Abstract
BackgroundThe visual system may process spatial frequency information in a low-to-high, coarse-to-fine sequence. In particular, low and high spatial frequency information may be processed via different pathways during object recognition, with LSF information projected rapidly to frontal areas and HSF processed later in visual ventral areas. In an electroencephalographic study, we examined the time course of information processing for images filtered to contain different ranges of spatial frequencies. Participants viewed either high spatial frequency (HSF), low spatial frequency (LSF), or unfiltered, broadband (BB) images of objects or non-object textures, classifying them as showing either man-made or natural objects, or non-objects. Event-related potentials (ERPs) and evoked and total gamma band activity (eGBA and tGBA) recorded using the electroencephalogram were compared for object and non-object images across the different spatial frequency ranges.ResultsThe visual P1 showed independent modulations by object and spatial frequency, while for the N1 these factors interacted. The P1 showed more positive amplitudes for objects than non-objects, and more positive amplitudes for BB than for HSF images, which in turn evoked more positive amplitudes than LSF images. The peak-to-peak N1 showed that the N1 was much reduced for BB non-objects relative to all other images, while HSF and LSF non-objects still elicited as negative an N1 as objects. In contrast, eGBA was influenced by spatial frequency and not objecthood, while tGBA showed a stronger response to objects than non-objects.ConclusionsDifferent pathways are involved in the processing of low and high spatial frequencies during object recognition, as reflected in interactions between objecthood and spatial frequency in the visual N1 component. Total gamma band seems to be related to a late, probably high-level representational process.
Highlights
The visual system may process spatial frequency information in a low-to-high, coarse-to-fine sequence
Post-hoc tests indicated that RTs were significantly slower when an object was present than when there was no object on low spatial frequency (LSF) (p < .001) and high spatial frequency (HSF) trials (p = .02), while there were no significant differences between objects and nonobjects on BB trials (p = .2)
Responses to objects on LSF trials were slower than responses to both BB and HSF non-objects, while responses on HSF object trials were slower than responses on BB (p = .04) non-object trials
Summary
The visual system may process spatial frequency information in a low-to-high, coarse-to-fine sequence. Low and high spatial frequency information may be processed via different pathways during object recognition, with LSF information projected rapidly to frontal areas and HSF processed later in visual ventral areas. Event-related potentials (ERPs) and evoked and total gamma band activity (eGBA and tGBA) recorded using the electroencephalogram were compared for object and non-object images across the different spatial frequency ranges. Several models of the visual system describe a coarse-to-fine sequence of parsing of visual information imposed by differential processing of spatial frequencies [1,2,3]; low spatial frequencies (LSF) are privileged at early processing stages whereas high spatial frequencies (HSF) are privileged at later processing stages. We did not directly contrast responses to objects with responses to non-objects, and it is not clear whether the differences in responses reflect an object-specific method of processing stimuli or a more general property of the visual system
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