Examining the Conspicuity of Infra-Red Markers For Use With 2-D Eye TrackingAbstract

Physical infra-red (IR) markers are sometimes used to help aggregate data collected by head-mounted eye trackers. In many environments, the use of such devices is problematic because the IR markers may serve as distractors. We present a study that quantitatively examines the conspicuity of these markers. Data was collected using both the corresponding head-mounted eye tracker and a simple tripod-mounted tracker. Results indicate the presence of markers does not appear to significantly divert attention.

Methodology

References

ResultsResults comparing fixation counts differ significantly depending on the choice of smoothing filter and classification filter (see other poster for details). The results presented are with the Butterworth smoothing filter and the Savitzky-Golay differential classifier.

ANOVA revealed no significance between any of the eye tracking metrics. No significance was found in the Presence Questionnaire or any preferential questionnaires. The results are summarized below (in Group A, the participants never saw markers. In Group B, they always saw markers). Variability was high for all metrics (see Figure 5).

Discussion & ConclusionA study was presented in which the conspicuity of Tobii’s IR markers was examined with two different eye trackers. The results appear to indicate that the markers are not conspicuous. However, due to the high variance, the validity of these results may be questionable.

Andrew D. Ouzts, Andrew T. Duchowski

SCHOOL OF COMPUTING,

CLEMSON UNIVERSITY

aouzts@g.clemson.edu

duchowski@acm.org,

Introduction & BackgroundThere is growing interest in using head-mounted eye

trackers for use with natural tasks [1]. Typical eye tracker experiments generally use a desktop-based device such as the Tobii 1750 (see Figure 1), which is immobile and presents the user with a feeling of artificiality. Recently released mobile eye trackers such as the Tobii Glasses present a possible alternative. Despite this, some users report that the glasses disrupt their sense of immersion, so in this experiment we also use the Mirametrix, a small, portable eye tracker that is physically unobtrusive.

Aggregating data from head-mounted trackers is a challenging problem. Users may approach from different vantage points and at different times. A proposed solution is the use of IR markers which allow 3-D eye tracking data to be aggregated onto a 2-D plane formed by the presence of the IR markers.

Since the goal of such units is to eliminate artificiality, the presence of these markers seems problematic. However, no research has been done to analyze how distracting these markers are.

The experiment was a 2 (eye tracker type) x 2 (IR marker presence) x 2 (image type) mixed within- and between-subjects design. Comparison of eye trackers was performed within subjects, whereas conspicuity of the markers was compared between subjects. 16 participants (8 male, 8 female) took part in the experiment. Each participant viewed two similar stimuli images and used both the Mirametrix and Tobii Glasses eye trackers, and half the participants viewed the stimuli with IR markers present. Figure 3 shows these four conditions.

Areas of Interest (AOIs; see Figure 4) were used to aggregate data on rectangular regions defined at the location of the IR markers. We examined the data with eye-tracking dependent measures: total number of fixations on the AOIs, total fixation duration in the AOIs, and the ratio of fixation on the AOIs to the total number of fixations. A modified version of the Witmer-Singer Presence Questionnaire [2] was also administered.

1) Jeff B. Pelz, Roxanne Canosa, and Jason Babcock. 2000. Extended tasks elicit complex eye movement patterns. In Proceedings of the 2000 symposium on Eye tracking research & applications (ETRA '00). ACM, New York, NY, USA, 37-43.

2) Bob G. Witmer and Michael J. Singer. 1998. Measuring Presence in Virtual Environments: A Presence Questionnaire. Presence: Teleoper. Virtual Environ. 7, 3 (June 1998), 225-240.

Toni Gomes

PACKAGING SCIENCE,

CLEMSON UNIVERSITY

tgomes@clemson.edu

Figure 1: Several different eye trackers. (top left) The Tobii 1750 desktop-based eye tracker, (top right) the Tobii Glasses eye tracker, (bottom left) the Mirametrix S1 eye tracker, (bottom right) an IR marker used in conjunction with the Tobii glasses.

Figure 3: A participant using the glasses without markers present (top left), with glasses with markers (top right), with the Mirametrix without markers (bottom left), and the Mirametrix with markers (bottom right).

Metric on AOIs Average – Group A Average – Group B p valueFixation Count 0.125 0.167 0.752Fixation Duration 0.024 0.064 0.380Fixation Ratio 0.013 0.017 0.791

Figure 5: Results of each of the eye tracking metrics and presence metrics (bottom right). IMM refers to the immersion subscale, INV refers to the involvement subscale, IFQ refers to the interface quality subscale, and M/G refer to the Mirametrix and Glasses respectively.

Figure 4: Heatmap of several participants with AOI locations overlaid as red squares.

AcknowledgementsThis research was supported, in part, by NSF Research Experience for Undergraduates (REU) Site Grant CNS-0850695.