Lecture 26: Eye Tracking - The University of · PDF file 2013-03-26 · Eye Tracking...

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Transcript of Lecture 26: Eye Tracking - The University of · PDF file 2013-03-26 · Eye Tracking...

  • Lecture 26: Eye Tracking Inf1-Introduction to Cognitive Science

    Diego Frassinelli

    March 21, 2013

  • Experiments at the University of Edinburgh

    Student and Graduate Employment (SAGE): www.employerdatabase.careers.ed.ac.uk

    Researchers (normally desperate PhD students) are looking for participants for their experiments

    You can learn new interesting methodologies

    You can gain some money

    In your 3rd year you can volunteer for helping

    Eye Tracking 2/14

  • An Eye is Not a Camera

    “Vision is a process that produces from images of the external world a description that is useful to the viewer and not cluttered with irrelevant information.” (David Marr, Vision, 1982)

    Back to lecture 4

    The eye is not a passive recorder

    Vision involves many layers of active interpretation and processing

    A process that maps one representation to a different one

    Eye Tracking 3/14

  • Eye Tracking

    The Eye-Mind Hypothesis (Just & Carpenter, 1980)

    Where participants are looking indicates what they are processing. How long they are looking at indicates how much processing effort is needed.

    An eye-tracker makes possible to record the eye-movements of participants while they are performing a cognitive task

    Based on a slide by Frank Keller.

    Eye Tracking 4/14

  • Some History

    Louis Emile Javal (1879)

    he attached a microphone to the closed eyelid of a person when the person was reading (with the other eye) the microphone was recording the noise produced by the cornea colliding with the microphone

    Edmond Delabarre (1898)

    he put a plaster cap in his eye (“sufficiently cocainised”) the cap had a hole for the pupil the cap was wired to a lever which drew horizontal lines on a panel when the eye was moving during reading

    Based on a slide by Tobii eye-tracking research.

    Eye Tracking 5/14

  • Nowadays

    More freedom and more natural information

    But also more noisy and less accurate data

    Eye Tracking 6/14

  • How does it work

    Find a mapping between the eye position and the image gazed

    A camera records the eye movements projecting some infra-red light against the eye of the subject

    The cornea and the pupil reflect infra-red light: easier to recognise and to track their movements (no heavy image recognition)

    Calibration process: providing some examples of the area fixed and the reflections produced by the cornea and the pupil

    An algorithm hew window should get opened when a link leads out of the current docuas to “superimpose” the fixations to the image recorded (gaze estimation)

    Eye Tracking 7/14

  • How does it work (contd.)

    The eye tracker records two eye movement events (but not only!):

    Fixations: collection of most of the visual information (200-300 ms) Saccades: a rapid movement from one fixation to the other (30-80 ms). They are the fastest body movements. We are blind during most of them

    The experimenter decides what a fixation is

    Eye Tracking 8/14

  • Different Scenarios

    Nowadays, eye-trackers are used in different fields:

    Scene Perception (Playing Cards)

    Web Design (Ikea Website)

    Marketing analyses (Supermarket)

    Sport studies (Ronaldo)

    Eye Tracking 9/14

    http://www.youtube.com/watch?v=lvypPbWAc7E http://www.youtube.com/watch?v=xKdOMgu0C5Q http://www.youtube.com/watch?v=SQxrsUXqKCM http://www.youtube.com/watch?v=2NcUkvIX6no

  • Different Scenarios - Google Glasses

    “We created Glass so you can interact with the virtual world without distracting you from the real world. We don’t want technology to get in the way.” Google designer Isabelle Olsson

    Still a prototype

    It adds another layer to reality

    Multitasking does not exist

    How does this information affect perception?

    Google Glasses Project

    Eye Tracking 10/14


  • Eye-tracking and Cognitive Science

    Can you think of other applications of eye-tracking? Come up with cases in which recording eye-movements is useful to study:

    Language Processing

    Visual Cognition


    Cognitive Impairment

    Based on a slide by Frank Keller.

    Eye Tracking 11/14

  • Designing your own experiment

    Clearly formulating the research question of your experiment is the first step for producing a good design

    The null hypothesis (H0): no effect is expected between two or more conditions

    An experiment is aimed to reject H0 supporting the alternative hypothesis (H1)

    Eye Tracking 12/14

  • Designing your own experiment - Independent Variables

    Independent variables: the conditions manipulated by the experimenter

    increasing the amount of IV requires a higher number of subjects:

    You have to find them You have to pay them You have to spend time collecting the data The equipments and the lab are not always available and they cost money

    Eye Tracking 13/14

  • Designing your own experiment - Dependent Variables

    Dependent Variables: the outcome variables not manipulated by the experimenter:

    Number of fixations towards a specific target Reaction times: time required to perform an action Error Rates: number of mistakes occurred

    The question is directly related to the technology we use

    Eye Tracking 14/14