Browsing by Subject "Event-related potentials"

Now showing 1 - 5 of 5

Open Access
Dipole source reconstruction of brain signals by using particle swarm optimization
(IEEE, 2009) Alp, Yaşar Kemal; Arıkan, Orhan; Karakaş, S.
Resolving the sources of neural activity is of prime importance in the analysis of Event Related Potentials (ERP). These sources can be modeled as effective dipoles. Identifying the dipole parameters from the measured multichannel data is called the EEG inverse problem. In this work, we propose a new method for the solution of EEG inverse problem. Our method uses Particle Swarm Optimization (PSO) technique for optimally choosing the dipole parameters. Simulations on synthetic data sets show that our method well localizes the dipoles into their actual locations. In the real data sets, since the actual dipole parameters aren't known, the fit error between the measured data and the reconstructed data is minimized. It has been observed that our method reduces this error to the noise level by localizing only a few dipoles in the brain.
Open Access
The involvement of centralized and distributed processes in sub-second time interval adaptation: an ERP investigation of apparent motion
(Blackwell Publishing Ltd, 2017) Kaya, Utku; Yildirim, Fazilet Zeynep; Kafaligonul, Hulusi
Accumulating evidence suggests that the timing of brief stationary sounds affects visual motion perception. Recent studies have shown that auditory time interval can alter apparent motion perception not only through concurrent stimulation but also through brief adaptation. The adaptation after-effects for auditory time intervals was found to be similar to those for visual time intervals, suggesting the involvement of a central timing mechanism. To understand the nature of cortical processes underlying such after-effects, we adapted observers to different time intervals using either brief sounds or visual flashes and examined the evoked activity to the subsequently presented visual apparent motion. Both auditory and visual time interval adaptation led to significant changes in the ERPs elicited by the apparent motion. However, the changes induced by each modality were in the opposite direction. Also, they mainly occurred in different time windows and clustered over distinct scalp sites. The effects of auditory time interval adaptation were centred over parietal and parieto-central electrodes while the visual adaptation effects were mostly over occipital and parieto-occipital regions. Moreover, the changes were much more salient when sounds were used during the adaptation phase. Taken together, our findings within the context of visual motion point to auditory dominance in the temporal domain and highlight the distinct nature of the sensory processes involved in auditory and visual time interval adaptation. © 2017 Federation of European Neuroscience Societies and John Wiley & Sons Ltd
Open Access
Mandarin and English adults’ cue-weighting of lexical stress
(International Speech Communication Association, 2020) Zeng, Z.; Mattock, K.; Liu, L.; Peter, V.; Tuninetti, Alba; Tsao, F.-M.
Listeners segment speech based on the rhythm of their native language(s) (e.g., stress- vs. syllable-timed, tone vs. non-tone) [1,2]. In English, the perception of speech rhythm relies on analyzing auditory cues pertinent to lexical stress, including pitch, duration and intensity [3]. Focusing on cross-linguistic impact on English lexical stress cue processing, the present study aims to explore English stress cue-weighting by Mandarin-speaking adults (with English adults as control), using an MMN multi-feature paradigm. Preliminary ERP data revealed cross-linguistic perceptual differences to pitch and duration cues, but not to intensity cues in the bisyllabic non-word /dede/. Specifically, while English adults were similarly sensitive to pitch change at the initial and final syllable of the non-word, they were more sensitive to the duration change at the initial syllable. Comparatively, Mandarin adults were similarly sensitive to duration change at each position, but more sensitive to pitch at the final syllable. Lastly, both the Mandarin group and the English group were more sensitive to the intensity sound change at the second syllable. Possible explanations for these findings are discussed.
Open Access
Probing sensory plasticity with rapid forms of motion adaptation
(2020-09) Akyüz, Sibel
Perception is shaped by both immediate pattern of sensory inputs and previous experience with the external environment. Visual adaptation, a temporary change in perception following exposure to a stimulus, has been widely employed to understand how previous sensory experience on different timescales shapes perception. Visual motion adaptation is a powerful investigative tool to understand sensory plasticity and neural adaptation. However, the neural mechanisms underlying adaptation induced changes by visual motion are still subject to debate. In the present thesis, spatiotemporal dynamics, neural substrates, and functional role of sensory plasticity in the human visual system was examined using rapid forms of motion adaptation paradigm combined with EEG. Specifically, how motion adaption-induced short-term sensory plasticity is reflected at the neural level and parallel with perceptual performance were explored. Participants were adapted to directional drifting gratings for either short (640 ms in Experiment 1; 188 ms in Experiments 2 and 3) or long (6.4 s in Experiment 1; 752 ms in Experiments 2 and 3) durations and used a counter-phase flickering (with constant polarity in experiments 1 and 2; polarity inverting within every step in Experiment 3) grating as a test pattern. Sinusoidal gratings of phi motion were employed in Experiment 1 whereas; square wave gratings were used for phi and reverse-phi adaptations in Experiments 2 and 3 to examine how ON and OFF pathways operate in the visual processing stream. Based on the EEG analyses in Experiment 1, the scalp sites relevant to motion adaptation were identified. Experiment 1 showed that both adapting durations led to significant motion aftereffects and EEG results showed that long adaptation produced stronger aftereffects than the short adaptation condition within 64-112 ms time range over occipital and parieto-occipital sites. Taken together, these findings provide important electrophysiological evidence that motion aftereffects reflect changes in cortical areas mediating low- and mid-level visual motion processing. They also suggest that adaptation is an active process that involves neural mechanisms operating at different time scales. In Experiments 2 and 3, the short-term adaptation induced changes over these identified scalp sites were further examined based on Experiment 1. Given that the phi and reverse-phi motion mainly engage within (ON or OFF) and across (ON and OFF) pathway mechanisms, the comparisons of adaptation induced changes across these motion types provided further insights into the nature of corresponding mechanisms over visual cortex. The behavioral and EEG findings pointed to efficient convergence of information provided by these pathways and some distinct characteristics of across pathway mechanisms.
Open Access
Short-and long-term forms of neural adaptation: an ERP investigation of dynamic motion aftereffects
(Elsevier, 2020) Akyüz, Sibel; Pavan, A.; Kaya, Utku; Kafalıgönül, Hulusi
Adaptation is essential to interact with a dynamic and changing environment, and can be observed on different timescales. Previous studies on a motion paradigm called dynamic motion aftereffect (dMAE) showed that neural adaptation can establish even in very short timescales. However, the neural mechanisms underlying such rapid form of neural plasticity is still debated. In the present study, short- and long-term forms of neural plasticity were investigated using dynamic motion aftereffect combined with EEG (Electroencephalogram). Participants were adapted to directional drifting gratings for either short (640 msec) or long (6.4 sec) durations. Both adaptation durations led to motion aftereffects on the perceived direction of a dynamic and directionally ambiguous test pattern, but the long adaptation produced stronger dMAE. In line with behavioral results, we found robust changes in the event-related potentials elicited by the dynamic test pattern within 64 e112 msec time range. These changes were mainly clustered over occipital and parietooccipital scalp sites. Within this time range, the aftereffects induced by long adaptation were stronger than those by short adaptation. Moreover, the aftereffects by each adaptation duration were in the opposite direction. Overall, these EEG findings suggest that dMAEs reflect changes in cortical areas mediating low- and mid-level visual motion processing. They further provide evidence that short- and long-term forms of motion adaptation lead to distinct changes in neural activity, and hence support the view that adaptation is an active time-dependent process which involves different neural mechanisms.