Lecture 4- Eye movements and perception Flashcards
Why do we study eye movements?
Informs us about culex cognitive processes such as reading
Helps us see humans are active viewers
Shows the clear link between sensory and action systems
Used as indicators of visual attention
Where does semantic processing for words occur?
Middle temporal gyrus
What is the spelling-sound conversion?
Inferior parietal cortex
Where is the phonological lexicon?
Angular and middle temporal gyrus
Where is light focused in the eye?
On the fovea for detailed vision
Why does the eye need to move?
Since the back of the eye is not completely uniform
What is the fovea?
Part of the eye with photoreceptors densely packed here
What do the cones do in the eye?
Pick up detail in bright light
What is peripheral vision?
Where there are less cones
What are the types of eye movement?
Gaze shifting mechanisms and gaze stabilising mechanisms
What are gaze shifting mechanisms?
Voluntary
What are gaze stabilising mechanisms?
Involuntary
What are examples of gaze shifting mechanisms?
Smooth pursuit, saccades and vergence
What is smooth pursuit?
Used a track a moving object and ensures that light from the object stays focused on the back of the eye
What does smooth pursuit require?
Requires a continuous feedback loop so the eye adjusts to the perceived position of the object
What are saccades?
Fast ballistic movements up to 700s
How long does it take to make saccades?
3-4 seconds
What do saccades show?
Characteristic patterns of acceleration
How do eyes move in saccades?
Together in an identical fashion
What is vergence?
When we move our eyes to focus on objects at different distances away from us
What are examples of stabilising eye movements?
Vestibulo-ocular reflex and optokinetic reflex
What is the vestibulo-ocular reflex?
Movements that cancel out the motion of the body and head
What are vestibulo-ocular reflex in reaction to?
In reaction to the signals from the vestibular organs of the inner ear
What is the optokinetic reflex?
Stabilising movements made in reaction to the whole visual field moving
How can optokinetic reflexes be studied?
By using rotating drums or tumbling rooms.
What are the further types of eye movements that occur when fixating?
Microsaccades and drifts+tremors
What is microsaccades?
Looked at the role of very small involuntary movement made when fixating on an object to help with avoiding fading of the visual scene
What is microsaccades linked to?
Attention
What are drifts?
Slow meandering motions between microsaccades
What are tremors?
Very small oscillations on top of drifts.
How are eye movements measured?
With an eye tracker
What does eye trackers involve?
A small infrared camera that focused on the eye that tracks where the pupil moves
What happens when eye trackers are calibrating?
The pupil position against fixed points on the screen one can work out where the participant is looking.
What do fixation measures measure?
Dwell time, frequency of fixation, total duration of fixation and order of fixation positions
What is the spillover effect?
The fixation time on a word preceded by a rare word
Who looked at fixation?
Reichle et al
What did Reichle et al find?
When we fixate a word until we have processed it
What is the E-Z reader model?
How the eye fixation in reading is influenced by the previous and next words
What are the assumptions of the E-Z reader model?
Readers check the familarity of the word currently fixated
Completion of frequency checking of the word
Readers engage in second stage of lexical access involving accessing the current words
What are the two stages of lexical processing of words in the E-Z reader model?
Checking word frequency and lexical access
What are regions of interest?
Considering how many fixation occur within a certain area or areas on the screen
Who looked at heatmaps?
Mosimann et al, 2004
What did Mosimann et al, 2004, find?
Reading time off the clock and seeing the fixations made when looking at the image. There was difficulty of allocating their attention to the right area in the alzheimer’s group
Why do we have eye movements?
Stabilisation
What is stabilisation?
Occurs through the optokinetic and vestibulo-ocular reflex to build a visual representation so the image on the back of the eye is kept still
What is Troxler’s fading?
When an image is kept fixed on the retina it fades in the periphery
What is Troxler’s fading caused by?
Adaptation of the neurones in the retina and do not fire after a while to the same stimulus
Where is the processing power given?
To the fovea
What causes detailed representations in the eye?
Part of the image the light from that part needs to land in the fovea
What is needed to build up a detailed representation?
Moving our eyes
Who found saccadic suppression?
Zuber and Stark
What did Zuber and Stark find?
Stimuli are more difficult to detect during the movement of the eye and the motion in the visual scene is ignored
What is the problem with eye movements?
The brain needs to know what part of motion on the retina is caused by eye movement and which part is caused by something moving in the scene
What does efference copy do?
Cancelling out the signal from the eye muscles and ignoring external movement of the world
What is also cancelled out with eye movements?
Cues from the scene such as whole image motion
Why do eye movements go wrong?
As some illusions can be caused by an inability to cancel out the motion of the eye
What is the passive approach to vision?
Sees the eye as just receiving information from the outside world
What is the active approach to vision?
The dynamic processing of sampling of visual scenes with reference to the role of the observer in guiding eye movements to relevant parts of the scene
Who looked at eye movements during tea making?
Land et al
What did Land et al find?
Real life eye movement are not only where but when people are looking is important
What occurs when combining motor and visual systems?
Involve strong coupling between visual and motor processes
What occurs in brain areas involved in eye movement?
Active when visual information is being processed and when eye movements are being made
What smooth pursuit is involved in controlling eye movement?
A continuous feedback loop where the eye position is updated according to when the object is
How are saccades ballistic?
As the movement needs to be pre-programmed so once initiated the trajectory cannot be changed
What process is reading?
A complex cognitive process
What is used for evidence for reading?
Eye movements to test the models
What evidence for reading can be used for?
Manipulating the type of information present at fixation at a given time
What occurs in the eye during reading?
We do not fixate every single word, regressions account for 10% of saccades, we easily move our eyes down to the next line, the shape of the word plays a role
What is the moving technique for reading?
Using information from up to 15 letters away in English
What is the fixation in reading?
200-250 ms
What movements occur in reading?
Rightward movement follow by return sweep and large leftward to start of next line
How many characters do we move with each saccade?
8
How much do we fixate on the content and on the function words?
80% on the content and 20% on the function words
