Differential vulnerability of global motion, global form, and biological motion processing in full-term and preterm children
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Young children born very prematurely show elevated thresholds for global motion and global form [Atkinson, J. & Braddick, O. (2007). Visual and visuocognitive development in children born very prematurely. Progress in Brain Research, 164, 123-149; MacKay, T. L., Jakobson, L. S., Ellemberg, D., Lewis, T. L., Maurer, D., & Casiro, O. (2005). Deficits in the processing of local and global motion in very low birthweight children. Neuropsychologia, 43, 1738-1748]. In adolescence, those with white matter pathology show reduced sensitivity to biological motion [Pavlova, M., Sokolov, A., Staudt, M., Marconato, F., Birbaumer, N., & Krageloh-Mann, I. (2005). Recruitment of periventricular parietal regions in processing cluttered point-light biological motion. Cerebral Cortex, 15, 594-601; Pavlova, M., Staudt, M., Sokolov, A., Birbaumer, N., & Krageloh-Mann, I. (2003). Perception and production of biological movement in patients with early periventricular brain lesions. Brain, 126, 692-701]. Here, we measured sensitivity to global form, global motion, and biological motion in a sample of 23, five- to nine-year-old children born at <32 weeks gestation, and in 20 full-term controls matched to the clinical sample in age, socioeconomic status, and estimated Verbal IQ. As a group, premature children showed reduced sensitivity, relative to controls, on all three tasks (F>4.1, p<0.05). By computing a deficit score for each task (the ratio between a premature child's threshold and the mean threshold for three age-matched controls) we were able to compare performance across tasks directly. Mean deficit scores were significantly greater than 1 (indicating some level of impairment) for biological motion and global motion (ps<0.03). In contrast, the mean deficit score for global form was not significantly different from 1 (indicating no impairment, relative to age-matched control children). Rates of impairment (deficit score>or=2) were four times higher for global motion than for global form (p<0.04); rates of impairment on the biological motion task fell at an intermediate level. In agreement with previous studies, we find impairments in the processing of global motion (Atkinson & Braddick; MacKay et al.) and of biological motion (Pavlova et al.), which are larger than the impairments in the processing of global form (Atkinson & Braddick). In addition, we show that the impairments are not correlated with each other. The differential vulnerability that we observed across tasks could not be accounted for by stereoacuity deficits, amblyopia, or attentional problems. We suspect, instead, that it reflects the fact that these forms of visual processing develop at different rates, and may be differentially vulnerable to early brain injury or atypical neurodevelopment [c.f., Atkinson, J. & Braddick, O. (2007). Visual and visuocognitive development in children born very prematurely. Progress in Brain Research, 164, 123-149; Braddick, O., Atkinson, J., & Wattam-Bell, J. (2003). Normal and anomalous development of visual motion processing: Motion coherence and 'dorsal-stream vulnerability'. Neuropsychologia, 41, 1769-1784].
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