Fundamental Frequency

Perceptual reports claim a levelling out of intonation overall, with intrusion of atypical movement. This seemingly conflicting picture is nevertheless reconcilable within instrumental findings.

Ryalls (1982) and Cooper, Soares, Nicol, Michelow, Goloskie (1984) report restricted ranges of fundamental frequency (FO) contour, while Danly and Shapiro (1982) report exaggerated FO variation. Their data are derived from different contexts. Ryalls and Cooper et al relate to sentences, Danly et al used single words.

Kent et al (1982) uncovered two FO patterns in AS. One they termed syllable segregation with abnormal intersyliable pauses, but where cross-sentence FO declination was maintained. In the other, syllable dissociation, there was no intersyliable dependency in the FO contour. Each syllable seemed to be an utterance in itself, with FO resetting for each syllable.

The latter points either to a conscious strategy to maintain syllabic and segmental integrity in the face of impairment, or a planning- execution system that is so disordered that it

can only operate in units of syllable size. Either way, syllable dissociation leads to abnormal prosody. This splitting in declination over a whole phrase can be seen as a constant strategy in some speakers, with others it represents an intermittently applied strategy. Such variation would give rise to the impression of inconsistent disturbed prosody.

Observations of Danly et al (1982) and others (Weniger 1984; Cooper, Klouda 1987; Snow, Wise 1988) point out additional features of FO control in AS, Speech dyspraxics seem to start, on average, at a lower FO peak than normals. They show a definite terminal fall but not, on the whole, word final lengthening as in normals. Further, whilst overall declination does occur, many subjects produce local continuation rises throughout words and utterances. This may point to a compensatory strategy to indicate continued communicative intent.

As regards a motor explanation for reduced range of FO, and shortened span, two or three forces are probably at work. Firstly, in AS fine expiratory control disruption has been noted (Keatley, Pike 1976; Marquardt, Nichols 1987), Secondly, because of impairment of force, onset and offset, tension etc control within the larynx itself, there may be reduced FO range. Thirdly, it may also be restricted by articulatory look-ahead and forward planning. If these can only cope with word or syllable size chunks, FO for longer stretches may be influenced in a knock-on fashion.

To conclude, at present, in AS speakers retain both basic FO patterns and some ability to manipulate these (e,g, continuation rises; exaggerated terminal fall to compensate for absent utterance final lengthening), FO can show resistance to overall disruption even in the face of perturbations from aerodynamic, laryngeal or articulatory disturbance. As such, this suggests that even if dyspraxic dysprosody is a primary disorder in AS, it is seldom, if at all, due to FO breakdown. This preserved capability is.

however, not readily apparent to the naked ear and easily camouflaged by segmental distortions and dysfluency.

5.4.3. Syllable Amplitude

Temporal regularity and amplitude uniformity (perceived as syllable timing and equalisation of stress) are alleged features of AS. Acoustic measurement has confirmed this. Two sources of equalisation may be at play.

Lebrun et al (1973) decided that the illusion of scanning speech arose from syllabic prominence and perceived isochronism, as well as frequent pronunciation of silent 'letters*, errors in vowel formation and slowed rate. Kent et al (1983) showed neutralisation of intensity across syllables. AS speakers still exhibited relatively greater intensity on tonic nuclei, but because the general range of variation was much smaller compared to normals, the prominence was less obvious. Normally unstressed syllables were not as markedly reduced. Taken together these two retractions from normal extremes gave the impression of equalised stress. Syllabic segregation and dissociation lent a further air of scanning speech.

A possible compensatory source of equalisation of stress is supplied coincidentally by Tonkovich and Marquardt (1977). They were primarily studying melodic intonation therapy. One task performed involved repetition of the same NPl (noun phrase) - verb - NP2 sentence with stress varied between the major constituents. Grammatical class and sentence position exercised no influence over error probability. Stressed elements, however, were consistently more accurately produced than unstressed. It is speculated that some dyspraxic speakers may give equal prominence to syllables to capitalise on this phenomenon.

5.4.4. Is there, then, a primary dysprosody in AS? Clearly some disruption to suprasegmental features is secondary to problems of segmental initiation, self corrections, changes in duration, dysfluency of transitions and loss and addition

of syllables and syntactic breakdown. Some speakers (Johns et al 1970) tread hesitantly to avoid known accident blackspots. Other speakers may be subconsciously induced to slow due to reduced motoric capacity. In this sense dysprosody in AS is a secondary feature. Reduced ability to uphold normal amplitude variation in stress assignment, loss of utterance final lengthening and narrowing of FO range independent of other segmental pronunciation derailments (Skenes 1987; Snow et al 1988 based measurements only on articulatorily correct tokens) hint at a primary disturbance.

Prosodic sound features all arise out of movement. Movement requires central planning and integration. If this is disturbed in AS, then it is no surprise that the neuropsychological processes underlying target prosodic realisations should be disrupted. The fact that they appear more immune to breakdown may relate to their closeness to automatic, reflexive processes, or because these processes act suprasegmentally their disintegration may be compensated for more easily (4.8.1).

Finally, of course, it must be remembered that multiple features converge to produce prosody. Prosody is not a unidimensional parameter. Thus it is possible that different contributing features may be disordered to varying degrees; dysfunction in one area may be compensated for in another; and typical of AS, disruption may arise from the very problem of integration/phasing of these subfeatures.