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Psychology%204051

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Psychology 4051 Assessing Vision in Infants and Toddlers Visual Evoked Potentials VEP: EEG electrodes are attached to the scalp over the visual cortex to measure ... – PowerPoint PPT presentation

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Title: Psychology%204051


1
Psychology 4051
  • Assessing Vision in Infants and Toddlers

2
Visual Evoked Potentials
  • VEP EEG electrodes are attached to the scalp
    over the visual cortex to measure electrical
    activity.

3
Visual Evoked Potentials
  • Electrical activity is measured while the child
    is presented with some form of visual pattern.

4
Visual Evoked Potentials
  • If the stimulus produces an electrical response,
    it is assumed that the stimulus can be detected.
  • If there is no electrical response, it is assumed
    that the stimulus can not be detected.

5
Types of VEPs
  • There are two types of VEPs.
  • Steady State VEPs
  • VEP response is measured as the subject is
    presented patterns that vary in spatial
    frequency.
  • Many different spatial frequencies are used.
  • The relationship between the strength of the
    response (amplitude) and the spatial frequency of
    the stimulus is examined closely.

6
Types of VEPs
  • Very precise.
  • This technique is rarely possible with infants.
  • Sweep VEPs
  • 10 to 20 spatial frequencies are presented in
    rapid succession during a 10 second sweep
  • The slope of the amplitude of the VEP response is
    determined.
  • The intercept to background noise is taken as an
    estimate of visual acuity.

7
Sweep VEP
  • Spatial Frequency
  • Background Noise

8
Sweep VEP
  • VEP

9
Sweep VEP
  • Amplitude Strength of the response

10
Sweep VEPs
  • Slope

11
Sweep VEPs
  • Intercept slope of the VEP response is equal to
    background noise level.
  • Provides the measure of visual acuity.

12
Advantages
  • Provides an objective measure of vision
  • Requires no behavioral response (minimal
    attention)
  • Procedure is very quick

13
Disadvantages
  • Equipment is expensive
  • Expertise is required.
  • E.g., electrode placement
  • Attachment of electrodes is difficult and be
    disturbing to parents.
  • Testing can be time-consuming.

14
VEPs vs. Behavioral Methods
  • There is generally good agreement between VEPs
    and behavioral methods in adults.
  • In infants, VEPs usually provide higher scores.
  • In behavioral methods, infants need to provide a
    clear behavioral response.
  • Responses probably reflect different underlying
    mechanisms.

15
VEPs vs. Behavioral Methods
  • Behavioral tests reflect what the infant chooses
    to look at.
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