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Binocular VEP summation in infants and adults with abnormal binocular histories
S L Shea1, R N Aslin, D McCulloch
1Center for Visual Science, University of Rochester, New York 14627, USA.
Insights
Binocular VEP summation in infants differs significantly from adults, suggesting VEP amplitude is mediated by independent monocular neurons rather than binocular cortical activation.
Area of Science:
- Neuroscience
- Developmental Biology
- Ophthalmology
Background:
- Binocular VEP summation is a measure used to assess binocular vision.
- Previous research suggested binocular VEP summation reflects binocular cortical neuron activation.
- Infant visual development and stereopsis onset are critical areas of study.
Purpose of the Study:
- To investigate binocular VEP summation in infants and compare it to stereodeficient and stereonormal adults.
- To explore the underlying mechanisms of VEP amplitude generation in different age groups and visual conditions.
Main Methods:
- Recorded visual evoked potentials (VEPs) under binocular and monocular viewing conditions.
- Utilized phase-alternated checkerboards of varying check sizes (10-52 min of arc) for VEP elicitation.
- Measured binocular VEP summation as the percentage increase of binocular VEP amplitude over the mean of monocular amplitudes.
Main Results:
- Stereodeficient adults showed no significant binocular VEP summation, unlike stereonormal adults.
- Infants exhibited significantly higher binocular VEP summation (approx. 95%) compared to adults.
- Infants under 5 months showed exceptionally high summation (nearly 145%) due to larger binocular VEP amplitudes.
Conclusions:
- Binocular VEP summation may not accurately represent binocular cortical neuron activation as previously hypothesized.
- VEP amplitude appears to be mediated by independent monocular cortical neuron pools.
- Binocular VEP amplitude saturation levels differ between infants and adults, suggesting developmental differences in visual processing.
Abstract:
Visual evoked potentials (VEPs) were recorded under binocular and monocular viewing conditions in 19 2- to 10-month-old infants, 19 stereodeficient adults, and 12 normal adults. VEPs were elicited by medium contrast, phase-alternated checkerboards with check sizes ranging from 10-52 min of arc. Binocular VEP summation was defined as the percentage by which the binocular VEP amplitude exceeded the mean of the two monocular VEP amplitudes. In the stereonormal adults, binocular VEP summation was significantly greater than zero and significantly less than 100%. In the stereodeficient adults, binocular VEP summation was not significantly greater than zero. These findings support the hypothesis that the magnitude of binocular VEP summation reflects the activation of binocular cortical neurons. However, binocular VEP summation in the infants averaged approximately 95%. Moreover, infants under 5 months of age, many younger than the reported age of onset for stereopsis, showed binocular VEP summation of nearly 145%. The significantly higher level of binocular VEP summation in the infants was the result of much larger binocular VEP amplitudes, while monocular VEP amplitudes were equivalent to those of stereonormal and stereodeficient adults. These results support the hypothesis that VEP amplitude is mediated by two independent pools of monocular cortical neurons and that binocular VEP amplitude in stereonormal and stereodeficient adults saturates at a lower level than in infants. Thus, it is hypothesized that binocular VEP summation is not representative of the activation of binocular cortical neurons.