BISC 421 1st Edition Lecture 16 Outline of Current LectureI.Eye Movements Current LectureEye MovementsAcuity falls off with eccentricity in visual space •When you foveate (point your eyes in the middle) that is where the visual acuity is the greatest•The leters in the middle have same level of acuity as the outside leters if staring exactly in the middle •We move our eyes to see beterEye Movements are Not Random•We tend to fxate on certain parts of the image-‐ most atenton spent on eyes and nose and mouth-‐ very important to scan the faces of people near us •“eye movements aren’t random”-‐ yarbisYarbus, 1967 Seven records of eyemovements by the same subject viewing a painting called the“Unexpected visitor” for 3 minutes. 1) Free examination. After that, the subjectwas asked to: 2) estimate the economic status of the family; 3) give the ages of thepeople; 4) guess what the family had been doing before the arrival of the"unexpected visitor;" 5) remember the clothes worn by the people; 6) rememberthe position of the people and objects in the room; 7) estimate how long the"unexpected visitor" had been away from the family. Yarbus 1967•gave people diferent goals when they looked at the picture•for 2) not focusing on faces but scanning objects in the room•for 3) fxate on faces of individuals •Tell us how important it is to fxate on something of interest-‐ looking at things that are most important to us•Now we use an infrared eye tracking systemEye movements help relay socially important facial expressionsUsual subject Subject with calcified amydala•Patent with syndrome where amygdala calcifed and can't recognize fear•Told her to assess how these actors felt-‐ she just looked at noses which is not the most expressive part of their faces-‐ she couldn't report emotons •When they told her to look at the whole face she did beter-‐ she needed to be cuedEye Muscles•How do we make these movements•Memorize all of the eye musclesDifferent Muscles Move the Eyes in Different DirectonsMuscles Responsible for Horizontal MovementLateral Rectus --abducton away from the noseMedial Rectus --adducton towards the noseMuscles Responsible for Vertical MovementSuperior Rectus --elevatonInferior Rectus --depressionMuscles Responsible for Torsional Movements(movement of top of the eye towards or away from the nose)Superior Oblique --intorsion (top of the eye towards the nose) Inferior Oblique--extorsion (top of the eye away from the nose)•Each muscle has a job and a directon to tug the eyeInnervaton of the Extraocular Muscles•How are these muscles innervated•Need to memorize this slide-‐ will come up again•The cranial nerve from the oculomotor mucleus 3 takes care of 4 of the muscles (medial rectus, superior rectus, inferior oblique, inferior rectus)-‐ ipsilateral (same side of the body)•Lateral rectus muscle innervated by cranial nerve 6 (ipsilateral) •Trochlear nerve innervates the contralateral superior obliqueTypes of eye movements:A) Those that direct gaze to targets of interest or track those targets as they move.e.g. saccades, smooth pursuit, optokinetc nystagmus (nystagmus just meansan involuntary movement of the eye).(chameleons movie)B) Those that help align the fovea of each eye on the target of interest when the distances between each eye and the target are different. These are disconjugate vs .conjugate movements – the eyes move in different directons. e.g. vergencemovements (L11EyeMovements, vergence)C) Movements that compensate for head movements to keep the target of interest centered on the fovea. vestbulo-ocular movements (later lecture).•Once you start a saccade you can't stop it-‐ very jerky-‐ oldest form of eye movement•Smooth pursuit is used to track objects•Conjugate eye movements are what you usually do-‐ both looking right or lef-‐ both going the same way•Vergeance movement-‐ crosseyed disconjugate•Movements that allow you to keep your eyes on one target when you move your head (C)Metrics of Saccades•Staring at the target and then the target moves-‐ take about 200ms to move the eye to the new target positon-‐ once the eye starts to move the eye can't be stopped (saccade)•Smooth pursuit-‐ much slower. Needed a catch up saccade to fnd the moving target and then you follow it. We need a target to keep our eyes doing thisNeural Firing During Movement and at Rest•How the eye muscles move-‐ move because they are innervated •Recording from a single motor neuron in the abducens neuron-‐ when we start the eye is pointng medially-‐ there is no tension on the lateral rectus muscle so no fring but now if we want to move eye the neuron fres and moves a litle bit-‐ then want to maintain the eye in the lateral positon must keep fringHorizontal Movement of the Eyes to the Right(axons of internuclear neurons)Horizontal gazecenterParamedian pontne retcular formaton•When eyes are moved to the right-‐ there are diferent levels of control for eye movements•Right now in the brainstem in the PPRF-‐ called the horizontal gaze center•Neuron in the PPRF will synapse onto cells that will control eye movements on both sides of the head•To move right eye right contract lateral rectus muscle and medial rectus muscle•To get to the other side of the head must move through the medial longitundinal fascucluus which will innervate the left ocular nucleus1 Pineal gland2 Superior colliculus3 Inferior colliculus4 Trochlear nerve5 Fourth ventricle6 Pulvinar of thalamus7 Superior cerebellar peduncle•Superior colliculus in the midbrain – gets input from the sensory systems and all of these signals move down to neurons that command motor neurons •Very near pineal glandVisual and Motor Maps in the Superior Colliculusvisual field coordinates anatomical coordinatesThere is a Cartesian map of visual space in the colliculus. Stmulate at any given point on the map, and the eyes will move towards that positon.•Superior colliculus is involved in commanding eye movementsHow tumors in one r egion influence the function in the next.A syndrome that you might come across in the clinical literature involves the superior colliculus. It is called the dorsal midbrain or PARINAUD syndrome, after HenriParinaud, and is usually caused by a tumorof the pineal gland