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H. K. Falkenberg, W. A. Simpson, G. N. Dutton; Sampling Efficiency and Internal Noise in Young Patients With and Without Symptomatic Visual Motion Impairment. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2890. doi: https://doi.org/.
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Impaired motion perception has been found in child patients with hydrocephalus and children with more diffuse cerebral damage, often in the presence of otherwise near normal visual functions. This study investigates how child patients with symptomatic motion impairments and children with hydrocephalus without impaired motion perception are limited by internal noise and sampling efficiency.
Energy contrast thresholds were measured as a function of external dynamic noise level in three tasks: detection of a drifting grating, detection of the sum of two oppositely drifting gratings and direction discrimination of oppositely drifting gratings. Thresholds were measured in seven child patients with and without symptomatic motion impairments, and in 168 children (5-14 years) with normal visual development.
Motion detection, summation and discrimination are impaired in patients with symptomatic motion impairments (p< .05). This is due to both increased levels of internal noise and reduced sampling efficiency. Children with hydrocephalus without symptomatic motion impairments perform equally well to child observers with normal development. Sampling efficiency for direction discrimination is much poorer in children than adults (p< .05), and is not yet mature by 14 years of age, in contrast to sampling efficiency for detection and summation which do not change with age. The internal noise levels do not change with age or task.
Patients with symptomatic impairment of motion perception have higher internal noise and lower sampling efficiency than children with normal development and patients without symptoms. It is also clear that motion direction discrimination is a difficult task for the visual system; the absolute efficiency is poor (< 2 %), and direction discrimination is not fully developed even in young teenagers. This suggests that motion detection and motion discrimination are processed by different mechanisms that have different maturation periods.
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