The effect of luminance on simulated driving speed

AbstractPerceived speed is modulated by a range of stimulus attributes such as contrast, luminance and adaptation duration. It has been suggested that such changes in perceived speed may influence driving behaviour. In order to evaluate the effect of luminance on driving speed we have measured subjects’ driving speed in a driving simulator for a range of luminance and speed over time. The results indicate that reducing luminance results in a decrease in driving speed for all speeds measured. This reduction in driving speed at low luminance is consistent with previous findings that perceived speed increases at low luminance. However, the results also indicated that driving speed remained stable over a 30s period. The stability of driving speed over time is inconsistent with previous findings that perceived speed reduces exponentially as a function of adaptation duration. The results are suggestive of a scheme whereby driving speed is consistent with the known effects of luminance upon perceived speed but may also be modulated by higher order processes that serve to maintain a constant speed over time

The effect of session order on the physiological, neuromuscular, and endocrine responses to maximal speed and weight training sessions over a 24-h period

Objectives: Athletes are often required to undertake multiple training sessions on the same day with these sessions needing to be sequenced correctly to allow the athlete to maximize the responses of each session. We examined the acute effect of strength and speed training sequence on neuromuscular, endocrine, and physiological responses over 24 hours. Design: 15 academy rugby union players completed this randomized crossover study. Method: Players performed a weight traiing session followed 2 hours later by a speed training session (WS) and on a separate day reversed the order (SW). Countermovement jumps (CMJ), perceived muscle soreness (MS), and blood samples were collected immediately prior, immediately post, and 24 hours post sessions one and two respectively. Jumps were analyzed for power, jump height, rate of force development, and velocity. Blood was analyzed for testosterone (T), cortisol (C), lactate and creatine kinase (CK). Results: There were no differences between CMJ variables at any of the post training time points (p > 0.05). Likewise, CK, T, C , and MS were unaffected by session order (p > 0.05). However, 10 meter sprint time was significantly faster (Mean ± SD; SW 1.80s ± 0.11 vs. WS 1.76 ± 0.08s; p > 0.05) when speed was sequenced second. Lactate levels were significantly higher immediately post speed sessions versus weight training sessions at both time points (p < 0.05). Conclusions: The sequencing of strength and speed training does not affect the neuromuscular, endocrine, and physiological recovery over 24 hours. However, speed may be enhanced when performed as the second session

Changes in the Dynamics of Postural and Locomotor Control as a Result of Varying Task Demands

The aim of this study was to examine changes in postural and locomotor control under varying task demands. Three experiments were designed to address the impact that fast walking had on standing posture over time, slow walking had on gait dynamics over time, and the extent to which gait speed interacts with the ability to walk randomly. For experiment I, the aim was to identify the time course in which postural adaptation occurred while walking at faster than preferred speeds. Postural motion was assessed at specific intervals over a 35-min walking trial. Findings revealed that walking at a faster speed increased the amount, variability, and structure (Approximate Entropy-ApEn) of postural motion compared to baseline assessments. Subsequent trials following baseline assessments revealed a leveling-off for specific center of pressure (COP) variables and decline in path length, although heart rate (HR) and rate of perceived exertion (RPE) increased over the entire walking trial. In experiment II, the aim was to examine changes in stride-to-stride variability over time while walking at slower than preferred speeds. The results revealed an increased stride-to-stride variability and signal regularity (lower ApEn) during walking at 80% preferred walking speed (PWS) compared to PWS. After 10-15 mins a decrease stride-to-stride variability and increase in signal irregularity was seen. Changes leveled-off for the remainder of the session. Experiment III was designed to examine the effect that intentionally increasing variability (random) had on gait dynamics. Participants were asked to vary their gait while walking on a treadmill at three different speeds. The results revealed gait speed was a significant factor in the amount of variability (CV, range), with higher levels produced during the slower speed than at PWS and the faster speed. Higher levels of complexity (higher SampEn) were seen in stride time and knee joint motion during the random condition irrespective of gait speed. Overall, young adults are able to walk at speeds faster or slower than preferred as well as increase gait variability when instructed. These changes in postural and locomotor dynamics reveal that a healthy motor control system can quickly adapt to the task demands imposed upon it

Stochastic accumulation of feature information in perception and memory

It is now well established that the time course of perceptual processing influences the first second or so of performance in a wide variety of cognitive tasks. Over the last20 years, there has been a shift from modeling the speed at which a display is processed, to modeling the speed at which different features of the display are perceived and formalizing how this perceptual information is used in decision making. The first of these models(Lamberts, 1995) was implemented to fit the time course of performance in a speeded perceptual categorization task and assumed a simple stochastic accumulation of feature information. Subsequently, similar approaches have been used to model performance in a range of cognitive tasks including identification, absolute identification, perceptual matching, recognition, visual search, and word processing, again assuming a simple stochastic accumulation of feature information from both the stimulus and representations held in memory. These models are typically fit to data from signal-to-respond experiments whereby the effects of stimulus exposure duration on performance are examined, but response times (RTs) and RT distributions have also been modeled. In this article, we review this approach and explore the insights it has provided about the interplay between perceptual processing, memory retrieval, and decision making in a variety of tasks. In so doing, we highlight how such approaches can continue to usefully contribute to our understanding of cognition

How speed and visibility influence preferred headway distances in highly automated driving

While the introduction of highly automated vehicles promises lower accident numbers, a main requirement for wide use of these vehicles will be the acceptance by drivers. In this study a crucial variable for the acceptance of highly automated vehicles, the vehicle to vehicle distance expressed in time headway, was researched in a driving simulator. Research has shown that time headway distances, perceived as comfortable in self-driving and assisted driving with adaptive cruise control, remain constant over a range of different speeds. This study aims to test these findings for highly automated driving. Since time headway is perceived visually, the driving situation was varied to investigate the influence of visibility on the subjective comfort of the driver in a highly automated driving situation. In a within-subject design, drivers followed a passenger car in clear weather conditions, the same passenger car in fog which occluded parts of the traffic environment, as well as a truck that occluded the lane ahead, also in clear weather condition. Subjective comfort of drivers in each condition was rated with a haptic rating lever. Results suggest that comfortable time headway following distances in highly automated driving are not constant over different speeds, but that these distances decrease with increasing speed. Reduced visibility generally led to a shift in comfortable following distances towards larger headways. These results have implications for the introduction of highly automated vehicles and their time headway adjustments, which will need to be adaptive to speed and visibility in the road environment

The impact of a fast bowling spell on physiological, perceptual and performance responses in non-elite cricketers

Background: The demands placed on fast bowlers may elicit unique responses that contribute towards increased injury risk and comprised performance capabilities. Despite this, very few investigations have attempted to quantify these demands and their impact on performance in cricketers.Objective: This investigation attempted to quantify the effects of a fast bowling protocol on the musculoskeletal, physiological and perceptual responses of fast bowlers; as well as ball speed and accuracy.Methods: Eight young adult bowlers (20 ± 2 years) participated in a 10-over bowling protocol that had been separated by intermittent fielding drills into three bowling spells respectively (4-, 3- and 3- overs). Selected responses were collected throughout the protocol.Results: Functional strength was measured and showed no change. Heart rate responses increased significantly (p&lt;0.05) at the start of the bowling protocol. Local ratings of perceived exertion increased significantly (p&lt;0.05) as a function of exercise duration, while low to moderate intensities of perceived discomfort were noted in the anterior and posterior shoulder areas, upper portion of the lower limb musculature, as well as in the middle and lower back regions. Performance responses experienced no significant change.Conclusion: There was no significant change in ball release speed and accuracy across the bowling protocol. Lower limb muscle power remained consistent and heart rates reached a steady state after the first over. In comparison, local ratings of perceived effort and body discomfort increased over time, which could mean that those unchanged measures do not accurately reflect fatigue or that perceptions are a more effective indicator of impending fatigue. Keywords: accuracy, speed, heart rate, body discomfort, ratings of perceived exertio

Speeding in urban environments: Are the time savings worth the risk?

Perceived time savings by travelling faster is often cited as a motivation for drivers’ speeding behaviour. These time savings, however, come at a cost of significant road injuries and fatalities. While it is known that drivers tend to overestimate the time savings attributable to speeding there is little empirical evidence on how much time drivers genuinely save during day-to-day urban driving and how this relates to speeding-related crashes. The current paper reports on a study to address the lack of empirical evidence on this issue using naturalistic driving data collected from 106 drivers over a period of five weeks. The results show that the average driver saves 26 seconds per day or two minutes per week by speeding. More importantly, the cost of these time savings is one fatality for every 18,947 hours saved by the population on 100 km/h roads and one injury for every 1,407 hours saved on the same roads. Full speed compliance – and consequently a dramatic reduction in the road toll – could be achieved through almost imperceptible increases in travel time by each driver

Effects of residual fatigue on pace regulation during sprint-distance triathlon running

Introduction: It has been suggested that unique relationships exist between perceived exertion, pacing and physiological responses during triathlon. However, research to date has not clearly established how the interaction of these factors is affected by residual physiological fatigue, particularly during running performance over distances relevant to sprint-distance triathlon. This study therefore investigated the effects of the preceding swim and cycle on pacing strategy, perceived exertion, and physiological status during sprint-distance triathlon running. Methods: Eight amateur male triathletes (mean ± SD: age 36.0 ± 5.7 yrs, mass 75.7 ± 5.3 kg) completed two field-based performance trials. The first was a sprint-distance triathlon (0.75 km swim, 20 km cycle, 5 km run) and the second an isolated 5 km run time-trial, each separated by 7-18 days and utilising the same flat out-and-back road course. Wrist-mounted GPS devices (Garmin 310XT, UK) recorded performance time, running speed (km•h-1) and heart rate during each trial. Participants recorded ratings of perceived exertion (Borg 6-20 scale) every kilometre using a wrist-mounted recording sheet and pen. Core temperature (CorTemp, HQInc, USA), blood lactate concentration (Lactate Pro, Kodak, Japan) and body mass (to 0.1 kg; Seca 875) were also measured immediately prior to, and after, each run. Results: Performance time for isolated running (19:28 ± 00:32) was ~7% quicker than triathlon running (20:48 ± 00:43) (p<0.01), with a similar positive pacing strategy displayed throughout both trials (figure 1). Initial core temperature, blood lactate concentration and heart rate values were all significantly higher for the triathlon run compared to the isolated run (p<0.01), with no differences in final values for these measures. No significant differences were observed for initial RPE, rate of RPE increase, or final RPE between runs. Discussion/Conclusion: Prior swimming and cycling impair performance but do not affect pacing strategy during sprint-distance triathlon running. Reduced performance may be attributed to the residual physiological strain observed at the start of the triathlon run. However, the maintenance of scalar-linear increases in RPE appears to be the primary regulator of pacing strategy during triathlon running, with physiological responses only indirectly related to this process