Eye tracking observers during color image evaluation tasks

This thesis investigated eye movement behavior of subjects during image-quality evaluation and chromatic adaptation tasks. Specifically, the objectives focused on learning where people center their attention during color preference judgments, examining the differences between paired comparison, rank order, and graphical rating tasks, and determining what strategies are adopted when selecting or adjusting achromatic regions on a soft-copy display. In judging the most preferred image, measures of fixation duration showed that observers spend about 4 seconds per image in the rank order task, 1.8 seconds per image in the paired comparison task, and 3.5 seconds per image in the graphical rating task. Spatial distributions of fixations across the three tasks were highly correlated in four of the five images. Peak areas of attention gravitated toward faces and semantic features. Introspective report was not always consistent with where people foveated, implying broader regions of importance than eye movement plots. Psychophysical results across these tasks generated similar, but not identical, scale values for three of the five images. The differences in scales are likely related to statistical treatment and image confusability, rather than eye movement behavior. In adjusting patches to appear achromatic, about 95% of the total adjustment time was spent fixating only on the patch. This result shows that even when participants are free to move their eyes in this kind of task, central adjustment patches can discourage normal image viewing behavior. When subjects did look around (less than 5% of the time), they did so early during the trial. Foveations were consistently directed toward semantic features, not shadows or achromatic surfaces. This result shows that viewers do not seek out near-neutral objects to ensure that their patch adjustments appear achromatic in the context of the scene. They also do not scan the image in order to adapt to a gray world average. As demonstrated in other studies, the mean chromaticity of the image influenced observers\u27 patch adjustments. Adaptation to the D93 white point was about 65% complete from D65. This result agrees reasonably with the time course of adaptation occurring over a 20 to 30 second exposure to the adapting illuminant. In selecting the most achromatic regions in the image, viewers spent 60% of the time scanning the scene. Unlike the achromatic patch adjustment task, foveations were consistently directed toward achromatic regions and near-neutral objects as would be expected. Eye movement records show behavior similar to what is expected from a visual search task

Can eye movements be quantitatively applied to image quality studies?

The aim of the study is to find out whether subjective image quality evaluations can be quantified by eye movement tracking. We want to map objective or physically measurable image quality to subjective evaluations and eye movement data. Results show that eye movement parameters consistently change according to the instructions given to the user, and according to physical image quality. These results indicate that eye movement tracking could be used to differentiate image quality evaluation strategies that the users have. Results also show that eye movements would help mapping between technological and subjective image quality. We also propose to extend the widely used image quality process model, the Image Quality Circle. We suggest adding the objective measurements of a viewer (e.g. eye tracking) in parallel with customer perceptions as an option to gather information of customer perceptions of image quality

Understanding visual behaviour within the urban environment to optimise lighting

A review of the literature suggests that current guidelines for road lighting lack a clear empirical basis. Where there is evidence, this tends to be based on motorists or pedestrians: there is little, if any, consideration given to the needs of cyclists. This thesis presents an investigation of lighting for cycling after dark within an urban environment. Three empirical investigations were conducted. A field survey was conducted to investigate the influence of the ambient light level on the tendency to cycle. Mobile eye-tracking was used to investigate the gaze behaviour of cyclists in natural settings, using two parallel measurements to reveal the critical of these fixations: performance on an audio dual-task and skin conductance response (SCR), and by that improved the ecological validity of previous similar research. A laboratory experiment was conducted to investigate obstacle detection under variations in the type, location, and level of lighting. The field study revealed that cycling increases when the ambient light level is higher. This suggests that road lighting might be a tool to encourage more cycling. The eye-tracking study suggested that observing the path ahead is a critical task, reflecting a tendency to search for possible obstacles on the road. Post hoc analysis of the eye-tracking data also suggested an influence of ambient light level on gaze towards aesthetic elements (architectural features) of the environment with such elements are suggested by the literature to be associated with positive cycling experience: this suggests that appropriate road lighting motivates the choice to cycle. The detection experiment revealed two significant effects: first; that road lighting and bicycle lighting may conflict. In other words, using bicycle lighting on a lit road may impair detection performance, not improve it. Second; that detection is improved when the front bicycle lamp is located on the wheel hub rather than the handlebar

Perceptual Image Quality Of Launch Vehicle Imaging Telescopes

A large fleet (in the hundreds) of high quality telescopes are used for tracking and imaging of launch vehicles during ascent from Cape Canaveral Air Force Station and Kennedy Space Center. A maintenance tool has been development for use with these telescopes. The tool requires rankings of telescope condition in terms of the ability to generate useful imagery. It is thus a case of ranking telescope conditions on the basis of the perceptual image quality of their imagery. Perceptual image quality metrics that are well-correlated to observer opinions of image quality have been available for several decades. However, these are quite limited in their applications, not being designed to compare various optical systems. The perceptual correlation of the metrics implies that a constant image quality curve (such as the boundary between two qualitative categories labeled as excellent and good) would have a constant value of the metric. This is not the case if the optical system parameters (such as object distance or aperture diameter) are varied. No published data on such direct variation is available and this dissertation presents an investigation made into the perceptual metric responses as system parameters are varied. This investigation leads to some non-intuitive conclusions. The perceptual metrics are reviewed as well as more common metrics and their inability to perform in the necessary manner for the research of interest. Perceptual test methods are also reviewed, as is the human visual system. iv Image formation theory is presented in a non-traditional form, yielding the surprising result that perceptual image quality is invariant under changes in focal length if the final displayed image remains constant. Experimental results are presented of changes in perceived image quality as aperture diameter is varied. Results are analyzed and shortcomings in the process and metrics are discussed. Using the test results, predictions are made about the form of the metric response to object distance variations, and subsequent testing was conducted to validate the predictions. The utility of the results, limitations of applicability, and the immediate ability to further generalize the results is presented

Motion cueing in driving simulators for research applications

This research investigated the perception of self-motion in driving simulation, focussing on the dynamic cues produced by a motion platform. The study was undertaken in three stages, evaluating various motion cueing techniques based on both subjective ratings of realism and objective measures of driver performance. Using a Just Noticeable Difference methodology, Stage 1 determined the maximum perceptible motion scaling for platform movement in both translation and tilt. Motion cues scaled by 90% or more could not be perceptibly differentiated from unscaled motion. This result was used in Stage 2‟s examination of the most appropriate point in space at which the platform translations and rotations should be centred (Motion Reference Point, MRP). Participants undertook two tracking tasks requiring both longitudinal (braking) and lateral (steering) vehicle control. Whilst drivers appeared unable to perceive a change in MRP from head level to a point 1.1m lower, the higher position (closer to the vestibular organs) did result in marginally smoother braking, corresponding to the given requirements of the longitudinal driving task. Stage 3 explored the perceptual trade-off between the specific force error and tilt rate error generated by the platform. Three independent experimental factors were manipulated: motion scale-factor, platform tilt rate and additional platform displacement afforded by a XY-table. For the longitudinal task, slow tilt that remained sub-threshold was perceived as the most realistic, especially when supplemented by the extra surge of the XY-table. However, braking task performance was superior when a more rapid tilt was experienced. For the lateral task, perceived realism was enhanced when motion cues were scaled by 50%, particularly with added XY-sway. This preference was also supported by improvements in task accuracy. Participants ratings were unmoved by changing tilt rate, although rapid tilt did result in more precise lane control. Several interactions were also observed, most notably between platform tilt rate and XY-table availability. When the XY-table was operational, driving task performance varied little between sub-threshold and more rapid tilt. However, while the XY-table was inactive, both driving tasks were better achieved in conditions of high tilt rate. An interpretation of these results suggests that without the benefit of significant extra translational capability, priority should be given to the minimisation of specific force error through motion cues presented at a perceptibly high tilt rate. However, XY-table availability affords the simulator engineer the luxury of attaining a slower tilt that provides both accurate driving task performance and accomplishes maximum perceived realism

Better Images : Understanding and Measuring Subjective Image-Quality

The objective in this thesis was to examine the psychological process of image-quality estimation, specifically focusing on people who are naïve in this respect and on how they estimate high-quality images. Quality estimation in this context tends to be a preference task, and to be subjective. The aim in this thesis is to enhance understanding of viewing behaviour and estimation rules in the subjective assessment of image-quality. On a more general level, the intention is to shed light on estimation processes in preference tasks. An Interpretation-Based Quality (IBQ) method was therefore developed to investigate the rules used by naïve participants in their quality estimations. It combines qualitative and quantitative approaches, and complements standard methods of image-quality measurement. The findings indicate that the content of the image influences perceptions of its quality: it influences how the interaction between the content and the changing image features is interpreted (Study 1). The IBQ method was also used to create three subjective quality dimensions: naturalness of colour, darkness and sharpness (Study 2). These dimensions were used to describe the performance of camera components. The IBQ also revealed individual differences in estimation rules: the participants differed as to whether they included interpretation of the changes perceived in an image in their estimations or whether they just commented on them (Study 4). Viewing behaviour was measured to enable examination of the task properties as well as the individual differences. Viewing behaviour was compared in two tasks that are commonly used in studies on image-quality estimation: the estimation of difference and the estimation of difference in quality (Study 3). The results showed that viewing behaviour differed even in two magnitude-estimation tasks with identical material. When they were estimating quality the participants concentrated mainly on the semantically important areas of the image, whereas in the difference-estimation task they also examined wider areas. Further examination of quality-estimation task revealed individual differences in the viewing behaviour and in the importance these viewing behaviour groups attached to the interpretation of changes in their estimations (Study 4). It seems that people engaged in a subjective preference-estimation task use different estimation rules, which is also reflected in their viewing behaviour. The findings reported in this thesis indicate that: 1) people are able to describe the basis of their quality estimations even without training when they are allowed to use their own vocabulary; 2) the IBQ method has the potential to reveal the rules used in quality estimation; 3) changes in instructions influence the way people search for information from the images; and 4) there are individual differences in terms of rules and viewing behaviour in quality-estimation tasks.Tämä väitöskirja käsittelee subjektiivista kuvanlaadun arviointiprosessia, etenkin keskittyen kuvanlaadun arvioinnin suhteen kouluttamattomien ihmisten korkea laatuisten kuvien arviointiin. Kuvanlaadulla tarkoitetaan tässä kuvan prosessointiin liittyviä tekijöitä. Tavoitteena on lisätä ymmärrystä kuvanlaadun arviointiprosessista ja sen mittaamisesta. Kuvanlaadun arviointiprosessissa on yleisesti keskitytty saamaan yksi arvio laadusta tai yksi arvio jollain etukäteen määritellyllä skaalalla. Tällöin emme tiedä mihin kouluttamaton arvioitsija olisi kiinnittänyt huomionsa ja millä perusteilla hän olisi kuvaa arvioinut. Tätä selvittämään kehitimme menetelmän, jolla voimme tarkastella ihmisten arvioissaan käyttämiä perusteita. Ihmiset kuvailivat perusteita vapaasti ja kun he saivat käyttää omaa sanastoaan, he olivat myös johdonmukaisia arvioissaan. Tätä menetelmää käytettiin myös selvittämään subjektiivisia kuvanlaatu-ulottuvuuksia, joita olivat värien luonnollisuus, tummuus ja tarkkuus. Toinen osa väitöskirjaa käsittelee kuvanlaadun arviointitehtävää prosessina. Selvitimme miten pieni muutos koehenkilöille annetussa ohjeistuksessa muuttaa heidän tapaansa katsella kuvaa heidän tehdessä siihen liittyviä arvioita. Tehtävänä oli kahdessa kuvassa näkyvien erojen arviointi joko erojen suuruuden tai kuvanlaadun erojen mukaan. Kuvanlaatua arvioitaessa huomio kiinnittyi enemmän kohtiin, jotka olivat semanttisesti merkityksellisiä, kun eroja arvioitaessa laajempi alue otettiin huomioon. Tarkastelimme myös kuvanlaadunarviointeihin liittyviä yksilöiden välisiä eroja. Koehenkilöt pystyttiin jakamaan kolmeen ryhmään heidän katselutapojensa perusteella. Nämä katselutaparyhmät erosivat toisistaan myös siinä kuinka paljon he käyttivät arvioinneissaan perusteina vaikutelmia, jotka syntyivät kuvanlaadun muutosten pohjalta. Toiset keskittyivät arvioimaan kuvanlaatua siihen liittyvien attribuuttien mukaan, kun toiset käyttivät perusteina näiden attribuuttien kuvan viestiin synnyttämiä vaikutelmia. Korkean kuvanlaadun arvioinnissa on usein kyseessä mieltymyksiin perustuva laadun arviointi. Tällöin on tärkeää antaa ihmisten käyttää omia käsitteitään, sekä ottaa huomioon että pienimmätkin tekijät, kuten sanavalinnat kysymyksissä ja ihmisten väliset eroavuudet, vaikuttavat arviointeihin. Tämä väitöskirja antaa eväitä tarkastella arviointiprosessia

Images in Electronic Performance Support Systems (EPSS): An Eye Tracking Study

Current forms of online help are increasingly making use of images (graphical illustrations or photographs), along with textual instructions to effectively assist users in performing a specific task. Users typically want to accomplish tasks quickly and devote limited attention to help systems. Hence, it is essential that these images facilitate efficient understanding of the task at hand and complement the instructions well. The first goal of the project was to create quick and inexpensive images that work better than or as well as existing graphical illustrations. The second goal was to conduct a usability test with eye tracking to compare guidance of visual attention by three types of images: graphic illustrations, digital photographs and modified digital photographs. During the test, other key measures like success rates and time on task were also measured. Subjective preferences for the three types of images were also evaluated. Results indicated that the modified photographs performed better in guiding the visual attention of users to the relevant areas of the image than the other two image types. Though not statistically significant, the trend showed that task completion times for tasks with the modified photographs were shorter than those with the other image types (i.e., tasks with modified photographs were quicker than those with other image types). Subjective ratings indicated that participants preferred photographs and modified photographs to the existing graphical illustrations

Saliency Prediction in the Data Visualization Design Process

L'abstract è presente nell'allegato / the abstract is in the attachmen

Assessment of Visual Literacy – Contributions of Eye Tracking

Visual Literacy (VL) is defined as a set of competencies to understand and express oneself through visual imagery. An expansive model, the Common European Framework of Reference for Visual Literacy (CEFR-VL) (Wagner & Schönau, 2016), comprises 16 sub-competencies, including abilities such as analyzing, judging, experimenting with or aesthetically experiencing images. To empirically assess VL sub-competencies different visual tasks were presented to VL experts and novices. Problem-solving behavior and cognitive strategies involved in visual logical reasoning (Paper 1), Visual Search (Paper 2), and judgments of visual abstraction (Paper 3) were investigated. Eye tracking in combination with innovative statistical methods were used to uncover latent variables during task performance and to assess the possible effects of differences in expertise level. Furthermore, the relationship between students' self-reported visual abilities and their performance on VL assessment tasks is systematically explored. Results show how effects of perceptual skills of VL experts are less pronounced and more nuanced than implied by VL models. The comprehension of visual logical models does not seem to depend much on VL, as experts and novices did not differ in their solution strategies and eye movement indicators (Paper 1). In contrast, the visual search task on artworks revealed how experts were able to detect target regions with higher efficiency than novices revealed by higher precision of fixations on target regions. Furthermore, latent image features were detected by experts with more certainty (Paper 2). The assessment of perceived level of visual abstraction revealed how, contrary to our expectations, experts did not outperform novices but despite that were able to detect nuanced level of abstraction compared to student groups. Distribution of fixations indicate how attention is directed towards more ambiguous images (Paper 3). Students can be classified based on different levels of visual logical comprehension (Paper 1), on self-reported visual skills, and the time spent on the tasks (Paper 2, Paper 3). Self-reported visual art abilities of students (e.g., imagination) influences the visual search and the judgment of visual abstraction. Taken together the results show how VL skills are not determined solely by the number of correct responses, but rather by how visual tasks are solved and deconstructed; for example, experts are able to focus on less salient image regions during visual search and demonstrate a more nuanced interpretation of visual abstraction. Low-level perceptual abilities of experts and novices differ marginally, which is consistent with research on art expertise. Assessment of VL remains challenging, but new empirical methods are proposed to uncover the underlying components of VL

Motor learning induced neuroplasticity in minimally invasive surgery

Technical skills in surgery have become more complex and challenging to acquire since the introduction of technological aids, particularly in the arena of Minimally Invasive Surgery. Additional challenges posed by reforms to surgical careers and increased public scrutiny, have propelled identification of methods to assess and acquire MIS technical skills. Although validated objective assessments have been developed to assess motor skills requisite for MIS, they poorly understand the development of expertise. Motor skills learning, is indirectly observable, an internal process leading to relative permanent changes in the central nervous system. Advances in functional neuroimaging permit direct interrogation of evolving patterns of brain function associated with motor learning due to the property of neuroplasticity and has been used on surgeons to identify the neural correlates for technical skills acquisition and the impact of new technology. However significant gaps exist in understanding neuroplasticity underlying learning complex bimanual MIS skills. In this thesis the available evidence on applying functional neuroimaging towards assessment and enhancing operative performance in the field of surgery has been synthesized. The purpose of this thesis was to evaluate frontal lobe neuroplasticity associated with learning a complex bimanual MIS skill using functional near-infrared spectroscopy an indirect neuroimaging technique. Laparoscopic suturing and knot-tying a technically challenging bimanual skill is selected to demonstrate learning related reorganisation of cortical behaviour within the frontal lobe by shifts in activation from the prefrontal cortex (PFC) subserving attention to primary and secondary motor centres (premotor cortex, supplementary motor area and primary motor cortex) in which motor sequences are encoded and executed. In the cross-sectional study, participants of varying expertise demonstrate frontal lobe neuroplasticity commensurate with motor learning. The longitudinal study involves tracking evolution in cortical behaviour of novices in response to receipt of eight hours distributed training over a fortnight. Despite novices achieving expert like performance and stabilisation on the technical task, this study demonstrates that novices displayed persistent PFC activity. This study establishes for complex bimanual tasks, that improvements in technical performance do not accompany a reduced reliance in attention to support performance. Finally, least-squares support vector machine is used to classify expertise based on frontal lobe functional connectivity. Findings of this thesis demonstrate the value of interrogating cortical behaviour towards assessing MIS skills development and credentialing.Open Acces