The perceptual segregation of simultaneous auditory signals: pulse train segregation and vowel segregation

In the experiments reported here, we attempted to find out more about how the auditory system is able to separate two simultaneous harmonic sounds. Previous research (Halikia & Bregman, 1984a, 1984b; Scheffers, 1983a) had indicated that a difference in fundamental frequency (F0) between two simultaneous vowel sounds improves their separate identification. In the present experiments, we looked at the effect of F0s that changed as a function of time. In Experiment 1, pairs of unfiltered or filtered pulse trains were used. Some were steady-state, and others had gliding F0s; different F0 separations were also used. The subjects had to indicate whether they had heard one or two sounds. The results showed that increased F0 differences and gliding F0s facilitated the perceptual separation of simultaneous sounds. In Experiments 2 and 3, simultaneous synthesized vowels were used on frequency contours that were steady-state, gliding in parallel (parallel glides), or gliding in opposite directions (crossing glides). The results showed that crossing glides led to significantly better vowel identification than did steady-state F0s. Also, in certain cases, crossing glides were more effective than parallel glides. The superior effect of the crossing glides could be due to the common frequency modulation of the harmonics within each component of the vowel pair and the consequent decorrelation of the harmonics between the two simultaneous vowels.     

The shift in infant preferences for vowel duration and pitch contour between 6 and 10 months of age

This study investigates the influence of the acoustic properties of vowels on 6‐ and 10‐month‐old infants’ speech preferences. The shape of the contour (bell or monotonic) and the duration (normal or stretched) of vowels were manipulated in words containing the vowels /i/ and /u/, and presented to infants using a two‐choice preference procedure. Experiment 1 examined contour shape: infants heard either normal‐duration bell‐shaped and monotonic contours, or the same two contours with stretched duration. The results show that 6‐month‐olds preferred bell to monotonic contours, whereas 10‐month‐olds preferred monotonic to bell contours. In Experiment 2, infants heard either normal‐duration and stretched bell contours, or normal‐duration and stretched monotonic contours. As in Experiment 1, infants showed age‐specific preferences, with 6‐month‐olds preferring stretched vowels, and 10‐month‐olds preferring normal‐duration vowels. Infants’ attention to the acoustic qualities of vowels, and to speech in general, undergoes a dramatic transformation in the final months of the first year, a transformation that aligns with the emergence of other developmental milestones in speech perception.     

The relationship between brightness contrast and illusory contours.

One group of subjects rated differences in brightness and another the clarity of illusory contours for eight figure-ground combinations of the Kanizsa and Ehrenstein patterns made from Munsell papers. For four combinations there was a difference in Munsell value (brightness) between figure and ground and for another four no difference. For the latter the pattern was derived from differences in hue or colour quality. For the combinations with a Munsell value difference the ratings of both brightness difference and contour clarity were high and for those of uniform value both were low. The results are interpreted as supporting the argument that illusory contours derive primarily from contrast-induced differences in brightness and possibly in colour between contiguous, physically uniform regions.     

Misreadings by beginning readers of Serbo-Croatian

Errors in reading aloud by the beginning reader have been interpreted as reflecting the difficulty and the importance of phonemic segmentation for the acquisition of reading skills. Results from previous studies on English words patterned as consonant-vowel-consonant showed: (1) more errors on vowels than on consonants; (2) more errors on word final consonants than on word initial consonants; and suggested that (3) consonant errors were based on phonetic confusions while vowel errors were not. In contrast to their English counterparts, the beginning readers of Serbo-Croatian tested in the present study committed proportionally fewer errors on their reading of vowels than of consonants but in common with their English counterparts, their reading of final consonants was more vulnerable to error than their reading of initial consonants. This pattern of errors was found for both word and pseudoword consonant-vowel-consonant structures and the pattern of vowel confusion, like the pattern of consonant confusions, was rationalized by speech-related factors. The differences between the patterns of confusions for Serbo-Croatian and for English could be due to the difference between the two orthographies in the precision with which they represent the phonology or to the fact that the vowels of English are qualitatively less distinct phonologically than the vowels of Serbo-Croatian.     

Tweaking the lexicon: organization of vowel sequences into words

The ability of listeners to distinguish between different arrangements of the same three vowels was investigated for repeating sequences having item durations ranging from 10 msec (single glottal pulses) up to several seconds/vowel. Discrimination was accomplished with ease by untrained subjects at all item durations. From 30 through 100 msec/vowel, an especially interesting phenomenon was encountered: The sequences of steady-state vowels were organized into words, with different words heard for the different arrangements of items. In a second experiment, repeating sequences of random arrangements of 10 40-msec vowels were employed. When sets of four such sequences were presented to listeners, distinctive words were heard, which permitted each arrangement to be discriminated from the others. In addition, minimal differences (reversing the order of a single contiguous pair of vowels) in the 10-item sequences could be detected via verbal mediation. Hypotheses are offered concerning mechanisms responsible for these results.     

Pitch characteristics of infant-directed speech affect infants’ ability to discriminate vowels

“Baby talk” or speech directed to prelinguistic infants is high in pitch and has exaggerated pitch contours (up/down patterns of pitch change) across languages and cultures. Using an acoustic model, we predicted that the large pitch contours of infant-directed speech should improve infants’ ability to discriminate vowels. On the other hand, the same model predicted that high pitch would not benefit, and might actually impair, infants’ ability to discriminate vowels. We then confirmed these predictions experimentally. We conclude that the exaggerated pitch contours of infant-directed speech aid infants’ acquisition of vowel categories but that the high pitch of infant-directed speech must serve another function, such as attracting infants’ attention or aiding emotional communication.     

Stochastic PERT networks as models of cognition: Derivation of the mean,variance, and distribution of reaction time using Order-of-Processing (OP) diagrams

It is frequently assumed that the mental activity which leads to a given response is made up of separable components or processes. One or more of the processes are assumed to contribute to the time required to respond. Computation of the mean, variance, and distribution of the reaction time is relatively straightforward when all processes are arranged in series or parallel. However, such is not the case when the processes have complex arrangements. A solution to a useful special case of the above problem is proposed. Specifically, it is shown that simple computations yield closed form expressions for the mean, variance, and distribution of reaction time when the processes can be arranged in a stochastic PERT network and when the durations of individual processes are sums of mutually independent, exponentially distributed random variables. The method of solution relies on the construction of an Order-of-Processing (OP) diagram from the original PERT network representation of behavior.     

The weckud wetch of the wast: lexical adaptation to a novel accent

Two experiments investigated the mechanism by which listeners adjust their interpretation of accented speech that is similar to a regional dialect of American English. Only a subset of the vowels of English (the front vowels) were shifted during adaptation, which consisted of listening to a 20-min segment of the "Wizard of Oz." Compared to a baseline (unadapted) condition, listeners showed significant adaptation to the accented speech, as indexed by increased word judgments on a lexical decision task. Adaptation also generalized to test words that had not been presented in the accented passage but that contained the shifted vowels. A control experiment showed that the adaptation effect was specific to the direction of the shift in the vowel space and not to a general relaxation of the criterion for what constitutes a good exemplar of the accented vowel category. Taken together, these results provide evidence for a context-specific vowel adaptation mechanism that enables a listener to adjust to the dialect of a particular talker.     

Temperament, personality, and developmental psychopathology as childhood antecedents of personality disorders

To contribute to the case for a dimensional conceptualization of psychopathology in general and maladaptive personality or personality disorders in particular, the present paper reviews the evidence for a dimensional representation of childhood temperament and personality. The review of temperament and variable-centered as well as person-centered approaches to childhood personality leads us to propose five broadband dimensions that capture individual differences in children and adolescents: extraversion, emotional stability, agreeableness, conscientiousness, and openness/intellect. Our analysis of the CBCL (Achenbach, 1991) and the DIPSI (currently under development at Ghent University), two dimensional models for childhood psychopathology, suggests two common broadband factors, internalizing and externalizing. The relations between the dimensional representation of childhood temperament/personality and psychopathology are documented with data from general population and clinical samples of children and adolescents. The article concludes with a proposal on how the higher-order dimensions emerging from studies of adaptive and maladaptive individual differences in childhood could be integrated in a common dimensional model.     

The effect of vibrato on the recognition of masked vowels

Five experiments on the identifiability of synthetic vowels masked by wideband sounds are reported. In each experiment, identification thresholds (signal/masker ratios, in decibels) were measured for two versions of four vowels: a vibrated version, in which FO varied sinusoidally around 100 Hz; and a steady version, in which F0 was fixed at 100 Hz. The first three experiments were performed on naive subjects. Experiment 1 showed that for maskers consisting of bursts of pink noise, vibrato had no effect on thresholds. In Experiment 2, where the maskers were periodic pulse trains with an F0 randomly varied between 120 and 140 Hz from trial to trial, vibrato slightly improved thresholds when the sound pressure level of the maskers was 40 dB, but had no effect for 65-dB maskers. In Experiment 3, vibrated rather than steady pulse trains were used as maskers; when these maskers were at 40 dB, the vibrated versions of the vowels were slightly less identifiable than their steady versions; but, as in Experiment 2, vibrato had no effect when the maskers were at 65 dB. Experiment 4 showed that the unmasking effect of vibrato found in Experiment 2 disappeared in subjects trained in the identification task. Finally, Experiment 5 indicated that in trained listeners, vibrato had no influence on identification performance even when the maskers and the vowels had synchronous onsets and offsets. We conclude that vibrating a vowel masked by a wideband sound can affect its identification threshold, but only for tonal maskers and in untrained listeners. This effect of vibrato should probably be considered as a Gestalt phenomenon originating from central auditory mechanisms.     

The relation between discriminability and memory for vowels,consonants, and silent-center vowels

People remember lists of vowel-contrasting syllables better than lists that vary only in stop consonant identity. Most views suggest that this difference is due to the structure of immediate memory and the greater discriminability of vowels compared with consonants. In all of these views, there is a presumed systematic relationship between discriminability and recall so that the more discriminable an item, the better that item should be recalled. The 11 experiments reported here measured the relative discriminability of and compared serial recall for (1) intact syllables that varied only in the medial vowel, (2) intact syllables that varied only in the initial consonant, and (3) syllables with the center vowel replaced by silence (so-called silent-center vowels). When item discriminability, as measured by identification, was equated for consonant-contrasting and silent-center lists, serial recall performance was also equal. However, even when the vowels were less discriminable than the consonants or silentcenter vowels, serial recall performance for the vowels was still better. These results are problematic for theories based on acoustic discriminability but can be explained parsimoniously by Nairne’s (1990) feature model.     

Visual curve tracing properties

Subjects decided whether 2 dots were on the same curve or 2 different curves, and the curvature of the curves or the proximity of other (distractor) curves to the target curve was varied. Response time increased as the arc length of the curve connecting the 2 dots increased, suggesting that the curve was traced to perform the task. Tracing rate was faster for low- than high-curvature contours and was increasingly slower as distractor contours were increasingly proximal to the traced curve. Proximity results were predicted by a model in which response time depends on the ratio of the distance between the dots and the distance between adjacent lines. Curve tracing operations used to integrate information along contours are sensitive to several properties of the contours. The implications of the sensitivity of tracing operations to these curve properties are discussed.     

Grouping has a negative effect on both subjective contours and perceived occlusion at T-junctions

Perceived occlusion of aligned T-junctions and subjective contours at implicit T-junctions are often assumed to be related but are rarely examined with respect to common mechanisms. Using the method of paired comparison, we measured the strength of perceived occlusion at explicit T-junctions and the strength of subjective contours at implicit T-junctions (using different subjects) along the aligned edges of eight sets of inducer shapes. Sets varied in the similarity of component shapes with respect to orientation, height, width, and color. With increasing shape similarity, there was a striking decrease in both the strength of subjective contours and the strength of perceived occlusion; the correlation between these two kinds of judgments was .97. We conclude that common mechanisms underlie these two percepts and that edge alignment is a much stronger indicator of occlusion for poorly grouped than for strongly grouped inducers.     

Shape constancy from novel views

Prior experiments on shape constancy from novel views are inconclusive: Some show that shapes of objects can be recognized reliably from novel views, whereas others show just the opposite. Our analysis of prior results suggests that shape constancy from novel views is reliable when the object has properties that constrain its shape: The object has volumetric primitives, it has surfaces, it is symmetrical, it is composed of geons, its contours are planar, and its images provide useful topological information about its three-dimensional structure. To test the role of some of these constraints, we performed a set of experiments. Solid shapes (polyhedra) were shown on a computer monitor by means of kinetic depth effect. Experiment 1 showed that shape constancy can be reliably achieved when a polyhedron is represented by its contours (most of the constraints are present), but not when it is represented by vertices or by a polygonal line connecting the vertices in a random order (all the constraints are absent). Experiments 2 and 3 tested the role of individual constraints. Results of these experiments show that shape constancy from novel views is reliable when the object has planar contours and when the shapes of the contours together with topological information about the relations among the contours constrain the possible interpretations of the shape. Symmetry of the object and the topological stability of its image also contribute to shape constancy.     

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.     

The quest for generalizations over consonants: Asymmetries between consonants and vowels are not the by-product of acoustic differences

Consonants and vowels may play different roles during language processing, consonants being preferentially involved in lexical processing, and vowels tending to mark syntactic constituency through prosodic cues. In support of this view, artificial language learning studies have demonstrated that consonants (C) support statistical computations, whereas vowels (V) allow certain structural generalizations. Nevertheless, these asymmetries could be mere by-products of lower level acoustic differences between Cs and Vs, in particular the energy they carry, and thus their relative salience. Here we address this issue and show that vowels remain the preferred targets for generalizations, even when consonants are made highly salient or vowels barely audible. Participants listened to speech streams of nonsense CVCVCV words, in which consonants followed a simple ABA structure. Participants failed to generalize this structure over sonorant consonants (Experiment 1), even when vowel duration was reduced to one third of that of consonants (Experiment 2). When vowels were eliminated from the stream, participants showed only a marginal evidence of generalizations (Experiment 4). In contrast, participants readily generalized the structure over barely audible vowels (Experiment 3). These results show that different roles of consonants and vowels cannot be readily reduced to acoustical and perceptual differences between these phonetic categories.     

Investigation of the process underpinning vowel‐size correspondence

Vowel‐size correspondence is frequently reported in the literature: Namely, the vowels a and i tend to elicit bigger and smaller images, respectively. Previous studies have speculated that two factors may contribute to this vowel‐size correspondence: the acoustical features of vowels and the speaker's kinesthetic experience of producing them. However, these two factors have been investigated without being considered separately in previous research. In this study, we investigated the process underpinning vowel‐size correspondence by using speeded classification tasks and manipulating the two factors mentioned above separately in two experiments. The results of Experiment 1 indicate that a and i elicited bigger and smaller images even in the absence of kinesthetic experience. The results of Experiment 2 indicate that the proprioception of the size of the oral cavity on its own may not contribute to vowel‐size correspondence. Thus, the acoustic features of vowels mainly contribute to vowel‐size correspondence, although other possibilities are also discussed.     

Principles of contour information: Reply to Lim and Leek (2012)

Lim and Leek (2012) presented a formalization of information along object contours, which they argued was an alternative to the approach taken in our article (Feldman & Singh, 2005). Here, we summarize the 2 approaches, showing that--notwithstanding Lim and Leek's (2012) critical rhetoric--their approach is substantially identical to ours, except for the technical details of the formalism. Following the logic of our article point by point, Lim and Leek (a) defined probabilistic expectations about the geometry of smooth contours (which they based on differential contour geometry, while we used a discrete approximation--the only essential difference in their approach), (b) assumed that information along the contour was proportional to the negative logarithm of probability, following standard information theory, and then (c) extended this formulation to closed contours. We analyze what they described as errors in our approach, all of which rest on mathematical misunderstandings or bizarre misreadings of our article. We also show that their extension to 3-dimensional surfaces and their "modified minima rule" contain fatal deficiencies.     

Constraints of vowels and consonants on lexical selection: Cross-linguistic comparisons

Languages differ in the constitution of their phonemic repertoire and in the relative distinctiveness of phonemes within the repertoire. In the present study, we asked whether such differences constrain spoken-word recognition, via two word reconstruction experiments, in which listeners turned non-words into real words by changing single sounds. The experiments were carried out in Dutch (which has a relatively balanced vowel-consonant ratio and many similar vowels) and in Spanish (which has many more consonants than vowels and high distinctiveness among the vowels). Both Dutch and Spanish listeners responded significantly faster and more accurately when required to change vowels as opposed to consonants; when allowed to change any phoneme, they more often altered vowels than consonants. Vowel information thus appears to constrain lexical selection less tightly (allow more potential candidates) than does consonant information, independent of language-specific phoneme repertoire and of relative distinctiveness of vowels.