Motion tracking/eye tracking

Question 1

What are the main types of eye movements?

Answer 1

1. smooth pursuit — following the continuous movement
2. saccades — moving the object of interest to the fovea
3. vergence shifts — convergence and divergence
4. vestibulo-ocular movements — eye movements compensating for head movements
5. microsaccades
6. ocular drift

Question 2

What are types of saccades?

Answer 2

visually-guided saccades (scanning and reflexive saccade), memory-guided saccades, predictive saccades, antisaccades

Question 3

What are the main characteristics of saccades?

Answer 3

1. They are ballistic (impossible to control and change after initiation)
   
   2. They are very fast (max 900 degrees/sec)
   3. They can cover to 90 degrees if the head is fixed
   4. They are part only of overt attention

Question 4

What are the main eye-tracker models?

Answer 4

1. Electrooculography
2. Infrared oculography
3. Image-based eye-tracking
4. Scleral eye coil

Question 5

What are the pros of scleral eye coil

Answer 5

It has the highest spatial resolution and can record vertical, horizontal, and rotational movements.

Question 6

What are the cons of scleral eye coil?

Answer 6

It is invasive and can scratch the cornea. Also, it is difficult to calibrate and has time-consuming set-up.

Question 7

What are the pros of image-based eye-tracking?

Answer 7

Hardware is easily accessible.

Question 8

What are the cons of image-based eye-tracking?

Answer 8

It has low temporal resolution and does not guarante high spatial resolution (depends on the hardware). It is also difficult to process an image.

Question 9

What are the pros of infrared oculography?

Answer 9

• 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.

Question 10

What are the cons of infrared oculography?

Answer 10

It is affected by eyelid movements. Also, the changes on reflection cannot be described by a linear system.

Question 11

What are the cons of electrooculography?

Answer 11

1. It has direct contact to the skin
2. It is time-consuming
3. It is very sensitive to blinking and brain signals

Question 12

What are the pros of electrooculography?

Answer 12

1. It detects vertical and horizontal eye movements with high precision
2. It is very cheap

Question 13

What are the subtypes of visually-guided saccade?

Answer 13

1. scanning saccade: triggered internally to search the environment
2. reflexive saccade: triggered externally by the appearance or absence of stimuli

Question 14

What are the subtypes of goal-based saccades?

Answer 14

1. memory-guided saccades: moving toward a stimulus that is not presented but remembered
2. predictive saccades: to track stimuli with predictable trajectories
3. antisaccade: a voluntary movement in an exactly opposite direction (often induced in psychological experiments)

Question 15

What principle is infrared oculography based on?

Answer 15

If eye is exposed to a constant light source, eye reflection changes with motion (differently coloured sclera and cornea -> different reflection)

Question 16

What does fixation consist of?

Answer 16

Microsaccades (equally fast but tiny saccade) and ocular drifts (a jittery motion that incessantly displaces stimuli over many photoreceptors)

Question 17

What are the applications of eye tracking?

Answer 17

1. abnormal eye movement diagnosis and eye movement disorders
2. studies of some cognitive functions, such as overt attention
3. controlling computer, wheel chair, and other devices
4. studies of attractive areas of websites, banners, and shops

Question 18

How is the saccade control realised?

Answer 18

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

Question 19

What brain areas are involved in saccade initiation?

Answer 19

Frontal eye fields, supplementary eye fields, parietal areas, occipital areas, cerebellum

Question 20

In which fields is movement analysed?

Answer 20

1. movement science, sport psychology (movement per se)
2. clinical psychology (movement assessment)
3. cognitive psychology, social psychology (movement as a dependent measure)

Question 21

What are two main types of motion capture systems?

Answer 21

Non-optical and optical systems

Question 22

What are three subtypes of non-optical systems?

Answer 22

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

Question 23

What are the subtypes of optical systems?

Answer 23

1. Optoelectronic system
2. Markerless optical motion tracking
3. RGBD cameras

Question 24

What are the main stages in operating optoelectronic system?

Answer 24

1. camera placement and adjustment
2. masking
3. wanding + ground setting
4. marker positioning (3 markers for object motion, reference model for human motion, necessary for marker labeling)
5. subject calibration
6. acquisition
7. data editing (digital interpolation, filtering)
8. export (.c3d)
9. data processing
10. data analysis

Question 25

What are the integral components of optoelectronic systems?

Answer 25

1. infra-red cameras producing and detecting the light
2. passive markers (dots reflecting the light)
3. active LED-infra-red-markers

+ the process of triangulation to determine the position of the markers in the 3D space

Question 26

What are the key movement kinematics features?

Answer 26

1. velocity
2. acceleration
3. jerk
4. trajectory
5. volume
6. curviness

Question 26

Why do we study movement?

Answer 26

Movement itself is an overt behaviour that can reflect internal processes