EEG frequency-tagging yields a neural signature of integration of parts into perceptually organized wholes Nihan Alp¹, Naoki Kogo¹, Goedele Van Belle², Johan Wagemans¹ and Bruno Rossion² 1. Laboratory of Experimental Psychology, University of Leuven (KU Leuven) 2. Institute of Research in Psychology and Institute of Neuroscience, Université Catholique de Louvain “Frequency Tagging” Technique Introduction Experimental Design “the whole is different from the sum of the parts” (Wertheimer, 1923) • How do we integrate all the information to form a Gestalt? 0.5 2.94Hz • Current methods have not been able to pinpoint how exactly a holistic representation emerges in the visual system. 3.57Hz 3.57Hz 2.94Hz 0.45 Contrast 0.4 Contrast Background • The “frequency tagging” technique has been applied to Gestalt phenomena before: Task: Press “space” whenever two or four pacmen change their color from black to blue briefly. 0.35 0.3 0.25 0.2 frequency tagging procedure 0.15 0.1 1) It is possible to track the neural basis of figure-ground perception¹ and of ambiguous figures such as Rubin’s face and vase figure² 0.05 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Time Time 2) Recent attempt to show the perception of illusory contours linked to neural grouping of inducers3 nf1 3) Neural activities of face perception can be distinguished from the individual processing of facial parts4 f1 f1 harmonics Aim f2 fundamentals • IM can be generated by neurons that receive both frequencies and create nonlinear interaction. nfdiagonal Two 1±mf2 pacman pairs changed their luminance contrast sinusoidally at different frequencies. • Do IM components correspond to intermodulation holistic perception? component (IM) mf2 • To investigate whether this technique has the potential to yield a neural marker of holistic representations and configural processing in general. What do intermodulation (IM) components mean? f2 f1 f2 Results (Topographies of three IM components) Illusory Condition Illusory condition Non-illusory condition Conclusion Non-illusory Condition EEG Spectrum of occipital channels (PPO6 and Oiz) 6 PPO6 • Fundamental frequencies (physically given frequencies: 3.57Hz & 2.94Hz) were equally strong for both illusory and non-illusory conditions. IC NIC f₂ f₁ + f₂ 2f₁ 2f₂ 5 4 f₁ SNR SNR 2f₁ + f₂ • Intermodulation components (IM: f₂-f₁=3.57-2.94=0.63Hz; 2f₁+f₂=(2*2.94)+3.57=9.45Hz) were significantly larger on the Kanizsa illusory surface condition where participants perceived an illusory square. 3 (f₁+f₂) Illusory Condition Non-illusory Condition • Topography of different IM components showed clearly different pattern than topography of fundamental frequencies. f₂ - f₁ 2 1 0 • Our results are the first to show convincingly that IM components can be regarded as a neural marker of long-range interactions when remote image parts are integrated in Gestalt formation. 0 1 2 3 4 5 6 7 8 9 10 Frequency (Hz) Frequency Hz 6 IC NIC Oiz References 5 (f₂-f₁) 4 Non-illusory Condition SNR SNR Illusory Condition f₁ f₂ 2f₁ f₁ + f₂ f₂ - f₁ 3 2f₂ 2f₁ + f₂ 2. Parkkonen, L., Andersson, J., Hämäläinen, M., & Hari, R. (2008). Early visual brain areas reflect the percept of an ambiguous scene. PNAS, 105 (51), 20500–20504. 2 3. Gundlach, C., & Müller, M. M. (2013). Perception of illusory contours forms intermodulation responses of steady state visual evoked potentials as a neural signature of spatial integration. Biological Psychology, 94(1), 55–60. 1 0 0 1 2 3 4 5 Frequency (Hz) (2f₁+f₂) Corresponding Author: [email protected] 1. Appelbaum, L. G., Wade, A. R., Pettet, M. W., Vildavski, V. Y., & Norcia, A. M. (2008). Figure-ground interaction in the human visual cortex. J. Vision, 8(9), 1–19. 6 Frequency Hz 7 8 9 10 4. Boremanse, A., Norcia, A. M., & Rossion, B. (2013). An objective neural signature for visual binding of object parts in the human brain. J. Vision, 13 (11),1–18. Supported by the Fonds Wetenschappelijk Onderzoek (FWO) and Methusalem program by the Flemish Government (METH/08/02).