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H Nakamura; Effects of Partial Visual Field Masking on Human Motion Perception; Magnetoencephalographic Study Using Random Dot Kinematograms . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4743.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the effect of parcial masking of the visual field on motion perception using MEG responses evoked by a random dot visual stimulation. Methods: Eight healthy volunteers participated in this study. Random dot kinematograms composed of 320 white square dots were projected on a global dark background in the magnetically-shielded room. Each dots moved smoothly with a constant speed. Coherent movement of 390 ms duration and random movement of 1320 ms were presented alternately. During the coherent period, the total dots moved in a uniform one of four directions; (right, left, up, down). Visual stimulations were given to the full-field, left hemi-field, left upper or lower quadrant of each subject. The subjects were instructed to look at the fixation point with their left eyes. The magnetic responses were recorded by a whole head planar type gradiometer, and averaged with respect to the onset of coherent motion. Results: We concentrated only on the first component in the right temporal area because they had relatively large amplitudes and were readily distinguished. The peak latencies of the first component did not show the significant difference between full-field, left hemi-field and left lower quadrant field. On the left upper quadrant field stimulation, we recognized the significant difference of peak latency for both full-field and left hemi-field stimulation. The mean latencies (S.D.) for the full-field, left hemi-field, left upper and lower quadrant field stimulation were 21925.117, 22924.704, 26551.687 and 23927.794 ms, respectively. Estimated sources of all subjects were consistently identified with the right lateral occipito-temporal cortex which corresponded to the human area V5/MT regardless of visual stimulation patterns. As the masking area was enlarged, the dipole strength correspondingly decreased from 10.3126.132, 6.4253.527, to 4.7383.167 and 5.1123.261 nAm in full-field, left hemi-field, left upper and lower quadrant field, respectively. Conclusion: These results suggest that an increase in the area of masking field reduces the dipole strength and that the peak latency is delayed when the masking was placed in the lower visual field.
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