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promoting access to White Rose research papers Universities of Leeds, Sheffield and York http://eprints.whiterose.ac.uk/ This is a copy of the final published version of a paper published via gold open access in Lighting Research and Technology. This open access article is distributed under the terms of the Creative Commons Attribution-NonCommercial Licence (http://creativecommons.org/licenses/by- nc/4.0/)which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. You may not use the work for commercial purposes. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/85183 Published paper Fotios, S., Uttley, J. and Yang, B. (2014) Using eye-tracking to identify pedestrians' critical visual tasks. Part 2. Fixation on pedestrians. Lighting Research and Technology, 47 (2). 149 - 160. Doi: 10.1177/1477153514522473 White Rose Research Online [email protected] Lighting Res. Technol. 2015; Vol. 47: 149–160 Using eye-tracking to identify pedestrians’ critical visual tasks. Part 2. Fixation on pedestrians S Fotios PhD, J Uttley BSc and B Yang MSc School of Architecture, University of Sheffield, Sheffield, UK Received 20 November 2013; Revised 8 January 2014; Accepted 13 January 2014 This article investigates different approaches to the interpretation of eye-tracking video records of pedestrians walking outdoors to determine the apparent importance of fixation on other pedestrians and how this is influenced by the frequency of occurrence. The three approaches were as follows: the proportion of time that fixations were on pedestrians (14%), a common approach to interpret- ation; the proportion of fixations at critical moments that were on pedestrians (23%), critical moments being defined by a delayed response to a dual task; and the probability of an approaching pedestrian being fixated at least once (86%). These data were compared against the number of pedestrians encountered during the trials; the proportion of all fixations and the probability of fixating people were affected by the number of people encountered – only the critical-fixations data did not exhibit a trend. 1. Introduction identifying critical visual tasks is to find out what pedestrians look at, and eye-tracking In residential roads, it is normal to provide offers one method for establishing the objects lighting that focuses more, but not exclu- fixated. There is reason to have some confi- sively, on the needs of pedestrians compared dence that distribution of gaze and cognitive to those of drivers.1 Following Caminada and processes are related4–6 to the extent that a Van Bommel,2 the key visual needs are study investigating pedestrians’ fixations in a typically suggested to be perceived safety, virtual environment found that specific tasks obstacle detection, recognition of the intent could be predicted from fixation data.7 and/or identity of other road users, and Two studies used eye-tracking to record lighting meeting these needs must also offer fixations on other pedestrians in laboratory 8 an acceptable appearance.3 However, there is, trials. Kitazawa and Fujiyama had test as yet, no empirical evidence to support these participants walk repeatedly forward and assumptions, whether these tasks are indeed back across a 15.6 m long  3.6 m wide plat- form alongside up to three target pedestrians: the most appropriate for characterising light- 4 ing, whether there are other essential visual Jovancevic-Misic and Hayhoe had test par- tasks that need to be considered and the ticipants and five target pedestrians walk 48 relative importance of each task. This laps around an oval track. In these studies, paper investigates the importance of visually the repeated exposure to the same target fixating on other people. One approach to pedestrians may have led to a learning effect and thus to a misleading understanding of interpersonal fixations for natural outdoor Address for correspondence: S Fotios, School of Architecture, University of Sheffield, Sheffield, UK. settings where we frequently do not have such E-mail: [email protected] advance knowledge of another person’s ß The Chartered Institution of Building Services Engineers 2014 10.1177/1477153514522473 Downloaded from lrt.sagepub.com at Royal Hallamshire on April 30, 2015 150 S Fotios et al. likely behaviour. Evidence for this can be were eventually stepped on. An experiment found in the fixation durations reported by carried out in a natural outdoor setting also Jovancevic-Misic and Hayhoe.4 Their target revealed that eye movements were affected by pedestrians were instructed to follow one of terrain, in this case the surfaces being either three behaviours: safe (no collisions), rogue irregularly placed steps or a cobbled road.14 A (veering towards a potential collision with the study of cyclists’ visual fixations when cycling test participant) or risky (equally safe and along a short (15 m) path in a gymnasium, rogue). For the first 12 laps, all types of with three lane widths and three velocities, pedestrians were fixated for the same dur- revealed that less demanding situations (i.e. ation, approximately 500 ms, but with con- the wider path) led to more task-irrelevant tinued laps, the duration of fixation on safe fixations.15 pedestrians reduced while that for rogue Laboratory studies have a number of pedestrians increased, these being approxi- limitations regarding estimation of pedestrian mately 200 ms and 900 ms, respectively, for fixations when walking naturally in outdoor the last four of the 48 laps. settings. Although walking is relatively Further laboratory-based studies have used simple, it entails a variety of subtasks (main- eye-tracking to investigate gait, balance and taining a heading, keeping track of one’s motion.9–12 These do not report data for surroundings and footing, avoiding potential fixation on other pedestrians, but what they collisions)16 and in real outdoor pavements do indicate is that task difficulty and visual these might demand more cognitive attention interest may affect allocation of fixations. than in the laboratory. Laboratory studies Consider Patla and Vickers12 who recorded tend to have purposeful visual targets; when visual fixations when walking three short Marigold and Patla9 found that their test (10 m) paths in a laboratory where test participants tended to look predominantly at participants were required to step on 17 the artificially irregular path, this is perhaps footprints on the floor. They found that because it was an unusual surface and there travel gaze fixation (i.e. fixation held on the was nothing else of interest to look at in the path a fixed distance slightly ahead of the laboratory. Internal environments generally pedestrian and carried along at the speed of have smooth floor surfaces and there are no locomotion) occurred for 59% of the dur- distractions such as dogs, buildings or vehi- ation and footprint fixations for 16%. More cles; in many studies there are no other pedes- difficult visual tasks, or tasks where action trians, and even when they are present, it is has safety implications, modify the propor- unlikely that they would be perceived as tional allocation of fixations. In an alternative potentially threatening. There is no account study where participants were required to step in these studies for the influence, if any, of on raised narrow wooden blocks, thus posing reassurance17,18 on visual search behaviour. a greater danger to stability, travel gaze Finally, and of importance to evidence for fixation duration was reduced to about 40% road lighting, the lighting conditions are not of travel time.13 The 8.5 m artificial path in a described. laboratory used by Marigold and Patla9 Two studies used eye-tracking to investi- included a middle section comprising a patch- gate pedestrians’ visual behaviour during work array of surfaces of different irregular- natural walking activity outdoors.19,20 In ity, firmness and friction; only 0.27% of this situation, test participants are more fixations among the participants were con- likely to adopt their natural gait and must sidered travel gaze fixations, and fixations be prepared to respond to irregular events – were predominantly directed to surfaces that uneven pavement surfaces, other obstacles Lighting Res. Technol. 2015; 47: 149–160 Downloaded from lrt.sagepub.com at Royal Hallamshire on April 30, 2015 Pedestrians’ critical visual tasks 151 and other pedestrians. Participants in the Table 1 Measures of fixation on pedestrians using 19 proportion of all fixations and fixation probability in study by Foulsham et al. carried out a 5– data from eye-tracking when walking outdoors19,20 10 minute outdoor walk to a cafe´in daytime. Fixations were categorised as being directed Foulsham Davoudian et al.19 and Raynham20 to people, the path or other objects, and these by near or far distance. The majority of Proportion of all 21 3 fixations (%) fixations were to the near path (29%) and far Probability of 83 100 objects (27%); fixations to pedestrians were fixation (%) 7% when near and 14% when far. Davoudian and Raynham20 examined visual fixations for pedestrians walking along three residential roads during the day and after dark. Again, the majority of fixations were on the foot- fixation frequency and fixation probability path, and in this study only 3% of fixations (Table 1). The high probability of fixation were on other people. suggests that looking at other pedestrians is A limitation of studying fixations when an important task, but this conclusion is less walking in an uncontrolled outdoor setting is likely to be drawn from consideration of the that each test participant has a different low proportion of fixations. experience, encountering different samples of Eye-tracking studies tend to count visual pedestrians and vehicles. Hence, one possible fixations in every frame of the video 12,19,20 19 reason why Davoudian and Raynham report record. Foulsham et al.