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Zoltán Derzsi, Ghaith Tarawneh, Kai Alter; Studying the cortical response to binocular disparity using EEG temporal frequency tagging. Journal of Vision 2015;15(12):1389. doi: 10.1167/15.12.1389.
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© ARVO (1962-2015); The Authors (2016-present)
Frequency tagging exploits the high temporal resolution of electroencephalography (EEG) to identify cortical mechanisms responding to a given stimulus, usually varying in luminance. Here, following pioneering work by Norcia & Tyler (1984) and others, we experiment with frequency tagging using binocular disparity. Each trial was a dynamic random-dot stereogram lasting 4s. For 1s, the dots had zero disparity, i.e. in the screen plane. For 3s, disparity was +/-0.065°. On “frequency-tagged” trials, the dots formed a horizontal disparity square-wave grating of spatial frequency 0.25 cycles/deg. The disparities were inverted with a temporal frequency of either F=5Hz or F=8Hz. On “control” trials during this 3s, two transparent planes were formed, one behind the other. We obtained data from 12 subjects, with an average of 68 good trials per condition, and EEG traces were band-pass filtered from 1 to 30 Hz before averaging. We see clear Event Related Potentials (ERPs) shortly after both the onset of the dot pattern (t=0s) and the onset of the disparity change (t=1s). Both ERPs show a N100-P200 complex, here a small negative peak at around 75ms followed by a larger positive peak at around 150ms. In the frequency domain, Fourier power is proportional to 1/sqrt(frequency) between 1 and 30Hz. The frequency-tagged conditions both show additional peaks at F and 2F, the first and second harmonics of the disparity modulation frequency, relative to the control condition. This confirms that a frequency-tagged signal can be observed in the disparity domain. However, the signal’s strength was much weaker than in previous studies, perhaps because we used a disparity grating rather than a plane. Surprisingly, we also found strong power in the alpha-band in all disparity conditions compared to the zero-disparity baseline. References Norcia AM, Tyler CW. 1984. Temporal frequency limits for stereoscopic apparent motion processes. Vision Res 24:395-401.
Meeting abstract presented at VSS 2015
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