Are your random effects normal? A simulation study of methods for estimating whether subjects or items come from more than one population by examining the distribution of random effects in mixed-effects logistic regression.

With mixed-effects regression models becoming a mainstream tool for every psycholinguist, there has become an increasing need to understand them more fully. In the last decade, most work on mixed-effects models in psycholinguistics has focused on properly specifying the random-effects structure to minimize error in evaluating the statistical significance of fixed-effects predictors. The present study examines a potential misspecification of random effects that has not been discussed in psycholinguistics: violation of the single-subject-population assumption, in the context of logistic regression.

Acoustic correlates and listener ratings of function word reduction in child versus adult speech.

The present study investigated "the" reduction in phrase-medial Verb-the-Noun sequences elicited from 5-year-old children and young adults (18-22 yr). Several measures of reduction were calculated based on acoustic measurement of these sequences. Analyses on the measures indicated that the determiner vowel was reduced in both child and adult speech relative to content word vowels, but it was reduced less in child speech compared to adult speech.

Speaking rate normalization across different talkers in the perception of Japanese stop and vowel length contrasts.

Perception of duration is critically influenced by the speaking rate of the surrounding context. However, to what extent this speaking rate normalization is talker-specific is understudied. This experiment investigated whether Japanese listeners' perception of temporally contrastive phonemes is influenced by the speaking rate of the surrounding context, and more importantly, whether the effect of the contextual speaking rate persists across different talkers for different types of contrasts: a singleton-geminate stop contrast and short-long vowel contrast in Japanese.

Non-native English listeners' adaptation to native English speakers.

Listeners often have difficulty understanding unfamiliar speech (e.g., non-native speech), but they are able to adapt to or improve their ability to understand unfamiliar speech.

Just give it time: Differential effects of disruption and delay on perceptual learning.

Speech perception and production are critical skills when acquiring a new language. However, the nature of the relationship between these two processes is unclear, particularly for non-native speech sound contrasts. Although it has been assumed that perception and production are supportive, recent evidence has demonstrated that, under some circumstances, production can disrupt perceptual learning.

Perceptual tracking of distinct distributional regularities within a single voice.

The speech signal is inherently variable and listeners need to recalibrate when local, short-term distributions of acoustic dimensions deviate from long-term representation. The present experiment investigated the specificity of this perceptual adjustment, addressing whether the perceptual system is capable of tracking differing simultaneous short-term acoustic distributions of the same speech categories, conditioned by context. The results indicated that instead of aggregating over the contextual variation, listeners tracked separate distributional statistics for instances of speech categories experienced in different phonetic/lexical contexts, suggesting that perceptual learning is not only influenced by distributional statistics, but also by external factors such as contextual information.

A psycholinguistic method for measuring coarticulation in child and adult speech.

A perceiver's ability to accurately predict target sounds in a forward-gated AV speech task indexes the strength and scope of anticipatory coarticulation in adult speech (Redford et al., JASA, 144, 2447-2461, 2018). This suggests a perception-based method for studying coarticulation in populations who may poorly tolerate the more invasive or restrictive techniques used to measure speech movements directly.

Investigating a bias for cue preservation in loanword adaptation.

Loanword adaptation exhibits a bias favoring sound cue preservation, possibly due to a conservative caution against deleting cues of unsure expendability in a foreign language. This study tests whether listeners are biased to preserve an acoustically ambiguous sound cue in a nonce word framed as originating from a foreign language. Results show the opposite: Listeners are less likely to transcribe an ambiguous sound cue as a phonological segment when the word containing it is framed as a loanword.

The maintenance of clear speech in naturalistic conversations.

Clear speech is a style that speakers adopt when talking with listeners whom these speakers anticipate may have a problem understanding speech. This study examines whether native English speakers use clear speech in conversations with non-native English speakers when native speakers are not explicitly asked to use clear speech (i.e.

Expectations about the source of a speaker's accent affect accent adaptation.

When encountering speakers whose accents differ from the listener's own, listeners initially show a processing cost, but that cost can be attenuated after short term exposure. The extent to which processing foreign accents (L2-accents) and within-language accents (L1-accents) is similar is still an open question. This study considers whether listeners' expectations about the source of a speaker's accent-whether the speaker is purported to be an L1 or an L2 speaker-affect intelligibility.

Interactions between speech perception and production during learning of novel phonemic categories.

A successful language learner must be able to perceive and produce novel sounds in their second language. However, the relationship between learning in perception and production is unclear. Some studies show correlations between the two modalities; however, other studies have not shown such correlations.

Not just a function of function words: Distal speech rate influences perception of prosodically weak syllables.

Listeners resolve ambiguities in speech perception using multiple sources, including non-local or distal speech rate (i.e., the speech rate of material surrounding a particular region).

Dimensions of similarity in the mental lexicon.

During language production planning, multiple candidate representations are implicitly activated prior to articulation. Lexical representations that are phonologically related to the target (phonological neighbors) are known to influence phonetic properties of the target word. However, the question of which dimensions of phonological similarity contribute to such lexical-phonetic effects remains unanswered.

Speaking rate consistency in native and non-native speakers of English.

Non-native speech differs from native speech in multiple ways. Previous research has described segmental and suprasegmental differences between native and non-native speech in terms of group averages. For example, average speaking rate for non-natives is slower than for natives.

Interactions between distal speech rate, linguistic knowledge, and speech environment.

During lexical access, listeners use both signal-based and knowledge-based cues, and information from the linguistic context can affect the perception of acoustic speech information. Recent findings suggest that the various cues used in lexical access are implemented with flexibility and may be affected by information from the larger speech context. We conducted 2 experiments to examine effects of a signal-based cue (distal speech rate) and a knowledge-based cue (linguistic structure) on lexical perception.

Production constraints on learning novel onset phonotactics.

Three experiments addressed the hypothesis that production factors constrain phonotactic learning in adult English speakers, and that this constraint gives rise to a markedness effect on learning. In Experiment 1, an acoustic measure was used to assess consonant-consonant coarticulation in naturally produced nonwords, which were then used as stimuli in a phonotactic learning experiment. Results indicated that sonority-rising sequences were more coarticulated than -plateauing sequences, and that listeners learned novel-rising onsets more readily than novel-plateauing onsets.