3. BINOCULARVISION
• Binocular vision is a sensorimotor process.
• Eye movements to keep lines of sight pointing same target.
(Otero-Millan et al, 2014)
4. EYE MOVEMENTS
What?
Refers to voluntary or involuntary movement of the eyes, helping in
acquiring, fixating and tracking the visual stimuli.
Eye movements place the image of interest on the fovea (part of retina
with highest acuity)
Controlled by 6 extraocular muscles innervated by cranial nerves III, IV
andVI.
8. EYE FIXATION-CONCEPT
During attempted visual fixation at a stationary object, our eyes
continually move involuntarily.
The movement can be slow or rapid small amplitude- make us
unaware of the movement.
The fixational eye movements change the degree of alignment
between 2 eyes and continuously move the retinal images.
Even there is movement, the image of the object is still retained
within an acceptable foveal retinal locus. (±30 minutes of arc)
(Ciuffreda & Tannen, 1995)
17. EYE FIXATION-CONCEPT
ALTERNATE EYE SACCADE AND FIXATION
• This is the typical pattern of eye movement during reading.
•The eyes never move smoothly over still text.
•Fixation lengths ~ 100 to 600 milliseconds length shows information processing.
• During this stop the brain starts to process the visual information received from the eyes
An example of fixations and saccades over text
18. EYE FIXATION-CONCEPT
PATTERN FOR SHOWING FIXATIONAL EYE MOVEMENTS
To experience it, look at the
central black dot for about a
minute, then look at the
white dot in the adjacent
dark square.
The dark after-image of the
white line pattern should be
seen in constant motion
owing to fixational eye
movements.
24. TREMOR, DRIFT & MICROSACCADES ACROSS
PHOTORECEPTORS
Curved lines:
High frequency tremors & drifts
Straight lines:
-Fast, jerk-like movements of
microsaccades
-Bring the image back towards
the centre of vision
Fovea diameter: 0.05mm
25. EYE FIXATION
EYE MOVEMENTS DURING VISUAL FIXATION
• An observer views a picture (left) while
eye positions are monitored (right).
• The eyes jump, seem to fixate or rest
momentarily, producing a small dot on the
trace, then jump to a new region of
interest.
• However, even during these fixation, or
‘rest’ times, the eyes are never still, but
continuously produce fixational eye
movements — drifts, tremor and
microsaccades.
27. VISUAL FADING: TROXLER’S EFFECT
1. Fixate at red spot.
2. After few secs, bluish annulus
will disappear.
3. Red spot surrounded by white
field.
28. FIXATIONAL EYE MOVEMENT:
MONOCULAR VS BINOCULAR VIEWING
Binocular performance can be superior to monocular
performance of the same visual task.Why?
Binocular summation – An ability of the brain to combine the info from two
eyes.
Binocular summation predicts improved fixation stability under binocular
viewing as compared to monocular viewing.
Increased fixation instability during monocular viewing,
especially for the occluded eye (González et al.,2012)
29. FIXATIONAL EYE MOVEMENT:
NEAR VS FAR VIEWING
No differences in fixational eye movement characteristics
between far and near viewing (Krauskopf et al., 1960)