Abstract
Gist perception refers to perceiving the substance or general meaning of a scene. To investigate its neuronal mechanisms, we used the steady-state visually evoked potential (SSVEP) method—an evoked oscillatory cortical response at the same frequency as a visual stimulus flickered at this frequency. Two neighboring stimuli were flickered at different frequencies f1 and f2, for example, a drawing of a sun on the left side of the screen flickering at 8.6 Hz and the drawing of a parasol on the right side of the screen flickering at 12 Hz. SSVEPs enabled us to separate the responses to the two distinct stimuli by extracting oscillatory brain responses at f1 and f2. Additionally, it allowed to investigate intermodulation frequencies, that is, the brain’s response at a linear combination of f1 and f2 (here at f1 + f2 = 20.6 Hz) as an indicator of processing shared aspects of the input, that is, gist perception (here: a beach scene). We recorded high-density EEG of 18 participants. Results revealed clear and separable neuronal oscillations at f1 and f2. Additionally, occipital electrodes showed increased amplitudes at the intermodulation frequency in related as compared to unrelated pairs. The increase in intermodulation frequency was associated with bilateral temporal and parietal lobe activation, probably reflecting the interaction of local object representations as a basis for activating the gist network. The study demonstrates that SSVEPs are an excellent method to unravel mechanisms underlying the processing within multi-stimulus displays in the context of gist perception.
Highlights
Encounters with an object under natural circumstances unlikely occur under isolated conditions
We applied steady-state visual evoked potentials (SSVEP), that is, an oscillatory cortical response at the same frequency as a visual stimulus flickered at this frequency (Regan 1989)
To examine the location of the cortical generators of gist perception, we modeled the SSVEP sources by means of a distributed source model variable resolution electromagnetic tomography (VARETA; BoschBayard et al 2001)
Summary
Encounters with an object under natural circumstances unlikely occur under isolated conditions. Many objects co-occur within a scene (e.g., the sun and a parasol). While object recognition (e.g., Singer 1995; Tanaka 1993) and scene perception (e.g., Henderson and Hollingworth 1999) are widely studied separately, the underlying neuronal processes of gist perception are not understood to their full extent. That is, grasping the meaning of a Communicated by Melvyn A. The present study aimed to further examine multi-stimulus processing and gist perceptions by means of electroencephalography (EEG). We applied steady-state visual evoked potentials (SSVEP), that is, an oscillatory cortical response at the same frequency as a visual stimulus flickered at this frequency (Regan 1989). In contrast to conventional neuroscientific methods (e.g., the BOLD response or event-related potentials) that reflect the total signal elicited by all components of a multi-stimulus display,
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