The Perception of Intonation Contours and the Use of Focus by Aphasic and Healthy Individuals

Transcription

1 The Perception of Intonation Contours and the Use of Focus by Aphasic and Healthy Individuals Dissertation submitted by Anna Vivian Raithel Bielefeld University Faculty of Linguistics and Literature July 2003 Summary Advisors: Prof. Dr. Dafydd Gibbon HD Dr. Martina Hielscher-Fastabend

2 This thesis has one major aim. It is to show, whether fluent and non-fluent aphasics have difficulties recognizing intonation contours and using focus for improved auditory language comprehension. Taking hypotheses as a point of departure that claim that prosody is an important cue for the understanding of spoken language, the durational pattern, fundamental frequency, and intensity and their manipulation are the focus of this research. It is known that aphasics have greater problems understanding spoken language than healthy individuals. Many different aphasia batteries have been able to show and diagnose that in aphasia all four language modalities reading, writing, speaking, and understanding are affected. These diagnostic instruments, however, do not look at prosody comprehension although it is known that aphasics do have impaired prosody perception. The definition adopted for this work is that prosody consists of the fundamental frequency, duration, and intensity of the speech sound, which are perceived as pitch, speech rate, and loudness. The speech signal may be manipulated consciously or unconsciously by the speaker. When the speech signal is manipulated in one or more of its three main parameters, the syllable is assigned stress or not, according to lexical stress rules. And stress is perceives as focus, which is one of the phenomena investigated in this study. While focus is applied to shorter segments such as the word, intonation is a property that affects the whole sentence. The main distinction between intonation contours is made in connection with syntactic categories, i.e. in German a question usually has a rising intonation contour and a statement a falling intonation contour. Aphasia is an acquired language disorder of central dimensions and may affect any of the components of the language system: phonology, lexicon, syntax, or semantics. These components are affected on the word, syllable, and sound levels. Aphasia affects the basic language modalities: speaking, understanding, reading, and writing, as well as naming and repeating. In the German speaking community aphasic patients are usually classified according to four syndromes, which also correspond to some extent to these four modalities. These four main aphasic syndromes are (1) global or total aphasia, (2) anomic aphasia, (3) Wernicke s aphasia, and (4) Broca s aphasia, of which I describe only the two in more detail which are of importance for this thesis. The main symptoms in Broca s aphasia are slowed, labored, 1

3 aprosodic speech with interjections. The syntactic structure is simple; a differentiation between various types of grammatical relation cannot be seen; however, the sequencing of the words usually is chronological; this is called agrammatism. The words produced tend to be garbled more by phonematic paraphasias than by semantic paraphasias. The speech of Broca s or non-fluent aphasic individuals is very often marked by misplaced word stress. The speech of Wernicke aphasics is marked by frequent elision, conversion, or by the addition of sounds which are called phonematic paraphasias. These phonematic paraphasias can be so dominant that they are called jargon. Wernicke aphasics have difficulties with the choice of their words, i.e. the words they choose belong to the same syntactic category as the target words but have only little semantic relation to them (semantic paraphasia). Above and beyond that, fluent or Wernicke s aphasics tend to produce neologisms as well as morphological mistakes and to violate selection criteria, for example,doubling sentence parts (paragrammatism). Their language comprehension is impaired, especially at the beginning of the disorder. It is undisputed that language is lateralized in the left hemisphere in most people. The issue of prosody lateralization remains partly unresolved. There are four main theses concerning the lateralization of prosody which claim that (1) all prosody is lateralized in the right hemisphere; (2) that emotional prosody is lateralized in the right hemisphere and that linguistic prosodic functions are highly dependent on subcortical processes and are not localized in the one or the other hemisphere; (3) that there is continuum from the emotional to the linguistic functions of prosody, i.e. that processing shifts to the left hemisphere with more linguistically-based tasks and to the right hemisphere with more emotionally-based tasks. Beyond this distinction, current research has been able to show that a further distinction has to be made, namely that there is left-hemisphere dominance in the processing of short frames, i.e. syllables, and right-hemisphere dominance in long frames, i.e. phrases. And, finally, the claim is advanced (4) that the fundamental frequency is lateralized in the right hemisphere and the durational pattern in the left hemisphere. Generally, aphasics are said to have impaired perceptual prosodic abilities. It has been shown that left-hemisphere damaged individuals do make use of both temporal and F parameters for the better identification of the 2

4 stimuli presented. In effect this could mean that an experiment such as the one conducted in this study influences the aphasics auditory language comprehension positively. The main hypotheses formulated for this study are (1) that rising intonation contours are recognized with more accuracy than falling intonation contours; (2) that the congruent condition is recognized better than the incongruent condition; (3) that the non-fluent aphasics have better performance on the focus-modified experiment than the fluent aphasics; (4) that the durationmodified condition and the pitch-modified condition influence the auditory language comprehension of aphasics positively. Following from the theoretical background the two experiments ICRS (Intonation Contour Recognition Screening) and MTTS (Modified Token Test Screening) were designed. The ICRS is made up of two parts. The first part contains the unmanipulated version of a set of sentences and the second part, the manipulated the low-pass-filtered version of these sentences, which makes the utterances lexically unintelligible. The utterances were filtered at 300 Hz adjusted to the female speaker s fundamental frequency. The screening consists of twelve sentences. The intention is to compare comprehension in regard to intonation under the two sets of conditions (unfiltered and filtered). Each sentence consists of seven syllables. Example sentences are Die Eltern essen Suppe The parents are eating soup or Kannst du mir heute helfen? Can you help me today? or Die Frau liest eine Zeitung? The woman is reading a newspaper? There is a difference in the way the sentences are rendered between a congruent and an incongruent condition. Congruent utterances are, for example, statements in content and syntax, and the intonation contour is falling. Or they are ones in which the content is syntactically a question and the intonation contour is rising. Both cases represent the canonical cases. In the incongruent version the content is syntactically a statement but prosodically a question ( queclarative ). The MTTS consists of five subtests which have increasing degrees of complexity and difficulty. The first four subtests begin with the identical structure point to (zeigen Sie) as in Point to the red circle (Zeigen Sie den roten Kreis). There are ten utterances in each subtest. The syntactical structure of the utterances in Subtest V is more complex. These utterances ask that the subject touch or pick up tokens in a specified order, i.e. pick 3

5 up one token after having touched another or pick it up before pointing to another. The subjects are presented with a test sheet showing rows of colored tokens and have to point to the token given in the utterances. In most of the subtests one of the content words (designated size, color, or shape) gets the focus by change of the duration, the fundamental frequency, or the intensity of the word. The modification was determined psycho-acoustically. The five subtests are preceded by the Matching Test which consists of seven token test utterances. The subjects are asked to decide whether the pairs presented sound the same or not. Here, one pair matches the sentences are exact copies of each other and the others do not because one sentence contains one of the content words which carry focus. The subjects that were chosen for these experiments are fluent and non-fluent aphasics. All the subjects were right-handed and native speakers of German. They had no visual field deficits, nor any noticeable memory deficits, nor any hearing deficits. All the patients were at least three months post-onset. There were 20 subjects in each of the three groups. The results show that the rising intonation contours were recognized best by all subjects. The content seems to be more dominant than the prosody for spoken language comprehension, and it also seems to be what listeners rely on more. In the case of the two congruent unmasked intonation contours (statement and question) the subjects recognized the intonation contour correctly because they recognized the content correctly. On the Matching Test all subjects performed below chance level. They showed answer behavior that seemed to perceive all the pairs as sounding the same. This way the subjects had no chance but to perform below chance level because six out of seven pairs were prosodically different. Few subjects, if any at all, pursued the opposite strategy of deciding that none of the pairs presented were exact matches. The analysis of the results of the MTTS showed that the non-brain-damaged control subjects perform significantly better on the focused conditions than on the unmodified condition. These results indicate that for healthy people the type of sentence used in the MTTS with contrastive focus further enhances comprehension. Without special focus performance decreases significantly but even with increasing complexity remains very good as compared to the aphasic subjects. The focus adds information to the content. This perfor- 4

6 mance is considered normal. The non-fluent aphasics perform significantly better on the utterances which contain a word with modified duration. This may indicate that the extra time in the duration-modified utterances has a positive influence on their performance. However, another possible explanation for the influence of duration may lie in the type of focus, i.e. duration, itself. The durational aspect of language is said to be processed in the left hemisphere. This may that temporal cues are not processed in the fronto-temporal region where predominantly non-fluent aphasics lesions are. Also, it is possible that the non-fluent aphasic subjects, who have greater verbal working memory deficits than the fluent aphasics, use this extra time more effectively. For subjects with fluent aphasia the entire process of semantic comprehension may be so absorbing that any further information coming from prosody is, in contrast to the non-brain-damaged and non-fluent aphasic population, if not a hindrance, at least not helpful because here no significant influence can be seen. Pitch has no significant influence on the recognition abilities of the aphasics, contrary to what had been postulated prior to the conduction of the experiment. Generally, the perception of intonation contours as in the ICRS and the discrimination of focus as in the MT and to some extent in the subtests of the MTTS, seems to be served by different areas in the brain. The results in regard to this question did not show any correlation between these two types of perceptual ability in the aphasic groups, a finding which supports the lateralization hypotheses which indicate that intonation contours and focus may be processed in different brain areas or even in different hemispheres. It was obvious that the aphasic subjects did not make use of amplitude-modified focus nor did they show an especially good performance on the unmodified sentences. It has become very obvious that healthy individuals as well as aphasic subjects cannot discriminate, or at least have a hard time discriminating, prosodic information in the form of narrow focus in MT-like tasks. This kind of local prosody, whose scope is restricted to one word only, seems to be much more an integral part of spoken language than intonation contours, which extend over an entire utterance. 5