Reversible inactivation of ferret auditory cortex impairs spatial and non-spatial hearing

A central question in auditory neuroscience is how far brain regions are functionally specialized for processing specific sound features such as sound location and identity. In auditory cortex, correlations between neural activity and sounds support both the specialization of distinct cortical subfields, and encoding of multiple sound features within individual cortical areas. However, few studies have tested the causal contribution of auditory cortex to hearing in multiple contexts. Here we tested the role of auditory cortex in both spatial and non-spatial hearing. We reversibly inactivated the border between middle and posterior ectosylvian gyrus using cooling (n = 2) or optogenetics (n=1) as ferrets discriminated vowel sounds in clean and noisy conditions. Animals with cooling loops were then retrained to localize noise-bursts from multiple locations and retested with cooling. In both ferrets, cooling impaired sound localization and vowel discrimination in noise, but not discrimination in clean conditions. We also tested the effects of cooling on vowel discrimination in noise when vowel and noise were colocated or spatially separated. Here, cooling exaggerated deficits discriminating vowels with colocalized noise, resulting in increased performance benefits from spatial separation of sounds and thus stronger spatial release from masking during cortical inactivation. Together our results show that auditory cortex contributes to both spatial and non-spatial hearing, consistent with single unit recordings in the same brain region. The deficits we observed did not reflect general impairments in hearing, but rather account for performance in more realistic behaviors that require use of information about both sound location and identity.

Asymmetries in Accessing Vowel Representations Are Driven by Phonological and Acoustic Properties: Neural and Behavioral Evidence From Natural German Minimal Pairs

In vowel discrimination, commonly found discrimination patterns are directional asymmetries where discrimination is faster (or easier) if differing vowels are presented in a certain sequence compared to the reversed sequence. Different models of speech sound processing try to account for these asymmetries based on either phonetic or phonological properties. In this study, we tested and compared two of those often-discussed models, namely the Featurally Underspecified Lexicon (FUL) model (Lahiri and Reetz, 2002) and the Natural Referent Vowel (NRV) framework (Polka and Bohn, 2011). While most studies presented isolated vowels, we investigated a large stimulus set of German vowels in a more naturalistic setting within minimal pairs. We conducted an mismatch negativity (MMN) study in a passive and a reaction time study in an active oddball paradigm. In both data sets, we found directional asymmetries that can be explained by either phonological or phonetic theories. While behaviorally, the vowel discrimination was based on phonological properties, both tested models failed to explain the found neural patterns comprehensively. Therefore, we additionally examined the influence of a variety of articulatory, acoustical, and lexical factors (e.g., formant structure, intensity, duration, and frequency of occurrence) but also the influence of factors beyond the well-known (perceived loudness of vowels, degree of openness) in depth via multiple regression analyses. The analyses revealed that the perceptual factor of perceived loudness has a greater impact than considered in the literature and should be taken stronger into consideration when analyzing preattentive natural vowel processing.

Perceiving isn't believing: Divergence in levels of sociolinguistic awareness

The influence of social knowledge on speech perception is a question of interest to a range of disciplines of language research. This study combines experimental and qualitative approaches to investigate whether the various methodological and disciplinary threads of research on this topic are truly investigating the same phenomenon to provide converging evidence in our understanding of social listening. This study investigates listeners’ perceptions of Spanish and Quechua speakers speaking Spanish in the context of a contact zone between these two languages and their speakers in central Bolivia. The results of a pair of matched-guise vowel discrimination tasks and subsequent interviews demonstrate that what people perceive, as measured by experimental tasks, is not necessarily what they believe they hear, as reported in narrative responses to interview prompts. Multiple methodological approaches must be employed in order to fully understand the way that we perceive language at diverging levels of sociolinguistic awareness. (Perception, sociophonetics, sociolinguistics, awareness, Andean Spanish)

The role of input in native Spanish Late learners’ production and perception of English phonetic segments

This study evaluated the effect of input variation on the production and perception of English phonetic segments by native Spanish adults who had immigrated to the United States after the age of 16 years. The native Spanish (NS) participants were assigned to three groups of 20 each according to years of English input (years of U.S. residence multiplied by percent English use outside the home). Experiment 1 assessed the perceived relation between English and Spanish vowels. It yielded similar results for the NS groups designated “Low input” (M = 0.2 years of input), “Mid” (M = 1.2 years) and “High” (M = 3.0 years). Experiments 2–4 examined English vowel discrimination, vowel production and consonant discrimination. Apart from a modest improvement in vowel discrimination, these experiments showed little improvement as years of English input increased. One possible explanation for the essentially null finding of this study is that input matters little or not at all when an L2 is learned naturalistically following the closure of a critical period. Another possibility is that adequate native speaker input is crucial for L2 speech learning but the input differences evaluated here were insufficient to yield measurable improvements in performance. We conclude the article by illustrating a new technique that might be used to choose between these competing explanations.