May 2003
Volume 44, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2003
Temporal Dependence of Direction-Reversal VEP in Infants
Author Affiliations & Notes
  • O.J. Braddick
    Dept of Experimental Psychology, University of Oxford, Oxford, United Kingdom
  • D. Birtles
    Visual Development Unit, Dept of Psychology, University College London, London, United Kingdom
  • J. Atkinson
    Visual Development Unit, Dept of Psychology, University College London, London, United Kingdom
  • J. Wattam-Bell
    Visual Development Unit, Dept of Psychology, University College London, London, United Kingdom
  • Footnotes
    Commercial Relationships  O.J. Braddick, None; D. Birtles, None; J. Atkinson, None; J. Wattam-Bell, None.
  • Footnotes
    Support  Medical Research Council G7908507
Investigative Ophthalmology & Visual Science May 2003, Vol.44, 1997. doi:
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      O.J. Braddick, D. Birtles, J. Atkinson, J. Wattam-Bell; Temporal Dependence of Direction-Reversal VEP in Infants . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1997.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Abstract: : Purpose: VEPs elicited by reversal of motion direction in a random dot pattern are an indicator of development of directional selectivity in infants' visual cortex (Wattam-Bell 1991). Comparison of direction-reversal (DR-)VEPs with orientation-reversal VEPs in the same infants suggest that directional selectivity has a relatively late onset in development (Atkinson et al, ARVO 2002). However, a complete picture of the development of direction selectivity requires information about how temporal properties of the system change with age. Methods: A group of infants were tested longitudinally between 6-18 weeks of age for DR-VEPs, with cross sectional data in age groups between 5-18 weeks from a larger group. Steady-state DR-VEPs were elicited by a moving random pixel pattern (velocity 5 deg/sec) with periodic reversals of direction. The random pattern was replaced at 2x reversal frequency to isolate direction-selective responses at the reversal frequency. Rates of 2 and 4 reversals/sec were tested in counterbalanced order in each session. The presence of a VEP response at the stimulus frequency with consistent phase was tested by Hotelling's T-squared test. Results: Significant responses at 2 rev/sec were first seen in the longitudinal at a median age of 10 weeks, and for 4 rev/sec at 12 weeks. The first individual significant responses were seen at 6 weeks. Over all infants, signal amplitude at the reversal rate rose from 5 to 13 weeks, and up to 11 weeks was consistently higher for 2 rev/sec than 4 rev/sec. Mean amplitudes fell between 13-18 weeks and in this age group 4 rev/sec elicits the stronger response. Conclusions: Motion processing revealed by the DR-VEP shows relatively increasing high-frequency response as the system develops from 6-18 weeks. Testing at 4 rev/sec may underestimate motion processing capability in the infant visual system. However, even at the lower frequency of 2 rev/sec few infants show directional cortical responses before 8 weeks of age. This can be compared with orientation reversal responses which also show earlier emergence of low-frequency responses, but at 3 weeks of age (Braddick, 1993. The result can also be related to behavioural measures at low reversal rates, showing a median age of onset around 7 weeks of age (Wattam-Bell 1996). The present results support the idea that while temporal response is an important aspect of functional cortical development, directional selectivity is consistently later to develop than orientation selectivity.

Keywords: visual development: infancy and childhood • motion-2D • visual cortex 
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