Eye Movements and Visual Attention

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Eye Movements and Visual Attention. Overview: Types of Eye Movement How to Measure Eye Movements Why Eye-Movement Research? Examples of Eye-Movement Studies and Paradigms. An Introduction to Eye-Movement Research. Eye Muscles. Eye Movements. Types of Eye Movement. Fixations: - PowerPoint PPT Presentation

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  • Eye Movements and Visual Attention

  • An Introduction to Eye-Movement Research Overview:

    Types of Eye MovementHow to Measure Eye MovementsWhy Eye-Movement Research?Examples of Eye-Movement Studies and Paradigms

  • Eye Movements

  • Types of Eye MovementFixations:

    The eye is almost motionless, for example, while reading a single, short word.The information from the scene is almost entirely acquired during fixation.Duration varies from 100-1000 ms, typically between 200-600 ms.Typical fixation frequency is about 3 Hz.Fixations are interspersed with saccades.

  • Types of Eye MovementSaccades:

    Quick jumps that connect fixationsDuration is typically between 30 and 120 ms Very fast (up to 700 degrees/second) Saccades are ballistic, i.e., the target of a saccade cannot be changed during the movement.Vision is suppressed during saccades to allow stable perception of surroundings.Saccades are used to move the fovea to the next object/region of interest.

  • Types of Eye MovementSmooth Pursuit Eye Movements:

    Smooth movement of the eyes for visually tracking a moving objectCannot be performed in static scenes (fixation/saccade behavior instead)

  • Types of Eye MovementTorsional Eye Movements:

    Rotation of the eye around the viewing axisStabilization of visual scene by compensating body rotation (up to about 15 degrees)

  • Types of Eye MovementVergence Eye Movements:

    Slow, smooth movements changing the vergence angle (the angle between the two viewing axes)Used for changing gaze from a near to a far object or vice versaCan take up to one secondExecution is often interrupted if no thorough inspection of the object is required.

  • Types of Eye MovementTremor:

    Fast, low-amplitude (seconds of arc) eye-movement jitter Improves the perception of high spatial frequenciesPrevents the fading of static images during fixations

  • How to Measure Eye MovementsMirror on Eyeball

    Used in first eye tracking experiments (Yarbus in 1960s)Suction cup attaches mirror to eyeball Light beam is directed at mirror and reflected onto photo sensitive paperGood spatial resolution but no temporal informationUnpleasant for the subject

  • How to Measure Eye MovementsElectrooculogram (EOG)

    Skin electrodes around the eyes measure potential differences Wide range -- poor accuracyBetter for relative than absolute eye movementsMainly used in neurological diagnosis

  • How to Measure Eye MovementsEye CoilsSubject wears contact lens with wire coilHomogeneous magnetic field around subject allows measurement of gaze angleVery high temporal and spatial precisionSpecial coil also allows measurement of torsional eye movementsVery uncomfortable

  • How to Measure Eye MovementsLimbus Tracker

    Photo diodes track the boundary between sclera and iris.High temporal resolutionPoor spatial precision; only for horizontal eye movementsInexpensive

  • How to Measure Eye MovementsPurkinje Eye Tracker

    Laser is aimed at the eye.Laser light is reflected by cornea and lensPattern of reflected light is received by an array of light-sensitive elements.Very preciseAlso measures lens accomodationNo head movements

  • How to Measure Eye MovementsVideo-Based Systems

    Infrared camera directed at eyeImage processing hardware determines pupil position and size (and possibly corneal reflection)Good spatial precision (0.5 degrees) for head-mounted systemsGood temporal resolution (up to 500 Hz) possible

  • How to Measure Eye MovementsEyeLink II System:BinocularHead-movement compensation (head camera looking at IR markers at monitor)Temporal resolution 500 HzSpatial precision about 0.5 to 1 degreeGaze-position data available in real-time

  • How to Measure Eye MovementsEyeLink II System Configuration

  • How to Measure Eye MovementsMeasuring vergence eye movements in anaglyphs with EyeLink II (poor subject!)

  • Why Eye-Movement Research?In most eye movement studies, the only types of eye movement that are considered are fixations and saccades.

    Why?

    These eye movements indicate a persons gaze trajectory while performing a certain task.Moreover, they yield information about a persons visual attention.

  • Visual AttentionVisual attention is the selective allocation of visual processing resources.For example, we can focus our attention on a particular object of interest in the visual field.Visual processing of that object is enhanced while being rather shallow for other objects.Also, we can respond more quickly and accurately to changes in an attended region.This prioritization is necessary due to our limited processing resources.

  • Visual AttentionExample: Posner task: Subjects are instructed to fixate on a central marker.One of two boxes (left/right) flashes to capture the subjects attention (an automatic, involuntary response).After a short delay (stimulus onset asynchrony - SOA) an asterisk appears in one of the boxes.The subject has to report as quickly as possible in which box the asterisk appeared.

  • The Posner Attention Taskx

  • The Posner Attention Taskx

  • The Posner Attention Taskx

  • The Posner Attention Task *x

  • The Posner Attention Taskx

  • The Posner Attention TaskFor short SOAs (< 200 ms), subjects respond faster if flash and asterisk appear on the same side than when they appear on different sides. Cueing of attention to relevant location allows faster response.For longer SOAs (up to 1000 ms), subjects respond more slowly if flash and asterisk appear on the same side. Inhibition-of-Return mechanism makes attention less likely to return to the side of the flash until the asterisk appears.

  • Why Eye-Movement Research?About eye movements and visual attention:Usually, saccades follow shifts of attention to provide high acuity at the attended position.It is possible to look at an object without paying attention to it (staring).It is possible to shift attention without eye movement (covert shifts of attention).It is impossible to perform a saccade while not shifting attention.During specific, natural tasks it is reasonable to assume that saccades follow shifts of attention.

  • Why Eye-Movement Research?The investigation of visual attention, in turn, is at the core of cognitive science.

    Studying visual attention yields insight into general attentional mechanisms. It can provide information on a persons stream of conscious and unconscious processing while solving a task. Attention is closely linked to the concept of consciousness. Attentional mechanisms could improve artificial vision systems.

  • Eye-Movement StudiesEye movements while watching a girls face (early study by Yarbus, 1967)

  • Eye-Movement StudiesEye movements as indicators of cognitiveprocesses (Yarbus):trace 1: examine at willtrace 2: estimate wealthtrace 3: estimate agestrace 4: guess previous activitytrace 5: remember clothingtrace 6: remember positiontrace 7: time since last visit

  • Eye-Movement StudiesVisual scan paths on instruments/dashboards studies for the improvement of human-computer interfaces

  • Eye-Movement StudiesGaze trajectory measurement for the optimization of web page layout

  • Eye-Movement StudiesImproving advertisements with eye-movement studies

  • Selectivity in Complex Scenes

  • Face RecognitionGaze-contingent window deteriorates face recognition, allows to identify relevant visual information.

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