Scan path analysis by Metrovision

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Introduction

Many tasks of daily leaving involve visual information. Reading, walking, driving a vehicle,.. bring into play factors that are sensory, motor and cognitive. A quantitative approach is desirable for the assessment of aptitudes, monitoring rehabilitation, analysis of the effectiveness of new treatments, etc. Today, a number of solutions are available for this purpose such as quality of life questionnaires, analyzes of speed and errors in reading tests. Scan path analysis can provide additional information to these global approaches:
- The quantification of the number of fixations and of the amplitudes of saccades, in relation to the perceptual span,
- The completeness of the exploration. Are some areas ignored? Does the subject compensate the alterations of his visual field?
- The systematization of exploration...

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Metrovision's eye tracker

The measurement of eye movements is obtained from video images recorded using a near infrared camera.
A reflective dot is used to determine the position of the head. The direction of gaze is measured from the position of the pupils with respect to this dot. This technique is quite insensitive to artefacts such as parasitic reflections.

Application to reading with IReST texts

IReST texts are today one of the main international standards for reading tests. They were developed by the IReST study group and are available in 17 different languages.
Each language version includes 10 texts of the same length, equalized in difficulty and linguistic complexity. 4 letter sizes are available on Metrovision's system, corresponding to visual acuities of 0.08, 0.13, 0.17 and 0.26.

The analysis of the gaze path highlights the fixations (red dots) as well as the saccades (green lines). The software automatically determines the reading speed (in words per minute), the number of fixations as well as the number of saccades and their average amplitude.

Application to the exploration of visual scenes

The analysis of eye scan path during the exploration of a visual scene shows the position and duration of fixations (position and size of the red dots) as well as the sequence of fixations. In the example of a driving scene, the program indicates which elements of the image have been looked at by the subject and which were ignored. .
The visual scene can also be divided into areas of interest. The program indicates the time before the first access to each zone and the time of fixation within each zone.