Browsing by Author "Badakul, Ayse Nur"

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Differential Modulation of Low- and High-Frequency Mu Oscillations During the Observation of Manual, Facial, and Non-Biological Movements
(Nature Portfolio, 2025) Badakul, Ayse Nur; Soyman, Efe
Mu suppression - desynchronization of neural oscillations in central EEG electrodes during action execution and observation - has been widely accepted as a marker for neural mirroring. It has been conventionally and predominantly quantified in the 8-13 Hz range, corresponding to the alpha frequency band, although few studies reported differences in lower and higher subbands that together constitute the mu frequency band. In the present study, we adopted a comprehensive analytical approach to examine the spectral and temporal dynamics of mu suppression when participants watched videos depicting hand and face actions and artificial pattern movements. Our analyses in central EEG electrodes revealed that neural oscillations were significantly suppressed during action observation only in the lower (8-10.5 Hz), not in the higher (10.5-13 Hz), subband. No such subband differentiation was observed for the alpha oscillations in the occipital electrodes. In addition, in the lower subband, significantly stronger suppressions were selective for hand actions in the central EEG electrodes placed over the hand region of the sensorimotor cortices and for facial actions in the frontotemporal electrodes placed over the face region of the sensorimotor cortices. In the higher subband, such stimulus selectivity was only observed for facial actions in the frontotemporal electrodes. Furthermore, the neural oscillations in the lower, but not the higher, subband followed the precise temporal patterning of biological motion in the videos. These results indicate that neural oscillations in the lower subband show the characteristics of neural mirroring processes, whereas those in the higher subband might reflect other mechanisms.
Distinct Temporal Dynamics of Speech and Gesture Processing: Insights From Event-Related Potentials Across L1 and L2
(American Psychological Association, 2026) Ozer, Demet; Soyman, Efe; Badakul, Ayse Nur; Arslan, Burcu; Yilmaz, Fatma Sena; Goksun, Tilbe
This study examined the neural and behavioral processing of speech and iconic gestures across L1-Turkish and L2-English when participants attended the speech or gesture channel. We recorded electroencephalogram activity in Experiment 1 and reaction times in Experiment 2 (24 participants in each) during a mismatch task where concurrent speech and gesture expressed either matching or mismatching information in relation to a preceding action. Participants were asked to detect whether the gesture (gesture-focused task) or the speech (speech-focused task) was related to the preceding action. Speech was presented in Turkish or English in separate blocks. In Experiment 1, we focused on N400 and N2 components as indices of late semantic processing and early sequential matching, respectively. In the gesture-focused task, our results demonstrated a gesture mismatch effect, which was evident in more negative N400 amplitudes for mismatching than matching gestures only in the context of simultaneous matching speech. In the speech-focused task, we observed the N2 effect, which was apparent in more negative N2 amplitudes for mismatching than matching speech, regardless of the simultaneous gesture. These dynamics were largely reflected in reaction times in Experiment 2. These results point to potentially distinct neural and temporal dynamics in processing speech versus gestures and suggest that speech processing might be instantiated earlier, whereas gestures recruit later stages of processing. Notably, we observed some differential patterns across L1-Turkish and L2-English, suggesting that speech and gesture processing may operate differently across languages. Our findings highlight a complex interplay between modality, modality focus, language, and neural processing of multimodal information.