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OJ Braddick, W Curran, J Atkinson, J Wattam-Bell, A Gunn; Infants' Sensitivity To Global Form Coherence . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3995.
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Purpose: Form coherence sensitivity is a measure of global extrastriate processing in a network of areas including parts of the ventral cortical stream (Braddick et al, Current Biology, 2000). On a number of measures, infants are known to develop sensitivity to local contour orientation within the first 2 months of life. This study examined at what age global form processing, integrating this local information, emerges in infant development. Methods: Test displays consisted of a background of randomly oriented short line segments, containing on one side a circular region where line segments are tangentially oriented to concentric circles. Coherence was varied by the percentage of randomly oriented segments within this region. Groups of infants aged 8-12 weeks and 16-20 weeks were tested by preferential looking with a dynamic version of this display, in which the whole array of random segments is replaced every 0.8 sec, and the coherent circular area is shifted on each replacement up and down one side of the screen. Each infant was tested with 100% coherence, and one other coherence value (60%, 70%, 80% or 90%). Results: The 16-20 week group showed significant preference for the side of the display containing form coherence of 80%or above. However, there is little variation of this preference between 80-100% coherence. The 8-12 week group performed at chance at all coherence levels. Conclusion: Infants over 16 weeks are capable of global form processing mediated by the extra-striate ventral cortical system. We have no evidence for this global function under 12 weeks, although younger infants are known to respond to local contour orientation. The fact that preference in the older group shows little variation above 80% coherence suggests that performance may be limited by the attention-gaining value of global form as well as by processing limitations on extraction of coherent signal from noise. These results will be discussed in comparison with motion coherence sensitivity of infants, which is an analogous measure of extra-striate global processing but in an independent cortical system including dorsal stream areas.
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