Dichotic Syllables Research Articles

PB8. Methylphenidate modulates gain modulation processes during competitive auditory attention in a dose–response fashion

The ability to selectively perceive and flexibly attend to relevant sensory signals in the environment is essential for adaptive behavior in everyday life. The fronto-striatal gain control mechanisms likely serve as an important regulatory interface of selective attention and perception. These gain control mechanisms are likely to be modulated by the dopaminergic system. In the current study, we administered methylphenidate (MPH) in two different dosages (0.25 mg/kg and 0.5 mg/kg) to healthy young adults in a single-blinded placebo-controlled study to examine the role of dopamine in regulating the gain control mechanisms. This was combined with high-density EEG recordings and source localization analyses in a dichotic listening task in which perceptual saliency was manipulated besides attentional focus resulting in conditions of low and high perceptual-attentional conflict. Compared to a placebo condition, we show that only at low MPH dosages (0.25 mg) performance was differentially modulated. No effects were observed using 0.50 mg MPH. The administration of 0.25 mg MPH reduced the effects of high perceptual-attentional conflict between discordant dichotic syllables. Interestingly, this was only the case for the right ear, which usually shows an advantage in verbal processing. This was reflected by specific EEG-correlates reflecting bottom-up attentional gating and top-down conflict monitoring processes. The results suggest that MPH modulates gain control processes during competitive auditory attention in a dose-dependent fashion. Yet, this modulatory effect depends on functional cerebral asymmetries.

The development of hand preference and dichotic language lateralization in males and females with congenital adrenal hyperplasia

ABSTRACTPeople with congenital adrenal hyperplasia (CAH) are exposed to elevated levels of androgens in utero due to overproduction by the adrenal cortex. In order to test whether high levels of prenatal androgens influence the development of handedness preferences and left-hemisphere language representation, we studied 39 patients with CAH (28 females, 11 males) and 25 unaffected sibling controls (17 females, 8 males). Hand preference for 15 unimanual activities was evaluated via questionnaire and pantomime, and a consonant–vowel dichotic listening test was administered. Contemporary theories disagree as to whether high testosterone is said to increase or decrease the probability of developing a typical right-hand preference. Results showed no significant differences on the handedness inventory. Relative to controls, however, patients with CAH showed a significantly larger right-ear advantage on the dichotic syllables task, indicating stronger left-hemisphere lateralization of language. These results support an emerging body of evidence suggesting that high testosterone may bias lateralized development toward the population norm, but run counter to the Geschwind–Behan–Galaburda model which associates high prenatal testosterone with a greater prevalence of left-handedness.

The processing of chimeric and dichotic emotional stimuli by connected and disconnected cerebral hemispheres

Hemispheric asymmetries have been widely explored in both the visual and the auditory domain, but little is known about hemispheric asymmetries in audio–visual integration. We compared the performance of a partially callosotomized patient, a total split-brain patient and a control group during the evaluation of the emotional valence of chimeric faces and dichotic syllables (an emotional syllable in one ear and white noise in the other ear) presented unimodally (only faces or only syllables) or bimodally (faces and syllables presented simultaneously). Stimuli could convey happy and sad expressions and participants were asked to evaluate the emotional content of each presentation, using a 5-point Likert scale (from very sad to very happy). In unimodal presentations, the partially callosotomized patient's judgments depended on the emotional valence of the stimuli processed by the right hemisphere, whereas those of the total split-brain patient showed the opposite lateralization; in these conditions, the control group did not show asymmetries. Moreover, in bimodal presentations, results provided support for the valence hypothesis (i.e., left asymmetry for positive emotions and vice versa) in both the control group and the partially callosotomized patient, whereas the total split-brain patient showed a tendency to evaluate the emotional content of the right hemiface even when asked to focus on the acoustic modality. We conclude that partial and total hemispheric disconnections reveal opposite patterns of hemispheric asymmetry in auditory, visual and audio–visual emotion processing. These results are discussed in the light of the right-hemisphere hypothesis and the valence hypothesis.

Reactive cognitive-control processes in free-report consonant–vowel dichotic listening

The relevance of cognitive-control processes has been frequently discussed and studied in the context of dichotic listening. Experimental and clinical studies indicate that directing attention to either of the two simultaneously presented phonological stimuli, but especially to the left-ear stimulus increases the requirements for cognitive-control processes. Here, we extend this view by reporting the results of a behavioural and a functional magnetic-resonance imaging (fMRI) experiment designed to analyse the involvement of cognitive-control processes also in a free-report dichotic-listening paradigm. It was hypothesised that dichotically presented pairs of stop–consonant–vowel syllables would provide different demands for cognitive-control processes as a function of the spectro-temporal overlap of the two stimuli. Accordingly, in Experiment 1 it was shown that dichotic syllables of high (e.g., /ba/ and /ga/) as opposed to low spectro-temporal overlap (e.g., /ba/ and /ka/) produce significantly faster and more correct answers, and are more often perceived as one syllable. In Experiment 2 it was further shown that pairs of low as compared to high spectro-temporal overlap trigger a more pronounced activation predominately in left-hemispheric, speech-associated brain regions, namely left posterior inferior sulcus/gyrus, bilaterally in pre-supplementary motor and mid-cingulate cortex as well as in the inferior parietal lobe. Taken together, behavioural and functional data indicate a stronger involvement of reactive cognitive control in the processing of low-overlap as opposed to high-overlap stimulus pairs. This supports the notion that higher-order, speech-related cognitive-control processes also are involved in a free-report dichotic-listening paradigm.

Evaluation of sound and ear advantage relationship via Turkish consonant–vowel dichotic syllables paradigm

Evaluation of sound and ear advantage relationship via Turkish consonant–vowel dichotic syllables paradigm

Endogenous and exogenous control of attention in dichotic listening.

Dichotic listening to verbal stimuli results in a right ear advantage (REA), indicating a left hemisphere processing superiority. The magnitude of the REA can be modulated by instructions to direct attention to the left or right ear stimulus. A previous study from our laboratory showed that presenting a prime syllable before the presentation of the dichotic syllables increases reports of the nonprimed syllable, apparently a negative priming effect that inhibits attention to the distracting prime representation. The present study combined attention instruction and priming, making up a 3 x 3 factorial design. The prime stimulus was a single consonant-vowel syllable presented binaurally just before onset of the dichotic consonant-vowel syllables. Results showed that both instructions and priming manipulations had an effect on which dichotic stimulus was selected. There was also a significant interaction between attention instruction and priming manipulation, indicating that the mechanism for instructed attention and the mechanism for negative priming work on the same level of processing.

Left temporal lobe dysfunction in schizophrenia: event-related potential and behavioral evidence from phonetic and tonal dichotic listening tasks.

Asymmetric reduction of the P3 event-related potential (ERP) has provided evidence of left temporal lobe dysfunction in schizophrenia. Prior studies have been limited by reliance on simple target detection (oddball) tasks with pure tones. This study investigated the time course and topography of ERPs to binaural syllables or complex tones in dichotic listening tasks. Event-related potentials of 26 patients meeting criteria for schizophrenia (n = 19) or schizoaffective disorder (n = 7) and 26 healthy controls were recorded from 30 scalp electrodes during 2 dichotic tasks in which different syllables or complex tones were simultaneously presented to each ear. A principal components analysis was used to derive factor scores corresponding to overlapping components in ERP waveforms--N1, N2, P3, and a late-positive potential. Healthy controls showed a right ear advantage for perceiving dichotic syllables, which was associated with greater N2 amplitude at left than right temporoparietal sites. Patients with schizophrenia did not show either this perceptual or N2 asymmetry. Patients also had smaller late-positive potential amplitude when compared with controls for both syllables and complex tones, with greatest decrement over left temporal sites. A right ear advantage in healthy adults for perceiving consonant-vowels was associated with a left-lateralized ERP component peaking at 200 milliseconds after syllable onset (N2). Patients with schizophrenia failed to show either of these task-dependent asymmetries, which may indicate a dysfunction of left temporal regions involved in phonetic classification. A task-independent asymmetric reduction of a later positive potential in patients with schizophrenia resembled left temporal P3 reductions reported for auditory oddball tasks.

Verbal Dichotic Listening in Boys at Risk for Behavior Disorders

The association between deficits in verbal processing skills and disruptive psychopathology remains one of the most frequently replicated findings in all of child psychiatry. This study uses a dichotic consonant-vowel listening test to examine the potential neural basis for this association. A series of 87 young boys recruited from a sample at risk for disruptive disorders received standardized psychiatric, neuropsychological, and language skills assessments. Approximately 1 year later, these boys received a reassessment of their psychiatric status and a test that assesses the neural basis of language-processing ability, a dichotic consonant-vowel listening test. Disruptive psychopathology predicted reduced right ear accuracy for dichotic syllables, indicative of a deficit in left hemisphere processing ability. Deficits in reading and language ability also correlated with right ear accuracy for dichotic syllables. Boys with disruptive behavior disorders, relative to at-risk but nondisruptive boys, exhibit a deficit in verbal processing abilities on dichotic listening tasks. This deficit in verbal processing ability is also manifested as low scores on standardized tests of reading achievement and language comprehension.

Factor analysis and the cerebral hemispheres: “Unlocalized” functions

Previous factor analyses have employed lateralized task tapping processes (functions) whose localizations are thought to be known at the level of the cerebral lobe or finer. Here nine tasks are introduced to factor analysis whose underlying processes have unknown localization. A new function identified as auditory emotional is found to be independent of asymmetry in a visual emotion judgment task, suggesting that lateralized emotion judgments depend on modality specific processes. A second new function identified as visual temporal is found to be independent of asymmetries in visual language recognition, posing constraints on theories that link lateralized language processes to processes dealing with temporal sequencing. Another important finding is that the recognition of dichotic syllables relies on a previously identified process, indicating that the process is better labelled auditory linguistic than auditory lexical and suggesting that lexical status may be irrelevant to auditory language asymmetries. Also, a word naming task is found to produce visual field asymmetry because of a stimulus encoding (visual lexical) process, with no clear evidence found of influence from asymmetric response processes. Taken together, the full set of lateralized processes appear to show high degrees of modality specificity and mutual independence (modularity).

Speech Perception and Brain Laterality: The Effect of Ear Advantage on Auditory Event-Related Potentials

Dichotic listening has been used for assessing asymmetries in processing auditory stimuli. It is known that there is better recognition of dichotic stimuli in the right ear with verbal stimuli (right ear advantage, REA) by the majority of the subjects. We were interested in the psychophysiological correlates of ear advantage as it is manifested in event-related potentials (ERP). We compared ERPs to monaural and dichotic syllables in stable REA and LEA subjects. The most consistent finding was that REA subjects show larger positive ERP deflections over the left hemisphere (maximal at T5) and LEA subjects over the right hemisphere (maximal at T6) both at the latency range of 320-340 msec. Thus, brain event-related potentials support the contention that the REA and LEA reflect differential activation of the left and right hemispheres, respectively.

Effects of discontinuous F3 transitions on phonetic identification and fusion

According to general perceptual principles, figural goodness and feature integration of stimuli should reflect the continuity between components; in CV syllables this continuity might be between phoneme-distinguishing glide (formant transition) and vowel formant. Two experiments examined continuity effects on identification and fusion for sinewave syllables based on common CV parameters. Experiment 1 provided a perceptual basis for equating isolated glides and stationary tones. Independent of glide direction, perceptual matches tended to be based upon temporally adjacent portions of the stimuli. Using matched stimuli, experiment 2 evaluated the relative contribution to phonetic identification of (1) frequency continuity of transition and formant and (2) transition direction. Subjects discriminated the original syllables from binaural and dichotic syllables containing either continuous or discontinuous F3 transitions. Identification was influenced more by transition direction than by goodness of physical continuity. Furthermore, very different patterns of results were obtained for binaural conditions and dichotic conditions in which responses indicated fusion. The nature of information provided by transitions and operation of schema are discussed. [Work supported by NSF and AFOSR.]

Do children with learning disabilities outgrow deficits in selective auditory attention? Evidence from dichotic listening in adults with learning disabilities.

Previous research suggests that children with learning disabilities (LD) evidence similar degrees of cerebral lateralization as nondisabled children, but they perform at a degraded level due to deficits in selective attention. The developmental lag hypothesis predicts that these deficits should attenuate in children with LD with maturity. The present study examined this notion by evaluating dichotic listening ability using both free recall and directed attention conditions in 24 adults with LD and their age- and sex-matched controls. Dichotic syllables, words, and sentences were employed. The results indicated similar degrees of cerebral lateralization but significantly degraded levels of accuracy in the adults with LD in the free recall and directed attention conditions across all levels of semantic processing. Thus, it would appear that adults with LD evidence similar deficits in lateralized selective auditory linguistic processing as found in children with LD.

Processing the intensity of dichotic syllables

Subjects were required to match the intensity levels of the left- and right-ear members of dichotically presented nonsense syllables. When subjects matched the overall average intensities of a sequence of differing dichotic pairs no ear differences were observed. When repetitions of single dichotic pairs were matched right-ear syllables were judged louder than left-ear syllables. The results support a model predicting left-hemisphere superiority in a task permitting higher-level encoding of speech input.

Stimulus dominance in fused dichotic syllables: trouble for the category goodness hypothesis.

Repp [J. Acoust. Soc. Am. 60, 456-469 (1976)] hypothesized that dichotic stimulus dominance relationships between fused speech sounds reflect the relative category goodness of the competing stimuli, i.e., their relative perceptual distances from the listener's linguistic category prototypes. In experiment I, 15 synthetic syllables from a /bae/-/dae/-/gae) continuum were dichotically fused with three selected stimuli from the same continuum and presented to listeners for identification. Stimuli in the vicinity of phonetic category boundaries were found to make weaker dichotic competitors than stimuli from well within a phonetic category, as predicted. However, some systematic deviations from the predictions and large individual differences were noted. In experiment II, synthetic syllables from a /ba/-/da/-/ga/ continuum were paired with either of the two endpoint stimuli (/ba/,/ga/) in dichotic or mixed presentation. The resulting fused hybrid stimuli were presented in identification and AXB discrimination tests. The hybrids were perceived quite categorically, and there was little difference between dichotic and mixed modes of presentation. These results did not replicate earlier data [Repp, Haskins SR-45/46, 123-139 (1976)] that had suggested that discrimination of dichotic hybrid stimuli might be based on a level of representation preceding phonetic categorization. The category goodness hypothesis, which implies such a level, was neither supported nor contradicted. In experiment III, the prediction was tested that increasing the aspiration amplitude of a /ta/ syllable, and thus its category goodness, would increase the perceptual dominance of this stimulus over a /da/ simultaneously presented to the other ear. This hypothesis was not supported by the data. Rather, the response pattern suggested that a listener's success in perceptually integrating the aspiration noise (of /ta/) with the fused vocalic portion (of /da/ and /ta/) into a single phonetic percept depended on the perceived spatial locations of these stimulus portions. Taken together, the results of the three experiments cast doubt on the category goodness hypothesis and suggest that dichotic stimulus dominance in fused speech sounds is determined by psychoacoustic factors, some as yet undefined.

Identification of dichotic fusions

Seven synthetic syllables from a ’’place continuum’’ (/bae/–/dae/–gae/) were presented in all dichotic combinations for identification. These syllables fused completely, so that dichotic pairs were perceived as single stimuli. The response pattern could not easily be explained by an ’’auditory averaging’’ hypothesis. Rather, stimuli that were good instances of a category seemed to ’’dominate’’ stimuli that were closer to a category boundary. To account for this finding, a three-stage pattern recognition (’’prototype’’) model is proposed, according to which the information from the two ears is linearly combined after ’’multicategorical’’ processing, which follows auditory processing and precedes the final phonetic decision. Electronically mixed stimuli led to a response pattern that was similar to that for dichotic syllables (apart from some systematic deviations ascribed to peripheral masking), so that the same processes of central interaction seem to be involved. Average dichotic right-ear advantages of small magnitude were obtained for the dichotic fusions. They could not be reliably discriminated from binaural stimuli, and selective attention to one ear had little effect. With respect to the measurement of dichotic ear asymmetries, dichotic fusions offer certain methodological advantages over other dichotic stimuli. The problem of determining the ’’true’’ ear advantage is discussed. Subject Classification: [43]70.30; [43]65.75.

Categorical perception, auditory memory, and dichotic interference: a “same”—“different” reaction time study

A “same”—“different” reaction time study was conducted in which stimuli from a voice onset time continuum were presented dichotically at seven different stimulus onset asynchronies (0–3.3 sec). There were two kinds of instructions: “phonetic match” (same or different category?) and “acoustic match” (same or different stimulus?). The study was aimed at the following questions: (a) Can the effect of acoustic differences on reaction time [Pisoni and Tash, Percept. Psychophys. 15, 285 (1974)] be replicated? (b) Does this effect decrease with temporal separation of the stimuli? (c) Do pretraining and “acoustic match” instructions lead to improved discrimination in this paradigm [cf. Pisoni and Lazarus, J. Acoust. Soc. Am. 55, 328 (1974)]? (d) Do they increase the Pisoni-Tash effect? (e) Is within-category discrimination greatly improved and as good as between-category discrimination with simultaneous dichotic syllables? (f) Are incorrect “different” responses under dichotic interference (at short time lags) related to distance of the stimuli from the category boundary [cf. Repp, J. Acoust. Soc. Am. 56, S53 (1974)]. Preliminary analysis suggests these answers: (a) yes; (b) no; (c) no; (d) yes; (e) yes and no; (f) no? Final results and their implications are discussed.

Errors and latencies for same-different judgments of dichotic CV syllables at various stimulus onset asynchronies (SOAs)

Three studies were conducted using this paradigm. The major independent variables were SOA and the number of feature contrasts (FC) between the syllables to be compared. Errors and latencies were found to decrease systematically with SOA and with FC. The effect of FC on latencies persisted over at least 500-msec SOA, which argues against comparisons of “holistic” phonemes after encoding is completed. The third study included variations in pitch and predictability of this variation (blocked versus random) as additional factors. They were found to have dramatic effects at very short SOAs but surprisingly little influence at longer SOAs. The results are discussed with reference to a two-process model of dichotic interaction: “integration” at very short SOAs versus “perceptual noise” at longer SOAs. Evidence for integration was seen in the frequency occurrence of incorrect “same” responses at short SOAs. Dichotic syllables that are not integrated are assumed to be compared after being categorized, the major evidence being a negative relationship between intelligibility and incorrect “different” responses.