title: Frequency tagging yields an objective neural signature of Gestalt formation.
abstract: The human visual system integrates separate visual inputs into coherently organized percepts, going beyond the information given. A striking example is the perception of an illusory square when physically separated inducers are positioned and oriented in a square-like configuration (illusory condition). This illusory square disappears when the specific configuration is broken, for instance, by rotating each inducer (non-illusory condition). Here we used frequency tagging and electroencephalography (EEG) to identify an objective neural signature of the global integration required for illusory surface perception. Two diagonal inducers were contrast-modulated at different frequency rates f1 and f2, leading to EEG responses exactly at these frequencies over the occipital cortex. Most importantly, nonlinear intermodulation (IM) components (e.g., f1+f2) appeared in the frequency spectrum, and were much larger in response to the illusory square figure than the non-illusory control condition. Since the IMs reflect long-range interactions between the signals from the inducers, these data provide an objective (i.e., at a precise and predicted EEG frequency) signature of neural processes involved in the emergence of illusory surface perception. More generally, these findings help to establish EEG frequency-tagging as a highly valuable approach to investigate the underlying neural mechanisms of subjective Gestalt phenomena in an objective and quantitative manner, at the system level in humans.
authors: Brain & Cognition, KU Leuven, Belgium. Electronic address: Nihan.Alp@ppw.kuleuven.be.
authors: Nihan
authors: N
authors: Alp
authors: Brain & Cognition, KU Leuven, Belgium.
authors: Naoki
authors: N
authors: Kogo
authors: Institute of Research in Psychology and Institute of Neuroscience, Université Catholique de Louvain, Louvain la Neuve, Belgium.
authors: Goedele
authors: G
authors: Van Belle
authors: Brain & Cognition, KU Leuven, Belgium.
authors: Johan
authors: J
authors: Wagemans
authors: Institute of Research in Psychology and Institute of Neuroscience, Université Catholique de Louvain, Louvain la Neuve, Belgium.
authors: Bruno
authors: B
authors: Rossion
mesh_terms: D000328:Adult; D004569:Electroencephalography; D005260:Female; D005556:Form Perception / Q000502:physiology; D007839:Functional Laterality; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D009778:Occipital Lobe / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: Frequency tagging; Gestalt formation; Holistic perception; Illusory contour; Illusory surface