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

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

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.

Types of VEPs

• There are two types of VEPs.1.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.

Types of VEPs

• Very precise.• This technique is rarely possible with infants.2.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.

• Spatial Frequency• Background Noise

Sweep VEP

• VEP

Sweep VEP

Sweep VEP

• Amplitude: Strength of the response

Sweep VEPs

• Slope

Sweep VEPs

• Intercept: slope of the VEP response is equal to background noise level.

• Provides the measure of visual acuity.

Advantages

• Provides an objective measure of vision• Requires no behavioral response (minimal

attention)• Procedure is very quick

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.

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.

VEPs vs. Behavioral Methods

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