349 research outputs found

    Predictive Brain Mechanisms in Sound-to-Meaning Mapping during Speech Processing

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    Prior experience modulates top-down predictive processing in the ventral visual areas

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    Repetition suppression(RS)refers to that the reduction of neural activities for repeated presentations of a given stimulus compared to its first presentation. Summerfield et al(2008) found the magnitude of RS is affected by the repetition probability of stimuli, called as P(rep) effect. Based on the predictive coding theory, prior experience about the sensory inputs is necessary to optimally achieve cognitive processes. But it remains unclear how prior experience modulates predictive processes. To address this issue, in Study I, we estimated the P(rep) effects for Chinese characters and German words in native Chinese and German participants to test whether prior experience affects the P(rep) effect of lexical stimuli. The results showed that the P(rep) effect is only manifest for words of a language with which participants had prior experience. Study II performed fMRI measurements before and after a 10-day perceptual learning (PL) training for cars to test the modulation of short-term experience on the P(rep) effect. The results replicated the P(rep) effect for faces and cars. More interestingly, the P(rep) effect can be temporarily abolished by the short-term PL experience. The third study investigated how prior experience modulates sensory inputs. Study 3a adopted a classic stimulus repetition paradigm to measure RS for faces, together with either concurrent short-term memory (STM) load or a control condition. The results showed that RS is significantly attenuated when visual STM is loaded. Study 3b manipulates attention by a face inversion detection task. The results showed that the RS effect appears in the STM condition when participants attend to faces. The main conclusions: i) predictive processes, as measured by the P(rep) effect, require extensive prior experiences with stimuli, but ii) these can also be modulated by short-term learning experience. Further, iii) STM and attention are two modulators of prior experiences on predictive processes

    How actors become attractors: A neurocognitive investigation of linguistic actorhood

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    Neural correlates of confusability in recognition of morphologically complex Korean words

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    When people confuse and reject a non-word that is created by switching two adjacent letters from an actual word, is called the transposition confusability effect (TCE). The TCE is known to occur at the very early stages of visual word recognition with such unit exchange as letters or syllables, but little is known about the brain mechanisms of TCE. In this study, we examined the neural correlates of TCE and the effect of a morpheme boundary placement on TCE. We manipulated the placement of a morpheme boundary by exchanging places of two syllables embedded in Korean morphologically complex words made up of lexical morpheme and grammatical morpheme. In the two experimental conditions, the transposition syllable within-boundary condition (TSW) involved exchanging two syllables within the same morpheme, whereas the across-boundary condition (TSA) involved the exchange of syllables across the stem and grammatical morpheme boundary. During fMRI, participants performed the lexical decision task. Behavioral results revealed that the TCE was found in TSW condition, and the morpheme boundary, which is manipulated in TSA, modulated the TCE. In the fMRI results, TCE induced activation in the left inferior parietal lobe (IPL) and intraparietal sulcus (IPS). The IPS activation was specific to a TCE and its strength of activation was associated with task performance. Furthermore, two functional networks were involved in the TCE: the central executive network and the dorsal attention network. Morpheme boundary modulation suppressed the TCE by recruiting the prefrontal and temporal regions, which are the key regions involved in semantic processing. Our findings propose the role of the dorsal visual pathway in syllable position processing and that its interaction with other higher cognitive systems is modulated by the morphological boundary in the early phases of visual word recognition

    Predicting speech from a cortical hierarchy of event-based timescales

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    How do predictions in the brain incorporate the temporal unfolding of context in our natural environment? We here provide evidence for a neural coding scheme that sparsely updates contextual representations at the boundary of events. This yields a hierarchical, multilayered organization of predictive language comprehension. Training artificial neural networks to predict the next word in a story at five stacked time scales and then using model-based functional magnetic resonance imaging, we observe an event-based “surprisal hierarchy” evolving along a temporoparietal pathway. Along this hierarchy, surprisal at any given time scale gated bottom-up and top-down connectivity to neighboring time scales. In contrast, surprisal derived from continuously updated context influenced temporoparietal activity only at short time scales. Representing context in the form of increasingly coarse events constitutes a network architecture for making predictions that is both computationally efficient and contextually diverse

    Investigating Semantic Alignment in Character Learning of Chinese as a Foreign Language: The Use and Effect of the Imagery Based Encoding Strategy

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    For learners of Chinese as a foreign language (CFL), character learning is frustrating. This research postulated that this difficulty may mainly come from a lack of semantic understanding of character-denoted meanings. Language theories support that when a learner’s semantic meaning increases, the orthographic structures that represent the underlying meanings also improve. This study aimed to reveal CFL learners’ cognitive abilities and processes in visual-semantic learning of Chinese characters. Particularly, this study investigated the process by which English-speaking adolescent CFL learners, at the beginning to intermediate level, made mental images of character-denoted meanings to visually encode and retrieve character forms. Quantitative and qualitative data were gathered from image making questionnaires, writing, and reading tests, after learning characters in three commonly-used teaching methods (i.e., English, pictorial, and verbal). The data were analyzed based on a triangulation of the literature from Neuro-Semantic Language Learning Theory, scientific findings in cognitive psychology, and neuroscience. The study found that participants’ semantic abilities to understand character-denoted meanings emerged, but were still restricted in familiar orthographic forms. The use of the imagery strategy as a semantic ability predicted better performances, most evidently in writing; however, the ability in using the imagery strategy to learn characters was still underdeveloped, and needed to be supported with sufficient contextual information. Implications and further research in visual-semantic learning and teaching characters were suggested

    Sensorimotor Modulations by Cognitive Processes During Accurate Speech Discrimination: An EEG Investigation of Dorsal Stream Processing

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    Internal models mediate the transmission of information between anterior and posterior regions of the dorsal stream in support of speech perception, though it remains unclear how this mechanism responds to cognitive processes in service of task demands. The purpose of the current study was to identify the influences of attention and working memory on sensorimotor activity across the dorsal stream during speech discrimination, with set size and signal clarity employed to modulate stimulus predictability and the time course of increased task demands, respectively. Independent Component Analysis of 64–channel EEG data identified bilateral sensorimotor mu and auditory alpha components from a cohort of 42 participants, indexing activity from anterior (mu) and posterior (auditory) aspects of the dorsal stream. Time frequency (ERSP) analysis evaluated task-related changes in focal activation patterns with phase coherence measures employed to track patterns of information flow across the dorsal stream. ERSP decomposition of mu clusters revealed event-related desynchronization (ERD) in beta and alpha bands, which were interpreted as evidence of forward (beta) and inverse (alpha) internal modeling across the time course of perception events. Stronger pre-stimulus mu alpha ERD in small set discrimination tasks was interpreted as more efficient attentional allocation due to the reduced sensory search space enabled by predictable stimuli. Mu-alpha and mu-beta ERD in peri- and post-stimulus periods were interpreted within the framework of Analysis by Synthesis as evidence of working memory activity for stimulus processing and maintenance, with weaker activity in degraded conditions suggesting that covert rehearsal mechanisms are sensitive to the quality of the stimulus being retained in working memory. Similar ERSP patterns across conditions despite the differences in stimulus predictability and clarity, suggest that subjects may have adapted to tasks. In light of this, future studies of sensorimotor processing should consider the ecological validity of the tasks employed, as well as the larger cognitive environment in which tasks are performed. The absence of interpretable patterns of mu-auditory coherence modulation across the time course of speech discrimination highlights the need for more sensitive analyses to probe dorsal stream connectivity

    Functional Magnetic Resonance Imaging

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    "Functional Magnetic Resonance Imaging - Advanced Neuroimaging Applications" is a concise book on applied methods of fMRI used in assessment of cognitive functions in brain and neuropsychological evaluation using motor-sensory activities, language, orthographic disabilities in children. The book will serve the purpose of applied neuropsychological evaluation methods in neuropsychological research projects, as well as relatively experienced psychologists and neuroscientists. Chapters are arranged in the order of basic concepts of fMRI and physiological basis of fMRI after event-related stimulus in first two chapters followed by new concepts of fMRI applied in constraint-induced movement therapy; reliability analysis; refractory SMA epilepsy; consciousness states; rule-guided behavioral analysis; orthographic frequency neighbor analysis for phonological activation; and quantitative multimodal spectroscopic fMRI to evaluate different neuropsychological states

    Ventral occipito-temporal cortex function and anatomical connectivity in reading

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    Previous functional neuroimaging studies of reading in skilled readers, acquired dyslexia and developmental dyslexia have all shown that the left ventral occipito-temporal cortex (vOT) is involved in visual word recognition. Specifically, a region in the left posterior occipito-temporal sulcus lateral to fusiform gyrus and medial to inferior temporal gyrus has been reported to play an important role. However, the precise functional contribution of this area in reading is yet to be fully explored. In this thesis, I empirically evaluated a claim that vOT responds not only to bottom-up processing demands of the visual stimuli but is also influenced by automatic, top-down non-visual processing demands, as proposed by the Interactive Account of vOT functioning. The first part of this thesis investigated the functional properties of vOT during reading, using functional magnetic resonance imaging. In the first project, the top-down influences on vOT were investigated, teasing apart visual and non-visual properties of written stimuli. In the second project, using the Japanese orthography I disentangled a word’s lexical frequency from the frequency of its visual form – an important distinction for understanding the neural information processing in regions engaged by reading and further explored the interactive nature of the vOT responses. The second part then investigated the anatomical basis of these functional interactions between vOT and other cortical regions. I used diffusion-weighted magnetic resonance imaging and tractography, the only method currently available to identify and measure white matter fibre pathways non-invasively and in vivo. My research has demonstrated that vOT integrates bottom-up visual information and top-down predictions from regions encoding non-visual attributes of the stimulus in an interactive fashion. It also illustrated the putative anatomical basis for functional connectivity during reading, which is consistent with the parallel cortical visual pathways seen in other primates. Altogether, the results provide strong support for the Interactive Account

    Testing for the Dual-Route Cascade Reading Model in the Brain: An fMRI Effective Connectivity Account of an Efficient Reading Style

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    Neuropsychological data about the forms of acquired reading impairment provide a strong basis for the theoretical framework of the dual-route cascade (DRC) model which is predictive of reading performance. However, lesions are often extensive and heterogeneous, thus making it difficult to establish precise functional anatomical correlates. Here, we provide a connective neural account in the aim of accommodating the main principles of the DRC framework and to make predictions on reading skill. We located prominent reading areas using fMRI and applied structural equation modeling to pinpoint distinct neural pathways. Functionality of regions together with neural network dissociations between words and pseudowords corroborate the existing neuroanatomical view on the DRC and provide a novel outlook on the sub-regions involved. In a similar vein, congruent (or incongruent) reliance of pathways, that is reliance on the word (or pseudoword) pathway during word reading and on the pseudoword (or word) pathway during pseudoword reading predicted good (or poor) reading performance as assessed by out-of-magnet reading tests. Finally, inter-individual analysis unraveled an efficient reading style mirroring pathway reliance as a function of the fingerprint of the stimulus to be read, suggesting an optimal pattern of cerebral information trafficking which leads to high reading performance
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