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Woo-Young Lee, Sang-Hun Lee; Dynamics of line motion illusion reflects the anatomical and functional architecture of the early visual cortex. Journal of Vision 2005;5(8):899. doi: 10.1167/5.8.899.
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BACKGROUND A static line gives a motion perception when it follows a cue appearing at one of its ends, dubbed line motion illusion (LMI) (Hikosaka et al., 1993). Despite many attempts to understand how attention affects LMI, its neural basis remained relatively unexplored until recently. However, a real-time optical imaging study on anaesthetized cats (Jancke et al., 2004) suggests that LMI can be mediated by subthreshold cortical activity triggered by a cue. In addition, psychophysical and fMRI studies on humans demonstrated that the dynamics of perceptual waves well coincides with the functional structure of V1 (Wilson et al., 2001; Lee et al., 2004). Inspired by these findings, we assessed how LMI is constrained by the properties of the early visual cortex. METHOD As carriers of LMI, Gabors (sf= 3 cycles/°, σ= .2°, peak contrast= .15∼.3) appeared on a 6°-radius annulus. In most trials, a single Gabor (‘cue’) briefly appeared randomly at one of the 8 locations equally spaced, and was followed by 8 neighboring Gabors (‘line probe’) covering a 90° arc at either side of the cue. The contrasts of Gabors were modulated in a manner that generates clock-wise or counter clock-wise physical motion. We asked subjects to judge motion direction to find the speed of physical motion that nulls LMI using a stair-case method. The orientations of Gabors were collinear to one another in half of trials and parallel in the other half. Trials without a cue were included to detect possible biases in motion perception over the annulus. RESULT The speed of LMI was faster for collinear line probes than for parallel ones. Furthermore, spatial inhomogeneity in LMI speed reflected the anatomy of the visual cortex: there was a time delay (.1∼.2 s) for interhemispheric LMI. CONCLUSION The dynamics of LMI is tightly linked to the functional and anatomical properties of the visual cortex, providing a means for investigating perceptual concomitants of the propagation of neural excitability in human brains.
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