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Kaoru Amano, Derek Arnold, Alan Johnston, Tsunehiro Takeda; Watching the brain oscillating : A neural correlate of illusory jitter. Journal of Vision 2006;6(6):69. doi: 10.1167/6.6.69.
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Moving borders defined by small luminance changes (or by colour changes), placed in close proximity to moving borders defined by large luminance changes, can appear to jitter at a characteristic frequency (Arnold & Johnston, 2003). To reveal the neurophysiological substrates of this illusion we measured brain activity using magnetoenceohalography (MEG). In conditions 1–3, vertical green bars, superimposed upon larger red squares, moved across a black background. The green bars were either (1) darker, (2) isoluminant with, or (3) brighter than the red squares. In condition 4, vertical green bars moved across an isoluminant red background. In condition 5, physical jitter was added to dark green bars centered in a moving red square to mimic illusory jitter. In conditions 1–4, subjects indicated if the green bar appeared to jitter. If illusory jitter was reported, subjects then matched the illusory jitter rate to the frequency of an adjacent physical jitter. The matched frequency for each subject was used in condition 5. Illusory jitter was only perceived in condition 2 and its frequency was ∼10 Hz. We also found that neural oscillations around 10 Hz were significantly enhanced in condition 2 relative to all other conditions. As these oscillations were enhanced relative to isoluminant motion (condition 4) and physical 10 Hz jitter (condition 5), we believe that the enhanced activity is related to illusory jitter generation rather than to jitter perception or to isoluminant motion per se, supporting our hypothesis that MISC is generated within cortex by a dynamic cortical feedback circuit.
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