Figure 4.

Results of Experiment 1. (A) Topographic plots of the first (upper row) and second (lower row) harmonics of the standardized SSVEPs elicited by the flickered grating, averaged across observers and flicker frequencies. Color-scale data were interpolated on the basis of a fine Cartesian grid. Positive and negative values indicate responses above and below the mean amplitude, respectively, in z units. The left column shows SSVEP topographies when the grating was presented to the right visual hemifield, and the right column shows SSVEP topographies when the grating was presented to the left visual hemifield. (B) Contralateral SSVEPs (gray bars) and ipsilateral SSVEPs (white bars) for the first and second harmonics averaged from the 10 indicated posterior scalp electrodes from which strong SSVEPs were obtained (see part A). The graphs confirm that the first harmonic was medial (nonlateralized) whereas the second harmonic was strongly contralateral. (C) The degree of lateralization (contralateral-minus-ipsilateral standardized SSVEPs) for the first (dotted curve) and second (solid curve) harmonics as a function of flicker frequency. The numbers within the plot represent the corresponding response frequencies (the same as the flicker frequencies for the first harmonic and doubled for the second harmonic). The asterisks indicate statistically significant lateralization (i.e., significant deviations from zero at p < .05). (D) The contralateral standardized SSVEPs (solid line) and ipsilateral standardized SSVEPs (dashed line) for the first harmonic (left panel) and second harmonic (right panel) as a function of flicker frequency. Error bars represent ± 1 SEM with the variance because of the overall differences across observers removed.