liu.seSearch for publications in DiVA
Change search
ReferencesLink to record
Permanent link

Direct link
Fixation identification in centroid versus start-point modes using eye-tracking data
Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Rehabilitation Medicine . Östergötlands Läns Landsting, Local Health Care Services in Central Östergötland, Paediatric Habilitation Community Service.
Linköping University, Department of Clinical and Experimental Medicine, Rehabilitation Medicine . Linköping University, The Institute of Technology.
Swedish National Road and Transport, Research Institute, VTI, Gothenburg, Sweden.
School for Technique and Health, KTH, Stockholm, Sweden.
Show others and affiliations
2008 (English)In: Perceptual and Motor Skills, ISSN 0031-5125, Vol. 106, no 3, 710-724 p.Article in journal (Refereed) Published
Abstract [en]

Fixation-identification algorithms, needed for analyses of eye movements, may typically be separated into three categories, viz. (i) velocity-based algorithms, (ii) area-based algorithms, and (iii) dispersion-based algorithms. Dispersion-based algorithms are commonly used but this application introduces some difficulties, one being optimization. Basically, there are two modes to reach this goal of optimization, viz., the start-point mode and the centroid mode. The aim of the present study was to compare and evaluate these two dispersion-based algorithms. Manual inspections were made of 1,400 fixations in each mode. Odds ratios showed that by using the centroid mode for fixation detection, a valid fixation is 2.86 times more likely to be identified than by using the start-point mode. Moreover, the algorithm based on centroid mode dispersion showed a good interpretation speed, accuracy, robustness, and ease of implementation, as well as adequate parameter settings.

Place, publisher, year, edition, pages
2008. Vol. 106, no 3, 710-724 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-15915DOI: 10.2466/PMS.106.3.710-724PubMedID: 18712192OAI: diva2:128343
Available from: 2008-12-16 Created: 2008-12-16 Last updated: 2009-10-12Bibliographically approved
In thesis
1. Psychophysiological and Performance Aspects on Motion Sickness
Open this publication in new window or tab >>Psychophysiological and Performance Aspects on Motion Sickness
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Rörelsesjuka, ingen sjukdom men väl en naturlig respons i en onaturlig miljö!
Abstract [en]

Motion sickness is not an illness, but rather a natural autonomic response to an unfamiliar or specific stimulus. The bodily responses to motion sickness are highly individual and contextually dependent, making them difficult to predict. The initial autonomic responses are similar to the ones demonstrated when under stress. When under the influence of motion sickness, motivation and ability to perform tasks or duties are limited. However, little is known about how specific cognitive functions are affected. Furthermore, standard mitigation strategies involve medications that induce fatigue or strategies that require cognitive capabilities. Both of them may result in reduced capability to perform assigned tasks or duties. Hence, there is a need for alternative mitigation strategies.

The aim of the thesis was to study psychophysiological and performance aspects on motion sickness. The long-term goal is to provide strategies for mitigation and prevention of motion sickness by identifying psychophysiological responses as predictors for both wellbeing and performance. This thesis comprises four studies, in which 91 participants were exposed to two different motion sickness stimuli, either an optokinetic drum or a motion platform. Before the tests, a method for extracting fixations from eye-tracking data was developed as a prerequisite for studying fixations as a possible mitigation strategy for reducing motion sickness. During exposure to stimuli that triggers motion sickness, performance was studied by testing short-term memory and encoding and retrieval. In the final study, the effects of an artificial sound horizon were studied with respect to its potential to subconsciously function as a mitigating source.

The results of the measurements of the psychophysiological responses were in accordance with previous research, confirming the ambiguity and high individuality of the responses as well as their contextual dependencies. To study fixations, a centroid mode algorithm proved to be the best way to generate fixations from eye-movement data. In the final study, the effects of the sound horizon were compared to the effects of a non-positioned sound. In the latter condition, both fixation time and the number of fixations increased over time, whereas none of them showed a significant time effect in the sound horizon condition. The fixation time slope was significantly larger in the non-positioned sound condition compared to the sound horizon condition. Number of fixations, heart rate, and skin conductance correlated positively with subjective statements that referred to motion sickness. Among participants that were susceptible to motion sickness symptoms, short-term memory performance was negatively affected. However, no effects of motion sickness on encoding and retrieval were found, regardless of susceptibility.

Future studies should continue focusing on autonomic responses and psychological issues of motion sickness. Factors such as motivation, expectancies, and previous experiences play a major and yet relatively unknown role within the motion sickness phenomena.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 71 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1071
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-15919 (URN)978-91-7393-837-2 (ISBN)
Public defence
2009-01-30, Berzeliussalen, Campus US, Linköpings Universitet, Linköping, 13:00 (English)
Available from: 2008-12-16 Created: 2008-12-16 Last updated: 2009-08-21Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textPubMedLink to articleLink to the Ph.D. Thesis

Search in DiVA

By author/editor
Falkmer, TorbjörnDahlman, Joakim
By organisation
Faculty of Health SciencesRehabilitation Medicine Paediatric Habilitation Community ServiceThe Institute of Technology
In the same journal
Perceptual and Motor Skills
Medical and Health Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 198 hits
ReferencesLink to record
Permanent link

Direct link