Crosslinguistic Influence in the Discrimination of Korean Stop Contrast by Heritage Speakers and Second Language Learners

The present study examines the extent of crosslinguistic influence from English as a dominant language in the perception of the Korean lenis–aspirated contrast among Korean heritage speakers in the United States (N = 20) and English-speaking learners of Korean as a second language (N = 20), as compared to native speakers of Korean immersed in the first language environment (N = 20), by using an AX discrimination task. In addition, we sought to determine whether significant dependencies could be observed between participants’ linguistic background and experiences and their perceptual accuracy in the discrimination task. Results of a mixed-effects logistic regression model demonstrated that heritage speakers outperformed second language learners with 85% vs. 63% accurate discrimination, while no significant difference was detected between heritage speakers and first language-immersed native speakers (85% vs. 88% correct). Furthermore, higher verbal fluency was significantly predictive of greater perceptual accuracy for the heritage speakers. The results are compatible with the interpretation that the influence of English on the discrimination of the Korean laryngeal contrast was stronger for second language learners of Korean than for heritage speakers, while heritage speakers were not apparently affected by dominance in English in their discrimination of Korean lenis and aspirated stops.

The off-line effect of affective touch on multisensory integration and tactile perceptual accuracy during the somatic signal detection task

Affective touch refers to the emotional and motivational facets of tactile sensation and has been linked to the activation of a specialised system of mechanosensory afferents (the CT system), that respond optimally to slow caress-like touch. Affective touch has been shown to play an important role in the building of the bodily self: the multisensory integrated global awareness of one’s own body. Here we investigated the effects of affective touch on subsequent tactile awareness and multisensory integration using the Somatic Signal Detection Task (SSDT). During the SSDT, participants were required to detect near-threshold tactile stimulation on their cheek, in the presence/absence of a concomitant light. Participants repeated the SSDT twice, before and after receiving a touch manipulation. Participants were divided into two groups: one received affective touch (CT optimal; n = 32), and the second received non-affective touch (non-CT optimal; n = 34). Levels of arousal (skin conductance levels, SCLs) and mood changes after the touch manipulation were also measured. Affective touch led to an increase in tactile accuracy, as indicated by less false reports of touch and a trend towards higher tactile sensitivity during the subsequent SSDT. Conversely, non-affective touch was found to induce a partial decrease in the correct detection of touch possibly due to a desensitization of skin mechanoreceptors. Both affective and non-affective touch induced a more positive mood and higher SCLs in participants. The increase in SCLs was greater after affective touch. We conclude that receiving affective touch enhances the sense of bodily self therefore increasing perceptual accuracy and awareness. Higher SCLs are suggested to be a possible mediator linking affective touch to a greater tactile accuracy. Clinical implications are discussed.

Developmental differences in perceptual anticipation underlie different sensitivities to coarticulatory dynamics

Anticipatory coarticulation is an indispensable feature of speech dynamics contributing to spoken language fluency. Research has shown that children speak with greater degrees of vowel anticipatory coarticulation than adults – that is, greater vocalic influence on previous segments. The present study examined how developmental differences in anticipatory coarticulation transfer to the perceptual domain. Using a gating paradigm, we tested 29 seven-year-olds and 93 German adult listeners with sequences produced by child and adult speakers, hence corresponding to low versus high vocalic anticipatory coarticulation degrees. First, children predicted vowel targets less successfully than adults. Second, greater perceptual accuracy was found for low compared to highly coarticulated speech. We propose that variations in coarticulation degrees reflect perceptually important differences in information dynamics and that listeners are more sensitive to fast changes in information than to a large amount of vocalic information spread across long segmental spans.

Tapping Force Encodes Metrical Aspects of Rhythm

Humans possess the ability to extract highly organized perceptual structures from sequences of temporal stimuli. For instance, we can organize specific rhythmical patterns into hierarchical, or metrical, systems. Despite the evidence of a fundamental influence of the motor system in achieving this skill, few studies have attempted to investigate the organization of our motor representation of rhythm. To this aim, we studied—in musicians and non-musicians—the ability to perceive and reproduce different rhythms. In a first experiment participants performed a temporal order-judgment task, for rhythmical sequences presented via auditory or tactile modality. In a second experiment, they were asked to reproduce the same rhythmic sequences, while their tapping force and timing were recorded. We demonstrate that tapping force encodes the metrical aspect of the rhythm, and the strength of the coding correlates with the individual’s perceptual accuracy. We suggest that the similarity between perception and tapping-force organization indicates a common representation of rhythm, shared between the perceptual and motor systems.

Locus coeruleus activity improves cochlear implant performance

Cochlear implants are neuroprosthetic devices that can provide hearing to deaf patients1. Despite significant benefits offered by cochlear implants, there are highly variable outcomes in how quickly hearing is restored and perceptual accuracy after months or years of use2,3. Cochlear implant use is believed to require neuroplasticity within the central auditory system, and differential engagement of neuroplastic mechanisms might contribute to outcome variability4-7. Despite extensive studies on how cochlear implants activate the auditory system4,8-12, our understanding of cochlear implant-related neuroplasticity remains limited. One potent factor enabling plasticity is the neuromodulator norepinephrine from the brainstem locus coeruleus. Here we examined behavioral responses and neural activity in locus coeruleus and auditory cortex of deafened rats fitted with multi-channel cochlear implants. Animals were trained on a reward-based auditory task, with considerable individual differences of learning rates and maximum performance. Photometry from locus coeruleus predicted when implanted subjects would begin responding to sounds and longer-term perceptual accuracy, which were augmented by optogenetic locus coeruleus stimulation. Auditory cortical responses to cochlear implant stimulation reflected behavioral performance, with enhanced responses to rewarded stimuli and decreased distinction between unrewarded stimuli. Adequate engagement of central neuromodulatory systems is thus a potential clinically-relevant target for optimizing neuroprosthetic device use.

Locus coeruleus activity improves cochlear implant performance

Cochlear implants are neuroprosthetic devices that can provide hearing to deaf patients1. Despite significant benefits offered by cochlear implants, there are highly variable outcomes in how quickly hearing is restored and perceptual accuracy after months or years of use2,3. Cochlear implant use is believed to require neuroplasticity within the central auditory system, and differential engagement of neuroplastic mechanisms might contribute to outcome variability4-7. Despite extensive studies on how cochlear implants activate the auditory system4,8-12, our understanding of cochlear implant-related neuroplasticity remains limited. One potent factor enabling plasticity is the neuromodulator norepinephrine from the brainstem locus coeruleus. Here we examined behavioral responses and neural activity in locus coeruleus and auditory cortex of deafened rats fitted with multi-channel cochlear implants. Animals were trained on a reward-based auditory task, with considerable individual differences of learning rates and maximum performance. Photometry from locus coeruleus predicted when implanted subjects would begin responding to sounds and longer-term perceptual accuracy, which were augmented by optogenetic locus coeruleus stimulation. Auditory cortical responses to cochlear implant stimulation reflected behavioral performance, with enhanced responses to rewarded stimuli and decreased distinction between unrewarded stimuli. Adequate engagement of central neuromodulatory systems is thus a potential clinically-relevant target for optimizing neuroprosthetic device use.

Neural indicators of human gut feelings

Understanding the neural processes that govern the human gut-brain connection has been challenging due to the inaccessibility of the body’s interior. In this study, we aimed to identify neural responses to gastrointestinal sensation (i.e., the neural basis of ‘gut feelings’) in healthy humans using a minimally invasive mechanosensory probe. Combining electroencephalography and electrogastrography with signal detection theory measures, we quantified brain, stomach, and perceptual (button-press) responses following the ingestion of a vibrating capsule. The relationship between vibration strength and perceptual sensitivity was evaluated using two stimulation conditions (normal and enhanced). Most individuals successfully perceived capsule stimulation in both conditions, as evidenced by above chance accuracy scores. Perceptual accuracy improved significantly during the enhanced relative to normal stimulation, which was associated with faster reaction time and reduced reaction time variability. Stomach stimulation induced responses in a cluster of parieto-occipital leads near the midline via a late positive potential emerging 300-600 milliseconds after stimulation onset. Moreover, these ‘gastric evoked potentials’ showed dose-dependent increases in amplitude and were significantly correlated with perceptual accuracy. Our findings are consistent with recent neurogastric and optogenetic studies demonstrating a role for posteromedial cortices in gastrointestinal interoception and body dissociation and highlight a unique form of enterically-focused sensory monitoring within the human brain. Overall, these results show that this minimally invasive approach could serve as a useful tool for understanding gut-brain interactions in healthy and clinical populations.Significance StatementThe human brain continuously receives input from the stomach and intestines. These sensations are intuitively incorporated as ‘gut feelings’ into decision-making during daily life, yet we still know very little about how the brain processes gut signals. Here, we developed a minimally invasive approach to studying human gut feelings. In healthy individuals we found that an ingestible vibrating capsule produced reliable changes in both stomach sensation and gastric-evoked brain activity. These changes were significantly associated, in a dose-dependent fashion. We propose that this approach provides an opportunity to better understand the role of gut-related symptoms in human pathological conditions and might yield fundamental insights into how gut feelings are communicated to the human brain.

Alpha oscillations shape sensory representation and perceptual accuracy

Alpha oscillatory activity (8–14 Hz) is the dominant rhythm in the awake brain, and is thought to play an important role in setting the brain’s internal state. Previous work has associated states of decreased alpha-band oscillatory power with enhanced neural excitability. However, opinions differ on whether and how such excitability enhancement modulates sensory signals of interest versus noise differently, and what, if any, the consequences are for the subsequent perceptual process. To address these questions, we used a novel paradigm to experimentally manipulate human subjects’ decision criteria in a visual detection task. In different blocks, we primed subjects with clearly visible stimuli to introduce either a liberal or conservative detection criterion for subsequent ambiguous stimuli. While we observed substantial criterion shifts under different priming conditions, such criterion shifts were not reflected in pre-stimulus alpha-band changes. Rather, we found that lower pre-stimulus alpha-band power in early visual cortices improved perceptual accuracy, accompanied by enhanced information content decodable from the neural activity patterns. Additionally, we showed that alpha oscillatory phase in parietal and frontal regions immediately before stimulus presentation modulated accuracy. Together, our results suggest that alpha-band dynamics modulate sensory signals of interest more strongly compared to noise, here resulting in enhanced information coding and improved perceptual accuracy.Significance StatementThe internal state of our brain fluctuates, giving rise to variability in perception and action. Neural oscillations, most prominently in the alpha-band, have been suggested to play a role in setting this internal state. Here, we show that ongoing alpha-band activity in early visual regions predicts the quality of visual information decodable in neural activity patterns, and subsequently human observer’s accuracy in a visual detection task. Our results provide the heretofore first evidence that visual representation is modulated by ongoing alpha-band activity, and advance our understanding on how, when faced with unchanging external stimuli, internal neural fluctuations influence perception and behavior.

Vowel Modification (Aggiustamento) in Soprano Voices

Singers convey meaning via both text and music. As sopranos balance tone quality and diction, vowel intelligibility is often compromised at high pitches. This study examines how sopranos modify their vowels against an increasing fundamental, and in turn how such vowel modification affects vowel intelligibility. We examine the vowel modification process of three non-central vowels in Cantonese ([a], [ɛ] and [ɔ]) using the spectral centroid. Acoustic results suggest that overall vowel modification is conditioned by vowel height in mid-ranges and by vowel frontness in higher ranges. In a following perception task, listeners identified and discriminated vowels at pitches spanning an octave from A4 (nominally 440 Hz) to G♯5 (nominally 831 Hz). Results showed that perceptual accuracy rates of the three vowels’ match their acoustic patterns. The overall results suggest that vowels are not modified in a unified way in sopranos’ voices, implying that research on sopranos’ singing strategies should consider vocalic differences.