Unisensory and bisensory perceptual and memory processing in stuttering adults and normal speakers

J. FLUENCY DISORD. 12 (1987), 291-304

UNISENSORY AND BISENSORY PERCEPTUAL AND MEMORY PROCESSING IN STUTTERING ADULTS AND NORMAL SPEAKERS MARY CARPENTER Akron Public Schools Akron, Ohio

RONALD

K. SOMMERS

Kent State University Kent, Ohio

The perceptual/memory process abilities of adult stutterers were compared with those of normal adult speakers. Unisensory tasks were used as standards for comparison of the simultaneous, bisensory processes. Subjects were tested individually on sensory oral form, manual form, and word recall tasks followed by combinations of word recall and oral form discrimination, and word recall and manual form discrimination. Four bisensory combinations were tested, and in each test subjects were asked for the discrimination of the forms or recall of the words. Results showed that on both bisensory tasks in which the subjects were asked for the words rather than the form discrimination the stutterers were significantly poorer than the normals. On the bisensory tasks in which the forms were called for, the stutterers’ performances were equal to the normals. No differences were found between the groups on the three unisensory tasks. These findings are related to some processing theories and to EEG studies of word recall in adult stutterers.

The purpose of the present investigation was to compare the performances of adult stutterers with those of normal speaking adults on a variety of perceptual/memory tasks, first in a traditional unisensory testing format, followed by a bisensory one. The concept of disturbed sensory feedback as one etiological factor in some stutterers rests upon the belief that during the speech act, feedback from various perceptual systems (audition, kinesthesia, tactile, and proprioception) is required in order to coordinate the flow of speech effectively (Ringel et al., 1967; Fucci and Robertson, 1971; Fiedler and Standop, 1983). Any disturbance in these sensory mechanisms could result in feedback information arriving at the left or right Address all correspondence to Ronald K. Sommers, Al09 Music & Speech Building, Kent State University, Kent, OH 44242. 0 1987 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., New York, NY 10017

291 00!&73OX/87/$03.30

292

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hemisphere asynchronously, resulting in differing transmission times over various neurologic pathways. The possibility that stuttering may be related to disturbed oral sensory feedback has been studied by a number of investigations. Martin et al. (1981) reported two investigations using 20 adult male stutterers and 20 adult nonstutterers. On both an oral stereognostic discrimination task and an oral stereognostic recognition task the stuttering adults’ performances were significantly poorer than those of the normal speaking subjects. Earlier evidence of poorer performances of stutterers on a lingual form perception task was provided by Class (1956). reported in Moser et al., (1967). Negative evidence supporting poorer performances on oral sensory tasks was reported by Jensen et al. (1975). However, there were a number of procedural differences in this investigation compared to Martin et al. (1981) and Class (1956) which might have accounted for the difference in findings. Haptic touch, the active manipulation of stimuli through exploratory movement of the hand, apparently has not been studied in stuttering children or adults. It has been investigated in normal children and young adults (Birch and Lefford, 1964; Henkin, 1970; Weinberg et al., 1970). The manual form discrimination skills of misarticulating children and those having neurologic disorders have also been studied (Birch and Lefford, 1964; Hetrick, 1983). Bishop et al. (1973) concluded that manual form identification abilities are related to general neurologic maturation. Curry and Gregory (1969) speculated that differences in neurologic organization separate stutterers from nonstutterers, and if there is a relationship, one or more of the following processes could be involved: cerebral dominance, perception, memory, and feedback. Some researchers (Silverman and Williams, 1967; Telser, 1971) found that young stutterers tend to perform less well on tasks involving structural complexity of sentences, symbol retrieval, and mean length of response than nonstutterers. A breakdown in auditory perception may lead to negative effects on linguistic performance, according to Rampp (1972), cited in Stocker and Parker (1977). Evidence showing that auditory recall abilities of 22 young stuttering children were inferior to those of 22 normal speaking children was supplied by Stocker and Parker (1977). Scores for the two groups on a meaningless recall task were not significantly different, but scores on the auditory recall of meaningful verbal material were significantly different. They reported that as their stuttering subjects became more fluent, they “improved significantly in their ability to retrieve previously suppressed linguistic skills” (p. 185). As a result, their capacities for decoding/encoding linguistic information were enhanced. Researchers have observed that the normal left hemispheric alpha suppression is reduced in stuttering adults when linguistic material is processed and more alpha suppression is seen in their right hemispheres

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(Moore and Haynes, 1980; Moore and Lorendo, 1980; Moore et al., 1982; Moore, 1985). In these investigations stutterers, particularly males, were found inferior to normal male and female speakers in their abilities to recall and recognize lists of words presented to them auditorily. Moore (1985) also found that the severity of stuttering correlates significantly with the degree of right hemispheric alpha suppression. Moore (1985) concluded that stuttering males were dependent on right hemispheric information processing strategies whereas fluent males and females used left hemispheric processing strategies to recall word strings. Sussman and MacNeilage (1975) compared the performance of stuttering adults with those of normal speakers on a dichotic pursuit auditory tracking task which involved matching a target signal received in one ear with a cursor tone received in the other ear by controlling motor movements of the jaw. Jaw tracking was signiticantly more accurate when the cursor tone was in the normal subjects’ right ears, but this presumed laterality effect was not found in the stutterers. The experimenters concluded that their auditory pursuit tracking task apparently involves the speech production system. Ongoing accuracy of speech production depends on the precise integration of feedback information from a number of sensory input sources. In the present investigation we examined the integrity of the auditory, haptic, tactile, and kinesthetic sources in a singular or unisensory mode, but the major interest in the investigation was to find out how effectively information was processed in the simultaneous, bisensory mode. To accomplish this, procedures used by Hetrick (1983), who found misarticulating children’s performances inferior to normal speaking children on some unisensory and most bisensory tasks, were employed.

METHOD Subjects Nine adult male stutterers and one adult female stutterer ranging in age from 21 to 34 yr, with a mean age of 26.3 yr, comprised the experimental group. Each experimental subject (S) was receiving speech therapy at the time of this investigation. With the exception of one person who had no hearing in his right ear but a normal hearing threshold in his left ear, all experimental Ss had a pure tone average in the normal range (O-20 dB HTL). Each subject’s hearing was screened at 500-8000 Hz at 20 dB using a Beltone (model 9D) audiometer. The stuttering performance of each experimental S was measured by the Stuttering Severity Instrument (Riley, 1980). Subjects in both the control and experimental groups had completed high school and some of them had attended college. The years of education

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completed by Ss in the stuttering group ranged from 12 to 20 yr with a mean of 15.3 yr, and their ages ranged from 21 to 34 yr with a mean of 26.3 yr. The years of education completed by the nonstutterers ranged from 12 to 17 yr with a mean of 13.7 yr, and their ages ranged from 17 to 24 yr with a mean of 20.3 yr. Each S performed within a range of normal ability on the Peabody Picture Vocabulary Test-Revised (PPVTR), Form M (Dunn and Dunn, 1981), which was used to determine cognitive-linguistic abilities. The means for the subjects’ raw scores on the PPVT-R were identical, both being 155.0. All Ss had normal structure and function of the oral musculature as determined by an oral peripheral examination of the type described by Hasson (1969). Tasks All unisensory and bisensory conditions were presented in a well-lighted, quiet room, free of distractions. The unisensory conditions were administered during the first testing session and the bisensory tasks were completed during the second session. Unisensory Manual Form Discrimination (MFD). Ten of the National Institute of Dental Research forms used in the Ringel et al. (1970) study were used to assess manual stereognosis in all Ss. The geometric forms included oval, triangular, rectangular, and biconcave shapes. Each of the plastic geometric forms was attached to a 4-inch plastic handle to allow for facilitated administration. The same technique applied by Hetrick (1983) to insure that form pairings were randomly selected was used in this investigation. All 12 forms were classified into three categories:

1. “Within-different” (WD) shapes-those forms having similar geometric shape, but differing in size (WS) shapes-all forms have the same shape and 2. “Within-same” size 3. “Between-different” (BD) shapes-those forms differing in both size and shape All possible diversifications of form pairing were pooled and randomly selected five times so that ten of each of the above three categories were represented. Each form was placed in a compartmentalized plastic tray. Only the experimenter had visual access to the forms. Each S was familiarized with the task and was allowed to practice before the actual scoring took place. For demonstration purposes, the “circle with a hole” and the “circle without a hole” were used since most Ss can easily identify the difference between the two (McDonald and Aungst, 1968; Teixeira et al.,

SENSORY MEMORY PROCESSING 1974). During actual administration of the task, subjects were blindfolded. The same instructions used by Hetrick (1983) were employed here: I want you to look at how well you are able to tell whether the forms are the “same” or “different” just by feeling them with your fingers. Move them around with your fingers and try to imagine what each one looks like. I will put one in your hands, let you feel it, then take it away and give you another form. You tell me whether the two are the same or different (p. 43). Using Hetrick’s paradigm for investigating haptic manual stimulation (stereognosis), the S was allowed to explore each form for up to 7 set and was required to tell the examiner whether he thought the two were the “same” or “different.” Hetrick (1983) followed the tactics employed in the Weinberg et al. (1970) study, in which mean response times for oral form perception were significantly longer when oral stereognostic testing preceded manual stereognostic testing. Hetrick administered the manual form condition before the oral form condition, and this procedure was also employed in the present investigation. Unisensory Oral Form Discrimination (OFD). A task identical to the one Hetrick (1983) used, consisting of a modification of the test used by Ringel et al. (1970), was employed here. The same shapes, trials, and orderings used in MFI task were used in the OFI task. Instructions to all Ss were: Now I want to see how well you are able to tell whether the forms are the “same” or “different” just by moving them around in your mouth. Move them around in the front of your mouth and try to imagine what each one looks like. I will put one in your mouth, let you feel it, then take it out and put another in. You tell me whether the two are the same or different (P. 45). CJnisensory Auditory Memory for Words (AMW). The same stimulus words used by Hetrick (1983) were used in this study. Each S had performed well enough on the PPVT-R to ensure their knowledge of the stimuli. Instead of requiring the Ss to repeat the words verbally, they were asked to write the words so that any moments of stuttering that might occur would not be a factor in their performances. Each S was instructed as follows: I am going to say some words. Listen carefully. When I am finished, please write them down in the exact order that I presented them (p. SO).

Stimulus words were conveyed through monitored live voice by an examiner at a rate of 1 word/set, and responses were written on a scoring form.

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Bisensory Tusks. The same bisensory tasks used by Hetrick (1983) were used in this investigation. Form identification trials and auditory word strings from the unisensory tasks were randomly selected to represent four bisensory conditions. As can be seen in Table 2, the member of the bisensory combination called for precedes the subscript of the second bisensory task, e.g., MFDA means that the manual form discrimination was called for as the words were also processed. Each S was given the following instructions: I am going to see how well you feel the forms (with your some words. Sometimes I will and sometimes I will ask you

you can do two things at the same time. As fingers or in your mouth), I am going to say ask you if the forms are the same or different to write what I have said (p. 50).

For each S, one plastic form was placed, either manually or orally, immediately followed by initiation of the auditory stimuli. Auditory stimulation commenced as the first form of the pair was placed for half of the trials, and for the other half of the trials, auditory stimulation commenced with the placement of the second form. Because subjects were blindfolded during the bisensory tasks, they were instructed to lift the blindfold when auditory memory for words was tested in order to write the words. The response called for (same/different or words) was randomly selected, with each being called for ten times. Each S was allowed to manipulate the forms for 3 to 7 set, depending on the length of the word string associated with the individual trial (at the rate of 1 set/word). Reliability Three subjects from the stuttering group and three from the control group were retested on all unisensory and bisensory tasks 60 days after data collection was completed. The percentage of mean agreement on the unisensory tasks was 94.4% for the stutterers with a range of 78.4%-100% and 96.0% for the control subjects with a range of 92%-100%. For the bisensory tasks the percentage of mean agreement was 92.1% for the stutterers with a range of 74%-100% and 94.1% for the control subjects with a range of 86%- 100%. RESULTS A summary of subjects’ performances on each of the three unisensory tasks is contained in Table 1. To score the AMW task, one point was given for each word correctly identified, in order, within a string. The percentage of correct responses on the three tasks was subjected to a two-factor mixed ANOVA. The between factor was stutterers versus normals and the within factor was tasks. The F for groups of 1.78 (df = 1,18)

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Table 1. Means and Standard Deviations Response on Three Unisensory Tasks

of Subjects;

Stutterers Task MFD OFD AMW

Percentages

of Correct

Control

Mean

SD

Range

Mean

SD

Range

85.20 83.40 77.80

5.99 7.86 12.25

73-93 67-93 53-93

86.90 85.70 84.70

7.20 7.81 7.77

73-97 67-97 72-95

the F of 1.52 (df = 3,34) was also nonsignificant; and the Tasks x Groups interaction failed to reach significance also [F(3,34) = 51, p > 0.051. Pearson product-moment correlation coefficient matrices were computed for the unisensory tasks, all combinations of the bisensory tasks, CA, educational levels, PPVT-R scores, and Riley stuttering severity scores. For all 20 subjects the bisensory conditions in which the words were called for (AMWw and AMWo) were highly correlated with CA (correlations of - .85, sig. < .Ol and - .83, sig. < .Ol). In the individual correlation matrices for the stutterers and normals significant relationships were also found. For the stutterers CA correlated with AMW~L~- .85 and with AMWo - .83, both sig. < .Ol. These relationships for the control subjects were AMWo and CA - .73 (sig. < .05) and for AMWM - .617, which was nearly significant (required - .632, df = 8). However, a significant (.05) correlation of - .73 for CA and MFDA scores in the control group was also found. The AMWM and AMWo scores of all subjects were significantly related (Y = .87, df = 18). Unisensory scores were not signiticantly correlated with subjects’ CAs. A nonsignificant correlation (r = .35, df = 18) between CA and educational level for all subjects occurred, and a range of nonsignificant correlations of from - .04 to - .422 was found for stuttering severity and each of the unisensory and bisensory tasks. In view of the high negative correlations between CA and many of the bisensory tasks, the form of the analysis of the bisensory data consisted of a two-factor mixed analysis of covariance (ANCOVA) using CA as the covariate. The data for this analysis consisted of the percentage of correct responses on each of the four combinations of bisensory tasks. The means and standard deviations of subjects’ performances on these tasks are contained in Table 2. Results of the ANCOVA revealed a significant main effect for groups [F(1,17) = 8.70, p < 0.011, a nonsignificant tasks effect (F(4,52)) = 2.56, p > 0.051, and a highly significant Task x Group interaction [F(4,52) = 5.49, p < O.OOl]. Post-hoc testing using the Tukey (b) (Winer, 1971) means comparison

was nonsignificant;

M. CARPENTER

298 Table 2. Means, Standard on Bisensory Tasks

Deviations

and R. K. SOMMERS

and Ranges of the Percentages Control

Stutterers Task MFDn AMWM OFDA AMW”

Correct

RtUlge

Mean

SD

RClnpC?

Mean

SD

84.00 71.10 90.00 73.70

6.99 18.57 9.42 19.89

SO-100 30-89 70- 100 41-94

81.99 87.20 83.00 86.20

6.32 9.00 17.02 6.14

90- 100 69- 100 70-100 73-94

test was employed to locate significant differences in the Task x Groups interaction. Results of the Tukey (b) indicated that normal speakers performed significantly better than stutterers on two of the four bisensory tasks: AMWM and AMWo. Figure 1 displays the nature of the interaction effect. It can be observed that the normal subjects scored higher on the MFDA task than the stutterers and the stutterers scored slightly higher on the OFDA task. The stutterers’ overall scores on the MFDA and OFDA 0

NORMAL

SPEAKERS

.

STUTTERERS

100 90 1

60 _ g 2 5 0

40 -

E

30 _

50-

AMWo

MFD,

AMW,, BISENSORY

Figure 1. The significant

OFD,

TASKS

Tasks

x

Group interaction

effect.

SENSORY

MEMORY

tasks, however, scores.

PROCESSING

did not differ significantly

299

from the normal subjects’

DISCUSSION Although the comparison of stutterers’ performance on the unisensory tasks of auditory memory for word strings and oral and manual form discrimination was of some interest in the present investigation, they served as standards from which comparisons of bisensory processing could be related. The unisensory results, perhaps due to the small sample size, failed to distinguish the performances of the stutterers with those of the normal speaking subjects. The finding that oral form discrimination scores of stutterers were not significantly different from the normal subjects is in agreement with that of Jensen et al. (1975) and conflicts with those of Class (1956) and Martin et al. (1981). It is conceivable that subtypes of stutterers exist that have various combinations of patterns of perceptual, linguistic, memory, and cognitive abilities, and our sample may have contained stutterers having reasonably normal oral form discrimination skills but other weaknesses which were not assessed. Explanations for the poorer performances of the stutterers on the bisensory tasks in which the examiners called for the words and not the discrimination of the oral or manual forms can be made from a number of theoretical orientations. Perhaps the most direct connection to these findings is the work reported by Moore and his colleagues (Moore and Haynes, 1980; Moore and Lorendo, 1980; Moore et al., 1982; Moore, 1985) who found right hemispheric alpha suppression in adult stutterers on word recall tasks. These findings suggest that stutterers may use different processing strategies when words are recalled, and our data may reflect a less efficient right hemispheric processing on the part of the stutterers. If oral form and manual form discrimination involve right hemispheric processing strategies exclusively or to a greater extent than left hemispheric processing, the view of Loveless et al. (1970), which contends that if stimuli in one sensory channel are functionally separate from those in another channel, an individual can attend to both stimuli fairly effectively, may contribute to this explanation. Stimuli occupying the same or adjacent space may be in stiff competition and interrupt each other’s processing. If our stutterers were processing information on the manual and oral form discrimination tasks largely in their right hemispheres and, indeed, as Moore and his associates have found in a number of EEG investigations, were processing the auditory words in the right hemisphere also, a disruption may have occurred resulting in poorer performances on the bisensory tasks in which words had to be recalled. Another explanation, other than one related to a disruption or interference hypothesis, is that our stutterers’ capacity for word recall may

M. CARPENTER

and R. K. SOMMERS

be diminished if they are processing them in their right hemispheres. Zaidel (1976, 1978, 1979) found that the right hemisphere’s capacity to process phonological and syntactical information is poor and has a shorter span for verbal short-term memory than the left hemisphere. Stuttering is thought by some to be the result of a disruption in the programming of sequencing and timing (MacKay and MacDonald, 1984). The fact that stutterers differ from nonstutterers in their ability to repeat the temporal pattern of a sentence or sequence of finger taps has been attributed to the mistiming of their neural clocks (Cooper and Allen, 1977). Their tasks included repetition of sentences, paragraphs, nursery rhymes, and finger tapping, It was felt that the timing breakdown in these experiments may be indicative of a “critical vulnerability of central mechanisms that generate or maintain the temporal structure of action” (p. 287) (Kent, 1984). It has been suggested that the motor control system can break down when maintaining simultaneous temporal patterns. Examples of temporal pattterns in speech may be those in segmental articulation and prosody. The bisensory tasks used in the present investigation are prime examples of the attempt to maintain simultaneous temporal patterns. Auditory sequential temporal patterns are thought to be processed in the left hemisphere of normal individuals (Springer and Deutsch, 1981). If stutterers do, in fact, have less accurate clocks than normal speakers, their inaccurate timing control for auditorily presented words may have contributed to their poorer scores on the AMW M and AMWo tasks. On the other hand, their normal performances on the OFDA and MFDA tasks may suggest that timing and sequencing of haptic, tactile, and kinesthetic stimuli was easier for them, perhaps because only a discrimination between pairs of stimuli was required. The word strings required the temporal ordering of as many as seven words. Speech is considered to consist of three timing nodes (MacKay and MacDonald, 1984): the sentence time node, the phonological time node, and the sequence node. These nodes can be independently controlled, i.e., when the sentence time node becomes activated, propositional thought occurs. If the phonological time node were to be added to the sentence node, internal speech without overt movement of the speech musculature would occur. The sequence node is responsible for activating movement of muscles within the laryngeal, respiratory, and articulatory systems. The simultaneous activity of these nodes instigates speech production. According to the hypothesis stating that disruptions in sequencing and timing are implicated in stuttering, it seems that auditory feedback is processed in the same way as other sensory inputs. These same nodes are involved in both producing and perceiving cognitive units (i.e., phrases, words, syllables, and phonemes). Top-down connections between nodes are inherent in the production of words, whereas bottomup connections are used to perceive words.

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After these nodes are primed, self-inhibition following their activation prevents undelayed (normal) auditory feedback from causing stuttering. Inputs arriving during this period of self-inhibition do not add sufficient priming to make self-inhibited nodes the most primed in their area. Therefore, just activated nodes do not become reactivated during ongoing production of the sentence. In normal speakers, it is thought that the effects of delayed auditory feedback activate nodes, after which they are self-inhibited and undergo a normal cycle of recovery. A delay of 200 msec produces maximal disruption of speech. During these 200 msec, nodes have greater than normal sensitivity. A peak occurs approximately 200 msec following onset of activation, and at 300 msec, the nodes return to resting level. Errors in the production of speech are thought to occur when an unintended node is activated. MacKay and MacDonald (1984) suggested that stuttering occurs when just activated nodes are primed to a greater degree than nodes to be activated next. One of the reasons this may occur is that the returning feedback is delayed about 200 msec within the sensory analysis nodes of stutterers. The nodes themselves may be abnormally slow. They may even require greater than normal amplitude, because the stapedial reflex may be functioning abnormally (this reflex normally attenuates the amplitude of self-produced feedback). The other reason this may occur is that the nodes of stutterers may have an abnormal recovery cycle. Both of these hypotheses support the fact that masking the returning auditory feedback reduces stuttering. They also support the reason stuttering is overcome when another person utters the word on which the stutterer is blocking. This input may aid in priming the appropriate nodes to the level at which they may become activated. Findings of the present investigation can be tied to these hypotheses concerning stuttering. Hence, they may be associated with a disruption in sequence and timing, which, in turn, may be related to the possibility that our stutterers were using right hemisphere processing strategies for word recall when also processing the manual and oral forms. Stutterers’ poorer performances on these bisensory tasks may have been the result of mistiming and faulty sequencing. Since unintended nodes may have become activated, the stutterers’ performances on the auditory response portion of the bisensory tasks may have been affected.

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