Sven P Heinrich1, Maresa Groten, Michael Bach. 1. Sektion Funktionelle Sehforschung, Klinik für Augenheilkunde, Universitätsklinikum Freiburg, Killianstr. 5, 79106, Freiburg, Germany, sven.heinrich@uniklinik-freiburg.de.
Abstract
PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: Our data are consistent with temporal superposition explaining an interindividually variable part of the checksize tuning curve without being its primary determinant.
PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: Our data are consistent with temporal superposition explaining an interindividually variable part of the checksize tuning curve without being its primary determinant.