On Experiencing Meaning: Irreducible Cognitive Phenomenology and Sinewave Speech

Upon first hearing sinewaves, all that can be discerned are beeps and whistles. But after hearing the original speech, the beeps and whistles sound like speech. The difference between these two episodes undoubtedly involves an alteration in phenomenal character. O’Callaghan (2011) argues that this alteration is non-sensory, but he leaves open the possibility of attributing it to some other source, e.g. cognition. I discuss whether the alteration in phenomenal character involved in sinewave speech provides evidence for cognitive phenomenology. I defend both the existence of cognitive phenomenology and the phenomenal contrast method, as each concerns the case presented here

Categorical speech representation in human superior temporal gyrus.

nature neurOSCIenCe advance online publication a r t I C l e S A fundamental property of speech perception is that listeners map continuously variable acoustic speech signals onto discrete phonetic sound categories A number of studies support the notion that the posterior superior temporal gyrus (pSTG) in Wernicke's area is important for higher order auditory processing of speech sounds To answer these questions, we recorded cortical local field poten tials from the pSTG in four human subjects undergoing awake crani otomy with speech mapping as part of their epilepsy 14 or brain tumor surgery RESULTS We employed a classic procedure first described in 1957 (ref. 6) to investigate the perceptual and neural organization of stop conso nant phonemes. Consonantvowel syllables were synthesized with 14 equal and parametric changes in the starting frequency of the F2 transition (second vocal tract resonance) that ranged perceptually across three initial consonants /ba/ to /da/ to /ga

On Experiencing Meaning: Irreducible Cognitive Phenomenology and Sinewave Speech

Upon first hearing sinewaves, all that can be discerned are beeps and whistles. But after hearing the original speech, the beeps and whistles sound like speech. The difference between these two episodes undoubtedly involves an alteration in phenomenal character. O’Callaghan (2011) argues that this alteration is non-sensory, but he leaves open the possibility of attributing it to some other source, e.g. cognition. I discuss whether the alteration in phenomenal character involved in sinewave speech provides evidence for cognitive phenomenology. I defend both the existence of cognitive phenomenology and the phenomenal contrast method, as each concerns the case presented here

Categorical representations of phonemic vowels investigated with fMRI

The present thesis investigates the sensitivity of the human auditory cortex (AC) to the contrast between prototype and nonprototype vowels as well as between phonemic and nonphonemic vowels. Activations to vowels were measured with functional magnetic resonance imaging (fMRI), which was also used to analyze the effect of categorical processing on modulations in AC and adjacent inferior parietal lobule (IPL) observed during active listening tasks. A prominent theoretical view suggests that native phonemic vowels (i.e., phonemes) are represented in the human brain as categories organized around a best representative of the category (i.e., phoneme prototype). This view predicts systematic differences in the neural representations and processing of phoneme prototypes, nonprototypes and nonphonemic vowels. In three separate studies, subjects were presented with vowel pairs and visual stimuli during demanding auditory and visual tasks. Study I compared activations to prototypical and nonprototypical vowels, whereas Study II focused on the contrast between phonemic and nonphonemic vowels. Study II also tested whether activations in IPL during a categorical vowel memory task depend on whether the task is performed on phonemic (easy to categorize) or nonphonemic (harder to categorize) vowels. Study III was designed to replicate the key findings of Studies I and II. Further, Study III compared activations to identical vowels presented during a number of different task conditions requiring analysis of the acoustical or categorical differences between the vowels. The results of this thesis are in line with the general theoretical view that phonemic vowels are represented in a categorical manner in the human brain. Studies I–III showed that information about categorical vowel representations is present in human AC during active listening tasks. Areas of IPL, in turn, were implicated in general operations on categorical representations rather than in categorization of speech sounds as such. Further, the present results demonstrate that task-dependent activations in AC and adjacent IPL strongly depend on whether the task requires analysis of the acoustical or categorical features of the vowels. It is important to note that, in the present studies, surprisingly small differences in the characteristics of the vowel stimuli or the tasks performed on these vowels resulted in significant and widespread activation differences in AC and adjacent regions. As the key findings of Studies I and II were also quite successfully replicated in Study III, these results highlight the importance of carefully controlled experiments and replications in fMRI research.Vallitsevan teorian mukaan äidinkielen foneemisten vokaalien (eli foneemien) representaatiot ovat luonteeltaan kategorisia eli äänteet ovat järjestyneet kategorian parhaan esiintymän (eli foneemin prototyypin) ympärille. Teoria ennustaa, että foneemiprototyyppien, nonprototyyppien ja nonfoneemisten vokaalien representaatiot ja niiden käsittely aivoissa eroavat toisistaan. Tässä väitöskirjassa selvitetään toiminnallisen magneettikuvauksen (fMRI) avulla, eroaako ihmisen kuuloaivokuoren ja sen lähialueiden aktivaatio prototyyppisten ja nonprototyyppisten sekä foneemisten ja nonfoneemisten vokaalien käsittelyn aikana ja miten aktiiviset kuuntelutehtävät vaikuttavat näihin eroihin. Väitöskirjan kolmessa osatutkimuksessa koehenkilöille esitettiin vokaalipareja ja visuaalisia ärsykkeitä kuuntelu- ja katselutehtävien aikana. Tutkimuksessa I vokaaliparit koostuivat prototyyppisistä ja nonprototyyppisistä foneemisista vokaaleista. Tutkimuksessa II puolestaan tarkasteltiin foneemisten ja nonfoneemisten vokaalien käsittelyn eroa. Lisäksi tutkimuksessa II selvitettiin, riippuuko kuuloaivokuoren ja sen lähialueiden tehtäväsidonnainen aktivaatio siitä, suoritetaanko kuuntelutehtävää helposti (foneemiset vokaalit) vai vaikeasti (nonfoneemiset vokaalit) kategorisoitavilla vokaaleilla. Viimeisessä tutkimuksessa (III) toistettiin tutkimusten I ja II päätulokset. Tutkimuksessa III selvitettiin myös sitä, miten aktivaatio äänten erottelutehtävän aikana eroaa silloin, kun vokaaleja erotellaan niiden fysikaalisten tai kategoristen ominaisuuksien perusteella. Väitöskirjan tutkimuksissa saadut tulokset tukevat oletetusta siitä, että foneemisten vokaalien representaatiot ovat luonteeltaan kategorisia. Tulokset osoittavat, että tieto vokaalikategorioiden representaatioista on käytettävissä kuuloaivokuorella aktiivisten kuuntelutehtävien aikana. Lisäksi tutkimuksissa havaittiin, että päälakilohkon alaosien aktivaatio voimistui niiden tehtävien aikana, jotka vaativat kategorisen tiedon käsittelyä. Näiden aivoalueiden aktivaatio ei kuitenkaan näytä liittyvän kategorioiden muodostamiseen (puheäänten kategorisointiin) sinänsä. On merkillepantavaa, että tutkimuksissa I–III näennäisen pienet erot vokaaliärsykkeissä ja kuuntelutehtävissä johtivat huomattaviin aktivaatioeroihin kuuloaivokuorella ja sen läheisillä aivoalueilla. Tämä korostaa huolellisesti kontrolloitujen koeasetelmien ja etenkin replikaatiotutkimusten tärkeyttä fMRI -tutkimuksissa

A multidimensional characterization of the neurocognitive architecture underlying age-related temporal speech processing.

Healthy aging is often associated with speech comprehension difficulties in everyday life situations despite a pure-tone hearing threshold in the normative range. Drawing on this background, we used a multidimensional approach to assess the functional and structural neural correlates underlying age-related temporal speech processing while controlling for pure-tone hearing acuity. Accordingly, we combined structural magnetic resonance imaging and electroencephalography, and collected behavioral data while younger and older adults completed a phonetic categorization and discrimination task with consonant-vowel syllables varying along a voice-onset time continuum. The behavioral results confirmed age-related temporal speech processing singularities which were reflected in a shift of the boundary of the psychometric categorization function, with older adults perceiving more syllable characterized by a short voice-onset time as /ta/ compared to younger adults. Furthermore, despite the absence of any between-group differences in phonetic discrimination abilities, older adults demonstrated longer N100/P200 latencies as well as increased P200 amplitudes while processing the consonant-vowel syllables varying in voice-onset time. Finally, older adults also exhibited a divergent anatomical gray matter infrastructure in bilateral auditory-related and frontal brain regions, as manifested in reduced cortical thickness and surface area. Notably, in the younger adults but not in the older adult cohort, cortical surface area in these two gross anatomical clusters correlated with the categorization of consonant-vowel syllables characterized by a short voice-onset time, suggesting the existence of a critical gray matter threshold that is crucial for consistent mapping of phonetic categories varying along the temporal dimension. Taken together, our results highlight the multifaceted dimensions of age-related temporal speech processing characteristics, and pave the way toward a better understanding of the relationships between hearing, speech and the brain in older age

Stimulus Complexity and Categorical Effects in Human Auditory Cortex: An Activation Likelihood Estimation Meta-Analysis

Investigations of the functional organization of human auditory cortex typically examine responses to different sound categories. An alternative approach is to characterize sounds with respect to their amount of variation in the time and frequency domains (i.e., spectral and temporal complexity). Although the vast majority of published studies examine contrasts between discrete sound categories, an alternative complexity-based taxonomy can be evaluated through meta-analysis. In a quantitative meta-analysis of 58 auditory neuroimaging studies, we examined the evidence supporting current models of functional specialization for auditory processing using grouping criteria based on either categories or spectro-temporal complexity. Consistent with current models, analyses based on typical sound categories revealed hierarchical auditory organization and left-lateralized responses to speech sounds, with high speech sensitivity in the left anterior superior temporal cortex. Classification of contrasts based on spectro-temporal complexity, on the other hand, revealed a striking within-hemisphere dissociation in which caudo-lateral temporal regions in auditory cortex showed greater sensitivity to spectral changes, while anterior superior temporal cortical areas were more sensitive to temporal variation, consistent with recent findings in animal models. The meta-analysis thus suggests that spectro-temporal acoustic complexity represents a useful alternative taxonomy to investigate the functional organization of human auditory cortex

Independent Component Analysis of Event-Related Electroencephalography During Speech and Non-Speech Discrimination: : Implications for the Sensorimotor ∆∞ Rhythm in Speech Processing

Background: The functional significance of sensorimotor integration in acoustic speech processing is unclear despite more than three decades of neuroimaging research. Constructivist theories have long speculated that listeners make predictions about articulatory goals functioning to weight sensory analysis toward expected acoustic features (e.g. analysis-by-synthesis; internal models). Direct-realist accounts posit that sensorimotor integration is achieved via a direct match between incoming acoustic cues and articulatory gestures. A method capable of favoring one account over the other requires an ongoing, high-temporal resolution measure of sensorimotor cortical activity prior to and following acoustic input. Although scalp-recorded electroencephalography (EEG) provides a measure of cortical activity on a millisecond time scale, it has low-spatial resolution due to the blurring or mixing of cortical signals on the scalp surface. Recently proposed solutions to the low-spatial resolution of EEG known as blind source separation algorithms (BSS) have made the identification of distinct cortical signals possible. The µ rhythm of the EEG is known to briefly suppress (i.e., decrease in spectral power) over the sensorimotor cortex during the performance, imagination, and observation of biological movements, suggesting that it may provide a sensitive index of sensorimotor integration during speech processing. Neuroimaging studies have traditionally investigated speech perception in two-forced choice designs in which participants discriminate between pairs of speech and nonspeech control stimuli. As such, this classical design was employed in the current dissertation work to address the following specific aims to: 1) isolate independent components with traditional EEG signatures within the dorsal sensorimotor stream network; 2) identify components with features of the sensorimotor µ rhythm and; 3) investigate changes in timefrequency activation of the µ rhythm relative to stimulus type, onset, and discriminability (i.e., perceptual performance). In light of constructivist predictions, it was hypothesized that the µ rhythm would show significant suppression for syllable stimuli prior to and following stimulus onset, with significant differences between correct discrimination trials and those discriminated at chance levels. Methods: The current study employed millisecond temporal resolution EEG to measure ongoing decreases and increases in spectral power (event-related spectral perturbations; ERSPs) prior to, during, and after the onset of acoustic speech and tone-sweep stimuli embedded in white-noise. Sixteen participants were asked to passively listen to or actively identify speech and tone signals in a two-force choice same/different discrimination task. To investigate the role of ERSPs in perceptual identification performance, high signal-to-noise ratios (SNRs) in which speech and tone identification was significantly better than chance (+4dB) and low SNRs in which performance was below chance (-6dB and -18dB) were compared to a baseline of passive noise. Independent component analysis (ICA) of the EEG was used to reduce artifact and source mixing due to volume conduction. Independent components were clustered using measure product methods and cortical source modeling, including spectra, scalp distribution, equivalent current dipole estimation (ECD), and standardized low-resolution tomography (sLORETA). Results: Data analysis revealed six component clusters consistent with a bilateral dorsal-stream sensorimotor network, including component clusters localized to the precentral and postcentral gyrus, cingulate cortex, supplemental motor area, and posterior temporal regions. Timefrequency analysis of the left and right lateralized µ component clusters revealed significant (pFDR\u3c.05) suppression in the traditional beta frequency range (13-30Hz) prior to, during, and following stimulus onset. No significant differences from baseline were found for passive listening conditions. Tone discrimination was different from passive noise in the time period following stimulus onset only. No significant differences were found for correct relative to chance tone stimuli. For both left and right lateralized clusters, early suppression (i.e., prior to stimulus onset) compared to the passive noise baseline was found for the syllable discrimination task only. Significant differences between correct trials and trials identified at chance level were found for the time period following stimulus offset for the syllable discrimination task in left lateralized cluster. Conclusions: As this is the first study to employ BSS methods to isolate components of the EEG during acoustic speech and non-speech discrimination, findings have important implications for the functional role of sensorimotor integration in speech processing. Consistent with expectations, the current study revealed component clusters associated with source models within the sensorimotor dorsal stream network. Beta suppression of the µ component clusters in both the left and right hemispheres is consistent with activity in the precentral gyrus prior to and following acoustic input. As early suppression of the µ was found prior the syllable discrimination task, the present findings favor internal model concepts of speech processing over mechanisms proposed by direct-realists. Significant differences between correct and chance syllable discrimination trials are also consistent with internal model concepts suggesting that sensorimotor integration is related to perceptual performance at the point in time when initial articulatory hypotheses are compared with acoustic input. The relatively inexpensive, noninvasive EEG methodology used in this study may have translational value in the future as a brain computer interface (BCI) approach. As deficits in sensorimotor integration are thought to underlie cognitive-communication impairments in a number of communication disorders, the development of neuromodulatory feedback approaches may provide a novel avenue for augmenting current therapeutic protocols

Department of Radiology-Annual Executive Summary Report-July 1, 2005 to June 30, 2006

98 page Department of Radiology Annual Executive Summary Report, July 1, 2005 to June 30, 2006, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania, United States