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Directional motion asymmetry in infant VEPs--which direction?
A J Mason1, O J Braddick, J Wattam-Bell
1Visual Development Unit, Department of Psychology, University College London, Gower Street, London WC1E 6BT, UK. alexandra.mason@ucl.ac.uk
Insights
Infant visual development shows asymmetries. This study found visual evoked potential (VEP) asymmetry in infants, with stronger responses to nasal-to-temporal visual motion, which contrasts with optokinetic nystagmus (OKN) direction.
Area of Science:
- Developmental neuroscience
- Visual system development
- Infant visual processing
Background:
- Early infancy visual development exhibits asymmetries in optokinetic nystagmus (OKN) and visual evoked potentials (VEPs).
- Understanding the relationship between these asymmetries is crucial for comprehending visual pathway maturation.
Purpose of the Study:
- To investigate the directionality of visual evoked potential (VEP) asymmetry in infants.
- To determine if VEP asymmetry is consistent with optokinetic nystagmus (OKN) asymmetry.
Main Methods:
- Recorded steady-state and transient visual evoked potentials (VEPs) in infants aged 5-21 weeks.
- Stimuli included gratings with unidirectional and oscillating movements (leftward/rightward).
- Monitored eye movements using electrooculography (EOG) to rule out retinal slip as a factor.
Main Results:
- Infants showed larger VEP amplitudes for nasal-to-temporal visual motion compared to temporal-to-nasal motion.
- No significant differences in eye movements were observed based on stimulus direction.
- The VEP asymmetry direction was opposite to the previously observed OKN asymmetry.
Conclusions:
- A distinct VEP asymmetry exists in early infancy, favoring nasal-to-temporal visual stimulation.
- This VEP asymmetry is independent of eye movements and retinal slip.
- The opposing directions of VEP and OKN asymmetries suggest a complex relationship in early visual system development.
Abstract:
Monocular viewing during early infancy reveals asymmetries in optokinetic nystagmus (OKN) and visual evoked potentials (VEPs). This study investigates the VEP asymmetry to see if it is consistent in direction with the OKN asymmetry. Steady-state VEPs were recorded from infants (5-21 weeks) viewing gratings that underwent successive displacements in the same direction, leftward or rightward. In addition, transient VEPs were recorded to the two directions of an oscillating stimulus. Both tests produced larger VEP amplitudes for nasal-to-temporal compared to temporal-to-nasal movement. Horizontal eye movements were monitored by EOG while viewing these stimuli to test whether the asymmetry was a consequence of eye movements. No difference in eye movements as a function of the stimulus was found, excluding differences in retinal slip as an explanation of the asymmetry. The stronger neural response for nasal-to-temporal displacements is opposite to the asymmetry of OKN. Oculomotor and VEP asymmetries may be related; however this relationship is not simply that the stronger neural response, indicated by the VEP, leads to a stronger optokinetic response.