Figure 1.
Outline of the experimental procedure and of the stimulus identification performance.
A. Experimental procedure. In each trial, an initial low-pass or high-passed version of a natural scene was presented. In the following steps, the severity of the spatial filtering was loosened to include a wider range of frequencies, until most of the original image was presented at step 16. B. Identification performance in the low-pass (left) and high-pass (right) condition. As high spatial frequencies were added in the low-pass condition (left), or low spatial frequencies were added in the high-pass condition (right), identification rate increased.
Figure 2.
The effects of spatial frequencies on the early ERPs.
A, B. For the first and last step of the procedure, waveforms are displayed in the three right-hand side panels. Waveforms represent the average across sensors in central and lateral sensor groups. The insets contain line plots displaying the effects of Step on the amplitude of the P1, at lateral and midline sites. In all plots, positive values are plotted downwards. C. Scalp topography and cortical localization of the P1 in the first and last step. In this representation, the low- and high-pass conditions were averaged together.
Figure 3.
The effects of spatial frequencies on the P2.
A. The modulation of the P2 by filter step. The topographies corresponding to the first and last step of the procedure are displayed at the bottom of the line plot, averaged for low- and high-passed pictures. B. Waveforms of the first, intermediate and final step of the procedure, in the low-pass and high-pass condition. Waveforms represent the average across sensors in central and lateral sensor groups. In all plots, positive values are plotted downwards.
Table 1.
MNI coordinates of the maximum estimated sLORETA activity values corresponding to the P1 and P2 ERP components.
Figure 4.
The relationship between spectral power, identification and the amplitude of the P1 (left) and of the P2 (right).
In the main panels, the relationship between the spectral power and ERP amplitude is displayed, separately for low- and high-passed pictures. In the insets, the relationship between identification rate and ERP amplitude is represented.
Table 2.
Summary of regression analysis for variables predicting the amplitude of the P1 and P2.