Abstract
We combined an external noise paradigm with an efficient procedure for obtaining contrast thresholds (Lesmes et al., 2006) in order to model developmental changes in the effect of noise on contrast discrimination during childhood. Specifically, we measured the contrast thresholds of 5-, 7-, 9-year-olds and adults (n = 20/age) in a two alternative forced-choice orientation discrimination task over a wide range of external noise levels and at three levels of accuracy. Overall, as age increased, contrast thresholds decreased over the entire range of external noise levels tested. The decrease was greatest between 5 and 7 years of age. The reduction in threshold after age 5 was greater in the high than the low external noise region, a pattern implying greater tolerance of the irrelevant background noise as children became older. To model the mechanisms underlying these developmental changes in terms of internal noise components, we adapted the original perceptual template model (Lu and Dosher, 1998) and normalized the magnitude of performance changes against the performance of 5-year-olds. The resulting model provided an excellent fit (r2 = 0.985) to the contrast thresholds at multiple levels of accuracy (60, 75, and 90%) across a wide range of external noise levels. The improvements in contrast thresholds with age were best modeled by a combination of reductions in internal additive noise, reductions in internal multiplicative noise, and improvements in excluding external noise by template retuning. In line with the data, the improvement was greatest between 5 and 7 years of age, accompanied by a 39% reduction in additive noise, 71% reduction in multiplicative noise, and 45% improvement in external noise exclusion. The modeled improvements likely reflect developmental changes at the cortical level, rather than changes in front-end structural properties (Kiorpes et al., 2003).
Highlights
Many aspects of basic vision improve rapidly over the first few years of life
We modeled our data with Perceptual Template Model (PTM) to investigate whether the developmental improvement in contrast threshold with age can be modeled by a combination of reduction in internal additive and multiplicative noise components as well as the improvement in filtering out irrelevant information
In a previous study (Jeon et al, 2012), we included a task similar to the current experiment as one of the outcome measures to gauge the effect of video game training on the vision of adult congenital cataract patients and normal adult controls
Summary
Many aspects of basic vision improve rapidly over the first few years of life. Visual acuity, whether measured using visually-evoked potentials or preferential looking, improves rapidly between birth and 6 months of age and continues to improve gradually until about 6 years of age (Norcia and Tyler, 1985; Chandna, 1991; Neu and Sireteanu, 1997). Front-end changes make a substantial contribution to the early improvements in basic visual abilities (e.g., Yuodelis and Hendrickson, 1986; Banks and Bennett, 1988). The development of cortical pathways appears to contribute to the changes both during and after infancy (Banks and Bennett, 1988; Toga et al, 2006; Braddick and Atkinson, 2011). Be it artificial or biological, neurons are not ideal transmitters of information
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