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Maturation of evoked potentials and visual preference in 6-45-day-old infants: effects of check size, visual acuity,
Insights
Visual evoked potentials (VEPs) and percentage time fixated (PTF) reveal developing visual acuity in infants. Early VEPs suggest subcortical function, while later VEPs and PTF indicate emerging cortical processing around 28-45 days.
Area of Science:
- Developmental Neuroscience
- Ophthalmology
- Visual Psychophysics
Background:
- Assessing visual development in human infants is crucial for early detection of visual impairments.
- Visual evoked potentials (VEPs) and behavioral measures like percentage time fixated (PTF) offer objective and subjective insights into visual function.
- Understanding the maturation of visual pathways, from subcortical to cortical, is key to characterizing infant visual development.
Purpose of the Study:
- To investigate visual evoked potentials (VEPs) and percentage time fixated (PTF) in response to varying checkerboard sizes in human infants.
- To determine the influence of check size, refractive lens strength, and infant age on VEP amplitude and PTF.
- To differentiate between subcortical and cortical contributions to visual processing in early infancy.
Main Methods:
- Recorded VEPs and PTF in 10 human infants (6-45 days old) using checkerboard stimuli of varying sizes (diffuse light to 180 min arc).
- Manipulated refractive lens strength (-6 to +6 diopters) to assess its impact on visual responses.
- Analyzed VEP components (early: <210ms, late: 240-400ms) and their correlation with behavioral PTF across different age groups (6-26 days vs. 27-45 days).
Main Results:
- Check size significantly affected VEP amplitude even in 6-day-old infants, with 11' checks suggesting visual acuity better than 20/220.
- Infants aged 27-45 days behaviorally discriminated checks (PTF), indicating visual acuity of 20/120.
- Two distinct modes of VEP response were observed: an inverted 'U-shaped' mode (likely subcortical) for smaller checks (<45') and a linear increase (likely cortical) for larger checks (45'-180'), correlated with PTF.
Conclusions:
- Infant visual acuity develops rapidly, with distinct subcortical and cortical processing modes identified via VEPs and PTF.
- Age significantly influences late VEP components and PTF, with enhanced responsivity and discriminating visual preference emerging between 28 and 45 days.
- These findings suggest the onset of increased cortical visual function in human infants within the first 2 months of life.
Abstract:
Visual evoked potentials (VEPs) and the percentage time fixated (PTF) were investigated in response to checkerboard light flashes in 10 human infaed as a function of the size of check in the evoking stimulus (diffuse light, 11, 22, 45, 90 and 180 min of arc), the refractive lens strength the checkerboards were viewed through (-6 to +6 diopters), and the age of the infants (6-26 or 27-45 days). Check size significantly influenced VEP amplitude in infants as young as 6 days. The 11' checks evoked greater responses that diffuse light suggesting a visual acuity of better than 20/220. Only the 27--45-day-olds behaviorally discriminated the checks, PTF indicating an acuity of 20/120. Evoked potential refraction with spherical lention between VEP amplitude and check size measured from different VEP components at different ages indicated the function contained two modes or components. The first mode was inverted "U-shaped" and was obtained in response to check sizes less than 45'. It was primarily due to changes in amplitude of the early VEP components (less than 210 msec after the evoking stimulus) and was poorly correlated with the behavioral PTF measure. It was proposed that this mode reflected subcortical activity. The second mode was a linear increase in amplitude as check size was increased from 45' to 180'. It was primarily due to changes in the amplitude of late VEP components (240--400 msec after the evoking stimulus) and was highly correlated with the percentage time the infants fixated the various check sizes. It was proposed that this mode reflected cortical activity. Age selectively influenced the late VEP components and the PTF behavioral measure, these measures being influenced by check size only in the 27--45-day-old infants. This change in responsivity of late VEP components and the transition from passive to more active and discriminating visual preference, suggest the onset of increased cortical function between 28 and 45 days of age.