Individual Differences in Categorization Gradience As Predicted by Online Processing of Phonetic Cues During Spoken Word Recognition: Evidence From Eye Movements

Individual variability in subcortical neural encoding shapes phonetic cue weighting

Recent studies have revealed great individual variability in cue weighting, and such variation is shown to be systematic across individuals and linked to differences in some general cognitive mechanism. The present study investigated the role of subcortical encoding as a source of individual variability in cue weighting by focusing on English listeners' frequency following responses to the tense/lax English vowel contrast varying in spectral and durational cues. Listeners differed in early auditory encoding with some encoding the spectral cue more veridically than the durational one, while others exhibited the reverse pattern. These differences in cue encoding further correlate with behavioral variability in cue weighting, suggesting that specificity in cue encoding across individuals modulates how cues are weighted in downstream processes.

The myth of categorical perception

Categorical perception (CP) is likely the single finding from speech perception with the biggest impact on cognitive science. However, within speech perception, it is widely known to be an artifact of task demands. CP is empirically defined as a relationship between phoneme identification and discrimination. As discrimination tasks do not appear to require categorization, this was thought to support the claim that listeners perceive speech solely in terms of linguistic categories. However, 50 years of work using discrimination tasks, priming, the visual world paradigm, and event related potentials has rejected the strongest forms of CP and provided little strong evidence for any form of it. This paper reviews the origins and impact of this scientific meme and the work challenging it. It discusses work showing that the encoding of auditory input is largely continuous, not categorical, and describes the modern theoretical synthesis in which listeners preserve fine-grained detail to enable more flexible processing. This synthesis is fundamentally inconsistent with CP. This leads to a different understanding of how to use and interpret the most basic paradigms in speech perception-phoneme identification along a continuum-and has implications for understanding language and hearing disorders, development, and multilingualism.

Don't force it! Gradient speech categorization calls for continuous categorization tasks

Research on speech categorization and phoneme recognition has relied heavily on tasks in which participants listen to stimuli from a speech continuum and are asked to either classify each stimulus (identification) or discriminate between them (discrimination). Such tasks rest on assumptions about how perception maps onto discrete responses that have not been thoroughly investigated. Here, we identify critical challenges in the link between these tasks and theories of speech categorization. In particular, we show that patterns that have traditionally been linked to categorical perception could arise despite continuous underlying perception and that patterns that run counter to categorical perception could arise despite underlying categorical perception. We describe an alternative measure of speech perception using a visual analog scale that better differentiates between processes at play in speech categorization, and we review some recent findings that show how this task can be used to better inform our theories.

Perceptual Cue Weighting Is Influenced by the Listener's Gender and Subjective Evaluations of the Speaker: The Case of English Stop Voicing

Speech categories are defined by multiple acoustic dimensions and their boundaries are generally fuzzy and ambiguous in part because listeners often give differential weighting to these cue dimensions during phonetic categorization. This study explored how a listener's perception of a speaker's socio-indexical and personality characteristics influences the listener's perceptual cue weighting. In a matched-guise study, three groups of listeners classified a series of gender-neutral /b/-/p/ continua that vary in VOT and F0 at the onset of the following vowel. Listeners were assigned to one of three prompt conditions (i.e., a visually male talker, a visually female talker, or audio-only) and rated the talker in terms of vocal (and facial, in the visual prompt conditions) gender prototypicality, attractiveness, friendliness, confidence, trustworthiness, and gayness. Male listeners and listeners who saw a male face showed less reliance on VOT compared to listeners in the other conditions. Listeners' visual evaluation of the talker also affected their weighting of VOT and onset F0 cues, although the effects of facial impressions differ depending on the gender of the listener. The results demonstrate that individual differences in perceptual cue weighting are modulated by the listener's gender and his/her subjective evaluation of the talker. These findings lend support for exemplar-based models of speech perception and production where socio-indexical features are encoded as a part of the episodic traces in the listeners' mental lexicon. This study also shed light on the relationship between individual variation in cue weighting and community-level sound change by demonstrating that VOT and onset F0 co-variation in North American English has acquired a certain degree of socio-indexical significance.

Idiosyncratic use of bottom-up and top-down information leads to differences in speech perception flexibility: Converging evidence from ERPs and eye-tracking

Listeners generally categorize speech sounds in a gradient manner. However, recent work, using a visual analogue scaling (VAS) task, suggests that some listeners show more categorical performance, leading to less flexible cue integration and poorer recovery from misperceptions (Kapnoula et al., 2017, 2021). We asked how individual differences in speech gradiency can be reconciled with the well-established gradiency in the modal listener, showing how VAS performance relates to both Visual World Paradigm and EEG measures of gradiency. We also investigated three potential sources of these individual differences: inhibitory control; lexical inhibition; and early cue encoding. We used the N1 ERP component to track pre-categorical encoding of Voice Onset Time (VOT). The N1 linearly tracked VOT, reflecting a fundamentally gradient speech perception; however, for less gradient listeners, this linearity was disrupted near the boundary. Thus, while all listeners are gradient, they may show idiosyncratic encoding of specific cues, affecting downstream processing.

The Problematic Concept of Native Speaker in Psycholinguistics: Replacing Vague and Harmful Terminology With Inclusive and Accurate Measures

Though the term NATIVE SPEAKER/SIGNER is frequently used in language research, it is inconsistently conceptualized. Factors, such as age, order, and context of acquisition, in addition to social/cultural identity, are often differentially conflated. While the ambiguity and harmful consequences of the term NATIVE SPEAKER have been problematized across disciplines, much of this literature attempts to repurpose the term in order to include and/or exclude certain populations. This paper problematizes NATIVE SPEAKER within psycholinguistics, arguing that the term is both unhelpful to rigorous theory construction and harmful to marginalized populations by reproducing normative assumptions about behavior, experience, and identity. We propose that language researchers avoid NATIVE SPEAKER altogether, and we suggest alternate ways of characterizing language experience/use. The vagueness of NATIVE SPEAKER can create problems in research design (e.g., through systematically excluding certain populations), recruitment (as participants' definitions might diverge from researchers'), and analysis (by distilling continuous factors into under-specified binary categories). This can result in barriers to cross-study comparison, which is particularly concerning for theory construction and replicability. From a research ethics perspective, it matters how participants are characterized and included: Excluding participants based on binary/essentialist conceptualizations of nativeness upholds deficit perspectives toward multilingualism and non-hegemonic modes of language acquisition. Finally, by implicitly assuming the existence of a critical period, NATIVE SPEAKER brings with it theoretical baggage which not all researchers may want to carry. Given the issues above and how 'nativeness' is racialized (particularly in European and North American contexts), we ask that researchers consider carefully whether exclusion of marginalized/minoritized populations is necessary or justified-particularly when NATIVE SPEAKER is used only as a way to achieve linguistic homogeneity. Instead, we urge psycholinguists to explicitly state the specific axes traditionally implied by NATIVENESS that they wish to target. We outline several of these (e.g., order of acquisition, allegiance, and comfort with providing intuitions) and give examples of how to recruit and describe participants while eschewing NATIVE SPEAKER. Shifting away from harmful conventions, such as NATIVE SPEAKER, will not only improve research design and analysis, but also is one way we can co-create a more just and inclusive field.