Psychology%204051

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Psychology 4051

• Assessing Vision in Infants and Toddlers

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Visual Evoked Potentials

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

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Visual Evoked Potentials

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

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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.

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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.

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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.

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Sweep VEP

• Spatial Frequency
• Background Noise

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Sweep VEP

• VEP

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Sweep VEP

• Amplitude Strength of the response

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Sweep VEPs

• Slope

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Sweep VEPs

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

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Advantages

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

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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.

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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.

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VEPs vs. Behavioral Methods

• Behavioral tests reflect what the infant chooses
  to look at.