Detecting categorical perception in continuous discrimination data

We present a method for assessing categorical perception from continuous discrimination data. Until recently, categorical perception of speech has exclusively been measured by discrimination and identification experiments with a small number of different stimuli, each of which is presented multiple times. Experiments by Rogers and Davis (2009), however, suggest that using non-repeating stimuli yields a more reliable measure of categorization. If this idea is applied to a single phonetic continuum, the continuum has to be densely sampled and the obtained discrimination data is nearly continuous. In the present study, we describe a maximum-likelihood method that is appropriate for analysing such continuous discrimination data

Inferior Frontal Cortex Contributions to the Recognition of Spoken Words and Their Constituent Speech Sounds

Speech perception and comprehension are often challenged by the need to recognize speech sounds that are degraded or ambiguous. Here, we explore the cognitive and neural mechanisms involved in resolving ambiguity in the identity of speech sounds using syllables that contain ambiguous phonetic segments (e.g., intermediate sounds between /b/ and /g/ as in "blade" and "glade"). We used an audio-morphing procedure to create a large set of natural sounding minimal pairs that contain phonetically ambiguous onset or offset consonants (differing in place, manner, or voicing). These ambiguous segments occurred in different lexical contexts (i.e., in words or pseudowords, such as blade-glade or blem-glem) and in different phonological environments (i.e., with neighboring syllables that differed in lexical status, such as blouse-glouse). These stimuli allowed us to explore the impact of phonetic ambiguity on the speed and accuracy of lexical decision responses (Experiment 1), semantic categorization responses (Experiment 2), and the magnitude of BOLD fMRI responses during attentive comprehension (Experiment 3). For both behavioral and neural measures, observed effects of phonetic ambiguity were influenced by lexical context leading to slower responses and increased activity in the left inferior frontal gyrus for high-ambiguity syllables that distinguish pairs of words, but not for equivalent pseudowords. These findings suggest lexical involvement in the resolution of phonetic ambiguity. Implications for speech perception and the role of inferior frontal regions are discusse

Segmental foreign accent

200 p.Tradicionalmente, el acento extranjero se ha estudiado desde una perspectiva holística, es decir, tratándolo como un todo en lugar de como una serie de rasgos individuales que suceden simultáneamente. Los estudios previos que se han centrado en alguno de estos rasgos individuales lo han hecho generalmente en el plano suprasegmental (Tajima et al., 1997, Munro & Derwing, 2001, Hahn, 2004, etc.). En esta tesis se lleva a cabo un análisis del acento extranjero desde un punto de vista segmental. Considerando que no existe mucha investigación en este campo, nuestro principal objetivo es averiguar si los resultados de estudios holísticos previos pueden ser extrapolados al nivel segmental. Con el objetivo de analizar el nivel segmental en detalle, en esta tesis se presentan técnicas que hacen uso de nuevas tecnologías. Para recabar la mayor información posible, los experimentos perceptivos son llevados a cabo con oyentes con muy distintos perfiles lingüísticos en términos de primera lengua o conocimiento de la segunda lengua y comparados con la literatura existente. Nuestros resultados muestran que algunos efectos importantes relativos a la producción y percepción de segmentos acentuados pueden pasar inadvertidos en un análisis holístico y acreditan la necesidad de continuar realizando estudios de unidades mínimas para comprender en profundidad los efectos del acento extranjero en la comunicación

Categorical versus gradient properties of handling handshapes in British Sign Language (BSL). Evidence from handling handshape perception and production by deaf BSL signers and hearing speakers

Sign languages include partially lexicalised signs (known as depicting constructions, DCs) that have been argued to blend linguistic and non-linguistic components, although it is unclear what these components are. To describe object handling, signers produce handshapes that represent how the hands shape for handling, but it has not yet been fully established whether the continuous object size is described by discrete handshapes in British Sign Language (BSL). The thesis examines whether experience with sign language influences perception and comprehension of BSL handling handshapes. In the first study, categorical perception (CP), using the identification and ABX discrimination tasks, is examined for handling handshapes (HHs) in BSL. The experiments reveal that adult deaf BSL signers and hearing non-signers perceive continuous HHs categorically while remaining perceptive to gradient aperture changes. Deaf BSL signers were more accurate than hearing non-signers when discriminating between handshape stimuli; this is likely due to visual language experience. However, reaction times showed no processing advantage suggesting that categorisation of BSL HHs has a general, visual-perceptual rather than linguistic basis. The second study examines whether deaf BSL signers compared with hearing non-signers express and interpret gradient sizes of manipulated objects categorically in discourse. Handling of objects gradiently increasing in size was recorded in BSL narratives, in English narratives via co-speech gesture and pantomime; recordings were shown to another group of judges who matched handling productions with the objects. All participants reliably associated smaller objects with smaller apertures and larger objects with larger apertures; however, in BSL and co-speech gesture, handshapes were not completely interpreted as gradient variations in comparison with pantomime. When gestures become more strategic or unusual, e.g. pantomime, speakers introduce finer-grained encoding of object sizes. The discontinuous patterns suggest that HHs have underlying representations outside of the linguistic realm; their categorisation arises from visual-perceptual experience that is embodied through interaction with real life entities. In discourse, handling constructions are partly conventionalised and may become decomposable in BSL overtime but it is suggested here that general cognitive and perceptual factors contribute to the conventionalisation, rather than purely linguistic. Further, the findings from both experiments lend support to the argument that HH category structure is graded. This thesis contributes to debates about the relationship between visual perception and language processing and the complex interface between language and gesture and highlights the nature of language as a multimodal phenomenon