Purpose: Previous research has shown a significant increase in flicker defined letter contrast sensitivity in 8-9 year old and 11-12 year old children compared with those of kindergarten age (5-6). We have also shown that temporal analysis of the VEP from adults gives temporal non-linearities with simple but distinct contrast response functions which resemble those of primate magno and parvocellular pathways. Hence this experiment aimed to examine the non-linearities of the VEP in children with a view to further delineating the development of magnocellular function. Methods: The achromatic multifocal VEP was recorded (between Oz and Fz with ear reference) from eight children of ages 6 to 12. The stimulus consists of a group of 61 hexagons, each of which was flashed on and off in a deterministic but seemingly random sequence. Through cross correlation, the evoked potential at each site was established. A series of recordings with different levels of luminance contrast were performed, each recording taking 4 minutes. Results: The chief difference in waveforms as a function of age was found in the first slice of the second order response where the adult pattern was replaced by a series of low amplitude peaks. While some variation was noted, the ratio of first slice response amplitude to second slice response amplitude (postulated as the ratio of magno/parvo response) showed a significant increase with age between 6 and 11 years old, indicative of a developmental increase in the dominance of the magnocellular pathway in normal visual function in upper primary school children. The traces recorded from the 11 year old were very similar to those from the adult. Conclusion: Development of magnocellular function as indicated by the changes in amplitude of the first slice of the second order VEP response extends in primary cortex to at least 11 years of age.
|Number of pages
|Investigative Ophthalmology and Visual Science
|Published - 15 Feb 1996