Microstructural and Rheological Transitions in Bacterial Biofilms.

Biofilms are aggregated bacterial communities structured within an extracellular matrix (ECM). ECM controls biofilm architecture and confers mechanical resistance against shear forces. From a physical perspective, biofilms can be described as colloidal gels, where bacterial cells are analogous to colloidal particles distributed in the polymeric ECM. However, the influence of the ECM in altering the cellular packing fraction (ϕ) and the resulting viscoelastic behavior of biofilm remains unexplored. Using biofilms of Pantoea sp. (WT) and its mutant (ΔUDP), the correlation between biofilm structure and its viscoelastic response is investigated. Experiments show that the reduction of exopolysaccharide production in ΔUDP biofilms corresponds with a seven-fold increase in ϕ, resulting in a colloidal glass-like structure. Consequently, the rheological signatures become altered, with the WT behaving like a weak gel, whilst the ΔUDP displayed a glass-like rheological signature. By co-culturing the two strains, biofilm ϕ is modulated which allows us to explore the structural changes and capture a change in viscoelastic response from a weak to a strong gel, and to a colloidal glass-like state. The results reveal the role of exopolysaccharide in mediating a structural transition in biofilms and demonstrate a correlation between biofilm structure and viscoelastic response.

The role of biofilm matrix composition in controlling colony expansion and morphology.

Biofilms are biological viscoelastic gels composed of bacterial cells embedded in a self-secreted polymeric extracellular matrix (ECM). In environmental settings, such as in the rhizosphere and phyllosphere, biofilm colonization occurs at the solid-air interface. The biofilms' ability to colonize and expand over these surfaces depends on the formation of osmotic gradients and ECM viscoelastic properties. In this work, we study the influence of biofilm ECM components on its viscoelasticity and expansion, using the model organism Bacillus subtilis and deletion mutants of its three major ECM components, TasA, EPS and BslA. Using a multi-scale approach, we quantified macro-scale viscoelasticity and expansion dynamics. Furthermore, we used a microsphere assay to visualize the micro-scale expansion patterns. We find that the viscoelastic phase angle Φ is likely the best viscoelastic parameter correlating to biofilm expansion dynamics. Moreover, we quantify the sensitivity of the biofilm to changes in substrate water potential as a function of ECM composition. Finally, we find that the deletion of ECM components significantly increases the coherence of micro-scale colony expansion patterns. These results demonstrate the influence of ECM viscoelasticity and substrate water potential on the expansion of biofilm colonies on wet surfaces at the air-solid interface, commonly found in natural environments.

Protected and unprotected cycle lanes' effects on cyclists' behaviour.

Previous research has suggested that in countries with low cycling rates, a barrier to cycling is the perception that cycling is unsafe. Unfortunately, this perception is accurate in many places, and protected cycle lanes have been advocated as a possible solution. Although some research shows that people tend to feel safer in them, there have been conflicting results regarding protected cycle lanes' safety benefits. Understanding the reasons protected cycle lanes may actually reduce safety is key to promoting active transport modes. One possible reason crash rates may increase is that cyclists may cycle faster in them due to either a decreased mental workload or from reduced perceptions of risk. In the present research, two studies were conducted to examine cyclists' speeds and perceptions of difficulty and safety in both protected and unprotected cycle lanes, as well as streets with no cycle lanes. The first study was an online questionnaire using short video clips from a cyclist's perspective, and the second study was an on-road experiment with a post-ride questionnaire. The studies found that cyclists felt safer with protected cycle lanes, were more willing to allow their children to bike on them and showed less concern towards hazards. There was no evidence of decreased attentional demand while using the protected cycle lanes, but there was some evidence of higher maximum cycling speeds.

The role of prior sleep for divergent thinking in infants.

Higher-order cognitive functions seem particularly vulnerable to disruptions in prior sleep in school-aged children and adult populations. This study tested whether divergent thinking in infants varied as a function of prior sleep. Forty-three infants aged 13-16 months participated in a behavioural assessment of divergent thinking. Length of wakefulness since last sleep was experimentally manipulated. In addition, potential relations between divergent thinking and sleep quantity and quality during the night immediately before the assessment, as well as during three consecutive nights preceding the assessment, were examined using actigraphy recordings in combination with parent diaries. Divergent thinking was not impaired by lack of sleep within the previous 4 h. Divergent thinking was consistently related to night-time sleep quality and quantity prior to the assessment. These results suggest that timing of prior naturally occurring daytime sleep is less relevant for emergent divergent thinking capacity than quality and quantity of preceding night-time sleep.

Commuting before and after COVID-19.

Major life events like COVID-19 have the potential to change how people think about and use transport systems. The COVID-19 pandemic has created an extended period of disruption in peoples' lives and could result in long-term changes towards travel attitudes, and use of transport services. There has previously been little research available on changes towards travel attitudes and use of domestic travel as a result of pandemics. To investigate the changes in attitudes to travel resulting from COVID-19 we distributed a survey to 787 respondents in Australia and New Zealand asking about car use, car sharing, public transport, and air travel before, during, and after COVID-19 travel restrictions. The results showed attitudes towards travel were negatively affected, particularly attitudes towards public transport and international air travel. Further, although respondents indicated some recovery in attitudes when asked to consider when travel restrictions were removed, they did not recover to the levels of positivity seen pre-COVID. There were slight differences between the two countries in their post-COVID attitudes, possibly due to their different experience of travel restriction. Both countries, however, may be useful as a preview for the rest of the world given the early cessation of the COVID-19 pandemic at the time of the survey.

Co-driving: Passenger actions and distractions.

Approximately one third of car trips involve one or more passengers and yet we know little about how the presence of a passenger helps or hinders safety and efficiency. To date, research in this area has focused on the possible distractive effects of passengers. Although we know that drivers conversing on a mobile phone is distracting and unsafe, epidemiological studies suggest that driving with a passenger has a lower crash risk than driving alone. This paper describes two studies into how drivers and passengers interact during a journey; a survey regarding the most common actions of passengers and how drivers view their helpfulness, and an on-road study of driver and passenger interactions. The results indicated several areas that drivers felt passenger assistance was quite helpful, but in some cases was exhibited very rarely. The on-road study revealed some interesting gender differences in who offers driving support, and who requests it. By understanding how passengers can contribute to safer journeys we can provide that information to drivers at risk, such as those very early or late in their driving careers.

The role of control in risk perception on rural roads.

Risk perception plays an important role in driver behaviour, particularly for speed choice. Risk perception studies use a range of techniques from on-road data collection to ratings of still photos, however participants' ratings differ depending on the study methodology, possibly due to their perception of control. To explore this we conducted a multiple methods study to investigate drivers' perceptions of risk on rural roads. One group of participants drove (Drivers, n = 13) a 180 km route along rural roads (accompanied by a research assistant) and provided verbal risk ratings at thirteen locations of interest. A second group (Passengers, n = 10) provided ratings at the same points when travelling as a passenger in a vehicle (driven by a research assistant). The third group (Observers, n = 14) were shown videos of the same rural roads (filmed from the drivers' perspective) and also provided risk ratings at the same locations. A week later participants were invited to the laboratory to review the video footage and comment on factors that contributed to the risk ratings. Overall, the Observers gave the highest risk ratings and Drivers the lowest. The Observers also provided twice the number of comments to justify their risk rating compared to the other two groups. The results suggest that control, and on-road experience play a significant role in how perceptions of driving risk are formed and the degree of risk experienced. These findings also bring into question the accuracy of using video-based tasks to assess drivers' risk perception (and speed choice), particularly if the findings are used to inform on-road safety interventions.

Inattentional blindness and information relevance of variable message signs.

It has been suggested that Variable Message Signs (VMS) become less effective at communicating important traffic information when irrelevant information is also displayed on them. The purpose of this study was to examine if practice reading irrelevant information on a VMS influenced compliance with, and memory for a detour message. Thirty-nine participants were randomly assigned to one of three groups who drove a simulated road; one receiving only a detour message on the VMS, one group received irrelevant VMS messages before the detour message, and a third group received the same messages but the detour message was inconsistent with their destination. Of interest were both the participants' compliance with the target detour message, as well as their later recall and recognition of the message. The results suggested that, first and foremost, there was significantly lower compliance with the detour message when it had been preceded by irrelevant messages on the VMS. All of the groups showed reasonably good memory for the detour message. The implications of the present study are that presentation of irrelevant messages, including advertisements and safety slogans, may result in reduced compliance to traffic-relevant messages on VMSs.

Nonlinear rheological characteristics of single species bacterial biofilms.

Bacterial biofilms in natural and artificial environments perform a wide array of beneficial or detrimental functions and exhibit resistance to physical as well as chemical perturbations. In dynamic environments, where periodic or aperiodic flows over surfaces are involved, biofilms can be subjected to large shear forces. The ability to withstand these forces, which is often attributed to the resilience of the extracellular matrix. This attribute of the extracellular matrix is referred to as viscoelasticity and is a result of self-assembly and cross-linking of multiple polymeric components that are secreted by the microbes. We aim to understand the viscoelastic characteristic of biofilms subjected to large shear forces by performing Large Amplitude Oscillatory Shear (LAOS) experiments on four species of bacterial biofilms: Bacillus subtilis, Comamonas denitrificans, Pseudomonas fluorescens and Pseudomonas aeruginosa. We find that nonlinear viscoelastic measures such as intracycle strain stiffening and intracycle shear thickening for each of the tested species, exhibit subtle or distinct differences in the plot of strain amplitude versus frequency (Pipkin diagram). The biofilms also exhibit variability in the onset of nonlinear behaviour and energy dissipation characteristics, which could be a result of heterogeneity of the extracellular matrix constituents of the different biofilms. The results provide insight into the nonlinear rheological behaviour of biofilms as they are subjected to large strains or strain rates; a situation that is commonly encountered in nature, but rarely investigated.

Driving With ADHD: Performance Effects and Environment Demand in Traffic.

Objective: This research investigated the on-road driving performance of individuals with ADHD across a range of road and traffic conditions to determine whether errors were linked to situational complexity and attentional demands. Method: The everyday driving performance of medicated drivers with ADHD, unmedicated drivers with ADHD, and controls was tested in urban, residential, rural, and highway environments using driver license testing procedures. Results: Unmedicated drivers with ADHD displayed fewer safe driving skills and committed more inattentive and impatient driving errors, particularly in low demand highway and rural driving conditions. Medicated drivers' performance was not reliably different than controls. Participants in both ADHD groups were more likely than controls to report risky driving and involvement in crashes. Conclusion: The results demonstrate that situations with low attentional demand are particularly risky for unmedicated ADHD drivers and suggest that focus on these situations may be useful in improving driving outcomes for this population.

Regulating, Measuring, and Modeling the Viscoelasticity of Bacterial Biofilms

Biofilms occur in a broad range of environments under heterogeneous physicochemical conditions, such as in bioremediation plants, on surfaces of biomedical implants, and in the lungs of cystic fibrosis patients. In these scenarios, biofilms are subjected to shear forces, but the mechanical integrity of these aggregates often prevents their disruption or dispersal. Biofilms' physical robustness is the result of the multiple biopolymers secreted by constituent microbial cells which are also responsible for numerous biological functions. A better understanding of the role of these biopolymers and their response to dynamic forces is therefore crucial for understanding the interplay between biofilm structure and function. In this paper, we review experimental techniques in rheology, which help quantify the viscoelasticity of biofilms, and modeling approaches from soft matter physics that can assist our understanding of the rheological properties. We describe how these methods could be combined with synthetic biology approaches to control and investigate the effects of secreted polymers on the physical properties of biofilms. We argue that without an integrated approach of the three disciplines, the links between genetics, composition, and interaction of matrix biopolymers and the viscoelastic properties of biofilms will be much harder to uncover.

Mind wandering during everyday driving: An on-road study.

This study was an investigation into mind wandering during everyday driving, and its association with crash patterns. We selected a 25 km route on urban roads for analysis of crashes, and an on-road study of mind wandering by a sample of drivers familiar with the route. We analysed reported crashes on the route over a five year period from New Zealand's crash database. For the on-road study a researcher accompanied 25 drivers on the route, asking them what they were thinking about at 15 predetermined road sections. The road sections were selected to include a range of different speed limits and traffic volumes as well as roundabouts, priority intersections and midblocks. Thought samples were categorised as either mind wandering or driving focus, and triggered by the senses, or internally. The frequencies of mind wandering at different road sections on the route were compared to the frequencies of reported crashes along the same route over the preceding five years. Results showed that although all drivers reported mind wandering, it was more likely to be reported at slower, quieter, less complex road sections. Overall, more crashes were reported at priority intersections and midblocks than at roundabouts, but the crash rate (per road section) was higher at roundabouts, where mind wandering was least likely to be reported. These findings suggest that although drivers' minds wander constantly, driving focus is commanded in demanding situations and in response to the actions of other road users. While mind wandering is ubiquitous, drivers are least likely to report mind wandering at locations showing the highest crash rates. More work is needed to test these findings and to provide direction for road safety interventions.

Transitions within a safe road system.

As drivers move through the road transport system they are exposed to a range of different situations and road conditions in a relatively short space of time. Drivers' expectations about what will happen on different types of roads have strong effects on their speed choices, and where they look and what they attend to. As a result it is important to assist drivers to change their expectations when they transition from one road type to another. In this experiment we investigated the effectiveness of different centreline road markings in preparing for a horizontal curve as drivers moved from a motorway to a two-lane rural country road. Fifty individuals were recruited to participate in a video-based simulated driving task to compare three centreline marking types in terms of their effects on speed choice and reactions to a driving hazard (horizontal curve). Although a complex marking previously associated with high risk produced the largest speed reductions during the transition from the motorway, it was the centreline more traditionally associated with rural country roads (dashed white centreline) that was associated with the best hazard reactions post-transition (brake reaction time and speed reduction before a horizontal curve). The findings demonstrated that the look of a road needs to convey a clear and unambiguous message to drivers. The transition to a two-star rural road is best achieved by making the road look like a typical two-star road as soon as possible.

Using road markings as a continuous cue for speed choice.

The potential for using road markings to indicate speed limits was investigated in a driving simulator over the course of two sessions. Two types of experimental road markings, an "Attentional" set designed to provide visually distinct cues to indicate speed limits of 60, 80 and 100 km/h, and a "Perceptual" set designed to also affect drivers' perception of speed, were compared to a standard undifferentiated set of markings. Participants (n = 20 per group) were assigned to one of four experimental groups (Attentional-Explicit, Attentional-Implicit, Perceptual-Explicit, Perceptual-Implicit) or a Control group (n = 22; standard road markings). The Explicit groups were instructed about the meaning of the road markings while those in the Implicit and Control groups did not receive any explanation. Participants drove five 10 km simulated roads containing three speed zones (60, 80 and 100 km/h) during the first session. The participants returned to the laboratory approximately 3 days later to drive five more trials including roads they had not seen before, a trial that included a secondary task, and a trial where speed signs were removed and only markings were present. The findings indicated that both types of road markings improved drivers' compliance with speed limits compared to the control group, but that explicit instruction as to the meaning of the markings was needed to realise their full benefit. Although previous research has indicated the benefit of road markings used as warnings to indicate speed reductions in advance of horizontal or vertical curves, the findings of the present experiment also suggest that systematically associating road markings with specific speed limits may be a useful way to improve speed limit compliance and increase speed homogeneity.

Driving on urban roads: How we come to expect the 'correct' speed.

The subjective categories that drivers use to distinguish between different road types have been shown to influence the speeds they choose to drive but as yet we do not understand the road features that drivers use to make their discriminations. To better understand how drivers describe and categorise the roads they drive, 55 participants were recruited to drive a video of familiar urban roads in a driving simulator at the speed they would drive these roads in their own cars (using the accelerator and brake pedal in the driving simulator to adjust their speed). The participants were then asked to sort photos of the roads they had just driven into piles so that their driving would be the same on all roads in one pile but different to the other piles. Finally, they answered a series of questions about each road to indicate what speed they would drive, the safe speed for the road, their speed limit belief as well as providing ratings of comfort, difficulty and familiarity. Overall, drivers' categorisation of roads was informed by a number of factors including speed limit belief, road features and markings (including medians), road width, and presence of houses, driveways and footpaths. The participants' categories were congruent with what they thought the speed limits were, but not necessarily the actual speed limits. Mismatches between actual speed limits and speed limit beliefs appeared to result from category-level expectations about speed limits that took precedence over recent experience in the simulator. Roads that historically had a 50km/h speed limit but had been reduced to 40km/h were still regarded as 50km/h roads by the participants, underscoring the point that simply posting a sign with a lower speed limit is not enough to overcome drivers' expectations and habits associated with the visual appearance of a road. The findings provided insights into how drivers view and categorise roads, and identify specific areas that could be used to improve speed limit credibility.

Driving under the influence of drugs: Perceptions and attitudes of New Zealand drivers.

This study explored the patterns of drug driving in New Zealand by investigating 1) drivers' perceptions about impairment caused by legal and illegal drugs 2) countermeasures employed by drivers when under the influence of drugs (e.g., decisions not to drive) 3) drivers' attitudes about police enforcement of drug driving and 4) the factors that predict the likelihood of engaging in drug driving. Participants (n=434) were licensed drivers who completed an online questionnaire. Results of the questionnaire indicated that drivers rated hallucinogens and opiates as being the illegal drugs producing the highest level of driving impairment and cannabis the lowest. For legal drugs, sedatives were rated as having the highest driving impairment and anti-nausea and anti-depressants the lowest. Respondents' drug use history had an effect on their ratings of impairment for anti-anxiety drugs, anti-depressants, kava, sedatives, cannabis and hallucinogens such that drug users reported higher impairment ratings than Non-user. Making a decision not to drive after taking drugs was reported by users of alcohol (73.6%), cannabis (57.0%), strong painkillers (42.5%), and anti-depressants (10.0%). Respondents who reported drink driving were 3.26 times more likely to report drug driving than those reporting no drink driving. Respondents also showed greater acceptance towards driving under the influence of legal drugs (43.5%) compared to illegal drugs (10.3%). Those who did not have favourable attitudes about drug driving were less likely to report having driven under the influence of drugs. Drivers in this sample were less aware of the potential negative effects of legal drugs on driving compared to illegal drugs. More than half the respondents from this study acknowledged drug driving as a road safety issue which needs more resources dedicated to it.

Fixating on the size-speed illusion of approaching railway trains: What we can learn from our eye movements.

Railway level crossing collisions have recently been linked to a size-speed illusion where larger objects such as trains appear to move slower than smaller objects such as cars. An explanation for this illusion has centred on observer eye movements - particularly in relation to the larger, longer train. A previous study (Clark et al., 2016) found participants tend to make initial fixations to locations around the visual centroid of a moving vehicle; however individual eye movement patterns tended to be either fixation-saccade-fixation type, or smooth pursuit. It is therefore unknown as to which type of eye movement contributes to the size-speed illusion. This study isolated fixation eye movements by requiring participants to view computer animated sequences in a laboratory setting, where a static fixation square was placed in the foreground at one of two locations on a train (front and centroid). Results showed that even with the square placed around the front location of a vehicle, participants still underestimated the speed of the train relative to the car and underestimation was greater when the square was placed around the visual centroid of the train. Our results verify that manipulation of eye movement behaviour can be effective in reducing the magnitude of the size-speed illusion and propose that interventions based on this manipulation should be designed and tested for effectiveness.

Risk in our midst: Centrelines, perceived risk, and speed choice.

The idea that drivers' perceptions of risk affect their decisions and choices, particularly as regards their speed, is at the heart of many years of our education, engineering, and enforcement strategies to improve road safety. Our previous research has shown that horizontal curvature, road width, vertical curvature and separation from on-coming traffic are principal determinants to perceptions of risk on rural roads. The present study examined the relationship between drivers' perceptions of risk and the speeds they choose to drive. Participants drove high definition videos of familiar rural roads in a driving simulator and a smaller group of participants drove the same roads in a university fleet vehicle similar to the one used in the simulator. The results showed that double yellow and wide centreline markings were associated with lower speed choices and higher perceptions of risk, an effect magnified under high traffic conditions. Similarly, in both the simulator and on the roads, driving on narrow roads was associated with significantly lower speeds and increased risk ratings, while wider roads showed a small but significant increase in speeds as compared to standard width control roads. Finally, a range of other road and traffic conditions such as one-lane bridges, level crossings, police cars, and crash area warning signs were also found to be associated with lower speed choices and higher risk perceptions.

Not all minds wander equally: The influence of traits, states and road environment factors on self-reported mind wandering during everyday driving.

Inattention is a road safety problem, but few studies have focused specifically on mind wandering during everyday driving. This paper explores differences in self-reported mind wandering according to driver demographic characteristics (including age and gender), cognitive traits (such as tendency toward cognitive failure or mindful attention), states (such as feeling tired or stressed) and road environment factors (such as route familiarity). Five hundred and two participants (113 male, average age 44.4 years, SD=14.0years) completed a series of questionnaires (Mindful Attention and Awareness Scale (MAAS), Cognitive Failures Questionnaire (CFQ) and Driver Behaviour Questionnaire (DBQ)), as well as study-specific questions about mind wandering during different personal states and across a range of road and traffic situations. All respondents reported mind wandering during driving at least some of the time. Mind wandering was more likely to be reported on familiar roads than on unfamiliar roads and when drivers are tired. Drivers who reported relatively more mind wandering were younger, reported less mindful attention in daily life, more cognitive failures, and more driving violations and lapses. Together, the findings suggest that mind wandering is common in everyday driving, however any link with crash risk remains unclear. Future research using self-report and naturalistic methods could provide more insight into relationships between mind wandering, error and crash risk.

The role of eye movements in the size-speed illusion of approaching trains.

Recent research on the perceived speed of large moving objects, compared to smaller moving objects, has revealed the presence of a size-speed illusion. This illusion, where a large object seems to be moving more slowly than a small object travelling at the same speed may account for collisions between motor cars and trains at level crossings, which is a serious safety issue in New Zealand and worldwide. One possible reason for the perceived size-speed difference may be related to the movement of our eyes when we track moving vehicles. In order to investigate this, we tested observers' relative speed perception of moving objects (both abstract and more detailed objects) moving in depth towards the observer, presented on a computer display and eye movements recorded with an eyetracker. Experiment 1 confirmed first the size-speed illusion when the observers were situated further away (18, 36m) from the simulated rail crossing or intersection. It also revealed that the eye movement behaviour of our participants was different when they judged the speeds of the small and large objects; eye fixations were localised around the visual centroid of longer objects and hence were further from the front of the moving large objects than the smaller ones. Experiment 2 found that manipulating eye movements could reduce the magnitude of the illusion. When observers tracked targets (dots) that were placed at corresponding locations at the front of the small object and the long object respectively, they perceived the speeds of the two objects as equal. When target dots were placed closer to the visual centroid, observers perceived the larger object to be moving slower. These results demonstrate that there is a close relationship between eye movement behaviour and our perceived judgement of an approaching train's speed.