Ann McNamara

Subtle gaze direction

This article presents a novel technique that combines eye-tracking with subtle image-space modulation to direct a viewers gaze about a digital image. We call this paradigm subtle gaze direction. Subtle gaze direction exploits the fact that our peripheral vision has very poor acuity compared to our foveal vision. By presenting brief, subtle modulations to the peripheral regions of the field of view, the technique presented here draws the viewers foveal vision to the modulated region. Additionally, by monitoring saccadic velocity and exploiting the visual phenomenon of saccadic masking, modulation is automatically terminated before the viewers foveal vision enters the modulated region. Hence, the viewer is never actually allowed to scrutinize the stimuli that attracted her gaze. This new subtle gaze directing technique has potential application in many areas including large scale display systems, perceptually adaptive rendering, and complex visual search tasks.

Improving search task performance using subtle gaze direction

A new experiment is presented which demonstrates the usefulness of an image space modulation technique called Subtle Gaze Direction (SGD) for guiding the user in a simple searching task. SGD uses image space modulations in the luminance channel to guide a viewers gaze about a scene without interrupting their visual experience. The goal of SGD is to direct a viewers gaze to certain regions of a scene without introducing noticeable changes in the image. Using a simple searching task we compared performance using no modulation, using subtle modulation and using obvious modulation. Results from the experiments show improved performance when using subtle gaze direction, without affecting the users perception of the image. Results establish the potential of the method for a wide range of applications including gaming, perceptually based rendering, navigation in virtual environments and medical search tasks.

Perception in graphics, visualization, virtual environments and animation

The advent of affordable display technology and seamless integration of real-world scenes with computer graphics fuels our continuing ability to create and display stunning realistic imagery. With the arrival of new technology, algorithms and display methods comes the realization that gains can be made by tailoring output to the intended audience - humans. Human beings have amazingly complex perceptual systems, which have the ability to quickly capture and process vast amounts of complex data. With all its capability however, the Human Visual System (HVS) has some surprising nuances and limitations that can be exploited to the benefit of numerous graphics applications. This short course will provide insight into those aspects of HVS and other perceptual systems that can serve as both a guide and yard-stick to further the development and evaluation of computer graphics imagery and presentations. The literature on perception provides a rich source of knowledge that can be applied to the realm of computer graphics for immediate and direct benefit, generating images that not only exhibit higher quality, but use less time and resources to process. In addition, knowledge of the HVS serves as a guide on how best to present the images to fulfill the application at hand.

Search task performance using subtle gaze direction with the presence of distractions

A new experiment is presented that demonstrates the usefulness of an image space modulation technique called subtle gaze direction (SGD) for guiding the user in a simple searching task. SGD uses image space modulations in the luminance channel to guide a viewers gaze about a scene without interrupting their visual experience. The goal of SGD is to direct a viewers gaze to certain regions of a scene without introducing noticeable changes in the image. Using a simple searching task, we compared performance using no modulation, using subtle modulation, and using obvious modulation. Results from the experiments show improved performance when using subtle gaze direction, without affecting the users perception of the image. We then extend the experiment to evaluate performance with the presence of distractors. The distractors took the form of extra modulations, which do not correspond to a target in the image. Experimentation shows, that, even in the presence of distractors, more accurate results are returned on a simple search task using SGD, as compared to results returned when no modulation at all is used. Results establish the potential of the method for a wide range of applications including gaming, perceptually based rendering, navigation in virtual environments, and medical search tasks.

Exploring perceptual equivalence between real and simulated imagery

We conducted a new psychophysical experiment which judges the quality of computer graphics imagery with respect to the real scene it depicts. The experimental framework facilitates perceptual judgment of images against a real scene. Unlike previous work, which examined at primitive objects under basic illumination, this new experiment examines complex geometry illuminated using a calibrated light source. Here we present the design and results of the experiment. To ensure valid results, a commercial lighting booth containing rapid prototyped three dimensional objects serves as the real scene. For comparison, a series of representative images, of varying quality, were rendered using the physically based Radiance lighting simulation software. Result from these experiments show that higher parameter settings, which lead to longer processing times, do not necessarily lead to higher quality images.

Subtle gaze manipulation for improved mammography training

We use the Subtle Gaze Direction technique (SGD) to guide novices as they try to find abnormalities in mammograms. SGD works by performing image-space modulations on specific regions of the peripheral vision to attract attention. Gaze is monitored and modulations are terminated before they are scrutinized with high-acuity foveal vision. This approach is preferred to overt techniques which permanently alter images to highlight areas of interest. SGD is used to guide novices along the scanpath of an expert radiologist. We hypothesized that this would increase the likelihood of novices correctly identifying irregularities. Results reveal that novices who were guided in this manner performed significantly better than the control group (no gaze manipulation). Furthermore, a short-term post-training lingering effect was observed among subjects guided using SGD. They continued to perform better than the control group once the training was complete and gaze manipulation was disabled.

Guiding attention in controlled real-world environments

The ability to direct a viewers attention has important applications in computer graphics, data visualization, image analysis, and training. Existing computer-based gaze manipulation techniques, which direct a viewers attention about a display, have been shown to be effective for spatial learning, search task completion, and medical training applications. In this work we extend the concept of gaze manipulation beyond digital imagery to include controlled, real-world environments. We address two main challenges in guiding attention to real-world objects: determining what object the viewer is currently paying attention to, and providing (projecting) a visual cue on a different part of the scene in order to draw the viewers attention there. Our system consists of a pair of eye-tracking glasses to determine the viewers gaze location, and a projector to create the visual cue in the physical environment. The results of a user study show that we can effectively direct the viewers gaze in the real-world scene. Our technique has applicability in a wide range of instructional environments, including pilot training and driving simulators.

Exploring visual and automatic measures of perceptual fidelity in real and simulated imagery

This paper introduces a new psychophysical experiment developed to enable observers to judge the quality of computer graphics imagery with respect to the real scene it depicts. This new framework facilitates perceptual judgment of images against a real scene. Unlike previous work, which examined primitive objects under basic illumination, this experiment examines complex geometry illuminated using a calibrated light source. To ensure valid results, a commercial lighting booth containing rapid prototyped three-dimensional (3D) objects serves as the real scene. For comparison, a series of representative images, of varying quality, were rendered using the physically based Radiance lighting simulation software. Results from these experiments show that higher parameter settings, which lead to longer processing times, do not necessarily lead to higher quality images. To demonstrate that there is only modest benefit to setting parameters higher, images are subjected to further testing using two different visual quality discrimination operators; the Visual Differences Predictor (VDP) and the Structural SIMilarity (SSIM) for image-quality assessment. The results from the automatic operators correspond well with each other, in addition to yielding comparable outcomes as the psychophysical experiment. Although, a single scene was considered in the experiment, several scenes are tested using the image-quality metrics to lend further reliability to the assertion that higher parameter settings, which lead to extended processing times, do not necessarily lead to superior quality results.

Directing gaze in narrative art

Narrative art tells a story, either as a moment in an ongoing story or as a sequence of events unfolding over time. In many works of art separate panels within the same frame are used to depict the sequence of events. Often, there is no clear delineation between these panels, or any indication of the optimal viewing order. To improve visual literacy we propose using Subtle Gaze Direction (SGD) to direct the viewers gaze across an image in a manner which reveals the story. SGD uses small image space modulations in the luminance channel to guide a viewers gaze about an image without disrupting their normal visual experience. Using a simple ordering task we compared performance using no modulation and using subtle modulation with the correct order of narrative episodes as intended by the artist. Results from experiments show improved performance when SGD is employed. This experiment establishes the potential of the method as an aid to visual navigation in images where the viewing order is unclear.

Perceptually-motivated graphics, visualization and 3D displays

This course presents timely, relevant examples on how researchers have leveraged perceptual information for optimization of rendering algorithms, to better guide design and presentation in (3D stereoscopic) display media, and for improved visualization of complex or large data sets. Each presentation will provide references and short overviews of cutting-edge current research pertaining to that area. We will ensure that the most up-to-date research examples are presented by sourcing information from recent perception and graphics conferences and journals such as ACM Transactions on Perception, paying particular attention work presented at the 2010 Symposium on Applied Perception in Graphics and Visualization.