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Herbert Goltz, Filomeno Cortese, Alton Wong, Douglas Cheyne, Agnes Wong; Spatiotemporal differences in local and global pattern perception in human amblyopia investigated with MEG. Journal of Vision 2010;10(7):463. doi: 10.1167/10.7.463.
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© ARVO (1962-2015); The Authors (2016-present)
Amblyopia is a monocular loss of vision caused by abnormal early childhood visual experience. Despite prior efforts, the neural basis of amblyopia remains elusive: there is contradictory evidence on whether early visual cortex or higher cortical areas are affected. Some studies indicate normal activation in V1/V2 and diminished activity in higher cortical areas; others have found that V1 and/or V2 are dysfunctional in amblyopia. We employed Glass patterns, which stimulate both early and higher visual cortical areas. Cortical activity was measured using magnetoencephalography (MEG) which was co-registered with anatomical MRI. Five adults with amblyopia and 9 visually normal subjects were tested. Prior to MEG recording, monocular Glass pattern detection thresholds were measured to determine the signal strength (% correlated dot-pairs) for the subject to perceive radial and rotational patterns correctly on 80% of trials. During MEG recording the Glass pattern signal strength was fixed at the individual's 80% threshold level so that the amblyopic eye (AE), the fellow (FE) and healthy eyes (HE) were equated for psychophysical performance. Stimuli were presented in two blocked conditions (radial or rotational, each by eye; 200 trials, 50% signal). Behaviorally, amblyopic observers needed higher stimulus signal strengths and exhibited slower reaction times when viewing with their AE compared to their FE. Using event-related beamformer-based spatial filtering, brain activity maps revealed differences in early visual areas (~120 ms), medial temporal complex (~190 ms) and temporal-parietal areas (~250 ms) during Glass pattern stimulation of AE compared to FE and HE. Multivariate analysis of the source waveforms at these brain locations revealed a different spatiotemporal pattern of interaction between early and later visual areas in amblyopic observers. The neural basis of amblyopia may be defined by altered patterns of interaction between striate visual cortex, later retinotopic extrastriate areas and specialized cortex as compared to normal visual brain function.
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