On the causes of compensation for coarticulation : evidence for phonological mediation

This study examined whether compensation for coarticulation in fricative-vowel syllables is phonologically mediated or a consequence of auditory processes. Smits (2001a) had shown that compensation occurs for anticipatory lip rounding in a fricative caused by a following rounded vowel in Dutch. In a first experiment, the possibility that compensation is due to general auditory processing was investigated using nonspeech sounds. These did not cause context effects akin to compensation for coarticulation, although nonspeech sounds influenced speech sound identification in an integrative fashion. In a second experiment, a possible phonological basis for compensation for coarticulation was assessed by using audiovisual speech. Visual displays, which induced the perception of a rounded vowel, also influenced compensation for anticipatory lip rounding in the fricative. These results indicate that compensation for anticipatory lip rounding in fricative-vowel syllables is phonologically mediated. This result is discussed in the light of other compensation-for-coarticulation findings and general theories of speech perception.peer-reviewe

Why not model spoken word recognition instead of phoneme monitoring?

Norris, McQueen & Cutler present a detailed account of the decision stage of the phoneme monitoring task. However, we question whether this contributes to our understanding of the speech recognition process itself, and we fail to see why phonotactic knowledge is playing a role in phoneme recognition.

Contrast

This thesis engages the contrast phenomenon in its various manifestations across the different sense modalities in order to assess the plausibility of contrast as a general perceptual principle. There is some question as to whether contrast may spill over into modalities it is not commonly associated with. In particular, a number of researchers have argued that contrast occurs in audition and has similarities to the brightness contrast illusion in visual perception. For example, studies of noise pitch have noted similar psychophysical properties to brightness contrast and invoked the same underlying neural mechanism. Furthermore, there is some suggestion that contrast may come in a non-simultaneous form characterised by perceptual exaggerations arising from the contrasting spectral content of successive auditory stimuli. The speech perception literature on context effects are engaged as it is in this domain that there is some evidence for non-simultaneous contrast. A study was conducted in which 34 subjects were presented synthesized tokens of "da" and "ga" diotically and dichotically following the precursors "al" and "ar". Significantly more "da" identifications were observed (F=62.85, p=.000) following "ar" precursors when stimuli were presented diotically, whereas no significant effects were observed in identifications of the target for different precursors (F=.553, p=.457) when targets were presented to the ear contralateral to that of the precursor. Results fail to support an explanation of the context effect in the form of a causal mechanism with a central locus. Rather, the locus of the context effect can only be hypothesized to occur at the periphery of the nervous system. This suggests that auditory contrast may be a plausible explanation for the context effect, and which if correct, may be a universal phenomenon common to all people regardless of environment and acquired knowledge. Given these results, contrast is explored more broadly. As generic use of the term is often encountered in musical contexts, aspects of music perception relating to contrast are examined. Some theoretical ideas are put forward in this capacity, focusing on an interactive neural network approach to understanding hypothetical structural contrasts, including tonal contrasts. The thesis closes with a consideration of contrast-like effects that may be of some relevance towards understanding contrast more generally

Auditory and speech processing in specific language impairment (SLI) and dyslexia

This thesis investigates auditory and speech processing in Specific Language Impairment (SLI) and dyslexia. One influential theory of SLI and dyslexia postulates that both SLI and dyslexia stem from similar underlying sensory deficit that impacts speech perception and phonological development leading to oral language and literacy deficits. Previous studies, however, have shown that these underlying sensory deficits exist in only a subgroup of language impaired individuals, and the exact nature of these deficits is still largely unknown. The present thesis investigates three aspects of auditory-phonetic interface: 1) The weighting of acoustic cues to phonetic voicing contrast 2) the preattentive and attentive discrimination of speech and non-linguistic stimuli and 3) the formation of auditory memory traces for speech and non-linguistic stimuli in young adults with SLI and dyslexia. This thesis focuses on looking at both individial and group-level data of auditory and speech processing and their relationship with higher-level language measures. The groups of people with SLI and dyslexia who participated were aged between 14 and 25 and their performance was compared to a group of controls matched on chronological age, IQ, gender and handedness. Investigations revealed a complex pattern of behaviour. The results showed that individuals with SLI or dyslexia are not poor at discriminating sounds (whether speech or non-speech). However, in all experiments, there was more variation and more outliers in the SLI group indicating that auditory deficits may occur in a small subgroup of the SLI population. Moreover, investigations of the exact nature of the input-processing deficit revealed that some individuals with SLI have less categorical representations for speech sounds and that they weight the acoustic cues to phonemic identity differently from controls and dyslexics