Koenig-Robert R, Vanrullen R, 2011, "SWIFT: A new method to track object representations" Perception 40 ECVP Abstract Supplement, page 140
SWIFT: A new method to track object representations
R Koenig-Robert, R Vanrullen
Here we present a novel technique called semantic wavelet-induced frequency tagging (SWIFT) in which advanced image manipulation allows us to isolate object representations using frequency-tagging. By periodically scrambling the image in the wavelets domain we modulate its semantic content (object form), without disturbing low-level attributes. In a first experiment, we presented SWIFT sequences to human observers (n=16) containing natural images (object sequences) and abstract textures (no-object sequences). Only those object sequences that were consciously recognized elicited ERP responses at the tagging frequency (1.5 Hz). In a second experiment we compared SWIFT to classic SSVEP (steady-state visual-evoked potentials) in tracking the deployment of spatial attention. Two faces were tagged at different frequencies on each side of the screen, and a central cue indicated the target face. Attention enhanced the SSVEP tagging response by ∼35%, but for SWIFT this increase reached 200%. In a third experiment (n=24) we investigated the dynamics of object representations in the visual system. We presented SWIFT object sequences at various frequencies from 1.5 to 12 Hz and assessed the amount of tagging. Our results suggest that the visual system can only form 3 to 4 distinct object representations per second.
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