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Mark Vergeer, Naoki Kogo, Andrey Nikolaev, Nihan Alp, Johan Wagemans; EEG frequency tagging reveals a neural signature of learning holistic shape representations. Journal of Vision 2016;16(12):1099. doi: 10.1167/16.12.1099.
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© ARVO (1962-2015); The Authors (2016-present)
Past research has shed light on the different brain areas involved in shape and object processing. Nevertheless, still relatively little is known about the neural mechanisms responsible for integrating parts into coherent wholes and about the learning mechanisms involved. In the current study, we addressed these questions using the EEG frequency tagging technique, where distinct stimulus parts of a stimulus are 'tagged' by modifying the contrast of these parts at different temporal frequencies. EEG frequency power analyses typically show clear peaks at both the tagged frequencies and their harmonics. However, additional peak responses can be observed at so-called intermodulation frequencies (e.g., f1+f2; 2*f1-f2). Evoked activity at such intermodulation frequencies is caused by nonlinear interactions between neural signals carrying the two individual frequencies. Previous findings have suggested that intermodulation components reflect the neural activity involved in the integration of local elements, for instance, in face processing (Boremanse et al., 2013). Correspondingly, the current study proposes that intermodulation components are indicative of strengthening the integration of shape parts during learning. In the 4 days prior to EEG recording, observers were trained behaviorally to discriminate highly similar novel shapes into two categories that were defined based on global, holistic properties. Different observers were trained on different families of shapes in a counterbalanced design. EEG was recorded post-training on frequency-tagged versions of the trained and untrained shape family. Results showed a stronger occipital intermodulation response for trained and untrained exemplars of the trained shape family, compared to the untrained shape family. These findings indicate that learning novel, holistic shape representations is reflected by increased intermodulation, which highlights that intermodulation strength relates to the strength of emerging holistic perceptual organizations. More generally, intermodulation responses, induced by EEG frequency tagging, provide a useful tool to investigate the neural activity underlying higher-level processes in perceptual organization.
Meeting abstract presented at VSS 2016
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