Magdalene H. Chalikia

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 (FO) between two simultaneous vowel sounds improves their separate identification. In the present experiments, we looked at the effect of FOs 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 FOs; different FO separations were also used. The subjects had to indicate whether they had heard one or two sounds. The results showed that increased FO differences and gliding FOs 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 FOs. 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 perceptual segregation of simultaneous vowels with harmonic, shifted, or random components

This experiment was an investigation of the ability of listeners to identify the constituents of double vowels (pairs of synthetic vowels, presented concurrently and binaurally). Three variables were manipulated: (1) the size of the difference in FO between the constituents (0, 1/2, and 6 semitones); (2) the frequency relations among the sinusoids making up the constituents: harmonic, shifted (spaced equally in frequency but not integer multiples of the FO), and random; and (3) the relationship between the F0 contours imposed on the constituents: steady state, gliding in parallel, or gliding in opposite directions. It was assumed that, in the case of the gliding contours, the harmonics of each vowel would “trace out” their spectral envelope and potentially improve the definition of the formant locations. It was also assumed that the application of different FO contours would introduce differences in the direction of harmonic movement (common fate), thus aiding the perceptual segregation of the two vowels. The major findings were the following: (1) For harmonic constituents, a difference in FO leads to improved identification performance. Neither tracing nor common-fate differences add to the effect of pitch differences. (2) For shifted constituents, a difference between the spacing of the constituents also leads to improved performance. Formant tracing and common fate contribute some further improvement (3) For random constituents, tracing does not contribute, but common fate does.

Greek bilingual listeners perceive the tritone stimuli differently from speakers of English

When listeners are presented with pairs of octave‐complex tones related by a tritone interval (a half‐octave), they hear the pattern as ascending or descending, according to an individual pitch class template. Deutsch (1991) has claimed that this template may be influenced by language. In order to test this hypothesis, data from Greek bilingual listeners were collected and compared with data from Texas, California, and the south of England. The results show significant differences in how Greek listeners hear the tritone stimuli, as compared to listeners in the other groups. There is also evidence that the Greek listeners may have developed two different pitch class templates, possibly representing the influence of English and the influence of Greek.

Phonemic Transformations: Mapping the Illusory Organization of Steady-State Vowel Sequences

Previous research has shown that listeners presented with repeated sequences of brief steady-state vowels (30–100 msec) experience phonemic transformations (that is, illusory changes in the identity of the constituent speech sounds) and report hearing verbal forms consisting of one or more syllables rather than a succession of vowels. Often the signal is split perceptually into two simultaneous organizations differing in both timbre and phonemic content. The present studies employed sequences of eight 80-msec vowels and mapped the perceptual phonemes to acoustic phones by terminating the repeated sequence at predetermined positions and determining the last speech sound heard in the perceived verbal organization (Experiments 1 and 2). When two simultaneous organizations were heard, they were both mapped (Experiments 2 and 3). It was found that: (1) all listeners reported hearing a polysyllabic verbal organization together with either a noise-like non-linguistic residue or a second verbal organization; (2) the verbal forms heard not only followed the phonotactic rules of English, but also corresponded to syllables actually found in English; (3) when two simultaneous organizations were heard, the primary or more salient one was usually longer; (4) simultaneous organizations had different timbres. Implications concerning the perceptual organization of speech are discussed.

Listeners in Sweden perceive tritone stimuli in a manner different from that of Americans and similar to that of British listeners

The tritone stimuli consist of two tones, each of which has octave‐related harmonics. The two tones are separated from each other by a half‐octave (a tritone interval). The tones are typically presented successively, and listeners decide whether or not the second tone in the pair is perceived as ascending or descending, relative to the first one. Responses tend to vary across listeners for the same stimuli, and for different stimuli. In this study, participants from Stockholm, Sweden, were presented with such tritone pairs and were asked to determine if they heard each pair as ascending or descending. Deutsch’s (1991) hypothesis, that language background may influence the perception of the tritone stimuli, was tested. All participants were speakers of both English and Swedish. Their data were compared to data of English monolinguals tested in Texas, and California, as well as listeners from the south of England. Preliminary results suggest that the overall perception pattern in Sweden differs from that fo...

Spectral fissioning in phonemic transformations

Listeners presented with a repeated sequence of brief (30- to 100-msec) steady-state vowels hearphonemic transformations—they cannot identify the vowels, but they perceive two simultaneous utterances that differ in both phonemic content and timbre (Warren, Bashford, & Gardner, 1990). These utterances consist of either English words or syllables that occur in English words. In the present study, we attempted to determine whether the two percepts represent alternative interpretations of the same formant structures, or whether different portions of the vowels are used for each verbal organization. It was found that separate spectral regions are employed for each verbal form; Components below 1500 Hz were generally used for one form, and components above 1500 Hz for the other. Hypotheses are offered concerning the processes responsible for the verbal organization of the vowel sequences and for the splitting into two spectrally limited forms. It appears that the tendency to organize spectral regions separately competes with, and can overcome, the tendency to integrate the different spectral components of speech into a single auditory image. A contralateral induction paradigm was used in a procedure designed to quantitatively evaluate these opposing forces of spectral fission and fusion.

The perception of tritone stimuli by listeners in the Midwest

The tritone stimuli [Deutsch (1986)], consist of two tones, each with octave‐related harmonics. The tones are separated from each other by a tritone (half‐octave) interval. The tones are presented successively, and listeners decide whether or not the second tone in the pair is perceived as ascending or descending, relative to the first one. Listeners tend to hear the tritone pattern as ascending or descending, according to an individual pitch class template, which Deutsch (1991) claims may be influenced by language or English dialect. Some similarities have been found among people from different areas of the U.S., suggesting a canonical manner of perceiving the tritone stimuli, probably propagated by the media [Ragozzine and Deutsch (1994)]. The present study tested the media exposure hypothesis, by presenting tritone stimuli to listeners who grew up in the Midwest. Results show that Midwesterners show a different perceptual pattern relative to that of listeners from Texas and the south of England, but th...

Perception of the tritone paradox by listeners in Texas: A re‐examination of envelope effects

Deutsch (1986, 1987) first reported that when listeners are presented with pairs of octave‐complex tones related by a half‐octave interval (a tritone), they hear the pattern as descending or ascending, according to an individual pitch class template. Individual pitch class effects were found to be stable across tests that use tones with different spectral envelopes. Repp (1994, 1997) has found envelope effects but, in a recent study, Giangrande (1999) has not. Perception of the tritone pattern can vary with the geographical region in which the listener grew up, even though similarities have been reported between listeners in California and South Florida. These similarities suggest a canonical manner of perceiving the tritone stimuli within the U.S., probably propagated by the media (Ragozzine and Deutsch, 1994). The present study tested the hypothesis that a canonical manner of perceiving the tritone stimuli exists, by presenting tritone tones to listeners who grew up in Texas. The influence of the spectr...

Spectral factors in the organization of vowel sequences into words

Previous research [Warren et al., Percept. Psychophys. 47, 423–432 (1990)] has shown that listeners presented with recylced sequences of steady‐state vowels hear illusory syllables and words rather than a succession of vowels. Often the signal is split perceptually into two simultaneous words differing in both timbre and phonemic content. The present study investigated the spectral composition of such dual organizations and found that it is possible to isolate for further study spectral bands corresponding to each word. When one such narrow band is presented to one ear and the broadband vowel sequence to the other, the narrow band word can be extraced from the lateralized broadband spectrum and heard at the medial plane. Under appropriate conditions, a monaural narrow band noise spanning the same frequency range as the narrow band word also can, through contralateral induction, excise the word from the broadband vowel sequence and move it to the medial plane. In contrast, it is not possible to delateraliz...

Do bilinguals perceive the tritone paradox as monolinguals do

When a two‐tone pattern in which the tones are related by a half‐octave interval (tritone) is played in any key, listeners hear it as descending or ascending, on the basis of an individual pitch class template (Deutsch, 1986). Perception of this pattern has been reported to vary with the geographical region in which the listener grew up, and it has been suggested (Deutsch, 1994; Ragozzine and Deutsch, 1994) that the characteristics of ones pitch class template may vary among speakers of different dialects and languages. This hypothesis was tested by asking how bilingualism may influence the perception of the tritone pairs. Spanish/English bilinguals were tested and their performance was compared with that of a group of English speakers. All listeners were from Texas. The results indicate that bilinguals perceive the patterns differently than the monolinguals. Envelope influences will also be discussed.