Motion tracking/eye tracking Flashcards
What are the main types of eye movements?
- smooth pursuit — following the continuous movement
- saccades — moving the object of interest to the fovea
- vergence shifts — convergence and divergence
- vestibulo-ocular movements — eye movements compensating for head movements
- microsaccades
- ocular drift
What are types of saccades?
visually-guided saccades (scanning and reflexive saccade), memory-guided saccades, predictive saccades, antisaccades
What are the main characteristics of saccades?
- They are ballistic (impossible to control and change after initiation)
- They are very fast (max 900 degrees/sec)
- They can cover to 90 degrees if the head is fixed
- They are part only of overt attention
What are the main eye-tracker models?
- Electrooculography
- Infrared oculography
- Image-based eye-tracking
- Scleral eye coil
What are the pros of scleral eye coil
It has the highest spatial resolution and can record vertical, horizontal, and rotational movements.
What are the cons of scleral eye coil?
It is invasive and can scratch the cornea. Also, it is difficult to calibrate and has time-consuming set-up.
What are the pros of image-based eye-tracking?
Hardware is easily accessible.
What are the cons of image-based eye-tracking?
It has low temporal resolution and does not guarante high spatial resolution (depends on the hardware). It is also difficult to process an image.
What are the pros of infrared oculography?
- It has high spatial resolution
- can record horizontal movements well
- Infrared light is invisible
- not affected by other lights and not annoying for the participant.
What are the cons of infrared oculography?
It is affected by eyelid movements. Also, the changes on reflection cannot be described by a linear system.
What are the cons of electrooculography?
- It has direct contact to the skin
- It is time-consuming
- It is very sensitive to blinking and brain signals
What are the pros of electrooculography?
- It detects vertical and horizontal eye movements with high precision
- It is very cheap
What are the subtypes of visually-guided saccade?
- scanning saccade: triggered internally to search the environment
- reflexive saccade: triggered externally by the appearance or absence of stimuli
What are the subtypes of goal-based saccades?
- memory-guided saccades: moving toward a stimulus that is not presented but remembered
- predictive saccades: to track stimuli with predictable trajectories
- antisaccade: a voluntary movement in an exactly opposite direction (often induced in psychological experiments)
What principle is infrared oculography based on?
If eye is exposed to a constant light source, eye reflection changes with motion (differently coloured sclera and cornea -> different reflection)
What does fixation consist of?
Microsaccades (equally fast but tiny saccade) and ocular drifts (a jittery motion that incessantly displaces stimuli over many photoreceptors)
What are the applications of eye tracking?
- abnormal eye movement diagnosis and eye movement disorders
- studies of some cognitive functions, such as overt attention
- controlling computer, wheel chair, and other devices
- studies of attractive areas of websites, banners, and shops
How is the saccade control realised?
Saccadic movement is unstoppable when it has started, so the control system is comparing the target and the eye location in the end of a saccadic movement
What brain areas are involved in saccade initiation?
Frontal eye fields, supplementary eye fields, parietal areas, occipital areas, cerebellum
In which fields is movement analysed?
- movement science, sport psychology (movement per se)
- clinical psychology (movement assessment)
- cognitive psychology, social psychology (movement as a dependent measure)
What are two main types of motion capture systems?
Non-optical and optical systems
What are three subtypes of non-optical systems?
mechanical:
* electrogoniometers (joint angles),
* can only record change from initial orientation, no recordings of global position
intertial:
* accelerometeres, gyroscopes,
* no recordings of global position,
* orientation is trackeble
magnetic (an external transmitter creates low-frequency magnetic field):
* global postion trackable,
* a lot of wires -> problems moving, interference of other magnetic fields
What are the subtypes of optical systems?
- Optoelectronic system
- Markerless optical motion tracking
- RGBD cameras
What are the main stages in operating optoelectronic system?
- camera placement and adjustment
- masking
- wanding + ground setting
- marker positioning (3 markers for object motion, reference model for human motion, necessary for marker labeling)
- subject calibration
- acquisition
- data editing (digital interpolation, filtering)
- export (.c3d)
- data processing
- data analysis
What are the integral components of optoelectronic systems?
- infra-red cameras producing and detecting the light
- passive markers (dots reflecting the light)
- active LED-infra-red-markers
+ the process of triangulation to determine the position of the markers in the 3D space
What are the key movement kinematics features?
- velocity
- acceleration
- jerk
- trajectory
- volume
- curviness
Why do we study movement?
Movement itself is an overt behaviour that can reflect internal processes
