R. WILSON & R. C. PEARCY Vickers (1992), by examining the quiet eye period in straight and breaking golf putts, as well as examining the gaze behavior during the preparation phase of the putt (reading the line). Results were generally supportive of the importance of maintaining a sufficiently long quiet eye period prior to and during the execution of the putt; however, further research is required to corroborate these findings over various types of breaking putt. Subsequent applied research may investigate the benefits of a structured quiet eye training program for golf putting (see Vickers, 2007, for examples of quiet eye training in other tasks). REFERENCES Behan, M., & Wilson, M. (2008) State anxiety and visual attention: the role of the quiet eye period in aiming to a far target. Journal of Sports Sciences, 26, Delay, D., Nougier, V., Orliaguet, J-P., & Coello, Y. (1997) Movement control in golf putting. Human Movement Science, 16, Karlsen, J., Smith, G., & Nilsson, J. (2008) The stroke has only a minor influence on direction consistency in golf putting among elite players. Journal of Sports Sciences, 26, Pelz, D. (1994) A study of golfers abilities to read greens. In A. J. Cochran & M. R. Farrally (Eds.), Science and golf: II. Proceedings of the 1994 World Scientific Congress of Golf. London: E. & F. N. Spon. Pp Pelz, D. (2000) Dave Pelz s putting bible. London: Aurum. Vickers, J. N. (1992) Gaze control in putting. Perception, 21, Vickers, J. N. (1996) Visual control when aiming at a far target. Journal of Experimental Psychology, 22, Vickers, J. N. (2007) Perception, cognition and decision training: the quiet eye in action. Champaign, IL: Human Kinetics. Williams, A. M., Singer, R. N., & Frehlich, S. G. (2002) Quiet eye duration, expertise, and task complexity in near and far aiming tasks. Journal of Motor Behavior, 34, Wilson, M., Smith, N. C., & Holmes, P. S. (2007) The role of effort in moderating the anxiety-performance relationship: testing the conflicting predictions of processing efficiency theory and the conscious processing hypothesis. British Journal of Psychology, 98, Accepted September 28, 2009.