Tomoe Hayakawa - Academia.edu (original) (raw)

Papers by Tomoe Hayakawa

Research paper thumbnail of Information flow related to visual search assessed using magnetoencephalography

Brain research. Cognitive brain research, 2003

The sequence of neural activation during a visual search task was investigated using magnetoencep... more The sequence of neural activation during a visual search task was investigated using magnetoencephalography and the source locations for the activations were analyzed using a single-dipole algorithm. Five components (M1-5) were detected at mean latencies of 110, 146, 196, 250 and 333 ms in both of two different stimulus conditions; a target popped out in one stimulus condition (pop-out), while it did not in the other condition (non-pop-out). Statistical analysis showed that the M3 amplitude was larger and the M5 latency was shorter in the pop-out condition than in the non-pop-out condition, while there was no difference in the other components between the conditions. Neural sources were localized in the calcarine sulcus (M1) and the posterior fusiform gyrus (M2) of the hemisphere contralateral to the stimuli, the intraparietal sulcus and the posterior superior temporal sulcus (M3) in either of the hemispheres, and the calcarine sulcus (M4) of the same hemisphere in which the early p...

Research paper thumbnail of Neural mechanisms of the lexically ambiguity resolution—An MEG study

Neuroscience Research, 2007

Research paper thumbnail of Masked immediate-repetition-priming effect on the early lexical process in the bilateral anterior temporal areas assessed by neuromagnetic responses

Neuroscience Research, 2010

A masked priming paradigm has been used to measure unconscious and automatic context effects on t... more A masked priming paradigm has been used to measure unconscious and automatic context effects on the processing of words. However, its spatiotemporal neural basis has not yet been clarified. To test the hypothesis that masked repetition priming causes enhancement of neural activation, we conducted a magnetoencephalography experiment in which a prime was visually presented for a short duration (50 ms), preceded by a mask pattern, and followed by a target word that was represented by a Japanese katakana syllabogram. The prime, which was identical to the target, was represented by another hiragana syllabogram in the "Repeated" condition, whereas it was a string of unreadable pseudocharacters in the "Unrepeated" condition. Subjects executed a categorical decision task on the target. Activation was significantly larger for the Repeated condition than for the Unrepeated condition at a time window of 150-250 ms in the right occipital area, 200-250 ms in the bilateral ventral occipitotemporal areas, and 200-250 ms and 200-300 ms in the left and right anterior temporal areas, respectively. These areas have been reported to be related to processing of visual-form/orthography and lexico-semantics, and the enhanced activation supports the hypothesis. However, the absence of the priming effect in the areas related to phonological processing implies that automatic phonological priming effect depends on task requirements.

Research paper thumbnail of Phonological influences on lexicosemantic processing of kanji words

NeuroReport, 2007

To investigate the phonological influences on the lexicosemantic process with a strong orthograph... more To investigate the phonological influences on the lexicosemantic process with a strong orthographic constraint, we used kanji (morphogram) homophone words and measured, using magnetoencephalography, the neural activities during the silent reading of prime-target pairs. The primes were phonologically the same as or different from the targets or pseudocharacters. The neural activities in the left posterior temporal and inferior parietal areas became weaker with phonological repetition. Furthermore, stronger activities for the different condition in the left anterior temporal area and for the same condition in the left inferior frontal cortex, respectively, suggest the roles of these areas of the brain in the semantic processing of words and in the selection of appropriate meanings. We conclude that phonological information affects the lexicosemantic process even with a strong orthographic constraint.

Research paper thumbnail of Influence of seamlessness between pre- and poststimulus alpha rhythms on visual evoked potential

NeuroImage, 2006

The influence of seamlessness between the prestimulus alpha rhythm and poststimulus alpha ringing... more The influence of seamlessness between the prestimulus alpha rhythm and poststimulus alpha ringing on the visual evoked potentials (VEPs) was investigated. Subjects passively viewed a series of 1000 flash stimuli with their eyelids closed, and their VEPs were recorded. The instantaneous phase angle of the alpha rhythm in each subject was calculated by using a two-cycle complex exponential sequence. VEPs were classified into four subsets according to seamlessness: how well the phase angle of the prestimulus alpha rhythm and the backwardextrapolated phase angle from poststimulus alpha ringing were synchronized. VEPs of each subset were averaged. A one-way repeated measures analysis of variance revealed that seamlessness significantly affected the amplitude of P100. Moreover, the level of seamlessness significantly affected the phase locking index. Two models for the generating evoked potentials have been proposed; one is the phase resetting model (Makeig, S., Westerfield, M., Jung, T.P., Enghoff, S., Townsend, J., Courchesne, E., Sejnowski, T.J., 2002. Dynamic brain sources of visual evoked responses. Science 295, 690 -694) and the other is the evoked model . Auditory event-related responses are generated independently of ongoing brain activity. Neuroimage 24, 961 -968). These results suggest that alpha ringing is possibly generated by the phase-resetting alpha rhythm and support the phase resetting model. D

Research paper thumbnail of Temporal characteristics of neural activity related to target detection during visual search

NeuroImage, 2006

A previous MEG study on neural activities during the orientation singleton search showed that bot... more A previous MEG study on neural activities during the orientation singleton search showed that both efficient and inefficient searches shared a common neural network and the search efficiency was determined by a neural process executed in the temporal and parietal areas. The target segmentation stage, however, remains to be elucidated. In the present study, MEG and fMRI experiments were conducted, and moment-magnitudes of equivalent current dipoles were estimated with an fMRI-constrained MEG multi-dipole method to obtain differences between target-present and -absent conditions in each brain region for the whole time course. The dipole moments around the calcarine sulcus (CaS) and posterior fusiform gyrus (pFuG) increased at latencies around 70-350 ms. Activity around the CaS consisted of a prominent and a subsequent smaller but still obvious peak (117, 215 ms); the first peak showed no difference between conditions, while the second peak was significantly larger in the target-present condition. Activity around the pFuG had a prominent peak (125 ms) and subsequent small activity (237 ms), whereas the target's presence or not had no influence on either activity. The activity of the right intraparietal sulcus (IPS) was significantly larger than that for the left IPS at latencies around 196 ms irrespective of the target's presence or not. The activity of the other brain regions such as the posterior superior temporal sulcus, cingulate sulcus and central sulcus showed no difference between target conditions. The results demonstrate that neural activities of multiple regions had different temporal characteristics, and the later activity around the CaS was related to the target segregation from its surroundings during the orientation contrast search.

Research paper thumbnail of Lexical access and selection of contextually appropriate meaning for ambiguous words

NeuroImage, 2007

To clarify the neural mechanisms of lexical access and selection of contextually appropriate mean... more To clarify the neural mechanisms of lexical access and selection of contextually appropriate meanings for ambiguous words, we investigated the spatio-temporal characteristics of neural activities during silent reading and semantic judgment of lexically ambiguous or unambiguous target words that were preceded by semantically related or unrelated words by using magnetoencephalography. The left posterior superior temporal/inferior parietal area and the left anterior middle/inferior temporal area consistently showed a clear context effect, regardless of the ambiguity: the activities for related words were weaker than those for unrelated words. The activities in the left inferior frontal cortex, in contrast, were influenced by ambiguities. From~200 to 300 ms, the activities in the left anterior inferior frontal cortex (aIFC) were stronger for ambiguous words than for unambiguous words, regardless of context. The stronger activities in the left aIFC, reflecting an increase in controlled semantic retrieval, indicate that multiple meanings for lexically ambiguous words are accessed irrespective of context. At~400 ms, the left posterior inferior frontal cortex (pIFC) showed a clear context effect for unambiguous words but not for ambiguous ones. In addition, the activation in the left pIFC was stronger for related ambiguous words than for related unambiguous ones. These results suggest that in ambiguous words, not only contextually appropriate meanings but also two or more inappropriate meanings would be semantically integrated with a context. We conclude that the left IFC plays an important role in selecting an appropriate meaning from multiple alternatives after the integration of contextual information.

Research paper thumbnail of An fMRI-Constrained MEG Source Analysis with Procedures for Dividing and Grouping Activation

NeuroImage, 2002

To analyze neural activity using magnetoencephalography (MEG) and functional magnetic resonance i... more To analyze neural activity using magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI), we developed a method for fixing equivalent current dipoles of MEG in activation areas of fMRI. It includes a procedure for dividing large fMRI activation volumes into subvolumes in each of which a dipole is placed and another procedure for grouping neighboring dipoles whose temporal changes are inseparable based on MEG data. To optimize the procedures' parameters, we carried out simulations and found that (1) any single dipole within 10 mm from a true source can explain MEG data with a correlation of 94% on average for the low signal-to-noise ratio of 3 and (2) a neighboring dipole within a few tens of millimeters from the dipole nearest to the true source tends to be highly incorporated in explaining MEG data. We applied the method to data measured in a language experiment and detected 13 significant sources. The results show that the present method is promising for detecting neural activity originating from a number of separate neural sources. © 2002 Elsevier Science (USA)

Research paper thumbnail of Information flow related to visual search assessed using magnetoencephalography

Brain research. Cognitive brain research, 2003

The sequence of neural activation during a visual search task was investigated using magnetoencep... more The sequence of neural activation during a visual search task was investigated using magnetoencephalography and the source locations for the activations were analyzed using a single-dipole algorithm. Five components (M1-5) were detected at mean latencies of 110, 146, 196, 250 and 333 ms in both of two different stimulus conditions; a target popped out in one stimulus condition (pop-out), while it did not in the other condition (non-pop-out). Statistical analysis showed that the M3 amplitude was larger and the M5 latency was shorter in the pop-out condition than in the non-pop-out condition, while there was no difference in the other components between the conditions. Neural sources were localized in the calcarine sulcus (M1) and the posterior fusiform gyrus (M2) of the hemisphere contralateral to the stimuli, the intraparietal sulcus and the posterior superior temporal sulcus (M3) in either of the hemispheres, and the calcarine sulcus (M4) of the same hemisphere in which the early p...

Research paper thumbnail of Neural mechanisms of the lexically ambiguity resolution—An MEG study

Neuroscience Research, 2007

Research paper thumbnail of Masked immediate-repetition-priming effect on the early lexical process in the bilateral anterior temporal areas assessed by neuromagnetic responses

Neuroscience Research, 2010

A masked priming paradigm has been used to measure unconscious and automatic context effects on t... more A masked priming paradigm has been used to measure unconscious and automatic context effects on the processing of words. However, its spatiotemporal neural basis has not yet been clarified. To test the hypothesis that masked repetition priming causes enhancement of neural activation, we conducted a magnetoencephalography experiment in which a prime was visually presented for a short duration (50 ms), preceded by a mask pattern, and followed by a target word that was represented by a Japanese katakana syllabogram. The prime, which was identical to the target, was represented by another hiragana syllabogram in the "Repeated" condition, whereas it was a string of unreadable pseudocharacters in the "Unrepeated" condition. Subjects executed a categorical decision task on the target. Activation was significantly larger for the Repeated condition than for the Unrepeated condition at a time window of 150-250 ms in the right occipital area, 200-250 ms in the bilateral ventral occipitotemporal areas, and 200-250 ms and 200-300 ms in the left and right anterior temporal areas, respectively. These areas have been reported to be related to processing of visual-form/orthography and lexico-semantics, and the enhanced activation supports the hypothesis. However, the absence of the priming effect in the areas related to phonological processing implies that automatic phonological priming effect depends on task requirements.

Research paper thumbnail of Phonological influences on lexicosemantic processing of kanji words

NeuroReport, 2007

To investigate the phonological influences on the lexicosemantic process with a strong orthograph... more To investigate the phonological influences on the lexicosemantic process with a strong orthographic constraint, we used kanji (morphogram) homophone words and measured, using magnetoencephalography, the neural activities during the silent reading of prime-target pairs. The primes were phonologically the same as or different from the targets or pseudocharacters. The neural activities in the left posterior temporal and inferior parietal areas became weaker with phonological repetition. Furthermore, stronger activities for the different condition in the left anterior temporal area and for the same condition in the left inferior frontal cortex, respectively, suggest the roles of these areas of the brain in the semantic processing of words and in the selection of appropriate meanings. We conclude that phonological information affects the lexicosemantic process even with a strong orthographic constraint.

Research paper thumbnail of Influence of seamlessness between pre- and poststimulus alpha rhythms on visual evoked potential

NeuroImage, 2006

The influence of seamlessness between the prestimulus alpha rhythm and poststimulus alpha ringing... more The influence of seamlessness between the prestimulus alpha rhythm and poststimulus alpha ringing on the visual evoked potentials (VEPs) was investigated. Subjects passively viewed a series of 1000 flash stimuli with their eyelids closed, and their VEPs were recorded. The instantaneous phase angle of the alpha rhythm in each subject was calculated by using a two-cycle complex exponential sequence. VEPs were classified into four subsets according to seamlessness: how well the phase angle of the prestimulus alpha rhythm and the backwardextrapolated phase angle from poststimulus alpha ringing were synchronized. VEPs of each subset were averaged. A one-way repeated measures analysis of variance revealed that seamlessness significantly affected the amplitude of P100. Moreover, the level of seamlessness significantly affected the phase locking index. Two models for the generating evoked potentials have been proposed; one is the phase resetting model (Makeig, S., Westerfield, M., Jung, T.P., Enghoff, S., Townsend, J., Courchesne, E., Sejnowski, T.J., 2002. Dynamic brain sources of visual evoked responses. Science 295, 690 -694) and the other is the evoked model . Auditory event-related responses are generated independently of ongoing brain activity. Neuroimage 24, 961 -968). These results suggest that alpha ringing is possibly generated by the phase-resetting alpha rhythm and support the phase resetting model. D

Research paper thumbnail of Temporal characteristics of neural activity related to target detection during visual search

NeuroImage, 2006

A previous MEG study on neural activities during the orientation singleton search showed that bot... more A previous MEG study on neural activities during the orientation singleton search showed that both efficient and inefficient searches shared a common neural network and the search efficiency was determined by a neural process executed in the temporal and parietal areas. The target segmentation stage, however, remains to be elucidated. In the present study, MEG and fMRI experiments were conducted, and moment-magnitudes of equivalent current dipoles were estimated with an fMRI-constrained MEG multi-dipole method to obtain differences between target-present and -absent conditions in each brain region for the whole time course. The dipole moments around the calcarine sulcus (CaS) and posterior fusiform gyrus (pFuG) increased at latencies around 70-350 ms. Activity around the CaS consisted of a prominent and a subsequent smaller but still obvious peak (117, 215 ms); the first peak showed no difference between conditions, while the second peak was significantly larger in the target-present condition. Activity around the pFuG had a prominent peak (125 ms) and subsequent small activity (237 ms), whereas the target's presence or not had no influence on either activity. The activity of the right intraparietal sulcus (IPS) was significantly larger than that for the left IPS at latencies around 196 ms irrespective of the target's presence or not. The activity of the other brain regions such as the posterior superior temporal sulcus, cingulate sulcus and central sulcus showed no difference between target conditions. The results demonstrate that neural activities of multiple regions had different temporal characteristics, and the later activity around the CaS was related to the target segregation from its surroundings during the orientation contrast search.

Research paper thumbnail of Lexical access and selection of contextually appropriate meaning for ambiguous words

NeuroImage, 2007

To clarify the neural mechanisms of lexical access and selection of contextually appropriate mean... more To clarify the neural mechanisms of lexical access and selection of contextually appropriate meanings for ambiguous words, we investigated the spatio-temporal characteristics of neural activities during silent reading and semantic judgment of lexically ambiguous or unambiguous target words that were preceded by semantically related or unrelated words by using magnetoencephalography. The left posterior superior temporal/inferior parietal area and the left anterior middle/inferior temporal area consistently showed a clear context effect, regardless of the ambiguity: the activities for related words were weaker than those for unrelated words. The activities in the left inferior frontal cortex, in contrast, were influenced by ambiguities. From~200 to 300 ms, the activities in the left anterior inferior frontal cortex (aIFC) were stronger for ambiguous words than for unambiguous words, regardless of context. The stronger activities in the left aIFC, reflecting an increase in controlled semantic retrieval, indicate that multiple meanings for lexically ambiguous words are accessed irrespective of context. At~400 ms, the left posterior inferior frontal cortex (pIFC) showed a clear context effect for unambiguous words but not for ambiguous ones. In addition, the activation in the left pIFC was stronger for related ambiguous words than for related unambiguous ones. These results suggest that in ambiguous words, not only contextually appropriate meanings but also two or more inappropriate meanings would be semantically integrated with a context. We conclude that the left IFC plays an important role in selecting an appropriate meaning from multiple alternatives after the integration of contextual information.

Research paper thumbnail of An fMRI-Constrained MEG Source Analysis with Procedures for Dividing and Grouping Activation

NeuroImage, 2002

To analyze neural activity using magnetoencephalography (MEG) and functional magnetic resonance i... more To analyze neural activity using magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI), we developed a method for fixing equivalent current dipoles of MEG in activation areas of fMRI. It includes a procedure for dividing large fMRI activation volumes into subvolumes in each of which a dipole is placed and another procedure for grouping neighboring dipoles whose temporal changes are inseparable based on MEG data. To optimize the procedures' parameters, we carried out simulations and found that (1) any single dipole within 10 mm from a true source can explain MEG data with a correlation of 94% on average for the low signal-to-noise ratio of 3 and (2) a neighboring dipole within a few tens of millimeters from the dipole nearest to the true source tends to be highly incorporated in explaining MEG data. We applied the method to data measured in a language experiment and detected 13 significant sources. The results show that the present method is promising for detecting neural activity originating from a number of separate neural sources. © 2002 Elsevier Science (USA)