Eye movement (Practical) Flashcards
What is the function of this piece of apparatus in the eye movement experiment?
Infrared oculometer: IR transducer for measuring eye position
How does the transducer used to measure eye movements work?
- An infrared emitter emits high frequency infrared pulses towards the eyes.
- An infrared detector detects the pulses reflected from the eyes.
- Comparator circuit in the transducer compares the amplitude of reflected light with that emitted.
- Difference in amplitude determined by position of eyes.
- The white sclera reflects more light compared to the darker iris. The smaller the amplitude difference, the more sclera can be detected.
- As the eyes move, gradually more iris covers the ‘spotlight’ for IR emitter and so amplitude difference increases.
What is the function of this piece of apparatus in the eye movement experiment?
- Bite-bar
- Fixes the head in place so that gaze is controlled by movements of the eyes alone.
What distance do stimuli need to be placed at in order for 1 cm to correspond to 1o?
~57cm
What type of movements are saccades?
Ballistic movements
What accounts for the extreme variability of saccades when moving the eyes by the same amount?
Decision time
What is the highest frequency of scanning stimulus that can be tracked by smooth pursuit?
~3 Hz
What type of eye movement is the optic fibre used to test for?
Convergence
What is the difference between saccadic movements and vergence movements?
- In saccadic movements, the eyes move at maximum velocity for fixed period of time due to being ballistic.
- In vergence movements, the velocity is exponential. As target is reached, velocity decreases. This is because direct negative feedback is used. Because error signal decreases as target is approached, so does the velocity.
How can optokinetic reflex be triggered?
Placing moving background with alternating black and white stripes in front of subject.
How can optokinetic reflex be stopped in presence of moving background?
Placing stationary fixation point in front of the subject
How can vestibular nystagmus be induced?
Constant rotation of the head
What is the difference between optokinetic nystagmus and vestibular nystagmus?
Optokinietic nystagmus continues as long as background is moving while vestibular nytagmus stops as semicircular canals adapt.
What are the types of gaze-holding movements?
- Vestibulo-ocular reflex (VOR)
- Optokinetic reflex (OKR)
What are the tyoes of gaze-shifting movements?
- Saccades
- Smooth pursuit
- Vergence