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Tobii EyeTracking's List: Ophthalmology & Vision science

  • Nov 23, 10

    ABSTRACT
    In this chapter, we present a framework to learn and predict regions of interest in videos, based on human eye movements. In our approach, the eye gaze information of several users are recorded as they watch videos that are similar, and belong to a particular application domain. This information is used to train a classifier to learn low-level video features from regions that attracted the visual attention of users. Such a classifier is combined with vision-based approaches to provide an integrated framework to detect salient regions in videos. Till date, saliency prediction has been viewed from two different perspectives, namely visual attention modeling and spatiotemporal interest point detection. These approaches have largely been vision-based. They detect regions having a predefined set of characteristics such as complex motion or high contrast, for all kinds of videos. However, what is ‘interesting’ varies from one application to another. By learning features of regions that capture the attention of viewers while watching a video, we aim to distinguish those that are actually salient in the given context, from the rest. The integrated approach ensures that both regions with anticipated content (top–down attention) and unanticipated content (bottom–up attention) are predicted by the proposed framework as salient. In our experiments with news videos of popular channels, the results show a significant improvement in the identification of relevant salient regions in such videos, when compared with existing approaches.

  • Nov 11, 10

    ABSTRACT
    In serial memory for spatial information, performance is impaired when distractors are interpolated between to-be-remembered (TBR) stimuli (Tremblay, Nicholls, Parmentier, & Jones, 2005). The so-called sandwich effect, combined with the use of eye tracking, served as a tool for examining the role of the oculomotor system in serial memory for spatial information. Participants had to recall the order in which sequences of TBR locations were presented. In some trials, to-be-ignored blue dots were presented after each TBR location. Our results show that response locations shift toward the location of the distractors, and this deviation is related to the eye movement deviation toward the distractor location. These results suggest that TBR and to-be-ignored locations are encoded onto a common map that could lie within the oculomotor system. Interference in memory for spatial information is interpreted in light of a model of oculomotor behavior (Godijn & Theeuwes, 2002b).

  • Nov 02, 10

    ABSTRACT
    Visual discomfort is a major problem for head-mounted displays and other stereo displays. One effect that is known to reduce visual comfort is double vision, which can occur due to high disparities. Previous studies suggest that adding artificial out-of-focus blur increases the fusional limits, where the left and right image can be fused without double vision. We investigate the effect of adding artificial out-of-focus blur on visual discomfort using two different setups. One uses a stereo monitor and an eye tracker to change the depth of focus based on the gaze of the user. The other one uses a video-see through head mounted display. A study involving 18 subjects showed that the viewing comfort when using blur is significantly higher in both setups for virtual scenes. However we can not confirm without doubt that the higher viewing comfort is only related to an increase of the fusional limits, as many subjects reported that double vision did not occur during the experiment. Results for additional photographed images that have been shown to the subjects were less significant. A first prototype of an AR system extracting a depth map from stereo images and adding artificial out-of-focus blur is presented.

  • Sep 14, 10

    ABSTRACT
    Introducing distortions into perspective views is a popular technique to direct our visual attention to specific objects, as seen in hand-drawn illustrations and cartoon animations. This type of image expression, called nonperspective projection, is feasible in visual communication, because the human visual system can reconstruct the target three-dimensional (3D) scene correctly provided that the corresponding image distortions are within a certain perceptual tolerance. In this paper, we develop a perceptual approach to guiding the design of such nonperspective images by referring to the 3D perception induced by pictorial depth cues. We formulate an acceptable tolerance by investigating how we perceive image distortion according to the change in the configuration of depth cues. The obtained formulation is then incorporated into our new algorithm, with which we can automatically control plausible image deformation by simply modifying the positions and sizes of specific objects in a scene.

  • Sep 14, 10

    ABSTRACT
    Size, color, and orientation have long been considered elementary features whose attributes are extracted in parallel and available to guide the deployment of attention. If each is processed in the same fashion with simply a different set of local detectors, one would expect similar search behaviours on localizing an equivalent flickering change among identically laid out disks. We analyze feature transitions associated with saccadic search and find out that size, color, and orientation are not alike in dynamic attribute processing over time. The Markovian feature transition is attractive for size, repulsive for color, and largely reversible for orientation.

  • Aug 19, 10

    ABSTRACT
    Motion parallax (MP) is a kinetic, monocular cue to depth that relies on both retinal image motion and a pursuit eye movement signal. With MP, depth sign is based on the direction of the smooth pursuit eye movement signal: Retinal motion in the same direction as the pursuit signal is perceived nearer than fixation. Retinal motion in the opposite direction is perceived farther away than fixation (M. Nawrot & Joyce, 2006). In previous research to understand the development of MP in infants we (E. Nawrot, Mayo, & M. Nawrot, 2009) used an infant control habituation procedure with an MP stimulus to determine the average age of dishabituation to a depth-reversed test stimulus. Dishabituation to the change in depth sign is evidence for depth discrimination from MP. Now, our goal is to determine when the developing smooth pursuit system has sufficiently matured in infancy and then directly measure pursuit eye movements in relation to a motion parallax task. We presented 12-20 week-old infants with both a depth-from-MP task and a visual tracking task designed to elicit smooth pursuit (SP). The MP stimulus and procedure is identical to previous research (E. Nawrot, Mayo, & M. Nawrot, 2009). Tracking is elicited with a schematic “happy-face” that translates at 10 deg/sec. Eye movements are recorded using a Tobii systems X120 Eye Tracker. We expect to find that SP gain (eye velocity/target velocity) increases across this age range and pursuit maturity will correlate with the onset of sensitivity to MP. Data collected from 16 infants so far supports the hypothesis that depth from MP requires maturation of SP. In general, younger infants demonstrate more saccadic and lower gain eye movements, without MP, while older infants demonstrate more smooth pursuit tracking of the stimulus and MP.

  • Aug 06, 10

    ABSTRACT
    Interacting with a dynamic environment calls for close coordination between the timing and direction of motor behaviors.
    Accurate motor behavior requires the system to predict where the target for action will be, both when action planning is
    complete and when the action is executed. In the current study, we investigate the time course of velocity information
    accrual in the period leading up to a saccade toward a moving object. In two experiments, observers were asked to generate
    saccades to one of two moving targets. Experiment 1 looks at the accuracy of saccades to targets that have trial-by-trial
    variations in velocity. We show that the pattern of errors in saccade landing position is best explained by proposing that trialby-
    trial target velocity is taken into account in saccade planning. In Experiment 2, target velocity stepped up or down after a
    variable interval after the movement cue. The extent to which the movement endpoint reflects pre- or post-step velocity can
    be used to identify the temporal velocity integration window; we show that the system takes a temporally blurred snapshot of
    target velocity centered È200 ms before saccade onset. This estimate is used to generate a dynamically updated prediction
    of the target’s likely future location.

  • Aug 06, 10

    ABSTRACT
    Initiating an eye movement is slowed if the saccade is directed to a location that has been fixated in the recent past. We show that this inhibitory effect is modulated by the temporal statistics of the environment: If a return location is likely to become behaviorally relevant, inhibition of return is absent. By fitting an accumulator model of saccadic decision-making, we show that the inhibitory effect and the sensitivity to local statistics can be dissociated in their effects on the rate of accumulation of evidence, and the threshold controlling the amount of evidence needed to generate a saccade.

  • Aug 06, 10

    ABSTRACT
    In this paper, we investigate how controlled changes to image properties and orientation affect eye movements for repeated viewings of images of natural scenes. We make changes to images by manipulating low-level image content (such as luminance or chromaticity) and/or inverting the image. We measure the effects of these manipulations on human scanpaths (the spatial and chronological path of fixations), additionally comparing these effects to those predicted by a widely used saliency model (L. Itti & C. Koch, 2000). Firstly we find that repeated viewing of a natural image does not significantly modify the previously known repeatability (S. A. Brandt & L. W. Stark, 1997; D. Noton & L. Stark, 1971) of scanpaths. Secondly we find that manipulating image features does not necessarily change the repeatability of scanpaths, but the removal of luminance information has a measurable effect. We also find that image inversion appears to affect scene perception and recognition and may alter fixation selection (although we only find an effect on scanpaths with the additional removal of luminance information). Additionally we confirm that visual saliency as defined by L. Itti and C. Koch’s (2000) model is a poor predictor of real observer scanpaths and does not predict the small effects of our image manipulations on scanpaths.

  • Aug 06, 10

    ABSTRACT
    We measured the eye movements of participants who watched 6-minute movie in stereoscopic and non-stereoscopic form. We analyzed four shots of the movie. The results indicate that in a 2D movie viewers tend to look at the actors, as most of the eye movements are clustered there. The significance of the actors start at the beginning of a shot, as the eyes of the viewer focus almost immediately to them. In S3D movie the eye movement patterns were more widely distributed to other targets. For example, complex stereoscopic structures and structures nearer than the actor captured the interest and eye movements of the participants. Also, the tendency to first look at the actors was diminished in the S3D shots. The results suggests that in a S3D movie there are more eye movements which are directed to wider array of objects than in a 2D movie.

  • Aug 06, 10

    ABSTRACT
    We used event-related functional magnetic resonance imaging (fMRI) to determine blood oxygen-leveldependent (BOLD) signal changes following microsaccades, visually-guided saccades, and eyeblinks in retinotopically mapped visual cortical areas V1–V3 and hMT+. A deconvolution analysis revealed a similar pattern of BOLD activation following a microsaccade, 0.16° voluntary saccade, and 0.16° displacement of the image under conditions of fixation. In all areas, an initial increase in BOLD signal peaking at approximately 4.5 s after the event was followed by a decline and decrease below baseline. This modulation appears most pronounced for microsaccades and small voluntary saccades in V1, diminishing in strength from V1 to V3. In contrast, 0.16° real motion under conditions of fixation yields the same level of BOLD signal increase in V1 through V3. BOLD signal modulates parametrically with the size of voluntary saccades (0.16°, 0.38°, 0.82°, 1.64°, and 3.28°) in V1–V3, but not in hMT+. Eyeblinks generate larger modulation that peaks by 6.5 s, and dips below baseline by 10 s post-event, and also exhibits diminishing modulation from V1 to V3. Our results are consistent with the occurrence of transient neural excitation driven by changes in input to retinal ganglion cell receptive fields that are induced by microsaccades, visually-guided saccades, or small image shifts. The pattern of results in area hMT+ exhibits no significant modulation by microsaccades, relatively small modulation by eyeblinks, and substantial responses to saccades and background jumps, suggesting that spurious image motion signal arising from microsaccades and eyeblinks is relatively diminished by hMT+.

  • Aug 06, 10

    ABSTRACT
    We propose a technique to calculate the saliency of animated meshes with material properties. The saliency computation considers multiple features of 3D meshes including their geometry, material and motion. Each feature contributes to the final saliency map which is view independent; and therefore, can be used for view dependent and view independent applications. To verify our saliency calculations, we performed an experiment in which we use an eye tracker to compare the saliencies of the regions that the viewers look with the other regions of the models. The results confirm that our saliency computation gives promising results. We also present several applications in which the saliency information is used.

  • Aug 06, 10

    ABSTRACT
    This paper describes a study that seeks to explore the correlation between eye movements and the interpretation of geometric shapes. This study is intended to inform the development of an eye tracking interface for computational tools to support and enhance the natural interaction required in creative design.
    A common criticism of computational design tools is that they do not enable manipulation of designed shapes according to all perceived features. Instead the manipulations afforded are limited by formal structures of shapes. This research examines the potential for eye movement data to be used to recognise and make available for manipulation the perceived features in shapes.
    The objective of this study was to analyse eye movement data with the intention of recognising moments in which an interpretation of shape is made. Results suggest that fixation duration and saccade amplitude prove to be consistent indicators of shape interpretation.

  • Aug 05, 10

    ABSTRACT
    This paper presents a detection algorithm that allows automatic classification of hypermetric and hypometric oculomotor plant behavior in cases when saccadic behavior of the oculomotor plant is assessed during the course of the step stimulus. Such behavior can be classified with a number of oculomotor plant metrics represented by the number of overshoots, undershoots, corrected undershoots/overshoots, multi-corrected overshoots/undershoots. The algorithm presented in this paper allows for the automated classification of nine oculomotor plant metrics including dynamic overshoots and express saccades. Data from sixty-five human subjects were used to support this experimental study. The performance of the proposed algorithm was tested and compared to manual classification methods resulting in a detection accuracy of up to 72% for several of the oculomotor plant metrics.

  • Aug 05, 10

    ABSTRACT
    How does expertise in the analysis of particular images influence the effects of visual saliency upon attention? Expert analysts of aerial photographs and untrained viewers undertook change-detection and location memory tasks using aerial photographs with eye movements recorded throughout. Experts were more accurate in both tasks. Significant differences were also seen in the scanpaths: Untrained viewers fixated preferentially upon salient features throughout stimulus presentation whereas experts did not. However, both groups showed a strong influence of saliency in change detection and memory tasks. We interpret this apparent contradiction by: (i) assuming that the use of saliency in visual search is discretionary, and experts can use semantic information to prioritise where to fixate next; whereas, (ii) in tasks requiring spatial memory, analysis of visual saliency delivers easily acquired landmarks to reference the location of items in an image; a previously overlooked function used by expert and untrained viewers alike.

  • Aug 05, 10

    ABSTRACT
    Sinusoidal motion of elements in a random-dot pattern can elicit a striking percept of a rotating volume, a phenomenon known as structure-from-motion (SFM). We demonstrate that if the dots defining the volume are 2D mirror-symmetric, novel 3D interpretations arise. In addition to the classical rotating cylinder, one can perceive mirror-symmetric, flexible surfaces bending along the path of movement. In three experiments, we measured the perceptual durations of the different interpretations in a voluntary control task. The results suggest that motion signals and symmetry signals are integrated during surface interpolation. Furthermore, the competition between the rotating cylinder percept and the symmetric surfaces percept is resolved at the level of surface perception rather than at the level of individual stimulus elements. Concluding, structure-from-motion is an interactive process that incorporates not only motion cues but also form cues. The neurofunctional implication of this is that surface interpolation is not fully completed in its designated neural “engine,” MT/V5, but rather in a higher tier area such as LOC, which receives input from MT/V5 and which is also involved in symmetry detection.

  • Aug 05, 10

    ABSTRACT
    We present a novel method for the measurement of the similarity between aggregates of scanpaths. This may be thought of as a solution to the "average scanpath" problem. As a by-product of this method, we derive a classifier for groups of scanpaths drawn from various classes. This capability is empirically demonstrated using data gathered from an experiment in an attempt to automatically determine expert/novice classification for a set of visual tasks.

  • Aug 05, 10

    ABSTRACT
    A remote eye tracker is used to explore its utility for ocular vergence measurement. Subsequently, vergence measurements are compared in response to anaglyphic stereographic stimuli as well as in response to monoscopic stimulus presentation on a standard display. Results indicate a highly significant effect of anaglyphic stereoscopic display on ocular vergence when viewing a stereoscopic calibration video. Significant convergence measurements were obtained for stimuli fused in the anterior image plane.

  • Jul 20, 10

    ABSTRACT
    Addressing data visualization challenges typically involves applying lessons from visualization theory to inform design and implementation approaches. This process is shaped to a large extent by the availability of tools that are aimed at enabling visualization designers to focus on visualization design rather than on low-level software engineering. Recently, such tools have become powerful enough to be used effectively. We discuss the ideation process informing our design approach and describe the use of Macromedia Flash MX 2004 for the rapid prototyping of a gaze data visualization tool. We highlight selected gaze data visualization ideas to illustrate the most innovative aspects of our design. In particular, we explain our strategy to reveal the underlying mechanisms that produce the summarizing visual constructs and why this is important. We introduce a new technique for visualizing gaze data for dynamic stimuli. The novelty of this approach is that it avoids the traditional frame-by-frame analyses typically carried out for such stimuli.

  • Jul 19, 10

    ABSTRACT
    This paper applies statistical design principles to a simple biological model of human vision so that we can more clearly interpret the apparent role of eye saccades. In doing so we show that many structural features of the biological system (such as the optical geometry of the retina) are strategies for minimising the resources required to construct a working image recognition system. The ideas presented have implications for the construction of artificial (computer) vision systems. The computational model is very closely related to (but not based upon) SIFT, but more strongly based on a consideration of vision as a process of measurment while also linking the idea of multi-scale analysis with biological structure.

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