Relating the steady-state visual evoked potential to single-stimulus responses derived from m-sequence stimulation
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Steady-state visual evoked potentials have various applications, including objective acuity testing. However, a non-monotonous spatial-frequency tuning (a “notch”) occurs at intermediate spatial frequencies in about half of the examinees. One possible reason lies in the temporal superposition of single-stimulus responses. This was investigated in 20 subjects.
Single-stimulus responses to checkerboard onsets were estimated through deconvolution of responses to m-sequence stimulation. Based on these, steady-state responses were predicted through superposition of temporally overlapping single-stimulus responses and compared to normally recorded steady-state responses. Discrepancies were analyzed in both the time and frequency domains.
The agreement between predicted and recorded steady-state responses varied greatly among subjects, ranging from a good match including non-monotonous features of the tuning curve to substantial deviations. Although in some subjects the tuning of the recorded responses was better matched by the predicted responses than by the deconvolved m-sequence responses from which the prediction was computed, the correlation was not significantly different at the group level. In most subjects, there was only a small to moderate contribution of higher harmonics. The match between predicted and recorded responses was not always uniform across electrode locations.
Our data are consistent with temporal superposition explaining an interindividually variable part of the checksize tuning curve without being its primary determinant.
KeywordsSteady-state evoked potential m-Sequence Rapid stimulation Superposition Spatial-frequency tuning Checksize tuning
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