Methods for enhancing the accuracy of fixation and saccade detection and the reliability of calibration in video gaze-tracking systems are discussed. The unique aspects of the present approach include effective low-delay noise reduction prior to the detection of fixation changes, monitoring of gaze position in real time by the operator, identification of saccades as small as 0.5° while eliminating false fixations, and a quick, high-precision, semiautomated calibration procedure.

/pdf/heuristic-filtering-and-reliable-calibration-methods-for-dattdfh1n9.pdf

Heuristic filtering and reliable calibration methods for video-based pupil-tracking systems

Gaze-tracking data have been used successfully in the design of new input devices and as an observational technique in usability studies. Polynomial-based Video-Oculography (VOG) systems are one of the most attractive gaze estimation methods thanks to their simplicity and ease of implementation. Although the functionality of these systems is generally acceptable, there has been no thorough comparative study to date of how the mapping equations affect the final system response. After developing a taxonomic classification of calibration functions, we examined over 400,000 models and evaluated the validity of several conventional assumptions. Our rigorous experimental procedure enabled us to optimize the calibration process for a real VOG gaze-tracking system and halve the calibration time while avoiding a detrimental effect on the accuracy or tolerance to head movement. Finally, a geometry-based method is implemented and tested. The results and performance is compared with those obtained by the general purpose expressions.

Study of Polynomial Mapping Functions in Video-Oculography Eye Trackers

PURPOSE Using a novel automated perimetry technique, we tested the hypothesis that older adults will have increased latency and decreased accuracy of saccades, as well as higher visual thresholds, to peripheral visual stimuli when compared with younger adults. METHODS We tested 20 healthy subjects aged 18 to 30 years ("young") and 21 healthy subjects at least 60 years old ("older") for detection of briefly flashed peripheral stimuli of differing sizes in eight locations along the horizontal meridian (±4°, ±12°, ±20°, and ±28°). With the left eye occluded, subjects were instructed to look quickly toward any seen stimuli. Right eye movements were recorded with an EyeLink 1000 infrared camera system. Limiting our analysis to the four stimulus positions in the nasal hemifield (-4°, -12°, -20°, and -28°), we evaluated for group-level differences in saccadic latency, accuracy, and visual threshold at each stimulus location. RESULTS Saccadic latency increased as stimulus size decreased in both groups. Older subjects had significantly increased saccadic latencies (at all locations; P < 0.05), decreased accuracies (at all locations; P < 0.05), and higher visual thresholds (at the -12°, -20°, and -28° locations; P < 0.05). Additionally, there were significant relationships between visual threshold and latency, visual threshold and accuracy, and latency and accuracy (P < 0.0001). CONCLUSIONS Older adults have increased latency and decreased accuracy of saccades, as well as higher visual thresholds, to peripheral visual stimuli when compared with younger adults. Saccadic latency and accuracy are related to visual threshold, suggesting that saccadic latency and accuracy could be useful as perimetric outcome measures.

/pdf/perimetric-evaluation-of-saccadic-latency-saccadic-accuracy-546am19taj.pdf

Perimetric Evaluation of Saccadic Latency, Saccadic Accuracy, and Visual Threshold for Peripheral Visual Stimuli in Young Compared With Older Adults

Purpose: To describe, validate, and provide preliminary normative data for an open-source eye-movement perimeter (Eyecatcher).

Methods: Visual field testing was performed monocularly in 64 normally sighted young adults, using (i) a Humphrey Field Analyzer (HFA) and (ii) the novel Eyecatcher procedure. Eyecatcher used a remote eye-tracker to position stimuli relative to the current point of fixation, and observers responded by looking towards the stimulus. In both tests, Goldman III stimuli were sampled from a 24-2 grid, and were presented against a 10 cd/m2 background. Participants completed each test twice to assess test–retest repeatability.

Results: Mean Sensitivity (MS) did not differ between Eyecatcher and the HFA (P = 0.086), and both tests exhibited similar test–retest repeatability (CoREyecatcher = ±1.86 dB; CoRHFA = ±1.95 dB). Eyecatcher was also able to detect changes in sensitivity across the normal visual field (the “Hill of Vision”), and could differentiate the physiological blind spot from adjacent retinal locations. Mean sensitivities and 95% limits of agreement are described for each pointwise location.

Conclusions: Eyecatcher can use eye movements to assess visual fields in young, normally sighted adults. In such observers, it provides results similar to the current gold standard clinical device (HFA).

Translational Relevance: Given further development, eye movement perimeters such as Eyecatcher could be particularly useful for individuals unable to perform traditional perimetric assessments, such as young children or stroke patients. Full technical details and information on how to freely acquire the source code are included.

An Open-source Static Threshold Perimetry Test Using Remote Eye-tracking (Eyecatcher): Description, Validation, and Preliminary Normative Data.

The authors describe a method of objective assessment of the visual field by means of the electro-oculographic registration of the refixation eye movements. The first results are encouraging. Several possible improvements of the method are discussed.

Visual Field Examination by Electro-Oculography

Traditional techniques for visual field plotting are described as acting in opposition to the underlying perceptual task. An approach is described which encourages the natural eye movement response and objectively classifies it as either an acquisition or a search response. Empirical results demonstrate the reliability of eye movement response as an index of perception of peripheral stimuli A visual field plotting example is given and implications for clinical practice are discussed.

Visual Field Plotting Using Eye Movement Response

A compensation scheme for the correction of both horizontal and vertical eye position measurements is developed. Based on the assumption that the distortion process can be modeled as piecewise linear, a new sample point structure is introduced. This structure permits both fixation-based and tracking-based sampling strategies. It also provides a convenient method for partitioning a display for estimation purposes. A minimum mean squared error estimate for the regional linear functions is derived. The problem of measurement assignment to linear regions is solved using a weighted distance metric. Performance is given both in terms of estimation error and the error remaining after correction for a test pattern. Results are presented for a specific example.

M. Edward Jernigan

Papers

Visual Field Plotting Using Eye Movement Response

Compensation for Distortion in Eye-Movement Monitors