eprintid: 1537585
rev_number: 20
eprint_status: archive
userid: 608
dir: disk0/01/53/75/85
datestamp: 2017-03-16 14:56:39
lastmod: 2019-10-17 07:57:11
status_changed: 2017-03-16 14:56:39
type: thesis
metadata_visibility: show
creators_name: Steinmetzger, K
title: The role of acoustic periodicity in perceiving speech
ispublished: unpub
divisions: A01
divisions: B02
divisions: C07
divisions: D05
abstract: 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.
date: 2017-02-28
date_type: published
oa_status: green
full_text_type: other
thesis_class: doctoral_open
language: eng
thesis_view: UCL_Thesis
primo: open
primo_central: open_green
verified: verified_manual
elements_id: 1204342
lyricists_name: Steinmetzger, Kurt
lyricists_id: STEIN29
actors_name: Steinmetzger, Kurt
actors_id: STEIN29
actors_role: owner
full_text_status: public
pages: 129
event_title: University College London
institution: UCL (University College London)
department: Speech, Hearing and Phonetics
thesis_type: Doctoral
citation:        Steinmetzger, K;      (2017)    The role of acoustic periodicity in perceiving speech.                   Doctoral thesis , UCL (University College London).     Green open access   
 
document_url: https://discovery.ucl.ac.uk/id/eprint/1537585/1/Steinmetzger%202017%20PhD%20Periodicity.pdf