Eye Movements, Eye Blinks, and Behavior

1
Eye Movements, Eye Blinks, and Behavior

• Nicole Tindall, Kylie Gray,
• and Sarah Leis

2
Part I Eye Movements and the EOG

• Nicole Tindall

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The Control of Eye Movements

• Eye movements are used to fixate objects so that
  they fall on the fovea of the eye
• Occipital and frontal cortices are involved in
  eye fixation
• The eye muscles are innervated by the 3rd
  (oculomotor), 4th (trochlear), and 6th (abducens)
  cranial nerves
• Three sets of muscles are used to move the eyes
• Superior and inferior rectus
• Lateral and medial rectus
• Superior and inferior obliques

4
Voluntary vs. Involuntary Eye Fixations

• Voluntary Fixations when the eye focuses on an
  object of choice
• Example reading
• Controlled by the prefrontal cortex
• Involuntary Fixations constantly occuring
• Controlled by the occipital cortex

5
Types of Eye Movements

• Saccadic- movements from one fixation point to
  the next
• Saccade variables
• Saccade latency- time between presentation of
  stimulus and fixation
• Saccade amplitude- distance covered by eye during
  saccade
• Direction of movement- whether it is horizontal
  or vertical movement
• Velocity- speed of the saccade
• Fixation pause time- occurs between fixations

6
Types of Eye Movements (Contd)

• Smooth Pursuit- movement the eyes make when
  following a moving object
• Example following a bird in the sky
• Smooth Compensatory- this movement corrects for
  differences in head tilt so that the image
  remains upright

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Types of Eye Movements (Contd)

• Nystagmoid- abnormal oscillations of the eye
• Causes
• Eye defects
• Impairment of vestibular (balance) system
• Impairment of visual or vestibular pathways in
  the CNS
• Rapid Eye Movements (REM)
• Occur during sleep
• Last anywhere from a few minutes to more than a
  half-hour
• Eye Blinks (3 types)

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3 Types of Eye Blinks

• Voluntary blink consciously close the eyes
• Blink Reflex when the eyes blink to act as a
  defense mechanism in response to a potentially
  harmful stimulus
• Keeps the cornea healthy by keeping the surface
  moist
• Occurs about 15,000 times/day (about 15-20
  times/min in relaxed state)

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Recording Eye Movements/Blinks

• Four methods
• Contact-lens method
• Corneal reflection method
• Television camera scanning
• Electrooculogram (EOG)

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Electrooculogram (EOG)

• Records the movements (and direction) of the eyes
  by electrodes placed over the muscles that move
  the eye
• Can have binocular or monocular set-up (binocular
  more reliable)
• Head must be kept still so the center of the
  visual field is constant
• Ideal impedance of the electrodes is under 2,000
  ohms (we have been dealing with impedances under
  50 Kohms)

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The EOG Can Record

• Saccadic movements
• Smooth pursuit movements
• Nystagmus
• Convergence and divergence of the eye
• REM during sleep

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EOG Complications

• 3 problems to be cautious of
• Small magnitude of EOG signal
• Skin potential that are the same frequency as the
  EOG signal
• Slow drift- steady deflection of recording in one
  direction
• Caused by unclean electrodes and poor contact
  with the skin

13
Binocular Electrode Placement

• Electrodes A B are used to measure horizontal
  eye movements
• Electrodes C D measure vertical eye movements
• Electrode E is the ground

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EOG Recording

• Channel 1 one second timer Channel 2
  horizontal unipolar reading Channel 3
  horizontal bipolar reading Channel 4 marking
  channel with artifact noise

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Part II Eye Movements and Behavior

• Kylie Gray

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Mental Activity and Eye Movements

• Primary Function of Eye Movements
• Allow change in eye position to focus on objects
  of interest
• Two different kinds of eye movement
• 1. Saccadic
• 2. Pursuit
• Video

17
Eye Movements and Learning

• Paired Associates Learning
• (Haltrecht McCormack, 1966)
• 1. Subject sees word pairs, one word at a time
• 2. Subject then sees stimulus words
• 3. Asked to recall second word of word pairs as
  stimulus words presented (response words)
• Hypothesized that subjects consolidated during
  initial phase (response-learning) then made
  connection in a second phase (hook-up)
• (McCormack, Haltrecht, Hannah, 1967)
• Fixation of response words decreased as learning
  progressed, whereas time spent viewing the
  stimulus words increased
• Viewing time of response and stimulus words
  diverged more quickly when subjects earned as
  easy list than a difficult one
• - Eye movement pattern varies with efficiency and
  stage of learning and may differ with difficulty
  of the learning task

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Eye Movements, Problem Solving, and Laterality

• Problem Solving
• ( Nakano, 1971) Subjects presented with 2
  horizontal arrays of pictures under 3 conditions
• 1. no problem solving required
• 2. when the pics were used in the solution of
  a problem
• 3. after problem solving
• - avg. number of eye fixations was greatest when
  pictures were needed to solve the problem and
  least after problem solving was completed
• ( Ehrlichman and Barrett, 1983) Saccadic eye
  movement during 2 kinds of cognitive activity
• Verbal
• Visual ( did not require viewing stimuli)
• More eye movements to questions calling for
  verbal processes than visual imagery
• Reflect differences in internal sampling or
  shifts in cognitive operations

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• Hemispheric Dominance
• Eyes move left or right in a consistent manner
  after asking a question that required some
  thought
• The eyes move rightward for verbal analytic
  problems and leftward for spatial problems
• Gur (1975) right-handed males were studied
• Eye movements left for spatial problems and
  right for verbal when the experimenter sat behind
  them, however, when experimenter sat in front the
  movements moved predominately to one side
  regardless of problem type
• Left handers were uncorrelated with problem
  type , even when experimenter sat behind
• Greater degree of lateralization for
  right-handers was found
• (Neubauer, Schulter, Pfurtscheller, 1988)
  Greater EEG activation in the hemisphere
  contralateral to predominant direction of gaze
  was observed for both left-movers and right-movers

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Eye Movements and Reading

• Reading Efficiency
• Buswell (1920) Eye movement reading patterns of
  students at 13 levels from first grade to college
• Results of reading skills
• 1. steady decrease in number of eye fixations
  per line of reading material with higher grade
  levels
• 2. fixations became shorter in duration
• 3. number of regressive movements decreased
  from an average of 5.1 per line for first graders
  to .5 for college students
• More efficient readers made fewer and shorter
  duration eye fixations and had fewer regressive
  movements than inefficient readers

21
Reading Disabilities and Eye Movements

• Lefton (1978) Studied eye movement patterns of
  fifth-grade children with reading disabilities
  while they did a letter-matching task
• Results Needed an unusually large number of eye
  fixations to do the task
• Abnormal eye movement patterns are the result of
  poor reading, and that training in systematic
  gathering of information should help poor readers
• Pavlidis (1981) Reported differences between
  dyslexics and normal readers eye movements in a
  tracking task
• Resuts 3 types of hypothesis
• 1. erratic eye movements reflect problems that
  dyslexics have with the reading material
• 2. erratic eye movements cause dyslexia
• 3. erratic eye movements and dyslexia are
  symptoms of independent but parallel brain
  deficits

22
Eye Movements and Psychopathology

• Schizophrenia
• Holzman, Proctor, Hughes (1973) difficulty
  following a slowly moving target that is in
  continuous motion
• Iacono (1988) inability to produce intact
  smooth eye movements
• Pursuit-tracking deficits are under genetic
  control and that it could possibly be used as a
  marker for individuals who may be predisposed to
  becoming schizophrenic
• It has been suggested that the deficit has its
  basis in a disorder affecting the frontal eye
  fields leads to inability to inhibit saccades
• Study done on manic depressives using lithium
  carbonate - didnt worsen pursuit performance,
  which supports the idea that smooth pursuit
  dysfunction is specific to schizophrenia

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Eye Movements and Perception

• Gould Schaffer (1967) eye movement recordings
  indicated that sbujects spent more time fixating
  patterns that exactly matched a memorized
  standard than on those that differed, suggesting
  that detailed comparisons of features were being
  made
• Scan Paths
• Noton Stark ( 1971) analyzed eye movements of
  subjects while they viewed different patterns in
  a learning phase and recognition phase
• Analyses of eye movements indicated that subjects
  followed similar paths for a given pattern, and
  the sequence of movements was usually the same in
  the recognition phase as it was in the learning
  phase.
• Suggests that memory for features of a picture is
  established sequentially by the memory of eye
  movements required to look from one feature to
  the next

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• Pictoral Information
• Mackworth Morandi (1967) portions of a
  picture rated as highly informative by one group
  of people were fixated more frequently by another
  group of individuals who examined the pictures
  while their eye movements were measured.
• Information one wishes to derive from a visual
  scene will determine the pattern of eye movement
  used in examining the picture
• Loftus (1972) durations of eye fixations did
  not affect recall of a picture, but the number of
  fixations made during a fixed period of viewing
  did affect later recognition
• The greater number of fixations, the more likely
  the person was to recognize the picture at
  another time
• Initial fixes were on informative regions
  initially and the less informative detail
  received a greater portion of the fixations later
  in the viewing sequence

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Part III Eye Illusions and the Startle Response

• Sarah Leis

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Muller-Lyer Illusion

• There has been some attention paid to the study
  of eye movements while persons experience various
  kinds of visual illusions. This is one example.

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Muller-Lyer Illusion (Contd)

• With prolonged inspection the magnitude of the
  illusion decreases.
• One hypothesis Due to feedback provided by
  erroneous eye movements
• If eye movements restricted to one portion of the
  figure less 411 will be fed back

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An experiment that supports the eye movements
hypothesis

• Festinger, White, and Allyn
• Found the Muller-Lyer illusion became less
  powerful when eye movements were made over the
  entire figure than when only one part of the
  figure was fixated.

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Rebound Illusion

• If a target moving at a constant velocity and
  tracked by the eyes comes to an abrupt stop, it
  appears to rebound sharply backward.
• Can occur when the eyes pursue a luminous object
  in the dark.
• Caused by an overshoot of the target by the eye
  at the point at which the target stops.
• Suggests that position information during
  tracking is derived from efferent signals rather
  than feedback from the muscles.

30
EB Eye Blink Stats

• Typical blink (measured by EOG) is about 380
  microvolts in amplitude and lasts 120 msec.
• Spontaneous eye blinks occur throughout the day.
• On average, 15-20 blinks a minute
• Interestingly, adults need only 2-4 blinks a
  minute to keep the eyeball moist
• So most blinks are unnecessary for a
  physiological viewpoint

31
Cognitive Activity and Eye Blinks

• Activities that lead to thought lead to an
  increase in blinking.
• Andreassi (1973) reported a significant increase
  in EB frequency when subjects were required to
  solve anagrams than when resting.
• Tecce (1992) found that people conversing or
  involved in an interview showed increases in
  blink frequency
• Blink frequency decreased when individuals gave
  close attention to outside visual events, perhaps
  to facilitate information processing
• Oculomotor system is very sensitive to fatigue,
  boredom and lapses inattention

32
Eye Blinks and Information Processing

• Long closure duration the time eyes remain
  closed during blinking
• Long closure duration is related to alertness
• During reading there is an inhibition of blinking
  which grows with interest in the material.
• A flurry of blinks occurs as the reader turns the
  page
• Stern (1985) found that blink rate and duration
  were both less in a visual task than an auditory
  one.
• Blink suppression is due to increased cognitive
  demands that directs attention to task-relevant
  stimuli

33
Eye Blinks and Information Processing (Contd)

• Blinks are delayed until decisions about external
  stimuli have been made and responses to those
  stimuli completed.
• So, blink rate and duration may be related to
  cognitive functions such as decision-making and
  discrimination.
• Fogarty and Stern (1989) found that a lower blink
  rate was found for a 6-item than a 2-item memory
  set.
• This suggests that a lower blink rate reflects
  the greater attention demanded for performing the
  more difficult task involving 6 items

34
Blink Rate and Stress

• Increased blink frequency generally reflects
  negative mood states such as nervousness, stress
  and fatigue
• Nixon Effect During President Nixons
  resignation speech he blinked over 50 times per
  minute. He also displayed rapid bursts of blinks
  (3 per second), showing overall stress and a
  negative emotional state
• Negative emotional states that accompany poor
  performance have been related to increases in
  blinking
• More positive states are accompanied by decreased
  blink frequency
• Tecce (1992) found that blink rate slows after
  hypnotic relaxation and successful problem
  solving
• Hedonia-blink hypothesis decreased blinking is
  related to pleasant feelings, whereas increased
  frequency of blinks accompanies unpleasant mood
  states

35
Eye Blink and the Startle Response

• Startle response the bodily reactions to a
  strong, rapid, unexpected stimulus
• Physiological changes produced by the startle
  response include increases in eye blink (EB),
  heart rate, skin conductance, etc.
• The fastest and most stable component of the
  response was the EB with a latency of 40 msec
• Other fast components were widening of the mouth
  (70 msec), forward head movement (80 msec), and
  tightening of neck muscles (90 msec).

36
Startle Response in Emotion

• Vrana, Spence and Lang (1988) used a high
  intensity noise burst to elect a startle response
  while college students viewed pleasant and
  unpleasant slides
• The startle response (measured by EB magnitude),
  was largest when subjects viewed unpleasant
  stimuli and smallest for positive stimuli, as
  compared to neutral slides
• The pleasant-unpleasantness of stimuli was
  confirmed by the participants ratings

37
Emotional Ratings and Physiological Arousal

• Witvliet and Vrana (1995) compared EB startle
  magnitude and latency under conditions of
  negative and positive imagery that included both
  high and low arousal components. (EX fear and
  joy are negative and positive and are both high
  arousal. Sadness (negative) and pleasant
  relaxation (positive) are both low arousal.)
• Found that EB magnitudes were larger and
  latencies were faster during negative as compared
  to positive imagery.
• Higher arousal also led to larger magnitude and
  shorter latency EBs

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Positive and Negative Sensory Experience

• The EB component of he startle response has also
  been used to evaluate the emotional effects of
  positively and negatively rated odors.
• Miltner, Matjak, Braun and Brody (1994) exposed
  subjects to an unpleasant odor (hydrogen sulfide)
  and a plesant odor (vanilla). They compared EB
  amplitude.
• The negative odor significantly enhanced EB
  amplitude in comparison with neutral air
• Reduction in EB with positive odor was not
  significant
• This may have occurred because the emotional
  valence of vanilla was only about half as
  positive as the emotional valance of the hydrogen
  sulfide was negative

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Positive and Negative Sensory Experience
(continued)

• Ehlichman (1997) followed up the study and used a
  design in which participants experienced either a
  pleasant odor or an unpleasant one. (not both)
• The odors wrre equal in terms of emotional
  valence ratings (pleasant coconut. Unpleasant
  limburger cheese)
• The unpleasant odor increased the magnitude of
  the EB and unlike the Miltner study, the pleasant
  odor attenuated the EB complex of the startle
  response.

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EB Component of Startle in Clinical Research

• The notion that schizophrenics have difficulty
  with assimilation of percepts or processing
  sensory stimuli has existed for some time
• Inhibition of the EB in startle reaction can
  index deficits in early information processing
  and may be related to underlying vulnerability
  factors
• A number of studies have indicated that
  schizophrenics patients show reduced startle
  inhibition at short prepulse intervals
• Normal individuals who score as psychosis prone
  on the Minnesota Multiphasic Personality
  Inventory also show less startle inhibition
  compared to control individuals

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More Clinical Research

• Hamm (1997) studied the EB startle reflex in
  people with high fear (phobics) and low fear (non
  phobics) of animals or mutilation.
• Participants viewed slides of fear relevant,
  unpleasant, neutral and pleasant scenes.
• Animal and mutilation phobics showed larger EB
  facilitation than the non phobics when viewing
  un-pleasant scenes.
• They showed greater EB magnitudes when viewing
  feared pictures than the nonphobics viewing the
  same or other unpleasant slides.
• So, EB startle reflex indexes the individuals
  basic motivational disposition and can provide
  information for the assessment of fear responses.
• Also, FYI, individuals with simple and social
  phobias, PTSD, and panic disorder all show
  enhancement of the startle EB while imagining
  scenes or viewing pictures that are threatening.

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References

• Andreassi, J.L. (2000). Psychophysiology
• Human Behavior Physiological Response.
• Mahwah, New Jersey Lawrence Erlbaum
• Associates, Inc.
• Figure taken from Psych 360- Lab 8- online at
  http//webpub.allegheny.edu/employee/a/adale/p360/
  lab8.html