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Psychology 4051

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 electrical activity. Visual Evoked Potentials.

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Psychology 4051

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  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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