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Lotte-Guri Bogfjellmo, Peter J Bex, Helle K. Falkenberg; Direction discrimination of global motion low contrast patterns in school aged children. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2742. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Direction discrimination of global motion develops during childhood and involves the detection of local directional signals that are then integrated across space. We used an equivalent noise (EN) paradigm to examine the limiting effects of internal noise (local directional selectivity) and sampling efficiency (global motion integration) on direction discrimination, and compared the results to motion coherence thresholds (MCT) for two patterns.
98 observers (6-15 years) identified in 2AFC, the global direction of motion of an 8 deg central stimuli in containing 100 limited-lifetime dots of 10% Michelson contrast, moving at 2.8 and 9.8°/s in two experiments; the EN experiment estimated the internal noise and sampling efficiency from direction discrimination thresholds as a function of external directional noise; the MCT experiment measured the lowest signal to noise ratio of moving dots for discriminating translational (up/down) and radial (expansion/contraction) motion. Direction discrimination thresholds and MCT were analysed as a function of age and speed, and a correlation analysis compared internal noise and sampling efficiency with MCT.
For the EN experiment, direction discrimination improved gradually until the age of 15 years (linear regression, p<0.05) for both speeds. This improvement was due to an increase in sampling efficiency (linear regression, p< 0.05) with age, and not changes in internal noise. Direction discrimination thresholds were lower at 2.8 than 9.8°/s for all observers (paired t-test, p<0.05). There was a small but not significant improvement in MCTs across the age range tested for both MCT patterns, but no difference with speed. MCT for radial motion correlated significantly with sampling efficiency, but not internal noise (p<0.05).
The EN task confirms that direction discrimination of low contrast global motion continues to improve in school children. Yet, this was not shown in the MCT tasks using the same stimulus parameters. This indicates that assessment of global motion depends on the parameters, and for low contrast stimuli, the MCT might not be sensitive enough to detect changes in this age group. That maturity of direction discrimination is caused by an increase in the efficiency with which direction signals are pooled, and no change in internal noise, suggests that global motion processes develop later than local motion processing.
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