very close to the centre line on a blind bend might be more likely to occur than encountering a broken down vehicle, the probability of occurrence is still likely to be relatively low. It is possible that the less cautious behaviour of the experienced riders on the right bend hazards reflects that they have ridden around numerous real life bends without encountering such a situation. Therefore, while training leads to an increase in the representation of right bend hazards and a potential over-estimation of the probability of these hazards occurring, experience leads to a decrease in the representation of these hazards with infrequent exposure. Unfortunately, this means that novices’ cautious behaviour on right bends is likely to diminish as increasing experience confirms that encountering oncoming traffic close to the centre line on a blind bend is relatively rare. The advanced riders however have been ostensibly primed for such low frequency events through their advanced training, thus evoking a shallower racing line that does not sacrifice visibility through the curve. As advanced riders have similar levels of experience (and presumably similar levels of probability estima- tion) as the experienced group [25], the training has either over- ridden their experience-based estimate of probabilities, or has introduced a completely different consideration such as the severity of the outcome. Certain facts pertaining to the outcome of motorcycle collisions might be sufficient to engender more cautious riding, even though the probability of a particular event could still be only 1:100,000. In both the left and right non-hazard bends, similar behavioural patterns were noted across the groups as were found in the hazard bends. For instance, there were no group differences in the speed that riders adopted for non-hazard bends. Speed tended to increase across all non-hazard bends (excluding the final post- hazard bend), suggesting that the more bends the riders encountered, the more comfortable they felt at higher speeds. As with the hazard bends, group differences on the non-hazard bends only became apparent in the analyses of lateral position. While all riders adopted a racing line, moving from the outside of the curve to the inside, the experienced riders, and to a lesser extent the novice riders, made early shifts of lateral position of significant magnitude. The lateral shift was so extreme that the experienced and novice riders tended to plateau before the apex of the curve, reaching a position that they presumably felt was the closest line they could take. In contrast, the advanced riders made small and continuous shifts through the majority of the curve sections, always remaining further towards the outside of the bend than the other groups through the majority of the curve. By the time the advanced riders had reached the exit spiral however, they had reached the same lateral position as the other two groups, or had moved even further to the inside. It is this safer behaviour in the early part of the bend that provided the advanced riders with the best positioning when they subsequently encountered the hazards. Encountering a hazard on L2B3 appeared to influence some measures of rider behaviour on the following bend (L2B4). For instance, speed tended to increase from L1B2 to L1B4 and from L1B2 to L2B2 suggesting that practice in negotiating the bends occurred within and between the laps. The bend immediately following the hazard (L2B4) did not follow the same pattern however: instead of showing an increase in speed there was a slight decrease. It is a possibility that the riders had reached a ceiling in regard to choosing a comfortable speed to navigate the bend, or alternatively it might be argued that the failure to increase speed on L2B4 merely reflects the fact that riders had already decreased speed significantly in L2B3 and therefore had not had time to accelerate back up to the higher speeds. We argue against this on Motorcyclist Behaviour on Bends the basis that the circuit was designed such that the bends could be taken safely at 55 mph to 60 mph (if the rider was confident enough) and that there was sufficient distance from bend 3 and bend 4 that the motorcycle could enter bend 4 at a higher speed than bend 3. Despite these precautions, it is still possible that the riders reached a subjective ceiling for speed, rather than an objective one. The lack of group differences in these interactions however renders them less interesting than the impact of the left bend hazard on the lateral position of riders on the subsequent post- hazard bend. The novice riders appeared to reposition themselves further towards the outside of the final left-hand bend after encountering the hazard. Advanced riders did not appear to need to reposition themselves on the final bend following the hazard. Prior to the hazard, the advanced riders had already illustrated that their positioning on the left L1B2 was undesirable, and thus moved further out on the subsequent bend (L1B4). This iterative calibration of their lateral position ensured that they adopted the most appropriate line on the hazard bend. While the novices also reassessed their lateral position, they were presumably insensitive to the more subtle cues picked up by the advanced riders in L1B2, and needed to encounter the more salient hazard before the error of their lateral position became apparent to them. Of most concern however is that the experienced riders did not change their lateral position on the final bend after experiencing the hazard. Overall the behaviour of the advanced riders fitted our predictions. While they did not differ in speed from the other groups, they took a safer approach to bends with a shallower racing line that optimised vision and progression, resulting in them being in a more appropriate position when the hazard appeared. Furthermore, there is a suggestion that they modified and recalibrated their position on the bends, presumably due to feedback from subtle cues and a continuous improvement strategy which comes from their advanced training. Experts in other domains have been found to be able to predict complex events from subtle cues that might be invisible to the non-expert. Fire- fighters use subtle cues from the movement of smoke to identify the source of a fire, radiologists discern cancer from slight variations in shadow, and presumably, expert motorcyclists can use subtle distinctions in optic flow, visibility and heading to realise that they have missed their optimal line through a curve (see [28] for an overview of non-transport related examples). The novice riders were also sensitive to risk, demonstrating relatively cautious behaviour on right-hand bends and appearing to learn from their positioning errors on the left-hand bends after encountering the hazard. Judging by the performance of the experienced riders however, we should be concerned that the caution adopted by the novice riders will eventually dissipate with increasing experience, and be replaced with a tendency to favour progression over safety. That experienced riders did not modify their approach to the post- hazard bend suggests that their devotion to progression negated the impact of the hazard (even though they had to make the most significant shift in position to avoid it). Current work in our laboratory is assessing whether this might be related to an attribution error in assessing blame for the near collision. Early results do indeed suggest that experienced riders are more likely to externalise blame, which possibly allows them to rationalise away any need to change their own behaviour. In contrast, the advanced riders tended to adopt internal attributions [25]. Hoffman and Fiore [28] argue that expertise requires perceptual relearning. Essentially this means to override previous mappings between visual cues and responses that may have been built up through general exposure and experience, and replace PLoS ONE | www.plosone.org 15 January 2012 | Volume 7 | Issue 1 | e29978