Harvey M. Sussman

Hemispheric specialization for speech production and perception in stutterers

Abstract A group of stutterers was tested on presumed indices of hemispheric specialization for speech production (pursuit auditory tracking) and speech perception (dichotic listening). Previous studies of normal subjects [18, 19] have revealed a significant right ear advantage (REA) for tracking with a speech articulator but not with manual tracking. Stutterers showed no significant REA in either tracking condition, but did show a significant REA, similar to that of normal speakers, in dichotic listening. Results were considered to differentiate this population of stutterers from normals in terms of hemispheric specialization for speech production but not for speech perception.

AN INVESTIGATION OF STOP PLACE OF ARTICULATION AS A FUNCTION OF SYLLABLE POSITION : A LOCUS EQUATION PERSPECTIVE

Locus equations were employed to phonetically describe stop place categories as a function of syllable-initial, -medial, and -final position. Ten speakers, five male and five female, produced a total of 2700 CVC and 4500 VCV utterances that were acoustically analyzed to obtain F2 onset, F2 vowel, and F2 offset frequencies for locus equation regression analyses. In general, degree of coarticulation, as indexed by locus equation slope, was reduced for post-vocalic (VC) stops relative to pre-vocalic stops (pooled data from initial and medial positions), but significant differences were observed as a function of stop consonant. All stops showed significantly reduced R2 values and increased standard errors of estimate for VC relative to CV productions. Separability of stop place categories in a higher-order slope X y-intercept acoustic space also diminished for VC vs CV stop productions. The degradation of classic locus equation form (high correlation and linearity) for VC relative to CV productions was attributed to greater articulatory precision in the production of pre-vocalic compared to post-vocalic stops. This greater articulatory precision was interpreted as reflecting a greater need to normalize vowel context-induced variability of the F2 transition for syllable onset relative to final stops. The decline in acoustic lawfulness of syllable-final stops is discussed in terms of coarticulatory interactions and expected perceptual correlates.

The dual task paradigm: Speech dominance or manual dominance?

Two hundred and sixty monolinguals divided into subgroups based on gender, handedness, and familial left-handedness, were given a concurrent task, verbal-manual interference paradigm. The primary purpose of the study was to test whether the dual task interference effects were more related to hemispheric speech or manual dominance factors. The dominant hand, regardless of handedness, underwent relatively more tapping interference than the nondominant hand. The obtained results seriously question the basic assumptions underlying the interpretation of the dual task paradigm as an assessment index for hemispheric language lateralization. A possible explanation of this result that is in keeping with known hemispheric language representation proportions in left-handers is offered based on left hemisphere ipsilateral control of the left hand.

The perception and production of rhyme in normal and developmentally apraxic children

The phonological competence of four children, aged 5-7 years old, who demonstrated a cluster of symptoms consistent with a diagnosis of developmental apraxia of speech (DAS), was contrasted to that of four normal children. Four rhyming tasks were used to assess the ability of the children to both spontaneously generate rhyming words to targets and to judge the (in)appropriateness of a rhyme in both a word series and forced-choice word pairs. The DAS children revealed a severe deficit in rhyming ability across all tasks and had rhyming abilities markedly inferior to those shown by normal children. The rhyming results were interpreted as possibly indicative of an impoverishment of an internalized phonemic representation system, which precludes accessing and evoking the needed sound image for the vowel + coda for a rhyme. These results, while preliminary in nature, lend support to a conceptualization of DAS as a fundamental disorder of the segmental phonological level of language that impacts on all hierarchically relevant language components. The hypothesis that the underlying etiology of DAS is a developmental dysmorphology of the neural substrates that mediate such basic phonological representational structure is discussed.

LOCUS EQUATIONS AS PHONETIC DESCRIPTORS OF CONSONANTAL PLACE OF ARTICULATION

This experiment tested whether locus equation coefficients, slope, andy-intercept could serve as indices of place of articulation for obstruents sharing the same place of articulation across different manner classes. Locus equations for 22 speakers were derived from CV/t/ words with initial voiced stop /d/, voiceless aspirated stop /t/, nasal /n/, voiced fricative /z/, and voiceless fricative /s/ preceding 10 vowel contexts. Post hoc tests revealed /d/ = /z/ = /n/ for slope means. Voiced /d/ and voiceless /t/ were also equivalent whenF2 transition onset measurement points were equated. Scatterplots of locus equation coefficients revealed three nonoverlapping and distinct clusters when the diverse coronal group was compared with labials and velars. A discriminant analysis using slope andy-intercept as predictors successfully categorized all five coronals into one alveolar group with 87.1% accuracy. The collective results support the contention that locus equations can serve as effective phonetic descriptors of consonant place of articulation across manner classes.

Studies of hemispheric specialization for speech production.

Subjects matched a continuously varying pure tone presented to one ear with a second tone presented to the other ear and controlled by unidimensional movements of part of their motor system. Performance was significantly better when the tone controlled by a speech articulator (tongue, jaw) was presented to the right ear, rather than the left (REA), but not if the tone was hand-controlled. Results suggest the presence in the left hemisphere of a speech-related auditorysensorimotor integration mechanism. A group of stutterers showed no REA. Magnitude of REA in tracking was not related to magnitude of REA in dichotic listening studies of speech perception either in normal subjects or in stutterers.

An assessment of cerebral dominance in language-disordered children via a time-sharing paradigm ☆

A time-sharing paradigm was used to assess language lateralization in language-disordered and normal children aged 4-7 years. Several expressive language tasks as well as a vocal, but nonlinguistic, task were administered concurrently with unimanual finger tapping. Dependent variables were percent disruption scores and number of syllables produced per concurrent trial. All language concurrent tasks produced tapping reductions for both hands for both groups. This result contrasts to similar time-sharing studies claiming asymmetrical interference and hence language lateralization in children (N. White & M. Kinsbourne, 1980, Brain and Language 10, 215-223; J. Obrzut, G. Hynd, A. Obrzut, & J. Leitgeb, 1980, Brain and Language 11, 181-194). A multiple regression analysis revealed a significant interaction effect differentiating language-disordered from normal children. Normals exhibited a parallel response pattern for speech and tapping (both increased or decreased in rate) under all lateralization conditions. Language-disordered children exhibited an inverse response pattern (e.g., if speech output increased, tapping rate decreased) only under left-hemisphere time-sharing.

Contrastive patterns of intrahemispheric interference to verbal and spatial concurrent tasks in right-handed, left-handed and stuttering populations.

A time-sharing paradigm was used to assess hemispheric lateralization for both language and visuo-spatial processing in right-handed, left-handed and stuttering populations. A right hand only tapping disruption, indicative of left hemisphere interference, accompanied concurrent verbal tasks only in the dextral group. Left-handers and stutterers revealed symmetrical patterns of hemispheric language interference. Significantly different absolute levels of language interference were found for the three groups, with dextrals having the least, followed by sinistrals, and being greatest for stutterers. These magnitude differences were explained in relation to a hypothesis of strength of language representation within a given hemisphere. Visuo-spatial right hemisphere interference was shown for left-handers with a concurrent object chimera task.

An acoustic analysis of the bidirectionality of coarticulation in VCV utterances

Abstract This study investigated the extent of vowel-to-vowel anticipatory and carry-over coarticulation in VCV utterances. Five speakers of American English produced open (V.CV) and closed (VC.V) syllable shapes with /i/, /ɔ/, /e/ and /u/ as “fixed vowel” contexts and /i/ and /ɔ/ as a “changing vowel” context. Medial consonants were /bdgptk/. Anticipatory coarticulation was indexed by measuring the difference in F 2 offset frequencies for V 1 , with a given fixed vowel context, when V 2 =/i/ vs. /ɔ/ (e.g., [ibi] vs. [ibɔ]); carry-over coarticulation was indexed by measuring the difference in F 2 onset frequencies for V 2 , with a given fixed vowel context, when V 1 =/i/ vs. /ɔ/ (e.g., [ibi] vs. [ɔbi]). In open syllables, anticipatory exceeded carry-over coarticulation for labial and velar stops, but carry-over effects predominated in alveolar contexts. Alveolars maximally resist anticipatory effects of V 2 and thus may allow greater V 1 carry-over effects. In closed syllables, carry-over exceeded anticipatory effects across all stops. This was attributed to a short V-to-V temporal interval indexing carry-over effects relative to a disproportionately longer interval separating vowels for anticipatory effects.

Nonword repetition and phoneme elision in adults who do and do not stutter.

UNLABELLED The purpose of the present study was to explore the phonological working memory of adults who stutter through the use of a non-word repetition and a phoneme elision task. Participants were 14 adults who stutter (M=28 years) and 14 age/gender matched adults who do not stutter (M=28 years). For the non-word repetition task, the participants had to repeat a set of 12 non-words across four syllable lengths (2-, 3-, 4-, and 7-syllables) (N=48 total non-words). For the phoneme elision task, the participants repeated the same set of non-words at each syllable length, but with a designated target phoneme eliminated. Adults who stutter were significantly less accurate than adults who do not stutter in their initial attempts to produce the longest non-words (i.e., 7-syllable). Adults who stutter also required a significantly higher mean number of attempts to accurately produce 7-syllable non-words than adults who do not stutter. For the phoneme elision task, both groups demonstrated a significant reduction in accuracy as the non-words increased in length; however, there was no significant interaction between group and syllable length. Thus, although there appear to be advancements in the phonological working memory for adults who stutter relative to children who stutter, preliminary data from the present study suggest that the advancements may not be comparable to those demonstrated by adults who do not stutter. EDUCATIONAL OBJECTIVES At the end of this activity the reader will be able to (a) summarize the nonword repetition data that have been published thus far with children and adults who stutter; (b) describe the subvocal rehearsal system, an aspect of the phonological working memory that is critical to nonword repetition accuracy; (c) employ an alternative means to explore the phonological working memory in adults who stutter, the phoneme elision task; and (d) discuss both phonological and motoric implications of deficits in the phonological working memory.