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C. Hou, R.O. Gilmore, M.W. Pettet, A.M. Norcia; Development of Spatial and Temporal Dynamics of Motion Coherence in Human Visual System . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3152.
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© ARVO (1962-2015); The Authors (2016-present)
In comparison to the development of spatial vision, little is known about the development of sensitivity to global versus local motion. Here we measured Visual Evoked Potential (VEP) responses to local and global motion information in infants and adults.
We used random–dot kinematograms (12.4 arcmin white dots on a black background, 10% density, lifetime 3 sec, field size 24 deg). A full .83Hz (F1) cycle of the stimulus consisted of .6s of circular coherent motion (clockwise or anticlockwise rotation around the fixation axis) and .6s of incoherent motion at the same dot speeds. VEP responses were measured over a wide range of dot displacements at three dot–update frequencies (F2: 30Hz, 20Hz and 15Hz). The combination of spatial and temporal frequencies resulted in a range of speeds from 0.8 deg/s to 18.6 deg/s. VEPs were recorded from 13 adults between 17–53 years of age and in 14 infants between 16–24 weeks of age at five electrode sites (PO7, O1, Oz, O2 and PO8) referenced to Cz. The infants provided data at 15 and 30 Hz at a subset of the displacements used in adults. VEP amplitude was measured at integer harmonics and combinations of the two driving frequencies (F1 and F2).
The first harmonic of the global change in motion coherence (1F1) showed displacement tuning across all electrode sites except for PO8 in both infants and adults. Adults showed clear speed tuning over the lateral right hemisphere site (PO8) with a broad peak between 3.1 and 6.2 deg/s. Responses at PO8 in infants were clearly different from the displacement tuning of the other sites, but were not strongly speed–tuned. Infant responses were maximal at larger dot displacements and faster speeds. In adults, 1F1 amplitudes were largest for the 30Hz dot–update rate, followed by 20Hz, followed by 15Hz. Infant responses were less consistent. The first harmonic of the local motion signal (1F2) increased monotonically with displacement in both infants and adults with the highest response at Oz.
Infants and adults sensitivity to motion differs primarily in the spatio–temporal tuning of the response to global motion measured at 1F1. Adults also show clearer evidence for speed tuning in lateral cortex. Local motion sensitivity, on the other hand is adult–like in terms of its spatio–temporal tuning with maximal responses over the occipital midline, suggesting that local motion sensitivity most likely reflects the function of early maturing lower level visual areas.
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