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Bruce C. Hansen, Aaron P. Johnson, Dave Ellemberg; Natural Scene Image Complexity Differentially Modulates the N1 and P1 Components of Early VEPs. Journal of Vision 2011;11(11):1121. doi: https://doi.org/10.1167/11.11.1121.
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© ARVO (1962-2015); The Authors (2016-present)
The contrast response function of early visual evoked potentials (VEPs) elicited by sinusoidal gratings is known to contain characteristic potentials closely associated with parvocellular and magnocellular processes. Specifically, the N1 component has been linked with parvocellular processes, while the P1 component has been linked with magnocellular processes. Recently, we examined the extent to which these components are modulated by the physical characteristics of natural scene imagery that varied according to image complexity (i.e., density of edges and lines within the imagery) as well as the distribution of contrast across spatial frequency (SF) (Hansen et al., 2010, VSS). We found that the N1 and P1 components differentially respond to natural scene images; with the P1 component being mostly modulated by the distribution of contrast across SF, and the N1 component being entirely modulated by image complexity. However, since natural scenes are broadband, it was not possible to determine whether this differential modulation resulted from interactions within or between the neural processes associated with the P1 and N1. Here we sought to address this issue by using band-pass filtered natural scene image stimuli varying in image complexity. Stimuli were filtered to preserve a 1-octave band of SFs centered on either 0.8 cpd or 8.0 cpd. EEGs were recorded while participants viewed each SF filtered natural scene image (500 msec). For the 8.0 cpd condition, the results show the N1 component to be entirely modulated by image complexity (larger N1 magnitudes for more complex imagery). Critically, for the 0.8 cpd image condition, the P1 was also modulated by image complexity, but in the opposite direction. These results suggest that the N1-P1 component modulation previously observed with broadband images consists of an interaction between the neural processes associated with each component, with the neural processes associated with the N1 possibly acting to suppress the image complexity response of the P1 component.
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