title: Stimulus intensity affects early sensory processing: visual contrast modulates evoked gamma-band activity in human EEG.
abstract: We studied the effect of different contrast levels on the visual evoked gamma-band response (GBR) in order to investigate whether the GBR is modulated in a similar manner as previously reported for visual evoked potentials. Previous studies showed that the GBR can be modulated by individual characteristics (age) and experimental conditions (task difficulty, attention). However, stimulus properties, such as size and spatial frequency, also have a large impact on the GBR, which necessitates identification and control of relevant stimulus properties for optimal experimental setups. Twenty-one healthy participants were investigated during a forced-choice discrimination task. Sinusoidal gratings were presented at three contrast levels with a constant spatial frequency of 5 cycles per degree visual arc (cpd). The present data replicate the results reported for visual evoked potentials and exhibit a contrast dependent modulation of the GBR. Gamma activity is increased for higher contrast levels. These results demonstrate the importance of stimulus contrast for evoked gamma activity. Thus, it appears meaningful to control the contrast of stimuli in experiments investigating the role of gamma activity in perception and information processing.
authors.affiliation: Department of Biological Psychology, Otto-von-Guericke University of Magdeburg, Germany.
authors.forename: Jeanette
authors.initials: J
authors.lastname: Schadow
authors.forename: Daniel
authors.initials: D
authors.lastname: Lenz
authors.forename: Stefanie
authors.initials: S
authors.lastname: Thaerig
authors.forename: Niko A
authors.initials: NA
authors.lastname: Busch
authors.forename: Ingo
authors.initials: I
authors.lastname: Fründ
authors.forename: Jochem W
authors.initials: JW
authors.lastname: Rieger
authors.forename: Christoph S
authors.initials: CS
authors.lastname: Herrmann
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D015350:Contrast Sensitivity / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation / Q000379:methods; D013057:Spectrum Analysis