مهارت های بزرگسالان جوان رانندگی با اختلال هماهنگی رشدی: سرعت تنظیم و مقابله با حواس پرتی

Abstract In two experiments, we used an automatic car simulator to examine the steering control, speed regulation and response to hazards of young adults with developmental coordination disorder (DCD) and limited driving experience. In Experiment 1 participants either used the accelerator pedal to regulate their speed, or used the brake pedal when they needed to slow down from a pre-set speed. In Experiment 2, we introduced an auditory distraction condition that shared similarities with maintaining a conversation. Overall, the DCD group produced a larger variance in heading and needed more steering adjustments on straight roads, compared to age-matched controls. When turning bends, the DCD group showed greater difficulty in controlling steering while regulating their speed with the accelerator pedal but this was less problematic when using the brake. The DCD group also responded slower than the control group to pedestrians who walked towards their path. The auditory distraction in Experiment 2 had no visible effects on steering control but increased the reaction times to pedestrians in both groups. We discuss the results in terms of the visuomotor control in steering and the learning of optimal mappings between optic flow and vehicle control.

. Introduction Driving is an important skill learned in late adolescence and early adulthood that contributes substantially to feelings of independence. It facilitates interactions with peers and can be instrumental in securing employment and in pursuing further education. For the small portion of people who suffer from developmental coordination disorder (DCD), however, driving a car may appear to be a considerable challenge. According to the diagnostic criteria set by international organisations, individuals with DCD show impaired control of voluntary motor activity in the absence of a known medical condition or pervasive developmental disorder, which impacts negatively on their activities of daily living (APA, 1994 and WHO, 1993). Much research has been dedicated to the identification of children with DCD and to therapeutic programmes aimed at ameliorating their symptoms (e.g., Gibbs et al., 2007 and Schoemaker et al., 1994), but there is far less research into the specific difficulties these individuals present when reaching adulthood (Cantell et al., 2003 and Losse et al., 1991). Difficulties in learning to drive have been linked with general coordination problems (Cousins and Smyth, 2003 and Missiuna et al., 2008) so it is not surprising that young adults with coordination difficulties mention learning to drive as one major source of concern (Losse et al., 1991). The sparse existing studies that mention driving, show that individuals with DCD are less likely to learn to drive than their age-matched control peers, or drive fewer miles per week (Kirby, Sugden, & Edwards, in press), and perceive themselves to be less competent drivers (Missiuna et al., 2008). Learning to drive may be particularly difficult for individuals with DCD for two reasons. First, spatial perception, sequencing and dual-tasking, are all crucial to driving and previous research on individuals with DCD has pointed out general difficulties on all these abilities (e.g., Wilmut and Wann, 2008, Wilmut et al., 2006 and Wilson and McKenzie, 1998). Such abilities are required for instance in perceiving the approach speed to an upcoming bend or selectively allocating attention to road hazards. Secondly, driving is a complex skill and one that does not lend itself to break-up into simpler sub-components that might facilitate learning. For instance, it requires the simultaneous control of both steering and speed. In Fig. 1 we offer a schematic representation of the three mechanisms involved in vehicle control. There is a mechanical coupling linking steering wheel and heading direction, which depends on the vehicle's characteristics (e.g., wheel base and turning arc). There is an optical coupling linking heading direction and the visual information available to the driver, or optic flow, which depends on the laws of optics and include travelling speed (Gibson, 1958). Finally there is a visuomotor link between optic flow and steering control, which depends on the human's ability to detect the relevant properties from optic flow and to implement an action that corrects any undesirable state and brings about a desired optic flow pattern (Wann & Wilkie, 2004). Importantly, the mapping between the steering actions and the optic flow pattern is bidirectional and dependent on speed control (de Oliveira et al., 2009). While driving on a straight road, one mainly needs to maintain heading direction using small steering adjustments and speed is adjusted on a less frequent basis, but in preparing for an upcoming bend one must regulate the speed to enable the effective execution of steering actions that will change direction in a timely manner. We were interested in the ability of individuals to exercise control over steering and speed, while at the same time, selectively attend to road hazards. Schematic illustration of the couplings involved in vehicle control. Mechanical ... Fig. 1. Schematic illustration of the couplings involved in vehicle control. Mechanical and optical couplings control two of the interactions and the human operator establishes the mapping between the steering actions and optic flow including speed regulation. The two-way arrow at the bottom of the figure illustrates the bidirectional mapping between steering and optic flow. The diagonal broken lines illustrate that the system may operate across different dynamic timescales, so this could be a small triangle representing short iterative adjustments, or operate over a longer time frame with less frequent adjustments. There is evidence to suggest that individuals adopt their own dynamic timescales for steering control and errors can occur when they are forced to operate under a different timescale (Fajen, 2008 and Wilkie et al., 2008). Figure options Thus, in the present study we examine the skills of young adults with DCD in the context of driving along straight roads and also when turning bends. In the first experiment we manipulate the mechanism for speed regulation by having participants use only the accelerator pedal to control their speed or by having participants use only the brake pedal to decelerate from a pre-set speed when they deem it necessary. In the second experiment we maintain the use of the brake pedal and manipulate the existence of an auditory distraction that shares similarities to conversing while driving. The dependent measures we adopted were, within steering control, the ability to keep to a straight path (i.e., heading variance) and the amount of iterative corrections to heading (i.e., number of steering adjustments), within speed regulation, the preferred travelling speed and the moment when participants started decelerating before entering a bend, and within responses to hazards, the time to react to pedestrians who walked towards the path of the driver. To study these factors we created a virtual environment with a set of city roads where we could record measures of vehicle control, as well as the responses to pedestrians. The main aim of this study was to assess the driving skills of young adults with DCD and examine specific contexts and conditions that may facilitate or hamper their performance.

. Results 3.1. Experiment 1 We examined the effect of different speed control mechanisms, i.e., using the accelerator vs. the brake pedal to control speed, on the ability to maintain steering control, regulate speed and respond to pedestrians. 3.1.1. Steering control 3.1.1.1. Heading variance Both on the straights and on the bends, there were significant main effects of group because the DCD group showed significantly larger heading variance than the TD group (see Table 1 and Fig. 3). On the bends, there was an additional main effect of pedal condition as well as a Pedal Condition × Group interaction that occurred because the DCD group showed significantly larger heading variance when using the accelerator than when using the brake (94 deg/s2, SE = 11 vs. 62 deg/s2, SE = 6; t(10) = 2.75, p < 0.05, r = 0.38) and also significantly larger variance in the accelerator condition than the TD group, t(10) = 2.40, p < 0.05, r = 0.35 (TD accelerator = 55 deg/s2, SE = 11, TD brake = 48 deg/s2, SE = 6). On the straights there were no significant effects of pedal condition or Pedal Condition × Group interaction on heading variance. Table 1. All statistically significant main effects and interactions for Experiments 1 and 2 (p < 0.05). Measures Factors Experiment 1 Experiment 2 Straights Bends Straights Bends F(1,21) ηp2 F(1,21) ηp2 F(1,21) ηp2 F(1,21) ηp2 Steering control Heading variance Group 17.63 0.46 5.55 0.21 8.32 0.28 Condition 10.94 0.34 Condition × Group 4.71 0.18 Steering adjustments Group 15.92 0.43 6.22 0.23 14.11 0.40 5.64 0.21 Speed regulation Average speed Condition 17.35 0.45 6.81 0.25 Deceleration before bend Condition 36.30 0.63 na na na Condition × Group 4.84 0.19 Pedestrians Response to pedestrians Group 10.36 0.33 na 5.78 0.22 na Condition 9.03 0.30 Conditions were the pedal condition in Experiment 1 (accelerator vs. brake pedal), and distraction condition in Experiment 2 (auditory distraction vs. no-distraction). Effect sizes are reported as partial eta squared. Empty cells mean the effect was not statistically significant, whereas na means the analysis was not performed. (See supplementary material for this table complete with non-significant results.) Table options Steering control in Experiment 1 under the accelerator and the brake pedal ... Fig. 3. Steering control in Experiment 1 under the accelerator and the brake pedal conditions. The left panel shows the average heading variance (deg/s2) for both groups on straights and bends. The right panel shows the number of steering adjustments for both groups on straights and bends (to turn a bend smoothly only 1 steering adjustment is needed). Data of the TD group is shown as open symbols and data of the DCD group is shown as filled symbols. Triangles are data from the straights and circles are data from the bends. Bars represent the standard errors of the mean. Figure options 3.1.1.2. Steering adjustments Both on the straights and on the bends, there were significant main effects of group on the number of steering adjustments because the DCD group used more than the TD group. There were no significant effects of pedal condition or Pedal Condition × Group interaction. 3.1.2. Speed regulation 3.1.2.1. Average speed On both the straights and on the bends, there were no significant main effects of group on the average speed. The main effects of pedal condition occurred because participants drove faster in the accelerator than in the brake condition. On the bends the average speed was 11 m/s (accelerator = 12 m/s, SE = 0.5; brake = 11 m/s, SE = 0.3). On the straights the average speed was 15 m/s (accelerator = 16 m/s, SE = 0.5; brake = 14 m/s, SE = 0.2). There were no Pedal Condition × Group interactions. In mph, the driving speed on the bends was 25 mph (speed difference between accelerator and brake pedals was 2 mph) and on the straight roads it was 34 mph (speed difference between accelerator and brake pedals was 4 mph). 3.1.2.2. Deceleration time before bends There was no main effect of group on the deceleration time before the bends. There were main effects of condition and significant Pedal Condition × Group interaction. While both groups started decelerating sooner in the accelerator condition and later in the brake condition, the difference in timing was considerably less pronounced in the DCD group (see Fig. 4). Speed regulation in Experiment 1 under the accelerator and brake pedal ... Fig. 4. Speed regulation in Experiment 1 under the accelerator and brake pedal conditions. The left panel shows the average speed (m/s) and the right panel shows the deceleration time before bends (s; larger values mean more preparation time before entering a bend). Data of the TD group is shown as open symbols and data of the DCD group is shown as filled symbols. Triangles are data from the straights and circles are data from the bends. Bars represent the standard errors of the mean. Figure options 3.1.3. Response to pedestrians 3.1.3.1. Reaction time to pedestrians The significant main effect of group showed that the DCD group was slower than the TD group in reacting to pedestrians who walked towards their path (DCD = 752 ms, SE = 33; TD = 607 ms, SE = 31). There were no significant effects of pedal condition or Pedal Condition × Group interaction. 3.2. Experiment 2 We examined the effects of an auditory distraction on the ability to maintain steering control, regulate speed and respond to pedestrians. We used the brake condition from Experiment 1 which appeared to be the easiest for the DCD group in terms of speed regulation and steering control, with the addition of a distraction condition where participants were instructed to respond verbally to the odd numbers they heard (see Section 2.3). 3.2.1. Steering control 3.2.1.1. Heading variance On the bends, there were no significant main effects or interaction. On the straight roads, there was a significant main effect of group on heading variance because the DCD group used larger excursions of the steering wheel than the TD group (DCD = 19°/s2, SE = 3; TD = 8°/s2, SE = 3). In addition, there were no effects of distraction condition or Distraction Condition × Group interaction. 3.2.1.2. Steering adjustments Both on the straights and on the bends, there were significant main effects of group on the number of steering adjustments because the DCD group used more than the TD group. There were no significant effects of distraction condition or Distraction Condition × Group interaction. 3.2.2. Speed regulation 3.2.2.1. Average speed In this second experiment speed was not continuously controlled, but could be reduced by using the brake. As might be expected there were no significant effects of group, distraction condition or interaction. The overall speed on the straight roads was 14 m/s (SE = 0.3) and on the bends it was 11 m/s (SE = 0.4), directly equivalent to Experiment 1. In mph, the driving speed on the bends was 25 mph and on the straight roads it was 31 mph. 3.2.3. Response to pedestrians 3.2.3.1. Reaction time to pedestrians There was a significant main effect of group. This was because the DCD group was slower than the TD group in reacting to pedestrians who walked towards the road (DCD = 793 ms, SE = 40; TD = 659 ms, SE = 39). The main effect of distraction condition occurred because both groups reacted slower under the auditory distraction condition. The DCD group reacted 71 ms slower (829 ms vs. 758 ms) and the TD group reacted 118 ms slower (724 vs. 594). There was, however, no significant Distraction Condition × Group interaction.