Perceptual organization of acoustic stimuli by budgerigars (Melopsittacus undulatus): II. Vocal signals

Operant conditioning and multidimensional scaling procedures were used to study auditory perception of complex sounds in the budgerigar. In a same-different discrimination task, budgerigars learned to discriminate among natural vocal signals. Multidimensional scaling procedures were used to arrange these complex acoustic stimuli in a two-dimensional space reflecting perceptual organization. Results show that budgerigars group vocal stimuli according to functional and acoustical categories. Studies with only contact calls show that birds also make within-category discriminations. The acoustic cues in contact calls most salient to budgerigars appear to be quite complex. There is a suggestion that the sex of the signaler may also be encoded in these calls. The results from budgerigars were compared with the results from humans tested on some of the same sets of complex sounds.     

Perceptual order and the effect of vocalic context of fricative perception

This three-part study demonstrates that perceptual order can influence the integration of acoustic speech cues. In Experiment 1, the subjects labeled the [s] and [sh] in natural FV and VF syllables in which the frication was replaced with synthetic stimuli. Responses to these "hybrid" stimuli were influenced by cues in the vocalic segment as well as by the synthetic frication. However, the influence of the preceding vocalic cues was considerably weaker than was that of the following vocalic cues. Experiment 2 examined the acoustic bases for this asymmetry and consisted of analyses revealing that FV and VF syllables are similar in terms of the acoustic structures thought to underlie the vocalic context effects. Experiment 3 examined the perceptual bases for the asymmetry. A subset of the hybrid FV and VF stimuli were presented in reverse, such that the acoustic and perceptual bases for the asymmetry were pitted against each other in the listening task. The perceptual bases (i.e., the perceived order of the frication and vocalic cues) proved to be the determining factor. Current auditory processing models, such as backward recognition masking, preperceptual auditory storage, or models based on linguistic factors, do not adequately account for the observed asymmetries.     

Perceptual order and the effect of vocalic context on fricative perception

This three-part study demonstrates that perceptual order can influence the integration of acoustic speech cues. In Experiment 1, the subjects labeled the [s] and [∫] in natural FV and VF syllables in which the frication was replaced with synthetic stimuli. Responses to these “hybrid” stimuli were influenced by cues in the vocalic segment as well as by the synthetic frication. However, the influence of the preceding vocalic cues was considerably weaker than was that of the following vocalic cues. Experiment 2 examined the acoustic bases for this asymmetry and consisted of analyses revealing that FV and VF syllables are similar in terms of the acoustic structures thought to underlie the vocalic context effects. Experiment 3 examined the perceptual bases for the asymmetry. A subset of the hybrid FV and VF stimuli were presented inreverse, such that the acoustic and perceptual bases for the asymmetry were pitted against each other in the listening task. The perceptual bases (i.e., the perceived order of the frication and vocalic cues) proved to be the determining factor. Current auditory processing models, such as backward recognition masking, preperceptual auditory storage, or models based on linguistic factors, do not adequately account for the observed asymmetries.     

The abstraction of musical ideas

Music presents information both sequentially, in the form of musical phrases, and simultaneously, in the form of chord structure. The ability to abstract musical structure presented sequentially and simultaneously was investigated using modified versions of the Bransford and Franks’ (1971) paradigm. Listeners heard subsets of musical ideas. The abstraction hypothesis predicted (1) false recognition of novel instances of the abstracted musical idea, (2) confidence of “recognition” should increase as recognition items approximate the complete musical idea, (3) correct rejection of “noncases,” which deviate from the acquired musical structure. Experiment 1 investigated sequential abstraction by using four-phrase folk melodies as musical ideas. Predictions 1 and 3 were confirmed, but the false recognition rate decreased as the number of phrases increased. Listeners were sensitive to improper combinations of phrases and to novel melodies different from melodies presented during acquisition. Experiment 2 investigated simultaneous abstraction using four-voice Bach chorales as musical ideas. Listeners spontaneously integrated choral subsets into holistic musical ideas. Musically trained listeners were better than naive listeners at identifying noncases.     

Between Open-minded Critical Thinking and Closed-minded Allegiance: Educational Tensions in Societies Involved in Intractable Conflict

In modern democratic societies, one of the main roles of education is to promote critical thinking and open-mindedness. However, this objective can sometimes be seen as clashing in many societies with another one of education's primary objectives—to inculcate in the younger generation a set of common values and beliefs that reinforces collective identity. The current article examines the tension between these two educational goals—fostering open-mindedness and critical-thinking skills, on the one hand, and promoting closed-minded national identity, on the other hand, in the context of intractable conflicts. In particular, we offer an analysis of the unique challenges of nurturing open-minded and critical thinking among students in the presence of processes and content common in education systems of conflict-ridden societies. These challenges are discussed in relation to the role that open-mindedness and critical thinking could play in promoting peace-building processes were they not hindered by nationalistic educational approaches designed to ensure unwavering support of the conflict.     

Perceptual organization of acoustic stimuli by budgerigars (Melopsittacus undulatus): I. Pure tones

A new combination of operant conditioning and psychophysical scaling procedures was used to study auditory perception in a small bird. In a same-different discrimination task, budgerigars learned to discriminate among pure tones that varied along one or more acoustic dimensions. Response latencies were used to generate a matrix of interstimulus similarities. Multidimensional scaling procedures were used to arrange these acoustic stimuli in a multidimensional space that supposedly reflects the bird's perceptual organization. For tones that varied in intensity, duration, and frequency simultaneously, budgerigars were much more sensitive to frequency changes. From a set of tones that varied only in intensity, it was possible to calculate the growth of loudness with intensity for the budgerigar. For tones that varied only in frequency, budgerigars showed evidence of an "acoustic fovea" for frequency change in the spectral region of 2-4 kHz. Budgerigars and humans also differed in their perceptual grouping of tone sequences that rise, fall, or remain constant in pitch. Surprisingly, budgerigars were much less responsive to pitch contour than were humans.     

Performance biases and recognition memory for semantic and formal changes in connected discourse

In an experiment comparing memory for formal and semantic information, the confounding effects of attentional and response biases were controlled using an adaptation of Sachs' (1967, 1974) method. Subjects attempted to recognize semantic or formal changes in test sentences following short passages of connected discourse. Attentional biases were controlled by using a single type of change in an experimental session, and response biases were controlled with methods from signal detection theory. Semantic recognition scores were consistently above formal scores, both within subjects and within passages, indicating that superiority of semantic performance is attributable to differences in memorability rather than to biases favoring semantic performance. However, formal scores were above chance, suggesting that the poor memory for formal information, as reported previously, may have been due to performance factors.     

Some effects of acoustic attributes of speech on the processing of phonetic feature information

How do acoustic attributes of the speech signal contribute to feature-processing interactions that occur in phonetic classification? In a series of five experiments addressed to this question, listeners performed speeded classification tasks that explicitly required a phonetic decision for each response. Stimuli were natural consonant-vowel syllables differing by multiple phonetic features, although classification responses were based on a single target feature. In control tasks, no variations in nontarget features occurred, whereas in orthogonal tasks nonrelevant feature variations occurred but had to be ignored. Comparison of classification times demonstrated that feature information may either be processed separately as independent cues for each feature or as a single integral segment that jointly specifies several features. The observed form on processing depended on the acoustic manifestations of feature variation in the signal. Stop-consonant place of articulation and voicing cues, conveyed independently by the pattern and excitation source of the initial formant transitions, may be processed separately. However, information for consonant place of articulation and vowel quality, features that interactively affect the shape of initial formant transitions, are processed as an integral segment. Articulatory correlates of each type of processing are discussed in terms of the distinction between source features that vary discretely in speech production and resonance features that can change smoothly and continuously. Implications for perceptual models that include initial segmentation of an input utterance into a phonetic feature representation are also considered.