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Perceptual and Motor Skills 2009 ... The mechanics of the putting stroke have received much attention ... a motor response (later defined as the quiet eye; Vickers, 1996) has been ..... From a practical point of view, it can be expected that a longer than ... eye training program for golf putting (see Vickers, 2007, for examples of.
Perceptual and Motor Skills, 2009, 109, 1-8. © Perceptual and Motor Skills 2009

VISUOMOTOR CONTROL OF STRAIGHT AND BREAKING GOLF PUTTS1 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) Tour2 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 Address correspondence to Dr. Mark Wilson, School of Sport and Health Sciences, University of Exeter, St. Luke’s Campus, Exeter EX1 2LU, UK or e-mail ([email protected]). 2 PGA Tour Putting Statistics. (2009) Retrieved May 24, 2009, from PGA Tour web site: http:// www.pgatour.com/r/stats/info/?405. 1

DOI 10.2466/PMS.109.2.

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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.

QUIET EYE, AIMING, AND GOLF PUTTING

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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 12.5. 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-

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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 (F2,122 = 12.33, p