Pupillometry

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Pupillometry

• Adam, Jessica Julie

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History

• Travisa (1495) - The blacke of theye.. is called
  pupilla in latyn for small ymages ben seen
  therin
• Pupilla in latin means little girl
• Romantic writers refer to eyes as windows to the
  soul
• Pupils controlled by Autonomic Nervous system

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Interpretations a pupillary response is the
contraction or dilation of the pupil. Interesting
Topics positive stimuli,negative stimuli,
information processing, perception, short term
memory, learning, and nonverbal communication.
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Anatomy and Physiology

• The pupil is the opening in the iris that light
  passes through.
• The iris is the colored part of the eye.
• The iris increases pupil dilation in low light
  and decreases pupil dilation in bright light.
• Range of dilation 1.5mm 9mm
• .2 second reaction time
• Parasympathetic NS innervates circular fibers for
  contraction.
• Sympathetic NS innervates radial fibers for
  dilation

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Iris Muscles
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Path of Contraction

• Circular muscles Sphincter Pupillae
• Signal starts in midbrain in the Edinger-Wastphel
  nucleus
• Fibers from nucleus travel along oculomotor nerve
  to the ciliary ganglion near the eyeball
• Ciliary ganglion connects to smooth circular
  muscles in the iris.

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Path of Dilation

• Radial muscles Dilator Pupillae
• Signal originates in the hypothalamus
• Nerve fibers connect hypothalamus to spinal cord
• Signal travels to synapse with the superior
  cervical ganglion
• The signal is then transmitted directly to the
  smooth radial muscle

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Emotion

• Pupil dilation has been scientifically connected
  to emotional responses since Claude Bernard and
  Charles Darwin in the 1850's
• Darwin's book The Expression of Emotions in Man
  and Animals described the connection between a
  fired gun and pupil dilation, linking pupil
  action to the startle response.

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Measurement of Pupil Dilation

• Most progress made in the last 30 years
• It's hard!
• There are constant 1mm fluctuations
• Pre-1967
• Photo electric measures
• Measure light that reflected from iris
• Infrared photogrophy
• Could take pictures in dim light
• These measures required large machinery and were
  not that accurate

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• 1967 Hakerem said that the best device was the
  Lowenstein Pupillograph
• Scanned the iris for reflected light
• Measured both pupils
• Provided information about the rates of change of
  pupil dilation (Calculas!)

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• 1972 Hess
• Used a movie camera, a projector and mirrors
• Used infrared film to measure any eye color
• Averaged 20 frames for a given stimulus
• Emphasized keeping the brightness and brightness
  contrast constant
• This method was economical but the hand
  measurements of the film were tedious and
  inaccurate

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Modern Labs

• Video-based Pupillometer
• Observe eye movements through closed-circuit TV
• Measure pupil diameter with signal processor
• Low-intensity infrared light illuminates the eye
• Low light level silicon matrix tube camera
• Allows for change in lab settings

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Using Modern Lab Techniques

• TEPR
• Task Evoked Pupillary Responses
• Pupil changes with respect to a task are averaged
  and background variations are ignored.
• Measurements are small enough in resolution that
  they stand out from the background noise after
  averaging
• Must have stable baseline
• Must have many presentations of stimulus

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Fatigue and Pupil Size

• Pupil diameter is maximal in a well rested person
• Pupil diameter decreases with fatigue
• Pupil diameter is smallest just before sleep
• During Pupillometry, too many stimuli in a row
  can alter results

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Work Fatigue Study

• Geacintov and Peavler (1974)
• Measured pupil sizes of telephone operators
  before and after work.
• Two types of workers
• Directory Assistance
• Microfilm Reader
• Beginning of word day
• Directory Assistance average 4.5mm
• Microfilm Reader average 4.6mm
• Only the microfilm readers showed a substantial
  difference (0.43 mm)
• Possible explanation
• The microfilm readers are reading at much faster
  rates

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Influential Factors

• Darkness Reflex
• Momentary dilation due to interruption of
  constant adapting light
• Consensual Reflex
• Stimulation of one eye affects both eyes equally
• Near Reflex
• Constriction due to decreasing the point of focus
• Lid-closure Reflex
• Momentary contraction followed by redilation

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Influential Factors Continued

• Psychosensory reflex
• Restoration of diminished reflexes due to
  external stimulation
• Age
• Decreased diameter and increased variability with
  age
• Habituation
• Pupil diameter decreases, speed of contraction
  increases, and magnitude of reflex decreases with
  continued stimulus presentations
• Binocular Summation
• Constriction greater when both eyes are
  stimulated simultaneously

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Pupillometry and Behavior
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Pupillometry and Behavior

• Eckhard Hess
• Most influential person in the application of
  pupillometry to psychology
• First study in 1960
• Interested in mental activity, information
  processing, perception, attitudes, and interests
• His work led to an increased interest in
  pupillometry

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Interest Value of Stimuli-Hess Polt 1960

• Females viewed pictures of babies and nude males
• Larger pupil dilation when looking at males
• Males viewed pictures of babies and nude females
• Larger pupil dilation when looking at females
• Concluded that pupil size related to the feeling
  tone of different pictures
• Later found support that there is a relationship
  between sexual arousal and pupil size

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Response to Pain-Chapman Et. al 1999

• Four intensities of electrical pain
• Ranged from very faint to barely tolerable
• Found that pupil size increased as intensity of
  shock increased.
• Concluded that pupil diameter increases as pain
  increases

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Sexual Arousal or Novelty

• Bernick, Kling, Borowitz- 1971
• Meterosexual males viewed three movies
• Erotic homosexual film, erotic heterosexual film,
  suspense film
• Heterosexual and homosexual films produced same
  amount of pupil dilation
• White Maltzman- 1977
• Subjects listened to two minute passages from a
  book
• Immediate dilation at start of each passage
• Erotic, mutilation, neutral
• Pupil size to neutral passage decrease after 10
  seconds, during other two passages, pupil size
  remained for 60 seconds.
• Concluded that novelty initially plays a role in
  pupil size, but interest sustains it

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Nonverbal Communication

• Hess 1975
• Manipulated pupil size in two images of the same
  woman
• Males described woman with larger pupils as soft,
  feminine, and pretty
• Males described woman with small pupils as hard,
  selfish, and cold
• People allowed to draw in the pupils of different
  pictures
• Subjects consistently drew large pupils on happy
  faces and small pupils on sad faces
• Cultural factors may have an effect on
  sensitivity to cues from pupil size

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Pupil Size and Mental Activity

• Hess and Polt- 1964
• Subjects completed mental multiplication
• Difficulty level increased gradually
• Pupil size increased as difficulty increased
• Polt- 1970
• Threat of mild electric shock for wrong answers
• Resulted in greater effort to answer correctly
• Pupil dilation increased

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Perception and Information Processing
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Task Difficulty

• Increased dilation with harder tasks
• Pitch Discrimination (Kahneman Beatty, 1967)
• Higher or lower tone
• Visual detection of weak light flash (Hakerem
  Sutton 1966)
• Tone detection (Beatty 1975)

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Stimulus Probability

• Low probability causes large pupil response
• Omitted stimuli also produces dilation
• Mental representation of expected stimuli
• Similar to P300 ERP
• Decreased pupillary response over time
• 48 minute testing period

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Affective Words

• Pupillary response to taboo words (Stelmack
  Manelzys, 1975)
• 12 taboo words (e.g. Whore)
• 12 emotional words (e.g. Vomit)
• 24 neutral words (e.g. Field)
• Introverts had largest average pupil size
• No mention of difference between word type

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Negative Affect

• Constriction of pupil size in response to
  negative stimuli (Hess 1972)
• Pictures of crippled children
• Shock content produces initial dilation
  followed by constriction
• Pictures of a mutilated person
• Perceptual avoidance?
• Bi-directionality questionable

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Attitude

• Pupil response to political leaders (Barlow 1969)
• Pictures of Lyndon Johnson, George Wallace and
  Martin Luther King
• Liberals dilation to Johnson King,
  constriction to Wallace
• Conservatives dilation to Wallace, constriction
  to Johnson King
• Indicator of political affiliation?

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Attitude

• Pictures of presidential candidates presented to
  supporters (Clark Ertas 1975)
• Constriction response to all images

Ronald Reagan
Bill McGovern
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Information Processing

• Processing speed (Poock 1973)
• Press buttons corresponding to numerals
• Increased dilation at 75 and 100 of maximum
  processing speed capacity
• Constriction at 125
• Digit string recall (Peavler 1974)
• Increased pupil size with each successive digit
• No increase after 10th digit
• Short-term memory capacity 9 digits

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Learning

• Verbal learning with incentives (Kahneman
  Peavler, 1969)
• 1 cent or 5 cent reward per item learned
• High incentives produced greater dilation
• Paired word associations (Coleman Paivio, 1970)
• Greater dilation with more abstract words and
  more difficult associations

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Schizophrenia

• Reduced pupil dilations vs. control group
• Guessing task
• Reduced ANS response to stimuli
• Pupillary constriction speed relapse
• Shorter time to max. constriction correlated with
  patients who relapsed after removal of medication
• Working Memory
• Digit recall performance and pupillary response
  lower than control group

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Caveats

• Light Reflex
• Pupil constriction from increased illumination
• Controls
• Fixation points
• Constant illumination
• Auditory stimulation
• Fatigue
• Parasympathetic nervous system

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References

• Andreassi, J. L. (1995). Psychophysiology Human
  Behavior Physiological Response. Hillsdale, New
  Jersey Earlbaum
• Photos
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  ye.jpg
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