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The study was carried out in accordance with the ethical review policy of Nottingham Trent University and approved by the School of Animal, Rural and Environmental Sciences Ethical Monitoring Group. Informed written consent for participation was obtained from participants. The horses were ridden according to NTU Equestrian Centre guidelines and were deemed fully able to carry out the exercises with ease. As such this was not a regulated procedure (Animals in Scientific Procedures Act 1986) and did not contravene the Animal Welfare Act 2006. The horses were owned by Nottingham Trent University or loaned under contract for use by the university in ridden work for any purpose. Nottingham Trent University gave permission for the use of the horses in this study.
The gaze behaviour of ten female riders was recorded. The riders were staff at the Nottingham Trent University Equestrian Centre, each with over 15 years riding experience and aged between 22 and 45 years (mean age 32 years). Their jumping skill was assessed by self-report (see below for details). The horses ridden were regularly used in the riding school and were all used for jumping lessons for riders of various levels of ability (mean height 167.13 cm, mean age 14.8 years). Each horse was ridden by two riders.
A 5×3 within-subjects design was employed comparing rider gaze behaviour across five rounds over three fences. Features of gaze behaviour were recorded (timing, location and duration of position of gaze) and the effects of round and jump number and of the skill level of the rider on this visual behaviour were assessed. The number of errors made at each jump was also recorded. A questionnaire was used to assess the skill level of the riders. The questionnaire was adapted from that used by Hall, Liley, Murphy and Crundall [11] and incorporated questions relating to jumping skill level (see Table 1). The questionnaire scores were then used as a measure of rider skill.
Table data removed from full text. Table identifier and caption: 10.1371/journal.pone.0097345.t001 Questionnaire used for rider self-reported assessment of competitive experience. Table showing the questions, optional responses and associated scores used to calculate the self-reported jumping skill of the riders.
The course of jumps was set up at in an indoor riding arena (40 m×55 m) with a silica sand wax and fibre mix surface (Softrack). The course consisted of three almost identical jumps (the only difference was that jump 1 and 3 had white supporting stands and jump 2 had black supporting stands). The course and practice jump were situated in one side of this arena in an area of 20 m×55 m which had been sectioned off by means of a central white plastic barrier 1.20 m in height. The jumps conformed to BSJA specifications and were produced by Jump 4 Joy. The jump cups were (FEI) approved safety cups also made by Jump 4 Joy. Each jump was an upright consisting of two black and white striped rails (straight poles resting on jump cups at 0.40 m and 0.70 m from the ground respectively), the overall height of which was 0.725 m, the overall width 4.00 m. The first and third jumps were placed at 90° to the long side and central barrier of the arena respectively. The second jump was placed across the diagonal in between the other two. All three jumps were situated in a line across the arena, 24 m from the end wall. The riders approached the first jump on the right rein, turned right to jump the second jump and then left over the third. The practice fence (a cross pole with a central height of 0.45 m) was positioned centrally and in parallel with the long side/central barrier at the opposite end of the arena to the test course. The test area, course of three jumps and the practice jump are shown in Figure 1.
Figure data removed from full text. Figure identifier and caption: 10.1371/journal.pone.0097345.g001 Test arena, course of 3 trial jumps and practice jump.The test area, three trial jumps and the practice jump are shown. The blue and yellow jump in the foreground was used as the practice jump. The course was approached from this end with the jump on the left being jumped first, followed by a right turn across the diagonal (jump 2) and then a left turn to approach jump 3 (adjacent to the white barriers).
A mobile eye tracking device (Applied Science Laboratories (ASL), Bedford, USA: Mobile Eye), was used to monitor the gaze behaviour of the riders. This required the rider to wear a spectacle-mounted unit (SMU: consisting of a scene camera and an eye camera) which was attached via the recorder mounted unit (RMU) to a digital video cassette recorder (DVCR) housed in a backpack worn by the rider. The ASL Mobile Eye recorded data at 60 Hz by interleaving images taken from the two cameras. The eye camera recorded the eye being tracked whilst the scene camera recorded the environment being observed by the wearer. Both image streams were recorded on the same digital videotape medium by alternating frames and position of gaze (POG) was shown by a red cursor and was recorded every frame of video or 33.33 milliseconds. A purple circle appeared within the frame and indicated that the pupil had been identified [13]. See Figure 2 for an example of scene camera/POG cursor as recorded during these trials (the resolution of this image is that recorded by the scene camera and cannot be improved).
Figure data removed from full text. Figure identifier and caption: 10.1371/journal.pone.0097345.g002 Frame showing POG cursor (red circle) and pupil indicator (purple circle) on jump approach.Frame taken from the ASL Mobile Eye recording showing POG (red circle) and pupil indicator (purple circle) as a rider approaches a jump. The image was taken from footage from the eye tracker and consequently the resolution of the image is limited. The frame provides an example of the information recorded by the equipment and the gaze behaviour measures were calculated using frame by frame analyses.
The Mobile Eye used a technique of eye tracking known as dark pupil tracking, which uses the relationship between two eye features, the pupil and a reflection from the cornea to compute gaze within a scene. Calibration of the equipment was carried out to determine the POG of each individual. The POG was calibrated every time the Mobile Eye was fitted to ensure that small differences in spectacle position did not affect the recording [13]. The equipment and calibration was checked repeatedly throughout the trials because of the movement associated with riding a horse over jumps and with mounting initially. An x-point calibration was performed with calibration points (N = 10) located at varying heights and planes of motion. The calibration of the spot cluster and pupil display settings of the equipment were checked before the rider mounted, then once the rider had mounted, after the warm-up period and practice fence and after each round within the trial session.
Within the test session the rider was fitted with the eye tracking device before mounting the horse and the initial POG calibration was carried out. The rider then walked the course of jumps while wearing the equipment to ensure that they were not adversely affected by it. After mounting the horse the equipment was checked to ensure that the eye and scene cameras were in the correct position and a second POG calibration was carried out. The rider then prepared the horse on the flat before jumping the practice fence twice in each direction. The eye tracking equipment was then re-checked before the rider jumped the test course (test course jumps shown in Figure 1). The course was jumped five times by each rider, who returned to have the equipment re-checked in between each round. Each rider jumped a total of 15 jumps within the session. Jumping errors were recorded and a score allocated (similar to the faults system in show jumping). If the pole was knocked but did not fall a score of 2 faults was allocated; a pole that was knocked down scored 4 faults. The maximum error that could be scored was 60 points. Total scores for each rider were calculated for each jump number and for each round number for comparison with gaze data.
Gaze Data Collection and Analysis: EyeVision data processing software was used to calibrate POG from the recorded data and the data stream for each of the ten riders was recorded from the DVCR using EyeVision for identification of POG. The location of POG was recorded for each frame as being either on the jump (defined as part or all of the gaze cursor being located on the jump or on the area between the two poles), on the ground (any area of the ground in front, to the side of or beyond the jump), or on other (which included all other locations within the scene, for example, the horse, arena wall, mirror, people, gallery and other jumps). Frames in which no gaze cursor was visible were recorded as no eye. In order to capture all of the visual behavior associated with the jump being approached POG location was recorded starting with the frame in which the jump in question was first visible on the scene camera and finishing when the jump pole disappeared from view. Following frame-by-frame analysis the number of consecutive locations of the POG on the jump was recorded. Minimum fixation duration was 100 ms (≥3 frames) as specified by Vickers and Adolphe [9] and defined as stabilization of the gaze on the jump. The number and duration of each fixation was calculated for each rider/round/jump combination. The timing of the start of the first fixation on the jump, the longest fixation and the offset of the final fixation on the jump was calculated. To take account of potential differences in the speed of approach, the number of canter strides taken by the horse during the approach time was counted from the scene camera footage (to the nearest stride) and the speed of each approach calculated from this as the number of strides per second. If the approach time had included trot then the speed was calculated from the time when the first canter stride occurred. This speed was used to calculate the number of strides from the jump that the first, longest and the offset of the final fixation on the jump occurred. The total duration of all fixations on the jump was assessed and calculated as a percentage of the approach time. The percentage of approach time when the POG was located on the jump for <100 ms (saccades) was calculated. The percentage of approach time where the POG was located on the ground, other or no eye was recorded was also calculated. The minimum number of strides recorded for any rider during the approach was identified as being five strides. To allow consistent comparison of the riders, regardless of their speed, their gaze behaviour during the last five strides of the approach to the jump was also analysed. The number and mean duration of fixations during the last five strides of the approach were calculated. If the first stride commenced mid fixation on the jump this fixation was included in the number and the duration was included in the calculation of the mean fixation duration. However, only frames within the stride window were included in the calculation of the percentage of time spent fixated on the jump. Percentages of time spent with POG on the ground, other and no eye were also calculated for the last five strides. The timing and duration of the first, longest and final fixation on the jump were calculated as a means of further assessing the visual strategy used by riders during the approach to the jump. If there was more than one fixation at the longest duration then the one closest to the take-off point was counted. When the percentage of missing data (no eye recorded) was calculated it was found that during the overall approach no eye was recorded for an average of 21.39±12.80% of the time and during the last five strides for an average of 20.05±4.65%. It could not be assumed that when no eye was recorded the rider was not looking at the jump and subsequently correlations with rider skill that included only trials where no eye was recorded for ≤20% of the approach time were investigated. This resulted in between 0 and 15 trials being included for each rider for the overall approach (a total of 84; 56% of all trials). For the analyses for the last five strides this also resulted in between 0 and 15 trials being included for each rider (a total of 88; 58.67%). No data from the lowest scoring rider could subsequently be included in either of the analyses. The distribution of the data was assessed for normality using the Kolmogorov Smirnov test and subsequently parametric and non-parametric analyses were conducted. Correlations between rider skill level, errors made and the measures of gaze behaviour were investigated (Spearman’s Rank Order Correlation). The effect of round and jump number on the speed and time of the approach, and on each measure of gaze behaviour during the overall approach and during the last five strides of the approach to the jump was assessed (two-way within subjects ANOVA). Pair-wise comparisons adjusted for multiple comparisons (Bonferroni) were subsequently conducted. The effect of round and jump number on jump errors made was also assessed (Friedman’s test) with subsequent pair-wise comparisons (Wilcoxon test). Analyses were carried out using SPSS version 21.
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