Formant Measurements Research Articles

Testing the effect of speech separation on vowel formant estimates

Abstract While recent advances in sociophonetic data processing have made it possible to analyze large datasets and audio not originally intended for linguistic analysis, overlapping speech in recordings with multiple speakers continues to be an issue that results in lost data. We evaluate whether current source separation models produce audio that is clean enough to produce reliable measurements for sociophonetic analysis. We compare formant estimates from a pair of pristine recordings and merged-and-separated versions of those same recordings using the Libri2mix, Whamr16K, and WSJ02mix source separation models. Based on auditory inspection of the separated files, visualization of vowel formant estimates, and statistical analysis, Libri2 performed best and WSJ02 was worst. While the mean formant measurements per vowel were usually small, differences for each observation were larger in unpredictable ways. We are cautiously optimistic about using these tools in sociophonetic analysis, so long as analysis is conducted on vowel means. We conclude with recommendations that researchers can implement when using source separation in sociophonetic research.

Investigating the acoustic fidelity of vowels across remote recording methods

Abstract Our study tests the acoustic fidelity of remote recordings, using a large variety of stimuli and recording environments. Remote recordings support crucial uses like reaching isolated populations and more speakers; however, it is important to be aware of any limitations therein. A 188-word list was constructed from each English consonant followed by each vowel. Words recorded by one male and one female speaker in a sound-attenuated booth were input for test recordings. Stimuli were played over an electronic speaker and recorded on six devices across five operating systems, four teleconferencing platforms, and two browsers, using internal and external microphones, a more extensive set than has been analyzed in prior research. Acoustic analysis investigates the impact of these recording configurations on fundamental frequency, loudness, and vowel formant measures. Across recording conditions, browser choice had less effect on the different vowel measures, while choice of hardware resulted in a greater number of significant differences and greater variability within and across conditions. Recording configuration effects were observed to exert different impacts across vowels and speakers, resulting in inconsistent perturbations. These results highlight the need for careful selection and detailed documentation of all recording configurations.

A descriptive study of vowels in Dialects of Pakistani English

The widespread use of English as a lingua franca has created many varieties of Global English. Pakistani English is an under-documented variety. As Pakistan is a multilingual country, it has been a difficult task for the linguists to document the dialects of Pakistani English and to determine how these dialects are influenced by regional languages (e.g. Pashto, Punjabi, Urdu etc.). Previous studies focused on Pakistani English of only a few locations (influenced by only a few regional languages). A broad-based study is required to document the phonetics of Pakistani English. The current study investigates two questions about the Pakistani English vowel system: how much variety there is, and whether the dialects of Pakistani English are influenced by regional languages. Speech data was collected from 208 undergrad students from thirteen cities representing thirteen regional languages of Pakistan (e.g. Lahore, Karachi, Peshawar etc.). Participants read thirty-two words expected to contain monophthongs in initial, medial and final position. Formant measurements are measured automatically in Praat. Preliminary analyses show variation in formant values of vowels in regional dialects; The results will allow for documentation of the vowel space of Pakistani English and will provide a broad representation of Pakistani English dialects.

Lifespan anatomic and vowel acoustic studies confirm prepubertal sexual dimorphism of the human vocal tract and absence of lengthening in aging

To study anatomic-acoustic relations across the lifespan, anatomic studies of the developing vocal tract (VT) using medical imaging studies were related to vowel acoustic space as synthesized from published data. However, the aggregate acoustic data highlighted the need to acquire sex-specific vowel acoustic data across the lifespan using controlled methodology for data collection and analysis; also, to acquire measurements of the higher formants. Lifespan anatomic and acoustic (4-to-92 years) data helped resolve two questions. First, anatomic studies revealed significant prepubertal sex differences in the oral region of the VT (3-to-7 years) that are masked by growth rate differences between males and females. Three-dimensional anatomic findings also revealed prepubertal sexual dimorphism in select regions of the mandible and pharynx. Second, anatomic findings confirmed that VT length does not increase with aging. Acoustic studies similarly confirmed sex differences in fundamental frequency emerging at age 7; and the presence of significant prepubertal sexual dimorphism of the higher formant frequencies (F3-F4) at the earliest age studied (4 years). Findings for adults showed significant age-related decreases in fundamental frequency in women only, and no changes in formant frequencies in either sex across several decades. The results underscore the importance of sex-specific and non-uniform growth of the VT structures. [NIDCD funding support R01DC006282.]

Acoustic cues in perception of reduced speech

In conversational speech, sounds undergo reduction and deletion, which challenges listeners to decode reduced forms using various cues. Previous research argues for the predominance of acoustic cues in a study of listeners’ perception of reduced speech such as “he’s” vs. “he was”, which can both be realized [ɨz]. Analyzing data from a previous perception experiment (Warner et al., Brain Sci., 2022), this study explores what types of acoustic cues listeners use to process reduced speech. Ambiguous [ɨz] with low second formant (F2) or long duration might be perceived as past due to an additional consonant (/w/) and potential contractions (low F2 as a cue to /w/). Low F2 is expected to result in smaller Bark F2-F1 and larger Bark F3-F2. Current study tests whether the stimuli show acoustic differences in the predicted direction and whether the formant and duration measures correlate with listeners’ identification of tense. It was found that there are no significant acoustic differences between past and present forms due to reduction, but that listeners significantly associated smaller Bark F2-F1 with past tense in singular verbs and longer duration with past tense in plural verbs. This confirms listeners' use of the predicted acoustic cues in perceiving reduced speech.

A practical guide to calculating vocal tract length and scale-invariant formant patterns

Formants (vocal tract resonances) are increasingly analyzed not only by phoneticians in speech but also by behavioral scientists studying diverse phenomena such as acoustic size exaggeration and articulatory abilities of non-human animals. This often involves estimating vocal tract length acoustically and producing scale-invariant representations of formant patterns. We present a theoretical framework and practical tools for carrying out this work, including open-source software solutions included in R packages soundgen and phonTools. Automatic formant measurement with linear predictive coding is error-prone, but formant_app provides an integrated environment for formant annotation and correction with visual and auditory feedback. Once measured, formants can be normalized using a single recording (intrinsic methods) or multiple recordings from the same individual (extrinsic methods). Intrinsic speaker normalization can be as simple as taking formant ratios and calculating the geometric mean as a measure of overall scale. The regression method implemented in the function estimateVTL calculates the apparent vocal tract length assuming a single-tube model, while its residuals provide a scale-invariant vowel space based on how far each formant deviates from equal spacing (the schwa function). Extrinsic speaker normalization provides more accurate estimates of speaker- and vowel-specific scale factors by pooling information across recordings with simple averaging or mixed models, which we illustrate with example datasets and R code. The take-home messages are to record several calls or vowels per individual, measure at least three or four formants, check formant measurements manually, treat uncertain values as missing, and use the statistical tools best suited to each modeling context.

Voice onset time and vowel formant measures in online testing and laboratory-based testing with(out) surgical face masks

Since the COVID-19 pandemic started, conducting experiments online is increasingly common, and face masks are often used in everyday life. It remains unclear whether phonetic detail in speech production is captured adequately when speech is recorded in internet-based experiments or in experiments conducted with face masks. We tested 55 Spanish–Basque–English trilinguals in picture naming tasks in three conditions: online, laboratory-based with surgical face masks, and laboratory-based without face masks (control). We measured plosive voice onset time (VOT) in each language, the formants and duration of English vowels /iː/ and /ɪ/, and the Spanish/Basque vowel space. Across conditions, there were differences between English and Spanish/Basque VOT and in formants and duration between English /iː/–/ɪ/; between conditions, small differences emerged. Relative to the control condition, the Spanish/Basque vowel space was larger in online testing and smaller in the face mask condition. We conclude that testing online or with face masks is suitable for investigating phonetic detail in within-participant designs although the precise measurements may differ from those in traditional laboratory-based research.

Acoustic characteristics of variation in vowels in Assamese

This study provides an overview of acoustic characteristics of the vowel system in three regional varieties of Assamese. Recordings were made of 24 speakers producing the vowels /i/, /e/, /ɛ/, /ɑ/, /u/, /ʊ/, /o/ and /ɔ/ from a wordlist of 128 tokens. The speakers came from three locations in Assam, India: namely Lower Assam, Upper Assam, and Guwahati, and were balanced for region, sex, age, and education background. Acoustic analysis was conducted in Praat. First, the formant settings for male and female speakers were adjusted accordingly: 5500 Hz for female speakers and 5000 Hz for male speakers, where the vowel onsets and offsets were identified perceptually in the waveform, coinciding with the spectrogram in Praat. First and second formants were measured at the midpoint of the vowels for each of the 24 talkers, for a total of 9216 formant measurements. Formant measurements were then plotted on an F1xF2 chart using R. Findings show that Upper Assamese speakers had a high /ʊ/ production, while Lower Assam speakers had a low /ʊ/ in the acoustic space, while within Guwahati, more educated speakers produced /ʊ/ that was higher compared to speakers with less education.

Identifying acoustic cues for dialect profiling: Policing in multilingual communities of India

A multilingual country such as India with numerous languages and dialects provides fertile grounds for evasive language crimes. From threat letters to ransom demands, the scope of crime is huge. The cases of illegal immigrants have only added to the fragility of international boundaries especially, during political upheavals. This leads to further vulnerability of society and also creates challenges for the police and law enforcement agencies towards timely intervention. The purpose of the study is to exhibit dialectal variation in Indian English by comparing two varieties. The current paper is based on the acoustic analysis of Indian English spoken by two distinct groups with different mother tongues. Ten native speakers of Hindi and Bangla were recorded in an anechoic chamber. A phonetically balanced passage was selected to be read. The analysis is based on Native Language Influence Detection (Perkins Grant, 2018) to derive acoustic phonetic correlates that can be used as significant identifying markers to distinguish Indian English speakers of Bangla and Hindi speech communities. The paper highlights that dialect profiling in the Indian context can be efficiently correlated with formant frequencies and Voice Onset Time for speech data. Acoustic analysis was done on PRAAT. PRAAT was used in this study because it has often been used by other similar studies to measure desired acoustic parameters simultaneously. Formant frequencies were measured at the midpoint of the vowels in the PRAAT using the LPC formant measurement algorithm. The normalization procedure was applied to the measured formant frequencies of vowels. The research affirms that acoustic analysis can provide verifiable cues for NLID. The framework can be used in the detection of native language influence in speech-centric criminal cases. The acoustic analysis shows that Indian English has subvarieties that could help in dialect profiling. The variation in Indian English vowel patterns could be due to the influence of the native language of the speakers.

Mechanical models as ground truth for vowel resonance analysis

It has long been established that LPC analysis results in formant estimates that are not accurate representations of the resonances; they are biased towards the nearest harmonic, and this bias worsens as F0 rises to 200 Hz or more. Manual measurement of formants with the reassigned spectrogram (RS) has been shown to be more accurate, but the ground truth is needed in order to test automatic measurement methods. Here, “vocal tract” models were 3D-printed to allow resonances to be excited replicably. Using the principle of acoustic reciprocity, source signals were played over an external loudspeaker, and the output filtered by the model was recorded via a microphone located in the model’s “glottis.” A white noise source signal was used to determine the resonances. Sawtooth and impulse train source signals (F0s 83–400 Hz) were filtered by the physical model and then analyzed with both LPC and RS. LPC formants were biased towards the nearest harmonic, resulting in errors from 10 Hz at low F0 to 250 at 300 Hz. RS errors ranged from 0 to 20 Hz and were not correlated with F0. These results indicate physical models are useful for creating known resonances for validating accuracy in our measurements.

Investigating the acoustic fidelity of remote recording methods

Our study tests the acoustic fidelity of remote recordings, using a large variety of stimuli and recording environments. With standard recording environments not available due to COVID-19, more studies investigate remote recordings for acoustic analyses [e.g., Guan and Li (2021); Freeman and De Decker (2021)]. High fidelity remote recordings also support crucial uses like reaching isolated populations and more speakers. A 188-word list was constructed from each English consonant followed by each vowel. Words recorded by a male and female speaker in a sound attenuated booth were input for test recordings. Stimuli were recorded on six devices across five operating systems, four tele-conferencing platforms, and three browsers, using internal and external microphones. Acoustic analysis investigates the impact of these recording configurations on features including pitch, relative intensity, vowel formant measures, spectral moments, spectral tilt, spectral rolloff, and Mel Frequency Cepstral Coefficients. Preliminary analyses found durational differences between original and test-recorded stimuli, posing challenges for automatic segmentation and alignment. Aperiodic noise was also introduced. We hypothesize further distortions in other measures. The findings from this study will allow us to identify acoustic measures which are robust across varied remote recording conditions and to highlight configurations least likely to introduce problematic artifacts.

Relationship Between Oropharyngeal Geometry and Vocal Parameters in Subjects With Parkinson's Disease

To verify whether the dimensions of different segments of the oropharyngeal cavity have different proportions between Parkinson's disease patients and vocally healthy subjects and investigate whether the measurements of these subjects' oropharyngeal geometry associate with their acoustic measurements of voice. Quantitative, descriptive, cross-sectional, and retrospective study with secondary data, approved by the Human Research Ethics Committee under no. 4.325.029. We used vocal samples and data from the oropharyngeal geometry of 40 subjects - 20 with Parkinson's disease stages I to III and 20 who formed the control group, matched for sex and age. Each group had 10 males and 10 females, mean age of 61 years (±6.0). Formant (F1, F2, and F3) and cepstral measures of the sustained vowel /ε/ were extracted and arranged in the database to determine their values using Praat software. The data were descriptively analyzed, with statistics generated with R software. The proportion of oropharyngeal geometry measurements was arranged by mean values and coefficients of variation. Pearson's linear correlation test was applied to relate voice parameters to oropharyngeal geometry, considering P < 0.05, and linear regression test, to justify F2. The Parkinson's disease group showed a linear relationship between oral cavity length and F1 in males (P = 0.04) and between glottal area and F2 in females (P = 0.00); linear relationships were established according to age in both groups, and a regression model for F2 was estimated (R2 = 0.61). There was no difference between pathological and healthy voices; there was a difference in the proportional relationship of oropharyngeal geometry between the groups. The proportional relationship of oropharyngeal geometry differs between the Parkinson's disease group and the control group, as well as the relationship between oropharyngeal geometry and formant and cepstral values of voice according to the subjects' sex and age.

Acoustic characteristics of fricatives, amplitude of formants and clarity of speech produced without and with a medical mask.

BackgroundPrevious research has found that high‐frequency energy of speech signals decreased while wearing face masks. However, no study has examined the specific spectral characteristics of fricative consonants and vowels and the perception of clarity of speech in mask wearing.AimsTo investigate acoustic–phonetic characteristics of fricative consonants and vowels and auditory perceptual rating of clarity of speech produced with and without wearing a face mask.Methods & ProceduresA total of 16 healthcare workers read the Rainbow Passage using modal phonation in three conditions: without a face mask, with a standard surgical mask and with a KN95 mask (China GB2626‐2006, a medical respirator with higher barrier level than the standard surgical mask). Speech samples were acoustically analysed for root mean square (RMS) amplitude (A RMS) and spectral moments of four fricatives /f/, /s/, /ʃ/ and /z/; and amplitude of the first three formants (A1, A2 and A3) measured from the reading passage and extracted vowels. Auditory perception of speech clarity was performed. Data were compared across mask and non‐mask conditions using linear mixed models.Outcomes & ResultsThe A RMS of all included fricatives was significantly lower in surgical mask and KN95 mask compared with non‐mask condition. Centre of gravity of /f/ decreased in both surgical and KN95 mask while other spectral moments did not show systematic significant linear trends across mask conditions. None of the formant amplitude measures was statistically different across conditions. Speech clarity was significantly poorer in both surgical and KN95 mask conditions.Conclusions & ImplicationsSpeech produced while wearing either a surgical mask or KN95 mask was associated with decreased fricative amplitude and poorer speech clarity.WHAT THIS PAPER ADDSWhat is already known on the subject Previous studies have shown that the overall spectral levels in high frequency ranges and intelligibility are decreased for speech produced with a face mask. It is unclear how different types of the speech signals that is, fricatives and vowels are presented in speech produced with wearing either a medical surgical or KN95 mask. It is also unclear whether ratings of speech clarity are similar for speech produced with these face masks. What this paper adds to existing knowledge Speech data collected using a real‐world, clinical and non‐laboratory‐controlled settings showed differences in the amplitude of fricatives and speech clarity ratings between non‐mask and mask‐wearing conditions. Formant amplitude did not show significant differences in mask‐wearing conditions compared with non‐mask. What are the potential or actual clinical implications of this work? Wearing a surgical mask or a KN95 mask had different effects on consonants and vowels. It appeared from the findings in this study that these masks only affected fricative consonants and did not affect vowel production. The poorer speech clarity in these mask‐wearing conditions has important implications for speech perception in communication between clinical staff and between medical officers and patients in clinics, and between people in everyday situations. The impact of these masks on speech perception may be more pronounced in people with hearing impairment and communication disorders. In voice evaluation and/or therapy sessions, the effects of wearing a medical mask can occur bidirectionally for both the clinician and the patient. The patient may find it more challenging to understand the speech conveyed by the clinician while the clinician may not perceptually assess patient's speech and voice accurately. Given the significant correlation between clarity ratings and fricative amplitude, improving fricative signals would be useful to improve speech clarity while wearing these medical face masks.

Regional Relocation and Phonetic Dialect Markers

&#x0D; This paper tracks phonological change in the (ING) morpheme in two YouTube personalities over time. Both participants relocated to a different dialect region than their hometowns over the course of their careers, motivating the hypothesis of this paper: geographic relocation is a catalyst for adult accent change. With a longitudinal study method, I selected audio clips from different periods in each YouTuber’s life and collected formant measurements of the targeted words. Based on a Pearson’s correlation analysis and hypothesis testing models, the participants showed statistically significant progression in their speech over time. Additionally, the speakers exhibited audible shifts most likely as an effect of aging. It is inconclusive whether this study’s observations are influenced by the difference in dialect or societal pressures of the relocated locations without further research in the other variables of each regional dialect.

Maintenance of phonetic and phonological distance in the English and Korean back vowel contours of heritage bilinguals

Bilingualism research demonstrates that the potential merger of vowel categories across a speaker’s two languages is affected by the age of acquisition of the second language. For heritage bilinguals, however, there is no clear L1 and L2, since they acquire their heritage language in early childhood, but become dominant in the mainstream language of society as adults. Heritage bilinguals may nevertheless will acquire distinct vowel systems in their two languages, rather than a merged system. In this study, the back vowels of California English and Seoul Korean, two varieties that are spoken by bilingual second-generation Korean Americans in California, were collected in natural speech. Formant measurements were analyzed using linear mixed effects regression modeling and generalized additive mixed modeling to see whether the vowels of each language were similar or different in their formant contours. As predicted, the bilinguals maintained distance between the vowels of both languages across their durations, and the phonological effects of coarticulation were found to be stronger in English than in Korean. The differences are attributed to “multicompetence” in heritage bilinguals’ phonology (Cook, 2020), or the interrelationship of multiple systems that exist and interact in the bilingual mind without merging completely, in opposition to models that frame heritage bilingualism as inherently imbalanced in favor of the dominant language.

Does F3-F2 distance predict transcriptions of preschoolers’ /r/ productions?

Children learning to speak American English are highly variable in early productions of /r/, often producing [w] as an error. One acoustic indicator of /r/ goodness is the difference between the second (F2) and third formant (F3), with smaller F3-F2 differences being associated with a ‘better’ /r/. This study analyzed the effectiveness of this acoustic measure in characterizing children's productions of the /r/-/w/ contrast on acoustic information extracted automatically from a large data set, where hand measurements are infeasible. LPC formant measures were extracted using Praat from productions of /r/- and /w/-initial words (n = 19) by 3.5- to 4.5-year old monolingual preschoolers (n = 136). These were rated by naive adult listeners (n = 142) on a visual-analog scale of phoneme goodness, and were narrowly transcribed by trained researchers into four categories: [r], [w], and two intermediate categories. Data visualization showed a weak relationship between F3-F2 measures, transcriptions, and ratings. Generalized linear mixed effects regressions found that the F3-F2 difference only modestly predicted transcription categories (R2 = 0.39) and listener ratings (R2 = 0.34). Hence, a description of preschoolers’ mastery of the /r/-/w/ contrast based on automatic analyses should include additional measures beyond the F3-F2 measures.

A Gaussian-mixture-model-based approach to classifying vowel place in speech signals

In recent years, speech recognition systems have dramatically improved in performance through the development of general machine learning techniques. However, it is not always straightforward to interpret the mapping from the signal to the detected category. In the present work, we focus on the goal of transparency, specifying the processing steps that lead to robust modeling of vowel place using simple, descriptive Gaussian mixture models. We present a pre-processing and detection framework for vowel place, involving formant measurements, smoothing, and the GMM. This research aims to classify vowel place as a part of a larger speech recognition system. Vowel place was divided into 8 groups based on tongue advancement [Front/Back], height [High/Mid/Low], and root [Atr/Ctr]. Studies were performed using ∼700 vowel-consonant-vowel utterances from the LAFF VCV database.

Beyond midpoints: Vowel dynamics of the low-back-merger shift

The Low-Back-Merger Shift—the lowering/retraction of /æ/, /ɛ/, and /ɪ/—is a now-well-studied phenomenon of American English. However, it is primarily described by the relative position of the vowels using single-point acoustic measurements. This study seeks to fill an apparent gap in the literature by describing change in these vowels’ formant trajectories. Data come from 45 h of sociolinguistic interviews conducted in southwest Washington (ages 18–86). A generalized additive mixed-effect model (Wood, 2007) fit to pairs of formant measurements extracted at 11 timepoints per vowel token confirms that the lax vowels are shifting and uncovers changes in their formant dynamics in apparent time. For instance, the bulk of /æ/ lowering and retraction is a result of its onset shifting rather than the offset. For all three vowels, the amount of change in F2 over the vowel’s duration decreased over time, resulting in qualitative changes in the shape of the vowel trajectory (when visualized in the F1-F2 space). Furthermore, though the men lagged behind the women in relative position in the vowel space, both genders changed the shape of their trajectories at the same time. This study shows that there is more to vowel shifts than changes in their midpoints.

Fundamental frequency feature warping for frequency normalization and data augmentation in child automatic speech recognition

Effective child automatic speech recognition (ASR) systems have become increasingly important due to the growing use of interactive technology. Due to the lack of publicly available child speech databases, young child ASR systems often rely on older child or adult speech for training data. However, there is a large acoustic mismatch between child and adult speech. This study proposes a novel fundamental frequency (fo)-based frequency warping technique for both frequency normalization and data augmentation to combat this acoustic mismatch and address the lack of available child speech training data. The technique is inspired by the tonotopic distances between formants and fo, developed to model human vowel perception. The tonotopic distances are reformulated as a linear relationship between fo and vowel formants on the Mel scale. This reformulation is verified using fo and formant measurements from child utterances. The relationship is further generalized such that the frequency warping technique only relies on two parameters. The LibriSpeech ASR corpus is used for training, and both the OGI Kids’ Speech and CMU Kids Corpora are used for both training and testing. A single word ASR experiment and a continuous read speech ASR experiment are performed to evaluate the fo-based frequency normalization and data augmentation techniques. In the single word experiment, the system using fo-based frequency normalization significantly improved over the baseline system with no normalization, with a relative improvement of up to 22.3%, when the mismatch between training and testing data was large. In the continuous speech experiment, the combination of fo-based frequency normalization and data augmentation resulted in a relative improvement of 19.3% over the baseline. Additionally, in all experiments, the fo-based techniques outperformed other techniques such as vocal tract length normalization (VTLN) or vocal tract length perturbation (VTLP). Results were validated using Gaussian mixture model (GMM), deep neural network (DNN), and bidirectional long–short term memory (BLSTM) acoustic models.

Leveraging the temporal dynamics of anticipatory vowel-to-vowel coarticulation in linguistic prediction: A statistical modeling approach

Previous research has shown that coarticulatory information in the signal orients listeners in spoken word recognition, and that articulatory and perceptual dynamics closely parallel one another. The current study uses statistical classification to test the power of time-varying anticipatory coarticulatory information present in the acoustic signal for predicting upcoming sounds in the speech stream. Bayesian mixed-effects multinomial logistic regression models were trained on several different representations of spectral variation present in V1 in order to predict the identity of V2 in naturally coarticulated transconsonantal V1…V2 sequences. Models trained on simple measures of spectral variation (e.g. formant measures taken at V1 midpoint) were compared with models trained on more sophisticated time-varying representations (e.g. the estimated coefficients of polynomial curves fit to whole formant trajectories of V1). Accuracy in predicting V2 was greater when models were trained on dynamic representations of spectral variation in V1, and those trained on quadratic and cubic polynomial representations achieved the greatest accuracy, with more than 15 percentage points in correct classification over using midpoint formant frequencies alone. The results demonstrate that spectral representations with high temporal resolution capture more disambiguating anticipatory information available in the signal than representations with lower temporal resolution.