A Mechanistic Approach to Cross-Domain Perceptual Narrowing in the First Year of Life

Language and face processing develop in similar ways during the first year of life. Early in the first year of life, infants demonstrate broad abilities for discriminating among faces and speech. These discrimination abilities then become tuned to frequently experienced groups of people or languages. This process of perceptual development occurs between approximately 6 and 12 months of age and is largely shaped by experience. However, the mechanisms underlying perceptual development during this time, and whether they are shared across domains, remain largely unknown. Here, we highlight research findings across domains and propose a top-down/bottom-up processing approach as a guide for future research. It is hypothesized that perceptual narrowing and tuning in development is the result of a shift from primarily bottom-up processing to a combination of bottom-up and top-down influences. In addition, we propose word learning as an important top-down factor that shapes tuning in both the speech and face domains, leading to similar observed developmental trajectories across modalities. Importantly, we suggest that perceptual narrowing/tuning is the result of multiple interacting factors and not explained by the development of a single mechanism

Cortical representations for phonological quantity

Different languages use temporal speech cues in different linguistic functions. In Finnish, speech-sound duration is used as the primary cue for the phonological quantity distinction ― i.e., a distinction between short and long phonemes. For the second-language (L2) learners of Finnish, quantity is often difficult to master if speech-sound duration plays a less important role in the phonology of their native language (L1). The present studies aimed to investigate the cortical representations for phonological quantity in native speakers and L2 users of Finnish by using behavioral and electrophysiological methods. Since long-term memory representations for different speech units have been previously shown to participate in the elicitation of the mismatch negativity (MMN) brain response, MMN was used to compare the neural representation for quantity between native speakers and L2 users of Finnish. The results of the studies suggested that native Finnish speakers' MMN response to quantity was determined by the activation of native-language phonetic prototypes rather than by phoneme boundaries. In addition, native speakers seemed to process phoneme quantity and quality independently from each other by separate brain representations. The cross-linguistic MMN studies revealed that, in native speakers of Finnish, the MMN response to duration or quantity-degree changes was enhanced in amplitude selectively in speech sounds, whereas this pattern was not observed in L2 users. Native speakers' MMN enhancement is suggested to be due to the pre-attentive activation of L1 prototypes for quantity. In L2 users, the activation of L2 prototypes or other L2 learning effects were not reflected in the MMN, with one exception. Even though L2 users failed to show native-like brain responses to duration changes in a vowel that was similar in L1 and L2, their duration MMN response was native-like for an L2 vowel with no counterpart in L1. Thus, the pre-attentive activation of L2 users' representations was determined by the degree of similarity of L2 sounds to L1 sounds. In addition, behavioral experiments suggested that the establishment of representations for L2 quantity may require several years of language exposure.Eri kielet käyttävät äänteiden kestovihjeitä erilaisissa kielellisissä tehtävissä. Suomessa äänteen kesto on kvantiteetin eli lyhyiden ja pitkien foneemien erottamisen tärkein vihje. Suomea toisena kielenä puhuvien on usein vaikea oppia kvantiteetti, jos äänteen kestolla on vähäisempi merkitys heidän äidinkielessään. Tämän väitöskirjan tutkimuksissa tarkasteltiin aivovastemittausten ja foneettisten testien avulla kvantiteettikategorioiden muistijälkiä äidinkieleltään suomenkielisten ja suomea toisena kielenä puhuvien aivokuorella. Koska äänteiden pitkäkestoisten muistijälkien on aiemmin todettu osallistuvan MMN-aivovasteen (engl. mismatch negativity) syntymiseen, sitä käytettiin selvittämään, miten äidinkieleltään suomenkielisten ja suomea toisena kielenä puhvien kvantiteettikategorioiden muistijäljet poikkeavat toisistaan. Tulosten mukaan äidinkieleltään suomenkielisten MMN-vasteen voimakkuus määräytyi äidinkielen foneettisten prototyyppien mukaan eikä foneemien rajojen mukaan. Lisäksi suomenkieliset näyttivät käsittelevän foneemin laadun ja kvantiteetin toisistaan riippumattomasti, eri kategorioiden kautta. Kieliryhmiä vertailevat MMN-tutkimukset puolestaan osoittivat, että äidinkieleltään suomenkielisillä MMN-vaste keston muutokselle oli nimenomaan puheäänteiden kohdalla voimakkaampi kuin toisen kielen oppijoilla. Tämä saattaa johtua foneettisten prototyyppien esitietoisesta aktivoitumisesta äidinkieleltään suomenkielisten aivokuorella. Toisen kielen oppijoilla toisen kielen prototyyppien aktivoituminen tai kielenoppiminen ylipäänsä eivät näkyneet MMN-vasteessa yhtä poikkeusta lukuun ottamatta. Vaikka suomea toisena kielenä puhuvien aivovasteiden voimakkuus äänteen keston muutokselle ei saavuttanut äidinkielisten tasoa vokaalissa, joka oli samankaltainen heidän äidinkielessään ja toisessa kielessään, he saavuttivat suomenkielisten tason vokaalissa, jolla ei ollut vastinetta heidän äidinkielessään. Näin ollen äidinkielen ja toisen kielen äänteiden samankaltaisuus näyttäisi vaikuttavan suomea toisena kielenä puhuvien muistijälkien esitietoiseen aktivoitumiseen. Tutkimuksen foneettisten kokeiden mukaan kategorioiden syntyminen toisen kielen kvantiteetille saattaa vaatia useiden vuosien altistusta toiselle kielelle

Neural Correlates of Face Processing: Perceptual Narrowing and Categorization

Perceptual narrowing is a developmental process that occurs between 6 and 9 months of age, during which infants transition from having more general perceptual abilities to more specific abilities. An example of this would be the other-species effect, in which infants experience a decline in the ability to individuate other species’ faces. It has been suggested that an infant’s growing ability to categorize could lead to a decline in their ability to discern individuals within other-species groups (Scott & Monesson, 2009), and that this difference is related to processing styles. In this study, 9-month-old infants were tested on their subordinate-level categorization ability with different species of monkey faces. Subordinate-level categorization is categorization on the species level. ERP data was recorded while the infants were shown presentations of the novel face/familiar species category and the novel face/novel species category after being familiarized to either a single face or a group of exemplars. It was predicted that the 9-month-olds in the categorization group would have a greater amplitude ERP response, namely the P400 component, to the Novel Other face category versus the Novel Same and Familiar face categories. This would provide evidence that infants at this age are not processing individual faces from other-species but are categorizing other species faces. It was also predicted that there would be differences in the Nc component between groups based on condition type. It was found that the categorization group showed an ability to categorize the monkey faces by species, as shown by a larger amplitude Nc and P400 for the Novel Other face category, whereas the individuation group did not. These findings add support to the idea that subordinate-level categorization could be a mechanism behind the effects seen from perceptual narrowing of other-species faces

Nonnative Phonetic Perception in Adult L2 Learners

Even with years of practice, adult learners have trouble perceiving and producing sounds in a second language (L2). Adults tend to need more focused and targeted input to achieve native-like perception and production of L2 sounds than children. The present study aims to clarify the mechanisms through which L2 perception is influenced by first language (L1) sounds, the neural basis of this perception, how learner differences influence learning, and how different training paradigms modulate both the neural and behavioral basis of L2 sound perception. Native English and native Spanish speakers participated in a five-day training paradigm during which they learned to discriminate Hindi sounds that do not belong to their L1 sound categories. Participants underwent electroencephalogram (EEG) recordings from the scalp, baseline discrimination tasks, training, and several memory and attention individual measures. We expected that the L1 would modulate the EEG waveform known as the mismatch negativity (MMN) at approximately 150-200ms after sound onset. This measure indexes early phonetic learning and previous research has shown that the waveform’s amplitude can change or shift with new phonetic learning, indicating a reorganization of early acoustic and phonetic processing with new input. Furthermore, we examined how the L1 and different training and feedback paradigms influence this MMN change. Results demonstrate that both learner groups showed a modulation in the MMN waveform after training, but the change was eclipsed by the native contrast that was tested as a control, depending on how well they performed during training. Furthermore, participants in the feedback condition performed better on the training than those in the no-feedback condition but this was not related to the ERP results, suggesting that feedback may be useful for overt behavioral responses, but not necessary for pre-attentive neural responses. These results are examined in light of the Perceptual Assimilation Model (PAM; Best, 1991, 1995), the Speech Learning Model (SLM; Flege, 1995), the Native Language Magnet model (NLM; Kuhl & Riviera-Gaxiola, 2008), and the Unified Competition Model (UCM; MacWhinney, 2005), examining similarity between L1s, neural hardwiring in the brain, and competition between phonetic contrasts

On The Way To Linguistic Representation: Neuromagnetic Evidence of Early Auditory Abstraction in the Perception of Speech and Pitch

The goal of this dissertation is to show that even at the earliest (non-invasive) recordable stages of auditory cortical processing, we find evidence that cortex is calculating abstract representations from the acoustic signal. Looking across two distinct domains (inferential pitch perception and vowel normalization), I present evidence demonstrating that the M100, an automatic evoked neuromagnetic component that localizes to primary auditory cortex is sensitive to abstract computations. The M100 typically responds to physical properties of the stimulus in auditory and speech perception and integrates only over the first 25 to 40 ms of stimulus onset, providing a reliable dependent measure that allows us to tap into early stages of auditory cortical processing. In Chapter 2, I briefly present the episodicist position on speech perception and discuss research indicating that the strongest episodicist position is untenable. I then review findings from the mismatch negativity literature, where proposals have been made that the MMN allows access into linguistic representations supported by auditory cortex. Finally, I conclude the Chapter with a discussion of the previous findings on the M100/N1. In Chapter 3, I present neuromagnetic data showing that the re-sponse properties of the M100 are sensitive to the missing fundamental component using well-controlled stimuli. These findings suggest that listeners are reconstructing the inferred pitch by 100 ms after stimulus onset. In Chapter 4, I propose a novel formant ratio algorithm in which the third formant (F3) is the normalizing factor. The goal of formant ratio proposals is to provide an explicit algorithm that successfully "eliminates" speaker-dependent acoustic variation of auditory vowel tokens. Results from two MEG experiments suggest that auditory cortex is sensitive to formant ratios and that the perceptual system shows heightened sensitivity to tokens located in more densely populated regions of the vowel space. In Chapter 5, I report MEG results that suggest early auditory cortical processing is sensitive to violations of a phonological constraint on sound sequencing, suggesting that listeners make highly specific, knowledge-based predictions about rather abstract anticipated properties of the upcoming speech signal and violations of these predictions are evident in early cortical processing

Plasticity in second language (L2) learning: perception of L2 phonemes by native Greek speakers of English

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Understanding the process of language acquisition is a challenge that many researchers spanning different disciplines (e.g. linguistics, psychology, neuroscience) have grappled with for centuries. One which has in recent years attracted a lot of attention has been in the area of non-native phoneme acquisition. Speech sounds that contain multiple phonetic cues are often difficult for foreign-language learners, especially if certain cues are weighted differently in the foreign and native languages. Greek adult and child speakers of English were studied to determine which cues (duration or spectral) they were using to make discrimination and identification judgments for an English vowel contrast pair. To this end, two forms of identification and discrimination tasks were used: natural (unedited) stimuli and another ‘modified’ vowel duration stimuli which were edited so that there were no duration differences between the vowels. Results show the Greek speakers were particularly impaired when they were unable to use the duration cue as compared to the native English speakers. Similar results were also obtained in control experiments where there was no orthographic representation or where the stimuli were cross-spliced to modify the phonetic neighborhood. Further experiments used high-variability training sessions to enhance vowel perception. Following training, performance improved for both Greek adult and child groups as revealed by post training tests. However the improvements were most pronounced for the child Greek speaker group. A further study examined the effect of different orthographic cues that might affect rhyme and homophony judgment. The results of that study showed that Greek speakers were in general more affected by orthography and regularity (particularly of the vowel) in making these judgments. This would suggest that Greek speakers were more sensitive to irrelevant orthographic cues, mirroring the results in the auditory modality where they focused on irrelevant acoustic cues. The results are discussed in terms of current theories of language acquisition, with particular reference to acquisition of non-native phonemes.School of Social Sciences, Brunel Universit

Out of the Mouth of Babes: Lessons from Research on Human Infants

Marine mammal behavior and cognition researchers often face a number of challenges, including the research subjects’ lack of interest and verbal abilities, as well as choosing a paradigm with appropriate stimuli for the subjects’ perceptual and cognitive abilities. Researchers who work with human infants often encounter similar challenges when studying infant cognition and have developed strategies to overcome these challenges, including using stimuli that capture the infants’ attention, determining what tasks are age-appropriate, and using conditioned responses to test discrimination abilities. This paper encourages marine mammal researchers to learn from the research paradigms and techniques used in human infant research and alter them appropriately for the intended study subjects. The conditioned head-turn response, Violation-of-Expectation paradigm, and the help/hinder paradigm have all been used in infant cognition research and show great promise for furthering the current understanding of marine mammal behavior and cognition. In addition, studying a subject’s spontaneous behavior can provide valuable insight in areas such as problem solving skills, creativity, and individual differences. Care must be taken to adapt the paradigms and use stimuli to fit each species’ perceptual abilities. For example, avoiding a task that requires color discrimination for species that do not possess color vision or using stimuli that fall within a particular species’ hearing range are necessary steps in designing an ecologically valid and informative study. Adapting paradigms previously used with human infants can help expand the current understanding of marine mammal communication, cognitive abilities, and social behavior