1. ABSTRACT In the present study cortical responses to two sustained Italian vowels, /a/ and /i/ ... more 1. ABSTRACT In the present study cortical responses to two sustained Italian vowels, /a/ and /i/ were analyzed in perception and production tasks by using the event-related potential (ERP) technique. We first aimed at re-testing whether EEG signal could mirror spectro-acoustical features of the two Italian vowels by measuring N1/P2 ERP components. Secondly, and more intriguingly, we also investigated whether the functional modulation of these earlier neural patterns could be detected in speech production tasks such as Acoustic Production, Silent production and Imagery articulation of linguistic sounds. It is important to highlight that research in language production processes by EEG measurements has been poorly investigated as yet. Actually, the main probes are carried out using indirect speech production tasks prevalently focused on lexical access aspect of word production and, moreover, these studies have achieved only by using invasive methods such as the electrocorticography: r...
By exploiting the N1 component of the auditory event related potentials we aimed to measure and l... more By exploiting the N1 component of the auditory event related potentials we aimed to measure and localize the processing involving the spectro-temporal and the abstract featural representation. We investigated the electroencephalography patterns of 11 Salento Italian speakers discriminating their native five stressed vowels [i, e, a, ɔ, u]. Findings showed two distinct N1 sub-components: the N1a peaking at 125–135 ms, localized in the bilateral primary auditory cortex (BA41), and the N1b peaking at 145–155 ms, localized in the superior temporal gyrus (BA22) with a strong leftward lateralization. Crucially, while high vowels elicited higher amplitudes than non-high vowels both in the N1a and N1b, back vowels generated later responses than non-back vowels in the N1b only. Overall, these findings suggest a hierarchical processing where from the N1a to the N1b the acoustic analysis shift progressively toward the computation and representation of phonological features.
How the brain encodes the speech acoustic signal into phonological representations (distinctive f... more How the brain encodes the speech acoustic signal into phonological representations (distinctive features) is a fundamental question for the neurobiology of language. Whether this process is characterized by tonotopic maps in primary or secondary auditory areas, with bilateral or leftward activity, remains a long-standing challenge. Magnetoencephalographic and ECoG studies have previously failed to show hierarchical and asymmetric hints for speech processing. We employed high-density electroencephalography to map the Salento Italian vowel system onto cortical sources using the N1 auditory evoked component. We found evidence that the N1 is characterized by hierarchical and asymmetric indexes structuring vowels representation. We identified them with two N1 subcomponents: the typical N1 (N1a) peaking at 125-135 ms and localized in the primary auditory cortex bilaterally with a tangential distribution and a late phase of the N1 (N1b) peaking at 145-155 ms and localized in the left super...
This work proposes a framework for future Silent Speech Interfaces (SSI) based on non-invasive EE... more This work proposes a framework for future Silent Speech Interfaces (SSI) based on non-invasive EEG recordings. Specifically, the information embedded in the brain signals related to the production – overt, covert and imagined production – of the Italian vowels /a/ and /i/ allowed to distinguish the vowels relying on discriminative features calculated by the Ambiguity Function in the context of time-frequency analysis, and ranked by the Fisher contrast. The vowels were classified by using a multilayer feed-forward ANN. Overall, intra-subject classification accuracies, as measured by the area under the ROC curve, ranged from 0.84 to 0.96 for overt production, from 0.83 to 0.96 for covert production, and from 0.89 to 0.98 for imagined vowels. Results indicate significant potential for the use of speech prosthesis controllers for clinical and military applications.
The main novelty of the study consists in using the EEG technique to elucidate the functioning of... more The main novelty of the study consists in using the EEG technique to elucidate the functioning of the auditory cortex in speech sound information processing. In searching for the cortical responses of two Italian vowels [a] and [i] we demonstrate that (i) as for the magnetic fields, also the modulations of the early electric N1 component is useful in exploring the mechanisms of phonetic feature extraction. The N1 amplitude and the N1 cortical generators seem to be affected by the vowel features as mapped in F2/F1 ratio so that the vowel [a] that shows a reduced inter-formant distance evokes weaker and anterior activity than [i]. The study thus, confirms that the cortical activity reflects the main spectro-acoustic dissimilarities supporting tonotopy as one of the most prominent organizing rules of the auditory cortices.
How the brain encodes the speech acoustic signal into phonological representations is a fundament... more How the brain encodes the speech acoustic signal into phonological representations is a fundamental question for the neurobiology of language. Determining whether this process is characterized by tonotopic maps in primary or secondary auditory areas, with bilateral or leftward activity, remains a long-standing challenge. Magnetoencephalographic studies failed to show hierarchical and asymmetric hints for speech processing. We employed high-density electroencephalography to map the Salento Italian vowel system onto cortical sources using the N1 auditory evoked component. We found evidence that the N1 is characterized by hierarchical and asymmetrical indexes in primary and secondary auditory areas structuring vowel representations. Importantly, the N1 was characterized by early and late phases. The early N1 peaked at 125–135 ms and was localized in the primary auditory cortex; the late N1 peaked at 145–155 ms and was localized in the left superior temporal gyrus. We showed that early in the primary auditory cortex, the cortical spatial arrangements—along the lateral-medial and anterior-posterior gradients—are broadly warped by phonemotopic patterns according to the distinctive feature principle. These phonemotopic patterns are carefully refined in the superior temporal gyrus along the inferior-superior and anterior-posterior gradients. The dynamical and hierarchical interface between primary and secondary auditory areas and the interaction effects between Height and Place features generate the categorical representation of the Salento Italian vowels.
1. ABSTRACT In the present study cortical responses to two sustained Italian vowels, /a/ and /i/ ... more 1. ABSTRACT In the present study cortical responses to two sustained Italian vowels, /a/ and /i/ were analyzed in perception and production tasks by using the event-related potential (ERP) technique. We first aimed at re-testing whether EEG signal could mirror spectro-acoustical features of the two Italian vowels by measuring N1/P2 ERP components. Secondly, and more intriguingly, we also investigated whether the functional modulation of these earlier neural patterns could be detected in speech production tasks such as Acoustic Production, Silent production and Imagery articulation of linguistic sounds. It is important to highlight that research in language production processes by EEG mea-surements has been poorly investigated as yet. Actually, the main probes are carried out us-ing indirect speech production tasks prevalently focused on lexical access aspect of word production and, moreover, these studies have carried out only by using invasive methods such as the electrocorticograp...
Speech sound perception is one of the most fascinating tasks performed by the human brain. It inv... more Speech sound perception is one of the most fascinating tasks performed by the human brain. It involves a mapping from continuous acoustic waveforms onto the discrete phonological units computed to store words in the mental lexicon. In this article, we review the magnetoencephalographic studies that have explored the timing and morphology of the N1m component to investigate how vowels and consonants are computed and represented within the auditory cortex. The neurons that are involved in the N1m act to construct a sensory memory of the stimulus due to spatially and temporally distributed activation patterns within the auditory cortex. Indeed, localization of auditory fields maps in animals and humans suggested two levels of sound coding, a tonotopy dimension for spectral properties and a tonochrony dimension for temporal properties of sounds. When the stimulus is a complex speech sound, tonotopy and tonochrony data may give important information to assess whether the speech sound parsing and decoding are generated by pure bottom-up reflection of acoustic differences or whether they are additionally affected by top-down processes related to phonological categories. Hints supporting pure bottom-up processing coexist with hints supporting top-down abstract phoneme representation. Actually, N1m data (amplitude, latency, source generators, and hemispheric distribution) are limited and do not help to disentangle the issue. The nature of these limitations is discussed. Moreover, neurophysiological studies on animals and neuroimaging studies on humans have been taken into consideration. We compare also the N1m findings with the investigation of the magnetic mismatch negativity (MMNm) component and with the analogous electrical components, the N1 and the MMN. We conclude that N1 seems more sensitive to capture lateralization and hierarchical processes than N1m, although the data are very preliminary. Finally, we suggest that MEG data should be integrated with EEG data in the light of the neural oscillations framework and we propose some concerns that should be addressed by future investigations if we want to closely line up language research with issues at the core of the functional brain mechanisms.
1. ABSTRACT In the present study cortical responses to two sustained Italian vowels, /a/ and /i/ ... more 1. ABSTRACT In the present study cortical responses to two sustained Italian vowels, /a/ and /i/ were analyzed in perception and production tasks by using the event-related potential (ERP) technique. We first aimed at re-testing whether EEG signal could mirror spectro-acoustical features of the two Italian vowels by measuring N1/P2 ERP components. Secondly, and more intriguingly, we also investigated whether the functional modulation of these earlier neural patterns could be detected in speech production tasks such as Acoustic Production, Silent production and Imagery articulation of linguistic sounds. It is important to highlight that research in language production processes by EEG measurements has been poorly investigated as yet. Actually, the main probes are carried out using indirect speech production tasks prevalently focused on lexical access aspect of word production and, moreover, these studies have achieved only by using invasive methods such as the electrocorticography: r...
By exploiting the N1 component of the auditory event related potentials we aimed to measure and l... more By exploiting the N1 component of the auditory event related potentials we aimed to measure and localize the processing involving the spectro-temporal and the abstract featural representation. We investigated the electroencephalography patterns of 11 Salento Italian speakers discriminating their native five stressed vowels [i, e, a, ɔ, u]. Findings showed two distinct N1 sub-components: the N1a peaking at 125–135 ms, localized in the bilateral primary auditory cortex (BA41), and the N1b peaking at 145–155 ms, localized in the superior temporal gyrus (BA22) with a strong leftward lateralization. Crucially, while high vowels elicited higher amplitudes than non-high vowels both in the N1a and N1b, back vowels generated later responses than non-back vowels in the N1b only. Overall, these findings suggest a hierarchical processing where from the N1a to the N1b the acoustic analysis shift progressively toward the computation and representation of phonological features.
How the brain encodes the speech acoustic signal into phonological representations (distinctive f... more How the brain encodes the speech acoustic signal into phonological representations (distinctive features) is a fundamental question for the neurobiology of language. Whether this process is characterized by tonotopic maps in primary or secondary auditory areas, with bilateral or leftward activity, remains a long-standing challenge. Magnetoencephalographic and ECoG studies have previously failed to show hierarchical and asymmetric hints for speech processing. We employed high-density electroencephalography to map the Salento Italian vowel system onto cortical sources using the N1 auditory evoked component. We found evidence that the N1 is characterized by hierarchical and asymmetric indexes structuring vowels representation. We identified them with two N1 subcomponents: the typical N1 (N1a) peaking at 125-135 ms and localized in the primary auditory cortex bilaterally with a tangential distribution and a late phase of the N1 (N1b) peaking at 145-155 ms and localized in the left super...
This work proposes a framework for future Silent Speech Interfaces (SSI) based on non-invasive EE... more This work proposes a framework for future Silent Speech Interfaces (SSI) based on non-invasive EEG recordings. Specifically, the information embedded in the brain signals related to the production – overt, covert and imagined production – of the Italian vowels /a/ and /i/ allowed to distinguish the vowels relying on discriminative features calculated by the Ambiguity Function in the context of time-frequency analysis, and ranked by the Fisher contrast. The vowels were classified by using a multilayer feed-forward ANN. Overall, intra-subject classification accuracies, as measured by the area under the ROC curve, ranged from 0.84 to 0.96 for overt production, from 0.83 to 0.96 for covert production, and from 0.89 to 0.98 for imagined vowels. Results indicate significant potential for the use of speech prosthesis controllers for clinical and military applications.
The main novelty of the study consists in using the EEG technique to elucidate the functioning of... more The main novelty of the study consists in using the EEG technique to elucidate the functioning of the auditory cortex in speech sound information processing. In searching for the cortical responses of two Italian vowels [a] and [i] we demonstrate that (i) as for the magnetic fields, also the modulations of the early electric N1 component is useful in exploring the mechanisms of phonetic feature extraction. The N1 amplitude and the N1 cortical generators seem to be affected by the vowel features as mapped in F2/F1 ratio so that the vowel [a] that shows a reduced inter-formant distance evokes weaker and anterior activity than [i]. The study thus, confirms that the cortical activity reflects the main spectro-acoustic dissimilarities supporting tonotopy as one of the most prominent organizing rules of the auditory cortices.
How the brain encodes the speech acoustic signal into phonological representations is a fundament... more How the brain encodes the speech acoustic signal into phonological representations is a fundamental question for the neurobiology of language. Determining whether this process is characterized by tonotopic maps in primary or secondary auditory areas, with bilateral or leftward activity, remains a long-standing challenge. Magnetoencephalographic studies failed to show hierarchical and asymmetric hints for speech processing. We employed high-density electroencephalography to map the Salento Italian vowel system onto cortical sources using the N1 auditory evoked component. We found evidence that the N1 is characterized by hierarchical and asymmetrical indexes in primary and secondary auditory areas structuring vowel representations. Importantly, the N1 was characterized by early and late phases. The early N1 peaked at 125–135 ms and was localized in the primary auditory cortex; the late N1 peaked at 145–155 ms and was localized in the left superior temporal gyrus. We showed that early in the primary auditory cortex, the cortical spatial arrangements—along the lateral-medial and anterior-posterior gradients—are broadly warped by phonemotopic patterns according to the distinctive feature principle. These phonemotopic patterns are carefully refined in the superior temporal gyrus along the inferior-superior and anterior-posterior gradients. The dynamical and hierarchical interface between primary and secondary auditory areas and the interaction effects between Height and Place features generate the categorical representation of the Salento Italian vowels.
1. ABSTRACT In the present study cortical responses to two sustained Italian vowels, /a/ and /i/ ... more 1. ABSTRACT In the present study cortical responses to two sustained Italian vowels, /a/ and /i/ were analyzed in perception and production tasks by using the event-related potential (ERP) technique. We first aimed at re-testing whether EEG signal could mirror spectro-acoustical features of the two Italian vowels by measuring N1/P2 ERP components. Secondly, and more intriguingly, we also investigated whether the functional modulation of these earlier neural patterns could be detected in speech production tasks such as Acoustic Production, Silent production and Imagery articulation of linguistic sounds. It is important to highlight that research in language production processes by EEG mea-surements has been poorly investigated as yet. Actually, the main probes are carried out us-ing indirect speech production tasks prevalently focused on lexical access aspect of word production and, moreover, these studies have carried out only by using invasive methods such as the electrocorticograp...
Speech sound perception is one of the most fascinating tasks performed by the human brain. It inv... more Speech sound perception is one of the most fascinating tasks performed by the human brain. It involves a mapping from continuous acoustic waveforms onto the discrete phonological units computed to store words in the mental lexicon. In this article, we review the magnetoencephalographic studies that have explored the timing and morphology of the N1m component to investigate how vowels and consonants are computed and represented within the auditory cortex. The neurons that are involved in the N1m act to construct a sensory memory of the stimulus due to spatially and temporally distributed activation patterns within the auditory cortex. Indeed, localization of auditory fields maps in animals and humans suggested two levels of sound coding, a tonotopy dimension for spectral properties and a tonochrony dimension for temporal properties of sounds. When the stimulus is a complex speech sound, tonotopy and tonochrony data may give important information to assess whether the speech sound parsing and decoding are generated by pure bottom-up reflection of acoustic differences or whether they are additionally affected by top-down processes related to phonological categories. Hints supporting pure bottom-up processing coexist with hints supporting top-down abstract phoneme representation. Actually, N1m data (amplitude, latency, source generators, and hemispheric distribution) are limited and do not help to disentangle the issue. The nature of these limitations is discussed. Moreover, neurophysiological studies on animals and neuroimaging studies on humans have been taken into consideration. We compare also the N1m findings with the investigation of the magnetic mismatch negativity (MMNm) component and with the analogous electrical components, the N1 and the MMN. We conclude that N1 seems more sensitive to capture lateralization and hierarchical processes than N1m, although the data are very preliminary. Finally, we suggest that MEG data should be integrated with EEG data in the light of the neural oscillations framework and we propose some concerns that should be addressed by future investigations if we want to closely line up language research with issues at the core of the functional brain mechanisms.
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