Auditory evoked potentials during selective listening to dichotic speech messages

The sensitivity of the scalp-recorded, auditory evoked potential to selective attention was examined while subjects monitored one of two dichotically presented speech passages for content. Evoked potentials were elicited to irrelevant probe stimuli (vowel sounds) embedded in both the right- and the leftear’s message. The amplitude of the evoked potential was larger to probe stimuli embedded in the attended message than to probe stimuli in the unattended message. Recall performance was unaffected by the presence of the probes. The results are interpreted as supporting the hypothesis that this evoked potential sensitivity reflects an initial “input selection” stage of attention.     

Red herring detectors and speech perception: In defense of selective adaptation

The selective adaptation paradigm was used extensively for about 5 years following its introduction to speech research in 1973. During the next few years, its use dropped dramatically; it is now little used. Several reasons for the abandonment of the paradigm are discussed, and theoretical and empirical justification is provided for rejecting these reasons. Experiment 1 demonstrates that “acoustic similarity” of an adapting sound and test items cannot account for the observed results. Experiments 2–4 demonstrate that adaptation effects are not equivalent to simple contrast effects. These experiments indicate that selective adaptation produces robust reaction time effects—items in the adapted category are identified more slowly than unadapted items. The effects found in a simple paired-contrast procedure differ from those found with selective adaptation. Most strikingly, contrast effects are extremely ear dependent—much larger effects occur if testing is conducted in the right ear than in the left; adaptation effects are relatively symmetrical with respect to ear. The empirical and theoretical analyses suggest that the selective adaptation paradigm can be a powerful tool for investigating the perception of complex acoustic stimuli like speech.     

Lateralisation of language and emotion in schizotypal personality: Evidence from dichotic listening

Striking disturbances have been reported in language and emotional prosody processing by patients diagnosed with schizophrenia. In view of this and of research suggesting that schizotypal personality traits can also be expressed sub-clinically, the present study aimed to discover whether similar disturbances would be reflected in cognitive laterality patterns when symptoms of schizotypy are present yet at a non-clinical level. A dichotic listening task was used to examine the sensitivity and speed with which 132 right-handed participants (85 females and 47 males, mean age = 32.44, SD = 12.29) detected both words and emotional prosody, all of whom also completed the Schizotypal Personality Questionnaire. Findings indicated that both high (n = 64) and low (n = 68) schizotypy groups demonstrated the typical right ear advantage for the detection of words and left ear advantage for the detection of emotional prosody. Individuals with higher schizotypal personality scores also demonstrated poorer sensitivity in detecting emotional prosody. These results reveal that within the healthy population, higher levels of schizotypy are not associated with the atypical lateralisation of language and emotion. Nevertheless, the existence of these symptoms does signal the presence of shared characteristics with the clinical sphere, namely poorer emotion recognition performance.     

Hormones and dichotic listening: evidence from the study of menstrual cycle effects

This report presents evidence for changes in dichotic listening asymmetries across the menstrual cycle, which replicate studies from our laboratory and others. Increases in the right ear advantage (REA) were present in women at phases of the menstrual cycle associated with higher levels of ovarian hormones. The data also revealed correlations between hormone levels and behavioural measures of asymmetry. For example, the pre-ovulatory surge in luteinising hormone (LH) was related to a decrease in left ear scores, which comprised a key part of the cycle related shift in asymmetry. Further analysis revealed a subgroup of women who had not reached postovulatory status by days 18-25 of the cycle, as verified by low progesterone levels. These women showed laterality profiles at days 18-25 that looked more like the other women when measured at the periovulatory phase (i.e., days 8-11). Data were combined with those from a previous study to highlight the stability of effects. Results showed a distinct menstrual cycle related increase in asymmetry in the combined sample. This final comparison confirmed the nature of sex differences in dichotic listening as being dependent on hormone status in women.     

Hemispheric specialization for voice recognition: evidence from dichotic listening

To measure lateralization of voice recognition abilities in normal subjects, listeners identified both the speaker (a famous male) and the word spoken on each trial in a dichotic listening paradigm. The voice identification task resulted in a zero ear advantage, which differed significantly from the significant right ear advantage found for word identification. This suggests that voice and word information, although carried in the same auditory signal, engage different cerebral mechanisms.     

Auditory and phonetic processes in speech perception: Evidence from a dichotic study

The distinction between auditory and phonetic processes in speech perception was used in the design and analysis of an experiment. Earlier studies had shown that dichotically presented stop consonants are more often identified correctly when they share place of production (e.g., /ba-pa/) or voicing (e.g., /ba-da/) than when neither feature is shared (e.g., /ba-ta/). The present experiment was intended to determine whether the effect has an auditory or a phonetic basis. Increments in performance due to feature-sharing were compared for synthetic stop-vowel syllables in which formant transitions were the sole cues to place of production under two experimental conditions: (1) when the vowel was the same for both syllables in a dichotic pair, as in our earlier studies, and (2) when the vowels differed. Since the increment in performance due to sharing place was not diminished when vowels differed (i.e., when formant transitions did not coincide), it was concluded that the effect has a phonetic rather than an auditory basis. Right ear advantages were also measured and were found to interact with both place of production and vowel conditions. Taken together, the two sets of results suggest that inhibition of the ipsilateral signal in the perception of dichotically presented speech occurs during phonetic analysis.     

Susceptibility of a stop consonant to adaptation on a speech-nonspeech continuum: Further evidence against feature detectors in speech perception

The present experiment uses the perceptual adaptation paradigm to establish the validity of a previous test of the feature detector model of speech perception. In the present study, a synthetic stimulus series varied from a CV syllable, [ba], to a nonspeech buzz. When the endpoint tokens were employed alternatively as adaptors, the category boundary was shifted relative to unadapted identification in each adaptor condition. This result suggests that a prior test which used a vowel as the speech endpoint was legitimate because a stop consonant, an exemplary speech sound, was also susceptible to perceptual adaptation in a speech-nonspeech context. Feature detector models predict, incorrectly, that this outcome is impossible. Therefore, this finding may be taken to undermine the interpretation of adaptation as fatigue in a set of detectors tuned to detect the distinctive features of linguistic analysis.     

The effects of background noise on dichotic listening to consonant-vowel syllables

Lateralization of verbal processing is frequently studied with the dichotic listening technique, yielding a so called right ear advantage (REA) to consonant-vowel (CV) syllables. However, little is known about how background noise affects the REA. To address this issue, we presented CV-syllables either in silence or with traffic background noise vs. 'babble'. Both 'babble' and traffic noise resulted in a smaller REA compared to the silent condition. The traffic noise, moreover, had a significantly greater negative effect on the REA than the 'babble', caused both by a decreased right ear response as well as an increased left ear response. The results are discussed in terms of alertness and attentional factors.     

Lateralization of speech processing in the brain as indicated by mismatch negativity and dichotic listening

The goal of the present study was to evaluate the differences between dichotic listening and mismatch negativity as measures of speech lateralization in the human brain. For this purpose, we recorded the magnetic equivalent of the mismatch negativity, elicited by consonant-vowel syllable change, and tested the same subjects in the dichotic listening procedure. The results showed that both methods indicated left-hemisphere dominance in speech processing. However, the mismatch negativity, as compared to the right-ear advantage, suggested slightly stronger left-hemisphere dominance in speech processing. No clear correlation was found between the laterality indexes of mismatch negativity and right-ear advantage calculated from dichotic listening results. The possible explanation for this finding would be that these two measures reflect different stages of speech processing in the human brain.     

Sensation seeking and selective attention: focused and divided attention on a dichotic listening task.

Differences in selective attention as a function of sensation seeking, extraversion, neuroticism, and psychoticism were examined in 108 undergraduates using a dichotic listening task. Dependent measures included shadowing performance, reaction times to a secondary light task, target detection, and recall. The results suggested that high sensation seekers have better focused attention than low sensation seekers, and these effects were strongest on the 1st trials of the shadowing tasks. High sensation seekers did not attend differently than low sensation seekers to words related to their interests (sexual, violent, or drug related). Extraversion was associated with greater recall of these kinds of words, although there were no overall differences in selective attention as a function of Eysenck's dimensions. The role of arousal in personality and attention is discussed, particularly in regard to the response of sensation seekers to task novelty.     

Perspectives on dichotic listening and the corpus callosum

The present review summarizes historic and recent research which has investigated the role of the corpus callosum in dichotic processing within the context of audiology. Examination of performance by certain clinical groups, including split brain patients, multiple sclerosis cases, and other types of neurological lesions is included. Maturational, age related, and genetic factors are also discussed. Finally, some attention is given to recent trends in audiology research to develop improved diagnostic and rehabilitation tools for individuals with dichotic deficits potentially related to callosal dysfunction.     

The role of auditory feature detectors in the perception of speech

Attention, Perception, & Psychophysics - Two adaptation experiments were conducted to determine some of the sufficient acoustic properties for excitation of the feature detectors underlying...     

The role of spatial complexity in the perception of speech and pure tones in dichotic listening

Ear advantages for CV syllables were determined for 28 right-handed individuals in a target monitoring dichotic task. In addition, ear dominance for dichotically presented tones was determined when the frequency difference of the two tones was small compared to the center frequency and when the frequency difference of the tones was larger. On all three tasks, subjects provided subjective separability ratings as measures of the spatial complexity of the dichotic stimuli. The results indicated a robust right ear advantage (REA) for the CV syllables and a left ear dominance on the two tone tasks, with a significant shift toward right ear dominance when the frequency difference of the tones was large. Although separability ratings for the group data indicated an increase in the perceived spatial separation of the components of the tone complex across the two tone tasks, the separability judgment ratings and the ear dominance scores were not correlated for either tone task. A significant correlation, however, was evidenced between the laterality measure for speech and the judgment of separability, indicating that a REA of increased magnitude is associated with more clearly localized and spatially separate speech sounds. Finally, the dominance scores on the two tone tasks were uncorrelated with the laterality measures of the speech task, whereas the scores on the tone tasks were highly correlated. The results suggest that spatial complexity does play a role in the emergence of the REA for speech. However, the failure to find a relationship between speech and nonspeech tasks suggest that all perceptual asymmetries observed with dichotic stimuli cannot be accounted for by a single theoretical explanation.     

The effect of selective adaptation on the identification of speech sounds

An experiment was performed to determine the effect of selective adaptation on the identification of synthetic speech sounds which varied along the phonetic dimensionplace of articulation. Adaptation with a stimulus of a particular place value led to a reduction in the number of test stimuli identified as having that place value. An identification shift was obtained even when the acoustic information specifying place value for the adapting stimulus had virtually nothing in common with the information specifying place value for any of the test stimuli. Removing the vowel portion of an adapting stimulus eliminated identification shift only when the resulting stimulus was no longer perceived as speech-like. The results indicate that at least part of the adaptation effect occurs at a site of phonetic, not merely acoustic, feature analysis.