The perceptual magnet effect in Australian English vowels

Recent research (Kuhl, 1991) has suggested that the internal structure of vowel categories is graded in terms of stimulus goodness. It has been proposed that a best instance stimulus reflects a central point or prototype, which effectively renders within-category members perceptually more similar. Discrimination experiments suggest a nonlinear relationship between acoustic and perceptual space near category centers (Iverson & Kuhl, 1995b). This phenomenon has been described as the perceptual magnet effect. The present study investigated the presence of the perceptual magnet effect in five Australian vowel categories. Australian English speakers identified, rated, and discriminated between a pool of 32 vowel stimuli that varied in F1 and F2 values. The results from Experiments 1 and 2 showed that subjects were able to judge the quality and identify of each stimulus and that a general grading of stimulus quality was reported. This was not symmetrical, and the subjects' responses varied considerably. In Experiment 3, closer control of the methodology in the discrimination task and of contextual factors influencing the test materials was exercised. Despite this, evidence of the warping of perceptual space in discrimination data was not found. In general, these results do not provide support for the existence of the perceptual magnet effect, and explanations for this finding are discussed.     

Measuring the perceptual magnet effect in the perception of /i/ by German listeners

In a study of the internal category structure of the vowel /i/, Kuhl found a “perceptual magnet effect”: Discrimination sensitivity was poorer for category instances that were acoustically similar to the category prototype than it was for category instances that were not. The typicality of category exemplars was determined by goodness judgments and was found to correlate with the acoustics of average production. Analysis and interpretation of discrimination performance relied on two important assumptions: that listeners perceived all stimuli presented as exemplars of the same vowel category and that, apart from the influence of phonetic coding, discrimination sensitivity was the same across the investigated part of the vowel space. In the present study, it is shown that production and perception estimates of the category prototype may diverge, possibly because listeners seem to prefer hyperarticulated variants of vowel categories. An approach towards measurement of intra-category discrimination minima is put forward and tested that protects against intercategory confounds and avoids the isosensitivity assumption. Received: 26 November 1997 / Accepted: 25 May 1998     

Auditory enhancement and the perception of concurrent vowels

Listeners identified both constituents of double vowels created by summing the waveforms of pairs of synthetic vowels with the same duration and fundamental frequency. Accuracy of identification was significantly above chance. Effects of introducing such double vowels by visual or acoustical precursor stimuli were examined. Precursors specified the identity of one of the two constituent vowels. Performance was scored as the accuracy with which the other vowel was identified. Visual precursors were standard English spellings of one member of the vowel pair; acoustical precursors were 1-sec segments of one member of the vowel pair. Neither visual precursors nor contralateral acoustical precursors improved performance over the condition with no precursor. Thus, knowledge of the identity of one of the constituents of a double vowel does not help listeners to identify the other constituent. A significant improvement in performance did occur with ipsilateral acoustical precursors, consistent with earlier demonstrations that frequency components which undergo changes in spectral amplitude achieve enhanced auditory prominence relative to unchanging components. This outcome demonstrates the joint but independent operation of auditory and perceptual processes underlying the ability of listeners to understand speech despite adversely peaked frequency responses in communication channels.     

Analysis and analogy in the perception of vowels

In two experiments, we investigated the creation of conceptual analogies to a contrast between vowels. An ordering procedure was used to determine the reliability of simple sensory and abstract analogies to vowel contrasts composed by naive volunteers. The results indicate that test subjects compose stable and consistent analogies to a meaningless segmental linguistic contrast, some invoking simple and complex relational properties. Although in the literature of psychophysics such facility has been explained as an effect of sensory analysis, the present studies indicate the action of a far subtler and more versatile cognitive function akin to the creation of meaning in figurative language.     

Vowel perception: A neuroradiological localization of the perception of vowels in the human cortex

Whether the perception of vowels takes place in the right or left cerebral hemisphere, or is dependent on bilateral cortical processes, is of importance in our treatment of patients with language deficiencies. To investigate this problem a phonetic test with a series of vowellike stimuli was administered to 68 right-handed adult patients with cerebral lesions, mainly of vascular origin. The results were compared to the results in a control group of 19 speech therapists. Second, a neuroradiologic method was developed in order to visualize the anatomic site of Wernicke's area in the left hemisphere on CT scans. This method formed the basis for an evaluation of the extent and localization of the patients' lesions in Wernicke's area. Of 46 patients with lesions in the left hemisphere, 19 had no perceptual disturbances and 27 had severe perceptual disturbances with lesions predominantly located in Wernicke's area. Twenty-two patients with lesions in the corresponding area in the right hemisphere showed no perceptual disturbances. The results of this investigation appear to indicate that the perception of vowels in right-handed persons is unilaterally located in Wernicke's area in the left hemisphere.     

The effect of perceptual grouping on haptic numerosity perception

Attention, Perception, & Psychophysics - We used a haptic enumeration task to investigate whether enumeration can be facilitated by perceptual grouping in the haptic modality. Eight...     

Adults' perception of children's height and reaching capability

This study investigated the influence of some characteristics of the task, the model, and the observer, in the estimation errors of adults while judging children's affordances. One hundred and eighteen adults, divided in 4 height groups, estimated height and vertical reaching capability of 3 girls (3.55-, 4.74- and 7.06-years old), in the presence and in the absence of the model. Constant errors (CE) (estimation-real value), absolute percent errors (APE) (|1 − estimation/real value| × 100), and error tendency (underestimations, right judgments, or overestimations) were calculated. A model and a condition effect were verified on APE. APE for the younger model were greater than for the other models (p < 0.001), and APE in the absence of the model were greater than in her presence (p < 0.05). Generally, adults underestimated height (51.8% of underestimations vs. 32.3% of overestimations) and overestimated reachability (51.3% of overestimations vs. 37.7% of underestimations). The overestimation of reachability was more notorious for the younger model, which might reflect adults' difficulty to consider the specificity of younger children's body proportions. Actually, the overestimation bias may suggest that adults perceive young children as on the basis of adult's geometrical proportions.     

Examination of perceptual reorganization for nonnative speech contrasts: Zulu click discrimination by English-speaking adults and infants

The language environment modifies the speech perception abilities found in early development. In particular, adults have difficulty perceiving many nonnative contrasts that young infants discriminate. The underlying perceptual reorganization apparently occurs by 10-12 months. According to one view, it depends on experiential effects on psychoacoustic mechanisms. Alternatively, phonological development has been held responsible, with perception influenced by whether the nonnative sounds occur allophonically in the native language. We hypothesized that a phonemic process appears around 10-12 months that assimilates speech sounds to native categories whenever possible; otherwise, they are perceived in auditory or phonetic (articulatory) terms. We tested this with English-speaking listeners by using Zulu click contrasts. Adults discriminated the click contrasts; performance on the most difficult (80% correct) was not diminished even when the most obvious acoustic difference was eliminated. Infants showed good discrimination of the acoustically modified contrast even by 12-14 months. Together with earlier reports of developmental change in perception of nonnative contrasts, these findings support a phonological explanation of language-specific reorganization in speech perception.     

Categories and context in the perception of isolated steady-state vowels

The noncategorical perception of isolated vowels has been attributed to the availability of auditory memory in discrimination. In our first experiment, using vowels from an /i/-/I/epsilon) continuum in a same-different (AX) task and comparing the results with predictions derived from a separate identification test, we demonstrated that vowels are perceived more nearly categorically if auditory memory is degraded by extending the interstimulus interval and/or filling it with irrelevant vowel sounds. In a second experiment, we used a similar paradigm, but in addition to presenting a separate identification test, we elicited labeling responses to the AX pairs used in the discrimination task. We found that AX labeling responses predicted discrimination performance quite well, regardless of whether auditory memory was available, whereas the predictions from the separate identification test were more poorly matched by the obtained data. The AX labeling reponses showed large contrast effects (both proactive and retroactive) that were greatly reduced when auditory memory was interfered with. We conclude from the presence of these contrast effects that vowels are not perceived categorically (that is, absolutely). However, it seems that by taking the effects of context into account properly, discrimination performance can be quite accurately predicted from labeling data, suggesting that vowel discrimination, like consonant discrimination, may be mediated by phonetic labels.     

The perception of back vowels: Centre of gravity hypothesis

According to the formant centre of gravity (FCOG) hypothesis, two vowel formants in close proximity are merged during perceptual analysis, and their contribution to vowel quality depends on the centre of gravity of the formant cluster. Findings consistent with this hypothesis are that two formants can be replaced by a single formant of intermediate centre frequency, provided their separation is less than 3-3.5 Bark; and that changes in their relative amplitudes produce systematic shifts in vowel quality. In Experiment 1, listeners adjusted the frequencies of F1 and F2 in a synthesized 6-formant vowel (with the F1-F2 separation fixed at 250 Hz, i.e. less than 3 Bark) to find the best phonetic match to a reference vowel with modified formant amplitudes. Contrary to FCOG predictions, F2 attenuation did not produce lower frequency matches. Raising the amplitude of F2 led to predicted upward shifts in formant frequencies of the matched vowel, but with increased variability of matches for some stimuli. In Experiment 2, listeners identified synthesized vowels with a range of separations of F1 and F2. Formant amplitude manipulations had no effect on listeners' judgements when the fundamental frequency was low (125 Hz). Small shifts in vowel quality appeared for stimuli with a high fundamental (250 Hz), but the shifts were significantly larger for F1-F2 separations greater than 3.5 Bark. These effects of formant amplitude are qualitatively different from those observed with single-formant vowels and are generally incompatible with a formant-averaging mechanism.     

Training new, nonnative speech contrasts: a comparison of the prototype and perceptual fading techniques

We trained unilingual adult Canadian francophone listeners to identify the English voiceless and voiced linguadental ("th") frictives, /theta/ and /delta/, using synthetic exemplars of each phoneme. Identification training with feedback improved listeners' abilities to identify both natural and synthetic tokens. These results show that training with appropriately selected prototype stimuli can produce a linguistically meaningful improvement in a listener's ability to identify new, nonnative speech sounds--both natural and synthetic. However, it is not yet clear whether such training with a single prototype can improve performance as effectively as the fading technique used by Jamieson and Morosan (1986), since prototype training produced only a moderate improvement in listeners' identifications of synthetic stimuli containing brief frication. Differences between the techniques may reflect the need for listeners to experience the appropriate types of intraphonemic and interphonemic variability during training. Such variability may help to define the category prototype by desensitizing the subjects to differences between exemplars of the same category and by sharpening sensitivity to differences between categories.     

Detection and resolution of audio-visual incompatibility in the perception of vowels

If audio and video recordings of a talker speaking consonant-vowel syllables containing different consontants are approximately synchronised, observers may fail to detect conflict between the modalities and perceive consonants presented in neither individual modality. The present experiments demonstrate an analogous effect in the perception of vowels. Vision can bias the identity of an acoustical vowel to be more like the vowel presented visually, even when observers detect conflict and are instructed to report only what they hear. The size of the effect is positively related to the size of the physical difference between the visible configuration of the lips and the configuration that would naturally accompany the acoustical vowel. In demonstrating these and other phenomena in audio-visual speech perception, observers behave as if they compute a continuous estimate of the filter function of the vocal tract from both visual and acoustical evidence. If the visual evidence is potent, observers may appear to interpret the acoustical evidence in novel ways. However, these compromises can be predicted from known patterns of acoustical similarity and visual distinctiveness and do not require ad hoc explanations involving categorical levels of perceptual process.     

Orthographic processing of polysyllabic words by native and nonnative English speakers

How polysyllabic English words are analyzed in silent reading was examined in three experiments by comparing lexical decision responses to words physically split on the screen. The gap was compatible either with the Maximal Onset Principle or the Maximal Coda Principle. The former corresponds to the spoken syllable (e.g., ca det), except when the word has a stressed short first vowel (e.g., ra dish), while the reverse is true for the latter (giving cad et and rad ish). Native English speakers demonstrated a general preference for the Max Coda analysis and a correlation with reading ability when such an analysis did not correspond with the spoken syllable. Native Japanese speakers, on the other hand, showed a Max Onset preference regardless of the type of word, while native Mandarin Chinese speakers showed no preference at all. It is concluded that a maximization of the coda is the optimal representation of polysyllabic words in English and that poorer native readers are more influenced by phonology than are better readers. The way that nonnative readers mentally represent polysyllabic English words is affected by the way such words are structured in their native language, which may not lead to optimal English processing.     

The role of distinctive features in the dichotic perception of vowels

A dichotic listening experiment was conducted to determine if vowel perception is based on phonetic feature extraction as is consonant perception. Twenty normal right-handed subjects were given dichotic CV syllables contrasting in final vowels. It was found that, unlike consonants, the perception of dichotic vowels was not significantly lateralized, that the dichotic perception of vowels was not significantly enhanced by the number of phonetic features shared, and that the occurrence of double-blend errors was not greater than chance. However, there was strong evidence for the use of phonetic features at the level of response organization. It is suggested that the differences between vowel and consonant perception reflect the differential availability of the underlying acoustic information from auditory store, rather than differences in processing mechanisms.     

Children's perception of sibilants: the relation between articulation and perceptual development

When synthetic fricative noises from an [s] continuum are followed by [a] and [u], adult listeners perceive fewer instances of in the context of the rounded vowel [u] (Mann & Repp, 1980). This perceptual context effect presumably reflects adjustment for certain coarticulatory effects and implies tacit knowledge of coarticulation and its consequences. To clarify the role of articulatory experience in the ontogeny of such knowledge and the consequent perceptual adjustment, the present study examined the effect of rounded and unrounded vowels on the perception of [s] and by adults, 5-, and 7-year-old children who produce and [s] and 7-year-old children who misarticulate these phonemes. All three groups of children showed a context effect equivalent to that of adults and independent of age and articulation ability. Therefore, productive mastery of [s] and is not critically responsible for perception of the [s] distinction, nor for perceptual sensitivity to the consequences of sibilant-vowel coarticulation.     

The ecological approach to perception: the place of perceptual content

The kind of perceptual systems that human beings possess enables each of us to respond in highly adaptive deliberate ways that take into account the suitability of particular behaviors to what we are aware of ourself as experiencing perceptually here and now. In deciding what to do next under the perceived circumstances, content is the dimension of perceptual experience that we consult. For perceptual content is how whatever the perceiver is now having perceptual experience of is given in or taken by the respective perceptual experience. Perceptual content includes presentational content, which is all the ways that what you are perceptually experiencing may be appearing to you, and intentional content, which is all the ways that your stream of perceptual experience may take to be that of which you have perceptual awareness in the environment or self. Therefore, perceptual content must be distinguished from the intentional object of perceptual awareness, which is that property, event, or entity of which you have perceptual awareness. Gibson proposed that there is no perceptual content independent of the particular intentional objects that one perceptually apprehends, which are always part of the ecological environment. This externalization of perceptual content was due, no doubt, to Gibson's conception of perceptually apprehending anything at all as not mediated by awareness of anything else, such as something immanent in perceptual experience itself. However, perceptual content need not be, theoretically, a replacement for what the perceiver has perceptual awareness of. During straightforward perceiving, the perceiver does not have awareness of perceptual content but of parts of the ecological environment including the perceiver. Perceptual content is how the external intentional object perspectivally appears from moment to moment and how it is perceptually taken to be, veridically or not. Perceptual taking of an ecological property is always in one or another of the latter's instantiations, and perceptual taking of an ecological entity or event is always with properties. The perceptual intentional object's appearing in a particular manner is distinct from perceptually taking the intentional object. For example, an ecological property may be taken quite veridically yet through a flow of varying appearance. And even when the property appears in a constant way, perceptual awareness may take it differently from one moment to the next. For example, a perceiver may have visual awareness of a surface without noticing the surface's color-texture, though the color-texture may appear to the perceiver throughout looking at the surface, before and after he or she stops noticing the color-texture.(ABSTRACT TRUNCATED AT 400 WORDS)     

Feature sampling in detection: implications for the measurement of perceptual independence

The article presents the feature sampling signal detection (FS-SDT) model, an extension of the multivariate signal detection (SDT) model. The FS-SDT model assumes that, because of attentional shifts, different subsets of features are sampled for different presentations of the same multidimensional stimulus. Contrary to the SDT model, the FS-SDT model enables the estimation of pure perceptual effects that are uncontaminated by strategic attention shifts. The consideration of feature sampling in detection and identification opens a new perspective on the problem of measuring, respectively, the separability and integrality of stimulus dimensions. Disregarding feature sampling as a component process in detection and identification usually results in biased estimations of perceptual independence concepts relevant for judgments of whether stimulus dimensions are processed independently.     

Infants show a facilitation effect for native language phonetic perception between 6 and 12 months

Patterns of developmental change in phonetic perception are critical to theory development. Many previous studies document a decline in nonnative phonetic perception between 6 and 12 months of age. However, much less experimental attention has been paid to developmental change in native-language phonetic perception over the same time period. We hypothesized that language experience in the first year facilitates native-language phonetic performance between 6 and 12 months of age. We tested 6-8- and 10-12-month-old infants in the United States and Japan to examine native and nonnative patterns of developmental change using the American English /r-l/ contrast. The goals of the experiment were to: (a) determine whether facilitation characterizes native-language phonetic change between 6 and 12 months of age, (b) examine the decline previously observed for nonnative contrasts and (c) test directional asymmetries for consonants. The results show a significant increase in performance for the native-language contrast in the first year, a decline in nonnative perception over the same time period, and indicate directional asymmetries that are constant across age and culture. We argue that neural commitment to native-language phonetic properties explains the pattern of developmental change in the first year.