Lecture 3, C 3

Question 1

eye movements are …?

Answer 1

eye movements are the most frequent and fastest of human movements

Question 2

what does “saccadic suppression” refer to?

Answer 2

saccadic suppression: we’re not able to “see” during a saccade

Question 3

name 7 types of eye movements

Answer 3

1. tremor - noise in muscle control
2. dirft - slow movements away from fixation
3. vergence eye movements - binocular focus
4. vestibular ocular reflex - correct for head movements
5. optokinetic reflex - smooth pursuit + saccade
6. smooth pursuit eye movement
7. microsaccades - small eye movements at fixation

Question 4

explain the “active vision” perspective

Answer 4

vision is active:

> movement is essential for vision

> anything we don’t fixate, we miss

> even covert attention is active (microsaccades)

> if we keep image stable, vision fades

Question 5

what drives information processing during visual search (Salience maps)

(3)

Answer 5

1. target features (top down)
2. physical salience (bottom up)
3. scene context (learned experience)

Question 6

what kind of words are more often fixated than others?

Answer 6

“content” words are more often fixated than “function” words

Question 7

Reading & eye movements

> how is attention distributed?

Answer 7

distribution of attention is asymmetrical

> 3-4 letters to the left

> 14-15 letters to the right

of fixation

Question 8

text difficulty affects 3 things

Answer 8

text difficulty influences

1. saccade size, decrease with difficulty
2. fixation duration, increase with difficulty
3. regression, frequency increase with difficulty

Question 9

eye tracking: explain spatial resolution

Answer 9

spatial resolution:

> the smallest distance between eye movements that can be detected

Question 10

eye tracking: explain accuracy

Answer 10

eye tracking accuracy

> whether you accurately measure the location the eye is looking at

Question 11

eye tracking: explain precision

Answer 11

eye tracking precision:

> whether you’re consistenly hitting the same spot

Question 12

how long does a period of fixation typically last?

when longer?

associated with?

Answer 12

fixation duration typically between 200 - 250 ms

> longer when viewing scenes, compared to reading

> associated with in depth processing

Question 13

explain the 2 different types of scanning in visual search

Answer 13

1. exploration

> larger amplitude saccades, shorter fixations

2. exploitation

> smaller amplitude saccades, longer fixations

Question 14

Yarbus Theory

Answer 14

Saccade Don’t paint a complete internal representation of a visual scene. They select task-relevant information

Question 15

Salience Map

Answer 15

• Drives information processing during visual search.
  1. Fast & parallel input for many features
  2. Slow & sequential focal attention stage

Question 16

Types of eye movement recording

Answer 16

• Mechanical
• Suction Cup
• Electromagnetic coils: High accuracy

Electrooculography: easy to use but low accuracy

Question 17

Properties of eye trackers

Answer 17

• Temporal resolution (sampling rate)
• Spatial resolution
• Spatial accuracy
• Spatial precision

Question 18

Temporal resolution

Answer 18

Faster is not better. 25 - 2000 Hz.

Affects what measures can be calculated

Saccadic peak can be estimated with 60 Hz but only for saccades > 10º

Question 19

Saccade Measures (6)

Answer 19

• Latency
• Direction
• Duration
• Amplitude
• Trajectory
• Velocity, acceleration, decceleration

Question 20

Areas of Interest (AOI)

Answer 20

• Defined areas over which experimental hypotheses are tested.
• A priori. Can’t be modified post-hoc.
• Longer for Scenes than reading. Associated with depth processing.

Question 21

Challenges of AOI

Answer 21

• Overlap of areas
• Size
• Fixations: Works better with them
• Accurate data hard to deal with

Question 22

Scan paths

Answer 22

• Viewing pattern

Different across people and tasks