Perception of illusory contours forms intermodulation responses of steady state visual evoked potentials as a neural signature of spatial integration

[jinglescode]

Paper

Link: https://www.sciencedirect.com/science/article/abs/pii/S0301051113001178
Year: 2013

Summary

• spectral decomposition of the measured EEG can show additional peaks at frequencies that are linear combinations of the driving frequencies
• show that the perception of an illusory rectangle resulted in a significant increase of amplitudes in two intermodulation frequencies

Methods

• flickered at two different frequencies (8.5 and 14.17) and manipulated perception of an illusory rectangle if the ring was complete or incomplete
• circular inducers had a size of 4 degrees of visual angle. They were placed 3.75 degrees left and right to the center of the screen
• experiment consisted of six blocks with 56 trials per block, 168 trials. Each trial lasted for 3170 ms with an inter-trial interval of 1000–1250 ms for cue.
• SSVEP amplitudes were extracted by fast-Fourier Transformations (FFTs) from the averaged epochs from a time window from 500 to 3100 ms after stimulus onset. first 500 ms were discarded
• analysis we focused on (f2 − f1) = 5.6 Hz, (2f1 − 2f2) = 11.33 Hz, (f1 + f2) = 22.67 Hz, and (2f1 + 2f2) = 45.33 Hz

Results

• amplitude at 22.67 Hz and 45.33 Hz were significantly greater when the ring was incomplete
• found significant increases in amplitude for the sum and twice the sum of the two driving frequencies (f1 + f2 and 2(f1 + f2)) when subjects were able to perceive the illusory rectangle compared to when that perception was inhibited
• show that the perception of an illusory rectangle resulted in a significant increase of amplitudes in two intermodulation frequencies