| 1. |
- Ahlström, Christer, et al.
(författare)
-
Fit-for-duty test for estimation of drivers sleepiness level: Eye movements improve the sleep/wake predictor
- 2013
-
Ingår i: Transportation Research Part C. - : Elsevier. - 0968-090X .- 1879-2359. ; 26, s. 20-32
-
Tidskriftsartikel (refereegranskat)abstract
- Driver sleepiness contributes to a considerable proportion of road accidents, and a fit-for-duty test able to measure a drivers sleepiness level might improve traffic safety. The aim of this study was to develop a fit-for-duty test based on eye movement measurements and on the sleep/wake predictor model (SWP, which predicts the sleepiness level) and evaluate the ability to predict severe sleepiness during real road driving. Twenty-four drivers participated in an experimental study which took place partly in the laboratory, where the fit-for-duty data were acquired, and partly on the road, where the drivers sleepiness was assessed. A series of four measurements were conducted over a 24-h period during different stages of sleepiness. Two separate analyses were performed; a variance analysis and a feature selection followed by classification analysis. In the first analysis it was found that the SWP and several eye movement features involving anti-saccades, pro-saccades, smooth pursuit, pupillometry and fixation stability varied significantly with different stages of sleep deprivation. In the second analysis, a feature set was determined based on floating forward selection. The correlation coefficient between a linear combination of the acquired features and subjective sleepiness (Karolinska sleepiness scale, KSS) was found to be R = 0.73 and the correct classification rate of drivers who reached high levels of sleepiness (KSS andgt;= 8) in the subsequent driving session was 82.4% (sensitivity = 80.0%, specificity = 84.2% and AUC = 0.86). Future improvements of a fit-for-duty test should focus on how to account for individual differences and situational/contextual factors in the test, and whether it is possible to maintain high sensitive/specificity with a shorter test that can be used in a real-life environment, e.g. on professional drivers.
|
|
| 2. |
|
|
| 3. |
- Andersson, Richard, et al.
(författare)
-
Sampling frequency and eye-tracking measures : how speed affects durations, latencies, and more
- 2010
-
Ingår i: Journal of Eye Movement Research. - : University of Bern. - 1995-8692. ; 3:3:6, s. 1-12
-
Tidskriftsartikel (refereegranskat)abstract
- We use simulations to investigate the effect of sampling frequency on common dependent variables in eye-tracking. We identify two large groups of measures that behave differently, but consistently. The effect of sampling frequency on these two groups of measures are explored and simulations are performed to estimate how much data are required to overcome the uncertainty of a limited sampling frequency. Both simulated and real data are used to estimate the temporal uncertainty of data produced by low sampling frequencies. The aim is to provide easy-to-use heuristics for researchers using eye-tracking. For example, we show how to compensate the uncertainty of a low sampling frequency with more data and post-experiment adjustments of measures. These findings have implications primarily for researchers using naturalistic setups where sampling frequencies typically are low.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Cronie, Ottmar, et al.
(författare)
-
Spatio-Temporal Modelling of Swedish Scots Pine Stands
- 2011
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Considering measurements of locations and radii at breast height made at three different time points of the individual trees in ten Swedish Scots pine plots, we employ the so called growth-interaction (GI) process for the spatio-temporal modelling of the plots. The GI-process places trees at random locations in the study region and assigns radii (sizes) to the trees, which interact and grow with time. It has been used to model Scots pine plots in previous studies, and to improve the fit we suggest some modifications of the model: A different location assignment strategy and a different function for the open-growth (growth in absence of competition). We believe also that the space-time data contain too small trees to reflect the open-growth properly, which primarily affectsthe carrying capacity parameter. We evaluate the open-growth froma separate set of data which consists of size and age measurements ofolder and larger single Scots pines. This data set better represents the open-growth of Scots pines than the space-time data sets. A linear relationship is found between the estimated site indexes of the plots and the sizes, and this relationship is exploited in the estimation of the carrying capacity. For each of the ten space-time data sets (plots) we estimate the remaining parameters of the GI-process and finally, by means of some Monte Carlo tests, we test the goodness-of-fit of simulated predictions from the fitted model.
|
|
| 9. |
- Cronie, Ottmar, 1979, et al.
(författare)
-
Spatiotemporal Modeling of Swedish Scots Pine Stands
- 2013
-
Ingår i: Forest Science. - : Oxford University Press (OUP). - 0015-749X .- 1938-3738. ; 59:5, s. 505-516
-
Tidskriftsartikel (refereegranskat)abstract
- The growth-interaction (GI) process is used for the spatiotemporal modeling of measurements of locations and radii at breast height made at three different time points of the individual trees in 10 Scots pine (Pinus sylvestris) plots from the Swedish National Forest Inventory. The GI process places trees at random locations in the study region and assigns sizes to the trees, which interact and grow with time. It has been used to model plots in previous studies and to improve the fit we suggest some modifications: a different location assignment strategy and a different open-growth (growth under negligible competition) function. We believe that the calibration data contain trees that are too small to reflect the open growth properly, which primarily affects the carrying capacity parameter. To better represent the open growth of Scots pines, we evaluate the open growth from a separate set of data (size and age measurements of older and larger single Scots pines). A linear relationship is found between the plot's estimated site indices and the sizes, and this is exploited in the estimation of the carrying capacity. We finally estimate the remaining GI process parameters and test the goodness of fit on simulated predictions from the fitted model.
|
|
| 10. |
|
|
| 11. |
- Dewhurst, Richard, et al.
(författare)
-
It depends on how you look at it: Scanpath comparison in multiple dimensions with MultiMatch, a vector-based approach
- 2012
-
Ingår i: Behavior Research Methods. - : Springer Science and Business Media LLC. - 1554-3528.
-
Tidskriftsartikel (refereegranskat)abstract
- Eye movement sequences---or scanpaths---vary depending on stimulus characteristics and task (Foulsham \& Underwood, 2008; Land, Mennie, \& Rusted, 1999). Common methods for comparing scanpaths, however, are limited in their ability to capture both the spatial and temporal properties of which a scanpath consists. Here we validate a new method for scanpath comparison based on geometric vectors, which compares scanpaths over multiple dimensions retaining positional and sequential information (Jarodzka, Holmqvist, \& Nyström, 2010). `MultiMatch' was tested in two experiments and pitted against ScanMatch (Cristino, Mathôt, Theeuwes, \& Gilchrist, 2010), the most comprehensive adaptation of the popular Levenshtein method. Experiment 1 used synthetic data, demonstrating the greater sensitivity of MultiMatch to variations in spatial position. In experiment 2 real eye movement recordings were taken from participants viewing sequences of dots, designed to elicit scanpath pairs with commonalities known to be problematic for algorithms (for example, when one scanpath is shifted in locus, or fixations fall either side of an AOI boundary). Results illustrate the advantages of a multidimensional approach, revealing how two scanpath differ. For instance, if one scanpath is the reverse copy of another the difference is in direction but not the position of fixations; or if a scanpath is scaled down, the difference is in the length of saccadic vectors but not overall shape. As well as having enormous potential for any task in which consistency in eye movements is important (e.g. learning), MultiMatch is particularly relevant for "eye movements to nothing" in mental imagery research and embodiment of cognition, where satisfactory scanpath comparison algorithms are lacking.
|
|
| 12. |
|
|
| 13. |
|
|
| 14. |
|
|
| 15. |
- Ehlers, Sarah, et al.
(författare)
-
Data assimilation in stand-level forest inventories
- 2013
-
Ingår i: Canadian Journal of Forest Research. - : Canadian Science Publishing. - 0045-5067 .- 1208-6037. ; 43, s. 1104-1113
-
Tidskriftsartikel (refereegranskat)abstract
- The development of remote sensing methods through research and large-scale application nowadays makes it possible to obtain stand-level estimates of forest variables at short intervals and at low cost. This offers substantial possibilities to forestry practitioners, but it also poses challenges regarding how cost-efficient data acquisition strategies should be developed. For example, should cheap but low-quality data be acquired and discarded whenever new data become available or should investments be made in high-quality data that are continuously updated to last over a longer period of time? We suggest that the solution could be to establish data assimilation (DA) procedures linked to forest inventories to make appropriate use of data from several sources. With DA, old information is updated through growth forecasts and when new information becomes available it is assimilated with the old information; the different sources of information are made use of to the extent motivated by their accuracy. In this study we made a general assessment of the usefulness of DA in connection with stand-level forest inventories and we compared two different methodological approaches, the extended Kalman filter and the Bayesian method. Not surprisingly, the relative advantage of DA was found to be largest for cases where low-precision estimates of growing stock volume were obtained at short intervals and forecasts were made with accurate growth prediction models. The methodological comparison revealed a tendency of the extended Kalman filter to underestimate the variance of the estimates.
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Eitel, Alexander, et al.
(författare)
-
How a picture facilitates the process of learning from text: Evidence for scaffolding
- 2013
-
Ingår i: Learning and Instruction. - : Elsevier BV. - 0959-4752. ; 28, s. 48-63
-
Tidskriftsartikel (refereegranskat)abstract
- Three experiments were conducted to study on a more fine-grained level how processing a picture facilitates learning from text. In Experiment 1 (N = 85), results from a drawing task revealed that the global spatial structure of a pulley system picture was extracted even from its brief inspection (for 600 ms, 2 s). In Experiment 2 (N = 105), students who initially inspected the pulley system picture (for 600 ms, 2 s, or self-paced) had better comprehension of the system's functions and made more eye movements in line with the system's global spatial structure when listening to text than students who listened to text only. In Experiment 3 (N = 39), students who first saw the picture (for 2 s) processed written text of the pulley system's spatial structure more efficiently than students who read text only. Results suggest that global spatial information extracted from the picture was used as a mental scaffold to facilitate mental model construction.
|
|
| 19. |
|
|
| 20. |
- Foulsham, Thomas, et al.
(författare)
-
Comparing scanpaths during scene encoding and recognition: A multi-dimensional approach
- 2012
-
Ingår i: Journal of Eye Movement Research. - 1995-8692. ; 5:4:3, s. 1-14
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedComplex stimuli and tasks elicit particular eye movement sequences. Previous research has focused on comparing between these scanpaths, particularly in memory and imagery research where it has been proposed that observers reproduce their eye movements when recognizing or imagining a stimulus. However, it is not clear whether scanpath similarity is related to memory performance and which particular aspects of the eye movements recur. We therefore compared eye movements in a picture memory task, using a recently proposed comparison method, MultiMatch, which quantifies scanpath similarity across multiple dimensions including shape and fixation duration. Scanpaths were more similar when the same participant's eye movements were compared from two viewings of the same image than between different images or different participants viewing the same image. In addition, fixation durations were similar within a participant and this similarity was associated with memory performance.
|
|
| 21. |
|
|
| 22. |
- Holmqvist, Kenneth, et al.
(författare)
-
Eye Tracking : A Comprehensive Guide to Methods and Measures
- 2011
-
Bok (övrigt vetenskapligt/konstnärligt)abstract
- This book is written by and for researchers who are still in that part of their careers where they are actively using the eye-tracker as a tool; those who have to deal with the technology, the signals, the filters, the algorithms, the experimental design, the programming of stimulus presentation, instructions to participants, working the varying tools for data analysis, and of course, worrying about all the different things that must not go wrong! A central theme of the book concerns the wide range of fields eye tracking covers. Suppose an educational psychologist wishes to use eye tracking to evaluate a new software pack- age designed to support learning to read. She may have an excellent idea as a starting point, and some understanding of the kind of results eye tracking could provide to tackle her re- search question, but unless she and the group around her are also adept in computer science, it is unlikely she will know how the eye movement data she collects is generated: How raw data samples are converted into fixations and saccades using event detection algorithms, how the different representations of eye movement data are calculated, and how all the measures of eye movements relate to these processes. All this is important because subtleties involved in working with eye-tracking data can have large consequences for the final results, and thus whether our educational psychologist can confidently conclude that her software package is effective or not in supporting the development of reading skills. This is not to say that hard-core computer science skills are the crux of good eye-tracking research, for this is certainly not the case. One can equally envisage a situation where an expert in programming and the manipulation of data plans and executes an eye-tracking study poorly, simply because she is not trained in the principles of experimental design, and the associated literature on the visual system and oculomotor control. There are many contrasts between the diverging schools of thought which use eye track- ing; practices and preferences vary, but certainly experts in different fields do not draw on each other’s strengths enough. We felt there was a need to pinpoint the relative merits of adopting methods based in one field alone, whilst highlighting that the lack of synergy be- tween different disciplines can lead to sub-optimal research practices, and new advancements being overlooked. Besides technical details and theory, however, the heart of this book revolves around practicality. At the Humanities Laboratory at Lund University we have been teaching eye- tracking methodology regularly since 2000. We commonly see newcomers to the technique run aground when encountering just the sort of issues raised above, but beginners struggle with problems which are even more practical in nature. Hands-on advice for how to actually use eye-trackers is very limited. Setting up the eye camera and performing a good calibration routine is just as important as the design of the study and how data is handled, for if the recording is poor your options are limited from the outset. There are fundamental methodological skills which underpin using eye-trackers, but at the other end of the spectrum there is also the vast choice of measures available to the eye-tracking researcher. For the present text to be complete, therefore, we felt a require- ment should also be to draw together eye-tracking measures, as well as methods, into an understandable structure. So, starting around 2005, we began producing a taxonomy of all eye-movement methods and measures used by researchers, examining how the measures are related to each other, what type of data quality they rely on, and previous data processing they require. Our classification work thus consisted of searching the method sections from thousands of journal papers, book chapters, PhD theses and conference proceedings. Every measure and method we found was catalogued and put into a growing system. Some of the measures were extremely elusive, as they are known by different names, not only between research fields, but even within, and often the precise implementations are missing in the WHY WE WROTE THIS BOOK | v vi | WHY WE WROTE THIS BOOK published texts. At first, we were very unclear how to classify measures. Some varieties of taxonomic structures that we rejected can be found on p. 463. We ended up with a classifica- tion structure where the operational definitions are at the centre. Users of eye-trackers often lack proficient training because there is little or no teaching community to rely on. As a result people are often self taught, or depend on second-hand knowledge which may be out of date or even incorrect. When they participate in our eye- tracking methodology courses, we find that many new users are very focused on their re- search questions, but are surprised how much time they need to invest in order to master eye tracking properly. Often people attending have just purchased an eye-tracker to compliment their research, or for use in their company to tackle ergonomic and marketing-related ques- tions. Our aim for this book is to make learning to use eye-trackers a much easier process for these readers. If you have a solid background in experimental psychology, computer sci- ence, or mathematics you will often find it straightforward to embrace the technologies and workflows surrounding eye tracking. But whatever your background, you should be able to achieve the same level of knowledge and understanding from this book as you would from training on eye tracking in-house in a fully competent laboratory. More specifically, this book has been written to be a support when: 1. Evaluating or acquiring a commercial eye-tracker, 2. Planning an experiment where eye tracking is used as a tool, 3. About to record eye-movement data, 4. Planning how to process and interpret the recorded data, before carrying out statistical tests on it, 5. Reading or reviewing eye-movement research. In our efforts to classify eye-tracking methods and measures, combined with useful prac- tical hints and tips, we hope to provide the reader with the first comprehensive textbook on methodology for new users of eye tracking, but which also caters for the advanced researcher. Previous versions of this book have been used in eye-tracking education in Lund. Also, col- leagues of ours in Potsdam, Tübingen, and Helsinki have used earlier manuscripts of the book when teaching and training masters and PhD level students in eye tracking. Lastly, although not the target audience, manufacturers have already shown a great interest in the book at the manuscript stage, which we hope may lead to even better eye-trackers in the future.
|
|
| 23. |
|
|
| 24. |
|
|
| 25. |
- Holsanova, Jana, et al.
(författare)
-
Visualisering av ögonrörelser som stöd för motivation, metakognition och lärande
- 2014
-
Ingår i: Vetenskapliga perspektiv på lärande, undervisning och utbildning i olika institutionella sammanhang : utbildningsvetenskaplig forskning vid Lunds universitet. - 9789174738629 ; , s. 369-380
-
Bokkapitel (refereegranskat)abstract
- Bidraget presenterar ett nytt pedagogiskt verktyg (EyeLearn) som baseras på ögonrörelsemätningsmetoden och används som stöd för motivation, metakognition och lärande. Genom visualiseringar av ögonrörelser kan man följa problemlösningsprocessen, ge stöd till lågpresterande elever, förbättra elevers metakognitiva förmågor och studieteknik, plocka fram exempel på framgångsrika och mindre framgångsrika strategier, motivera elever genom att engagera dem i jämförande diskussioner om alternativa lösningar samt anpassa digitala läromedel efter elevernas förmåga och preferens. Verktyget stödjer därmed interaktivitet, ger återkoppling till eleven, respekterar individernas lärstilar, erbjuder former av samarbete och stödjer metakognition.
|
|
| 26. |
|
|
| 27. |
- Hunter, Amanda, et al.
(författare)
-
Effect of wood smoke exposure on vascular function and thrombus formation in healthy fire fighters
- 2014
-
Ingår i: Particle and Fibre Toxicology. - : BioMed Central (BMC). - 1743-8977. ; 11
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Myocardial infarction is the leading cause of death in fire fighters and has been linked with exposure to air pollution and fire suppression duties. We therefore investigated the effects of wood smoke exposure on vascular vasomotor and fibrinolytic function, and thrombus formation in healthy fire fighters. Methods: In a double-blind randomized cross-over study, 16 healthy male fire fighters were exposed to wood smoke (~1 mg/m3 particulate matter concentration) or filtered air for one hour during intermittent exercise. Arterial pressure and stiffness were measured before and immediately after exposure, and forearm blood flow was measured during intra-brachial infusion of endothelium-dependent and -independent vasodilators 4–6 hours after exposure. Thrombus formation was assessed using the ex vivo Badimon chamber at 2 hours, and platelet activation was measured using flow cytometry for up to 24 hours after the exposure. Results: Compared to filtered air, exposure to wood smoke increased blood carboxyhaemoglobin concentrations (1.3% versus 0.8%; P < 0.001), but had no effect on arterial pressure, augmentation index or pulse wave velocity (P > 0.05 for all). Whilst there was a dose-dependent increase in forearm blood flow with each vasodilator (P < 0.01 for all), there were no differences in blood flow responses to acetylcholine, sodium nitroprusside or verapamil between exposures (P > 0.05 for all). Following exposure to wood smoke, vasodilatation to bradykinin increased (P = 0.003), but there was no effect on bradykinin-induced tissue-plasminogen activator release, thrombus area or markers of platelet activation (P > 0.05 for all). Conclusions: Wood smoke exposure does not impair vascular vasomotor or fibrinolytic function, or increase thrombus formation in fire fighters. Acute cardiovascular events following fire suppression may be precipitated by exposure to other air pollutants or through other mechanisms, such as strenuous physical exertion and dehydration.
|
|
| 28. |
- Jarodzka, Halszka, et al.
(författare)
-
A Vector-based, Multidimensional Scanpath Similarity Measure
- 2010
-
Ingår i: [Host publication title missing]. ; , s. 211-218
-
Konferensbidrag (refereegranskat)abstract
- A great need exists in many fields of eye-tracking research for a robust and general method for scanpath comparisons. Current measures either quantize scanpaths in space (string editing measures like the Levenshtein distance) or in time (measures based on attention maps). This paper proposes a new pairwise scanpath similarity measure. Unlike previous measures that either use AOI sequences or forgo temporal order, the new measure defines scanpaths as a series of geometric vectors and compares temporally aligned scanpaths across several dimensions: shape, fixation position, length, direction, and fixation duration. This approach offers more multifaceted insights to how similar two scanpaths are. Eight fictitious scanpath pairs are tested to elucidate the strengths of the new measure, both in itself and compared to two of the currently most popular measures - the Levenshtein distance and attention map correlation.
|
|
| 29. |
|
|
| 30. |
|
|
| 31. |
|
|
| 32. |
|
|
| 33. |
|
|
| 34. |
- Larsson, Linnéa, et al.
(författare)
-
Compensation of Head Movements in Mobile Eye-Tracking Data Using an Inertial Measurement Unit
- 2014
-
Ingår i: Proceedings of the 2014 ACM International Joint Conference on Pervasive and Ubiquitous Computing: Adjunct Publication. - New York, NY, USA : ACM. - 9781450330473 ; , s. 1161-1167
-
Konferensbidrag (refereegranskat)abstract
- Analysis of eye movements recorded with a mobile eye-tracker is difficult since the eye-tracking data are severely affected by simultaneous head and body movements. Automatic analysis methods developed for remote-, and tower-mounted eye-trackers do not take this into account and are therefore not suitable to use for data where also head- and body movements are present. As a result, data recorded with a mobile eye-tracker are often analyzed manually. In this work, we investigate how simultaneous recordings of eye- and head movements can be employed to isolate the motion of the eye in the eye-tracking data. We recorded eye-in-head movements with a mobile eye-tracker and head movements with an Inertial Measurement Unit (IMU). Preliminary results show that by compensating the eye-tracking data with the estimated head orientation, the standard deviation of the data during vestibular-ocular reflex (VOR) eye movements, was reduced from 8.0 to 0.9 in the vertical direction and from 12.9 to 0.6 in the horizontal direction. This suggests that a head compensation algorithm based on IMU data can be used to isolate the movements of the eye and therefore simplify the analysis of data recorded using a mobile eye-tracker.
|
|
| 35. |
- Lång, Kristina, et al.
(författare)
-
Can horizontally oriented breast tomosynthesis image volumes or the use of a systematic search strategy improve interpretation? An eye tracking and free response human observer study
- 2011
-
Ingår i: Proc. SPIE. - : SPIE. ; 7966:796606
-
Konferensbidrag (refereegranskat)abstract
- Our aim was to evaluate if there is a benefit in diagnostic accuracy and efficiency of viewing breast tomosynthesis (BT) image volumes presented horizontally oriented, but also to evaluate the use of a systematic search strategy where the breast is divided, and analyzed consecutively, into two sections. These image presentations were compared to regular vertical image presentation. All methods were investigated using viewing procedures consisting of free scroll volume browsing, and a combination of initial cine loops at three different frame rates (9, 14, 25 fps) terminated upon request followed by free scroll volume browsing if needed. Fifty-five normal BT image volumes in MLO view were collected. In these, simulated lesions (20 masses and 20 clusters of microcalcifications) were randomly inserted, creating four unique image sets for each procedure. Four readers interpreted the cases in a random order. Their task was to locate the lesions, mark and assign a five level confidence scale. The diagnostic accuracy was analyzed using Jackknife Free Receiver Operating Characteristics (JAFROC). Time efficiency and visual search behavior were also investigated using eye tracking. Results indicate there was no statistically significant difference in JAFROC FOM between the different image presentations, although visual search was more time efficient when viewing horizontally oriented image volumes in medium cine loops.
|
|
| 36. |
- Lång, Kristina, et al.
(författare)
-
Optimizing viewing procedures of breast tomosynthesis image volumes using eye tracking combined with a free response human observer study
- 2011
-
Ingår i: Medical Imaging 2011: Image Perception, Observer Performance, and Technology Assessment / SPIE Proceedings. - : SPIE. ; 7966:796602
-
Konferensbidrag (refereegranskat)abstract
- The purpose of this study was to evaluate four different viewing procedures as part of improving viewing conditions of breast tomosynthesis (BT) image volumes. The procedures consisted of free scroll volume browsing, and a combination of initial cine loops at three different frame rates (9, 14 and 25 fps) terminated upon request followed by free scroll volume browsing. Fifty-five normal BT image volumes in MLO view were collected. In these, simulated lesions (20 masses and 20 clusters of microcalcifications) were randomly inserted, creating four unique image sets for each procedure. Four readers interpreted the cases in a random order. Their task was to locate a lesion, mark and assign a five level confidence scale. The diagnostic accuracy was analyzed using Jackknife Free Receiver Operating Characteristics (JAFROC). Time efficiency and visual search behavior were also investigated using eye tracking. The results indicate that there was no statistically significant difference in JAFROC FOM between the different viewing procedures, however the medium cine loop speed seemed to be the preferred viewing procedure in terms of total analyze time and dwell time.
|
|
| 37. |
|
|
| 38. |
- Nyström, Kenneth
(författare)
-
Skötselstrategier för högförädlat plantmaterial
- 2010
-
Ingår i: Ökad tillgång och användning av förädlade plantor : bilagor : uppdrag om förbättrat växtodlingsmateril, Jo2008/1883.
-
Bokkapitel (populärvet., debatt m.m.)
|
|
| 39. |
- Nyström, Kenneth, et al.
(författare)
-
Stand establishment and early growth
- 2010
-
Ingår i: The Heureka Research Programme. Final Report for Phase 2, October 2005-September 2009. ; , s. 34-39
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
|
|
| 40. |
|
|
| 41. |
- Nyström, Marcus, et al.
(författare)
-
An adaptive algorithm for fixation, saccade, and glissade detection in eyetracking data.
- 2010
-
Ingår i: Behavior Research Methods. - 1554-3528. ; 42:1, s. 188-204
-
Tidskriftsartikel (refereegranskat)abstract
- Event detection is used to classify recorded gaze points into periods of fixation, saccade, smooth pursuit, blink, and noise. Although there is an overall consensus that current algorithms for event detection have serious flaws and that a de facto standard for event detection does not exist, surprisingly little work has been done to remedy this problem. We suggest a new velocity-based algorithm that takes several of the previously known limitations into account. Most important, the new algorithm identifies so-called glissades, a wobbling movement at the end of many saccades, as a separate class of eye movements. Part of the solution involves designing an adaptive velocity threshold that makes the event detection less sensitive to variations in noise level and the algorithm settings-free for the user. We demonstrate the performance of the new algorithm on eye movements recorded during reading and scene perception and compare it with two of the most commonly used algorithms today. Results show that, unlike the currently used algorithms, fixations, saccades, and glissades are robustly identified by the new algorithm. Using this algorithm, we found that glissades occur in about half of the saccades, during both reading and scene perception, and that they have an average duration close to 24 msec. Due to the high prevalence and long durations of glissades, we argue that researchers must actively choose whether to assign the glissades to saccades or fixations; the choice affects dependent variables such as fixation and saccade duration significantly. Current algorithms do not offer this choice, and their assignments of each glissade are largely arbitrary.
|
|
| 42. |
|
|
| 43. |
- Nyström, Marcus, et al.
(författare)
-
Effect of Compressed Offline Foveated Video on Viewing Behavior and Subjective Quality
- 2010
-
Ingår i: ACM Transactions on Multimedia Computing, Communications, and Applications. - : Association for Computing Machinery (ACM). - 1551-6857 .- 1551-6865. ; 6:1, s. 1-14
-
Tidskriftsartikel (refereegranskat)abstract
- Offline foveation is a technique to improve the compression efficiency of digitized video. The general idea behind offline foveation is to blur video regions where no or a small number of previewers look without decreasing the subjective quality for later viewers. It relies on the fact that peripheral vision is reduced compared to central vision, and the observation that during free-viewing humans' gaze positions generally coincide when watching video. In this article, we conduct two experiments to assess how offline foveation affects viewing behavior and subjective quality. In the first experiment, 15 subjects free-viewed six video clips before and after offline foveation whereas in the second experiment we had 17 subjects assessing the quality of these videos after one, two, and three consecutive viewings. Eye movements were measured during the experiments. Results showed that, although offline foveation prior to encoding with H. 264 yielded data reductions up to 52% (20% average) on the tested videos, it had little or no effect on where people looked, their intersubject dispersion, fixation duration, saccade amplitude, or the experienced quality during first-time viewing. However, seeing the videos more than once increased the intersubject dispersion and decreased the subjective quality. In view of these results, we discuss the usage of offline foveated video in practical applications.
|
|
| 44. |
- Nyström, Marcus, et al.
(författare)
-
Post-saccadic oscillations in eye movement data recorded with pupil-based eye trackers reflect motion of the pupil inside the iris
- 2013
-
Ingår i: Vision Research. - : Elsevier BV. - 1878-5646 .- 0042-6989. ; 92, s. 59-66
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedCurrent video eye trackers use information about the pupil center to estimate orientation and movement of the eye. While dual Purkinje eye trackers suffer from lens wobble and scleral search coils may be influenced by contact lens slippage directly after saccades, it is not known whether pupil-based eye trackers produces similar artifacts in the data. We recorded eye movements from participants making repetitive, horizontal saccades and compared the movement in the data with pupil- and iris movements extracted from the eye images. Results showed that post-saccadic instabilities clearly exist in data recorded with a pupil-based eye tracker. They also exhibit a high degree of reproducibility across saccades and within participants. While the recorded eye movement data correlated well with the movement of the pupil center, the iris center showed only little post-saccadic movement. This means that the pupil moves relative to the iris during post-saccadic eye movements, and that the eye movement data reflect pupil movement rather than eyeball rotation. Besides introducing inaccuracies and additional variability in the data, the pupil movement inside the eyeball influences the decision of when a saccade should end and the subsequent fixation should begin, and consequently higher order analyses based on fixations and saccades.
|
|
| 45. |
- Nyström, Marcus, et al.
(författare)
-
The influence of calibration method and eye physiology on eyetracking data quality
- 2013
-
Ingår i: Behavior Research Methods. - : Springer Science and Business Media LLC. - 1554-3528. ; 45:1, s. 272-288
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedRecording eye movement data with high quality is often a prerequisite for producing valid and replicable results and for drawing well-founded conclusions about the oculomotor system. Today, many aspects of data quality are often informally discussed among researchers but are very seldom measured, quantified, and reported. Here we systematically investigated how the calibration method, aspects of participants' eye physiologies, the influences of recording time and gaze direction, and the experience of operators affect the quality of data recorded with a common tower-mounted, video-based eyetracker. We quantified accuracy, precision, and the amount of valid data, and found an increase in data quality when the participant indicated that he or she was looking at a calibration target, as compared to leaving this decision to the operator or the eyetracker software. Moreover, our results provide statistical evidence of how factors such as glasses, contact lenses, eye color, eyelashes, and mascara influence data quality. This method and the results provide eye movement researchers with an understanding of what is required to record high-quality data, as well as providing manufacturers with the knowledge to build better eyetrackers.
|
|
| 46. |
- Suty, Nicole Susanne, et al.
(författare)
-
Assessment of bias due to random measurement errors in stem volume growth estimation by the Swedish National Forest Inventory
- 2013
-
Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 28, s. 174-183
-
Tidskriftsartikel (refereegranskat)abstract
- We evaluated the performance of two methods for estimating stem volume increment at individual tree level with respect to bias due to random measurement errors. Here, growth is either predicted as the difference between two consecutive volume estimates where single-tree volume functions are applied to data from repeated measurements or by a regression model that is applied to data from a single survey and includes radial increment. In national forest inventories (NFIs), the first method is typically used for permanent plots, the second for temporary plots. The Swedish NFI combines estimates from both plot types to assess growth at national and regional scales and it is, therefore, important that the two methods provide similar results. The accuracy of these estimates is affected by random measurement errors in the independent variables, which may lead to systematic errors in predicted variables due to model non-linearity. Using Taylor series expansion and empirical data from the Swedish NFI we compared the expected bias in stem volume growth estimates for different diameter classes of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.). Our results indicate that both methods are fairly insensitive to random measurement errors of the size that occur in the Swedish NFI. The empirical comparison between the two methods showed greater differences for large diameter trees of both pine and spruce. A likely explanation is that the regressions are uncertain because few large trees were available for developing the models.
|
|
| 47. |
- Timberg, Pontus, et al.
(författare)
-
Investigation of viewing procedures for interpretation of breast tomosynthesis image volumes: a detection-task study with eye tracking.
- 2013
-
Ingår i: European Radiology. - : Springer Science and Business Media LLC. - 0938-7994 .- 1432-1084. ; 23:4, s. 997-1005
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To evaluate the efficiency of different methods of reading breast tomosynthesis (BT) image volumes. METHODS: All viewing procedures consisted of free scroll volume browsing and three were combined with initial cine loops at three different frame rates (9, 14 and 25 fps). The presentation modes consisted of vertically and horizontally orientated BT image volumes. Fifty-five normal BT image volumes in mediolateral oblique view were collected. In these, simulated lesions were inserted, creating four unique image sets, one for each viewing procedure. Four observers interpreted the cases in a free-response task. Time efficiency, visual attention and search were investigated using eye tracking. RESULTS: Horizontally orientated BT image volumes were read faster than vertically when using free scroll browsing only and when combined with fast cine loop. Cine loops at slow frame rates were ruled out as inefficient. CONCLUSIONS: In general, horizontally oriented BT image volumes were read more efficiently. All viewing procedures except for slow frame rates were promising when assuming equivalent detection performance. KEY POINTS : • Breast tomosynthesis is increasingly used for breast cancer detection • There is a benefit in reading breast tomosynthesis image volumes presented horizontally • Align image content to visual field, especially for dynamic 3D images • Reading at slow frame rates was considered inefficient.
|
|
| 48. |
|
|
| 49. |
- Wallmenius, Katarina, et al.
(författare)
-
Spotted fever Rickettsia species in Hyalomma and Ixodes ticks infesting migratory birds in the European Mediterranean area
- 2014
-
Ingår i: Parasites & Vectors. - : Springer Science and Business Media LLC. - 1756-3305. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Background: A few billion birds migrate annually between their breeding grounds in Europe and their wintering grounds in Africa. Many bird species are tick-infested, and as a result of their innate migratory behavior, they contribute significantly to the geographic distribution of pathogens, including spotted fever rickettsiae. The aim of the present study was to characterize, in samples from two consecutive years, the potential role of migrant birds captured in Europe as disseminators of Rickettsia-infected ticks. Methods: Ticks were collected from a total of 14,789 birds during their seasonal migration northwards in spring 2009 and 2010 at bird observatories on two Mediterranean islands: Capri and Antikythira. All ticks were subjected to RNA extraction followed by cDNA synthesis and individually assayed with a real-time PCR targeting the citrate synthase (gltA) gene. For species identification of Rickettsia, multiple genes were sequenced. Results: Three hundred and ninety-eight (2.7%) of all captured birds were tick-infested; some birds carried more than one tick. A total number of 734 ticks were analysed of which 353 +/- 1 (48%) were Rickettsia-positive; 96% were infected with Rickettsia aeschlimannii and 4% with Rickettsia africae or unidentified Rickettsia species. The predominant tick taxon, Hyalomma marginatum sensu lato constituted 90% (n = 658) of the ticks collected. The remaining ticks were Ixodes frontalis, Amblyomma sp., Haemaphysalis sp., Rhipicephalus sp. and unidentified ixodids. Most ticks were nymphs (66%) followed by larvae (27%) and adult female ticks (0.5%). The majority (65%) of ticks was engorged and nearly all ticks contained visible blood. Conclusions: Migratory birds appear to have a great impact on the dissemination of Rickettsia-infected ticks, some of which may originate from distant locations. The potential ecological, medical and veterinary implications of such Rickettsia infections need further examination.
|
|
