Visual attention in naturalistic scenes across the lifespan.

Abstract

Visual attentional skills continue to develop through childhood and do not reach maturity until adolescence. On the other end of the spectrum, older adults’ visual attentional skills are declining with age. The development and decline of these skills can lead to difficulties in day to day activities such as throwing or catching a ball, cycling, crossing a road, or even maintaining stability when walking. Alongside this, children and older adults are among the most vulnerable groups in road crossing situations, with older adults accounting for almost 50% of road crossing fatalities in the EU. A link has been suggested between visual attentional control skills and the vulnerability of older adults and children to pedestrian accidents but little has been done to investigate this link. In this PhD, I set out to investigate in fine- grained detail the involvement of attentional control skills in road crossing decisions in children, younger, and older adults. To this aim four experiments were run. The first experiment tested younger adults and children from five to 15 years old in a road crossing situation where participants had to watch videos of road traffic and decide when they could safely cross the road. The participants’ eye movements were recorded. I found that younger children made riskier crossing decisions compared to older children and young adults. Younger children were also less able to inhibit attentional capture by distractors and were less able to disengage overt attention from moving targets when the visual load was high. In the second experiment, I used a similar paradigm with young and older adults. My findings revealed that older adults were less able to inhibit attentional capture by distractors compared to younger adults. Despite this attentional bias, older adults made safe crossing decisions. This experiment involved only one direction of traffic and more complex situations (several traffic directions, different speeds, large field of view) might be more taxing for older people and impact their abilities to make safe crossing decisions. As such, in the third experiment I used a virtual reality set-up in order to test scenarios of varying complexity. I also tracked the participants’ eye movements across a wide field of view (180°). My results showed that older adults were able in simple situations to make safe crossing decisions and they chose larger gaps between vehicles than younger adults. In more complex situations such as when cars travel faster, older adults made more risky crossing decisions. In experiments one and two, participants looked predominantly at the point where cars appeared on the road and did not overtly follow the cars down the road. This finding suggested a dissociation between overt and covert attention in the context of road-crossing. In order to explore this dissociation and its potential deficit in children and older people, I developed a technique using in conjunction eye-tracking and steady state visually evoked potential (SSVEP). In this paradigm, participants overtly tracked a moving object and covertly monitored the appearance of a new object at the appearance point. I found a drop in the SSVEP power signal prior to the appearance of the second moving object while the participants’ eyes were still overtly tracking the first object. This result suggests during smooth pursuit a decrease in attentional resources allocated to the foveated object when there is a shift of covert attention towards a second object. In future studies, I aim to use this paradigm to explore more precisely the dynamic of overt and covert attention in more realistic scenario and with children and older participants. This research used novel approaches to address the socially relevant and timely question of pedestrian safety. To this aim, I used a variety of methods ranging from eye-tracking to image processing, EEG and VR, and I developed new techniques tailored to the questions at hand. For the first time, I directly investigated the relationships between visual exploration, road crossing decisions and changes in attentional control through the lifespan. My findings show that children below the age of 10 are less able to inhibit attentional capture by distractors, which increased the risk of unsafe crossing decisions. In similar, simple situations, older adults also show an attentional bias towards distractors, but they maintain the ability to make safe crossing decisions. VR experiments with systematic manipulations of the complexity of the road crossing scene revealed that older adults make riskier crossing decisions in specific situations such as when cars travel quickly, or from different directions. This research furthers our understanding of attentional control through the lifespan as well as providing insights for pedestrian safety. As such, it provides avenues for the development of training and safety guidelines for pedestrians.