No evidence for a benefit from masker harmonicity in the perception of speech in noise

When assessing the intelligibility of speech embedded in background noise, maskers with a harmonic spectral structure have been found to be much less detrimental to performance than noise-based interferers. While spectral "glimpsing"in between the resolved masker harmonics and reduced envelope modulations of harmonic maskers have been shown to contribute, this effect has primarily been attributed to the proposed ability of the auditory system to cancel harmonic maskers from the signal mixture. Here, speech intelligibility in the presence of harmonic and inharmonic maskers with similar spectral glimpsing opportunities and envelope modulation spectra was assessed to test the theory of harmonic cancellation. Speech reception thresholds obtained from normal-hearing listeners revealed no effect of masker harmonicity, neither for maskers with static nor dynamic pitch contours. The results show that harmonicity, or time-domain periodicity, as such, does not aid the segregation of speech and masker. Contrary to what might be assumed, this also implies that the saliency of the masker pitch did not affect auditory grouping. Instead, the current data suggest that the reduced masking effectiveness of harmonic sounds is due to the regular spacing of their spectral components

Effects of acoustic periodicity and intelligibility on the neural oscillations in response to speech

Although several studies have investigated neural oscillations in response to acoustically degraded speech, it is still a matter of debate which neural frequencies reflect speech intelligibility. Part of the problem is that effects of acoustics and intelligibility have so far not been considered independently. In the current electroencephalography (EEG) study the amount of acoustic periodicity (i.e. the amount of time the stimulus sentences were voiced) was manipulated, while using the listeners’ spoken responses to control for differences in intelligibility. Firstly, the total EEG power changes in response to completely aperiodic (noise-vocoded) speech and speech with a natural mix of periodicity and aperiodicity were almost identical, while an increase in theta power (5–6.3 Hz) and a trend for less beta power (11–18 Hz) were observed in response to completely periodic speech. These two effects are taken to indicate an information processing conflict caused by the unnatural acoustic properties of the stimuli, and that the subjects may have internally rehearsed the sentences as a result of this. Secondly, we separately investigated effects of intelligibility by sorting the trials in the periodic condition according to the listeners’ spoken responses. The comparison of intelligible and largely unintelligible trials revealed that the total EEG power in the delta band (1.7–2.7 Hz) was markedly increased during the second half of the intelligible trials, which suggests that delta oscillations are an indicator of successful speech understanding

The role of acoustic periodicity in perceiving speech

This thesis investigated the role of one important acoustic feature, periodicity, in the perception of speech. In the context of this thesis, periodicity denotes that a speech sound is voiced, giving rise to a sonorous sound quality sharply opposed to that of noisy unvoiced sounds. In a series of behavioural and electroencephalography (EEG) experiments, it was tested how the presence and absence of periodicity in both target speech and background noise affects the ability to understand speech, and its cortical representation. Firstly, in quiet listening conditions, speech with a natural amount of periodicity and completely aperiodic speech were equally intelligible, while completely periodic speech was much harder to understand. In the presence of a masker, however, periodicity in the target speech mattered little. In contrast, listeners substantially benefitted from periodicity in the masker and this socalled masker-periodicity benefit (MPB) was about twice as large as the fluctuatingmasker benefit (FMB) obtained from masker amplitude modulations. Next, cortical EEG responses to the same three target speech conditions were recorded. In an attempt to isolate effects of periodicity and intelligibility, the trials were sorted according to the correctness of the listeners’ spoken responses. More periodicity rendered the event-related potentials more negative during the first second after sentence onset, while a slow negativity was observed when the sentences were more intelligible. Additionally, EEG alpha power (7–10 Hz) was markedly increased before the least intelligible sentences. This finding is taken to indicate that the listeners have not been fully focussed on the task before these trials. The same EEG data were also analysed in the frequency domain, which revealed a distinct response pattern, with more theta power (5–6.3 Hz) and a trend for less beta power (11–18 Hz), in the fully periodic condition, but again no differences between the other two conditions. This pattern may indicate that the subjects internally rehearsed the sentences in the periodic condition before they verbally responded. Crucially, EEG power in the delta range (1.7–2.7 Hz) was substantially increased during the second half of intelligible sentences, when compared to their unintelligible counterparts. Lastly, effects of periodicity in the perception of speech in noise were examined in simulations of cochlear implants (CIs). Although both were substantially reduced, the MPB was still about twice as large as the FMB, highlighting the robustness of periodicity cues, even with the limited access to spectral information provided by simulated CIs. On the other hand, the larger absolute reduction of the MBP compared to normal-hearing also suggests that the inability to exploit periodicity cues may be an even more important factor in explaining the poor performance of CI users than the inability to benefit from masker fluctuations

Effects of acoustic periodicity, intelligibility, and pre-stimulus alpha power on the event-related potentials in response to speech

Magneto- and electroencephalographic (M/EEG) signals in response to acoustically degraded speech have been examined by several recent studies. Unambiguously interpreting the results is complicated by the fact that speech signal manipulations affect acoustics and intelligibility alike. In the current EEG study, the acoustic properties of the stimuli were altered and the trials were sorted according to the correctness of the listeners’ spoken responses to separate out these two factors. Firstly, more periodicity (i.e. voicing) rendered the event-related potentials (ERPs) more negative during the first second after sentence onset, indicating a greater cortical sensitivity to auditory input with a pitch. Secondly, we observed a larger contingent negative variation (CNV) during sentence presentation when the subjects could subsequently repeat more words correctly. Additionally, slow alpha power (7–10 Hz) before sentences with the least correctly repeated words was increased, which may indicate that subjects have not been focussed on the upcoming task

Development and Applications of Fluorogen/Light-Up RNA Aptamer Pairs for RNA Detection and More.

The central role of RNA in living systems made it highly desirable to have noninvasive and sensitive technologies allowing for imaging the synthesis and the location of these molecules in living cells. This need motivated the development of small pro-fluorescent molecules called "fluorogens" that become fluorescent upon binding to genetically encodable RNAs called "light-up aptamers." Yet, the development of these fluorogen/light-up RNA pairs is a long and thorough process starting with the careful design of the fluorogen and pursued by the selection of a specific and efficient synthetic aptamer. This chapter summarizes the main design and the selection strategies used up to now prior to introducing the main pairs. Then, the vast application potential of these molecules for live-cell RNA imaging and other applications is presented and discussed.journal article2020importe

Are the literacy difficulties that characterize developmental dyslexia associated with a failure to integrate letters and speech sounds?

The ‘automatic letter-sound integration hypothesis’ (Blomert, 2011) proposes that dyslexia results from a failure to fullyintegrate letters and speech sounds into automated audio-visual objects. We tested this hypothesis in a sample of English-speaking children with dyslexic difficulties (N = 13) and samples of chronological-age-matched (CA; N = 17) and reading-age-matched controls (RA; N = 17) aged 7–13 years. Each child took part in two priming experiments in which speech soundswere preceded by congruent visual letters (congruent condition) or Greek letters (baseline). In a behavioural experiment,responses to speech sounds in the two conditions were compared using reaction times. These data revealed faster reaction timesin the congruent condition in all three groups. In a second electrophysiological experiment, responses to speech sounds in the two conditions were compared using event-related potentials (ERPs). These data revealed a significant effect of congruency on (1)the P1 ERP over left frontal electrodes in the CA group and over fronto-central electrodes in the dyslexic group and (2) the P2ERP in the dyslexic and RA control groups. These findings suggest that our sample of English-speaking children with dyslexic difficulties demonstrate a degree of letter-sound integration that is appropriate for their reading level, which challenges the letter-sound integration hypothesis