A possible auditory basis for internal structure of phonetic categories

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162

Studies of the McGurk effect have shown that when discrepant phonetic information is delivered to the auditory and visual modalities, the information is combined into a new percept not originally presented to either modality. In typical experiments, the auditory and visual speech signals are generated by the same talker. The present experiment examined whether a discrepancy in the gender of the talker between the auditory and visual signals would influence the magnitude of the McGurk effect. A male talker's voice was dubbed onto a videotape containing a female talker's face, and vice versa. The gender-incongruent videotapes were compared with gendercongruent videotapes, in which a male talker's voice was dubbed onto a male face and a female talker's voice was dubbed onto a female face. Even though there was a clear incompatibility in talker characteristics between the auditory and visual signals on the incongruent videotapes, the resulting magnitude of the McGurk effect was not significantly different for the incongruent as opposed to the congruent videotapes. The results indicate that the mechanism for integrating speech information from the auditory and the visual modalities is not disrupted by a gender incompatibility even when it is perceptually apparent. The findings are compatible with the theoretical notion that information about voice characteristics of the talker is extracted and used to normalize the speech signal at an early stage of phonetic processing, prior to the integration of the auditory and the visual information.Over the past four decades, extensive research has been done on the psychological processes underlying the perception and production of spoken language. Much of this research has focused on how the listener processes the acoustic structure of speech in order to arrive at the intended meaning of an utterance.Although speech perception has primarily been considered an auditory process, recent studies have shown that visual information provided by movements of a talker's mouth and face strongly influences what an observer perceives (Green

“…Several experiments have demonstrated the use of prototypes in phonetic categorization (Kuhl, 1991;J. L. Miller, Connine, Schermer, & Kluender, 1983;Samuel, 1982).…”

Section: Discussionmentioning

confidence: 99%

Integrating speech information across talkers, gender, and sensory modality: Female faces and male voices in the McGurk effect

Green

Kuhl

Meltzoff

et al. 1991

189

162

“…Thus phonetic categories have an internal structure that is reminiscent of the kind of structure seen for nonspeech perceptual/ cognitive categories (Medin & Barsalou, 1987;Nosofsky, 1988;Rosch, 1978). The internal structure ofphonetic categories is evident in tasks requiring the overt judgment of category goodness (Kuhl, 1991;Massaro & Cohen, 1983;Miller & Volaitis, 1989;Samuel, 1982), as well as in tasks that measure the functional salience of category members by assessing, for example, dichotic competition (Miller, 1977;Repp, 1977), selective adaptation (Miller, Connine, Schermer, & Kluender, 1983;Samuel, 1982), and discrimination (Kuhl, 1991). I The issue we address in the present research concerns the developmental origins of this internal category structure.…”

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confidence: 99%

Internal structure of voicing categories in early infancy

Miller

Eimas

1996

Self Cite

It is well established that young infants process speech in terms of perceptual categories that closely correspond to the phonetic categories of adult language users. Recently, Kuhl (1991) has provided evidence that this correspondence is not limited to the region of category boundaries: At least by 6-7 months of age, vowel categories of infants, like those of adults, have an internal perceptual structure. In the current experiments, which focused on a consonantal contrast, we found evidence of internally structured categories in even younger infants-3-4 months of age. The implications of these findings for the nature ofthe infant's earliest language-universal categories are discussed, as is the role of exposure to the native language in shaping these categories over the course of development.One of the fundamental issues in speech perception is how listeners map the continuously varying signal of speech onto the phonetic categories of their language. Much of the research on phonetic categorization over the years has focused on the boundaries between phonetic categories, addressing such issues as why boundaries fall where they do along given acoustic continua, what kinds ofcontextual factors playa role in determining boundary location, and the effects of specific linguistic experience in altering boundary location over the course of development (see, e.g., Repp & Liberman, 1987). This emphasis on boundaries derived in part from the much-studied phenomenon of categorical perception, which emphasized the relative difficulty experienced by listeners in discriminating members of a given phonetic category compared with the ease in discriminating tokens that cross a category boundary (Repp, 1984;Studdert-Kennedy, Liberman, Harris, & Cooper, 1970).It has become increasingly clear, however, that phonetic categories are much richer in form than this emphasis on boundaries would suggest. It is now known that listeners can discriminate stimuli from a given category with a relatively high degree of accuracy, given specific stimulus and task conditions (Carney, Widin, & Viemeister, 1977;Samuel, 1977; see also Macmillan, Goldberg, & Braida, 1988). Moreover, and of particular relevance for the current research, there is a growing literature indicating that phonetic categories have a graded internal struc-

“…There is some evidence relevant to these issues. For example, it has been demonstrated that members of a phonetic category differ in perceptual potency; certain stimuli are more effective adaptors in selective adaptation experiments (Miller, Connine, Schermer, & Kluender, 1983;Samuel, 1982) and are more effective competitors in dichotic competition experiments (Miller, 1977;Repp, 1977). Moreover, when listeners are asked to rate the category goodness of individual members, it has been shown that individual exemplars vary in the degree to which they are perceived as good exemplars of the category (Grieser & Kuhl, 1989;Kuhl, 1986;Miller & Volaitis, 1989).…”

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confidence: 99%

Human adults and human infants show a “perceptual magnet effect” for the prototypes of speech categories, monkeys do not

Kuhl

1991

943

752

Many perceptual categories exhibit internal structure in which category prototypes play an important role. In the four experiments reported here, the internal structure of phonetic categories was explored in studies involving adults, infants, and monkeys. In Experiment 1, adults rated the category goodness of 64 variants of the vowel Iii on a scale from 1 to 7. The results showed that there was a certain location in vowel space where listeners rated the Iii vowels as best instances, or prototypes. The perceived goodness of Iii vowels declined systematically as stimuli were further removed from the prototypic Iii vowel. Experiment 2 went beyond this initial demonstration and examined the effect of speech prototypes on perception. Either the prototypic or a nonprototypic Iii vowel was used as the referent stimulus and adults' generalization to other members of the category was examined. Results showed that the typicality of the speech stimulus strongly affected perception. When the prototype of the category served as the referent vowel, there was significantly greater generalization to other Iii vowels, relative to the situation in which the nonprototype served as the referent. The notion of a perceptual magnet was introduced. The prototype ofthe category functioned like a perceptual magnet for other category members; it assimilated neighboring stimuli, effectively pulling them toward the prototype. In Experiment 3, the ontogenetic origins of the perceptual magnet effect were explored by testing 6-month-old infants. The results showed that infants' perception of vowels was also strongly affected by speech prototypes. Infants showed significantly greater generalization when the prototype of the vowel category served as the referent; moreover, their responses were highly correlated with those of adults. In Experiment 4, Rhesus monkeys were tested to examine whether or not the prototype's magnet effect was unique to humans. The animals did not provide any evidence of speech prototypes; they did not exhibit the magnet effect. It is suggested that the internal organization of phonetic categories around prototypic members is an ontogenetically early, species-specific, aspect of the speech code.Human perceptual systems group stimuli into categories, many of which exhibit internal structure. Evidence of internal structure and organization derives from data indicatingthat all members of a category are not perceived as equal. Category goodness is a matter of degree, where some members are perceived as better exemplars, more representative or prototypic, than others (Rosch, 1975).Work on the internal structure of categories and prototypes of categories has typically been done using stimuli in the visual domain (e.g., color or physical objects). Studies of visual categories show that good exemplars of a category have privileged status; they are more quickly encoded, they are more durably remembered, and they are often preferred over other members of the category