(PDF) Verbal information-processing capa

Verbal Information-processing Capabilities and Cochlear Implants: Implications for Preoperative Predictors of Speech Understanding Bjorn Lyxell Jan Andersson Stig Arlinger Goran Bredberg Henrik Harder Jerker Ronnberg Linkoping University, Linkoping, Sweden In this study, we examined preoperative verbal cognitive ca- ever, the outcome of such implantation varies widely pacity in 11 deafened adults who were cochlear implant can- among the recipients. Some individuals can communi- didates and reexamined level of speech understanding after cate over the telephone and easily follow and under- Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 6—8 months' experience with the implant. Verbal cognitive performance in the implant group was compared in a group stand a speaker who is out of sight, whereas others can of normal hearing subjects and in a nonimplanted group of only differentiate between the presence and absence of deafened adults. The three groups performed on par with sound (Knutson, Hinrichs, Tyler, Gantz, Schartz, & each other with one exception: The individuals in the co- Woodworth, 1991; Osberger, Todd, Berry, Robbins, & chlear implant group and the nonimplanted group of deaf- ened adults performed significantly worse than those of nor- Miyamoto, 1991). It is important, for a number of rea- mal hearing in tasks in which use of internal speech is a key sons, to create means that allow for preoperative pre- feature (i.e., rhyme judgement and lexical decision tasks). dictions of the outcomes. Such predictions could, for Postoperative observations of the implanted individuals' level example, give candidates an opportunity to put their of speech understanding suggest that it is possible to predict expectations about the outcome in realistic perspective. the level of speech understanding by means of a preoperative cognitive assessment. The characteristics of three verbal cog- It can also help to inform teams working with implant nitive abilities proved to be critical indicators of 6—8 months' patients about rehabilitative efforts most fruitful for a postoperative outcome: internal speech functioning, speed of given patient (cf., Knutson, et al., 1991; Summerfield & verbal information processing, and working memory capac- Marshall, 1994). ity—the first factor proved the most decisive. We discuss the results with respect to direct versus indirect predictors of Listening with normal hearing in normal condi- outcomes from cochlear implant operations and the effect of tions is a quite effortless and highly automatized infor- auditory deprivation on deafened adults' capability to process mation-processing task. However, any kind of distor- auditory information. tion (e.g., from noise or hearing impairment) of the spoken signal, places extra demands on the informa- A cochlear implantation gives deafened individuals an tion-processing system. For example, variations in per- opportunity to experience some sense of hearing. How- formance on visual speechreading tasks can partly be explained by the individual's perceptual and cognitive capability to process incomplete verbal information Thij research is supported by grants from the Swedish Council for Social (Gailey, 1987; LyxeU, 1994; Ronnberg, 1995). That is, Research (93-0116) awarded to Bjorn LyxeH We thank UUa-Britt Per- sson for checking the language. Parts of thii research were presented at in situations in which the spoken signal is poorly speci- the Eighth Conference of the European Society for Cognitive Psychol- fied, as in visual speechreading, the individual must ogy, Rome, Italy, September, 1995. Correspondence should be sent to Bjarn Lyxell, Department of Education and Psychology, LinkSping Uni- compensate for missing information by explicit use of versity, S-S81 83 Linkoping, Sweden (e-mail:

[email protected]

). alternative verbal information Copyright C 19% Oxford University Press. CCC 1081-4959 The purpose of this study is to examine possible predictors for successful speech understanding follow- ing a cochlear implant operation. As in speechreading and other kinds of communicative situations in which the stimulus signal is poor, it is reasonable to assume that speech perception with cochlear implants would tax the individual's information-processing sys- tem more than normal listening conditions. Thus, it should, in principle, be possible to predict some part of the variation in speech understanding by means of examining the individual's cognitive capability to pro- cess verbal information. The reason for this relatively straightforward assumption is that a cochlear implant can never fully simulate the functioning of a normal ear. This suggestion is supported by clinical and exper- imental evidence demonstrating that relatively few im- planted individuals reach a level of speech understand- ing comparable to that of normal hearing individuals. Clinical observations and postoperative follow-up studies indicate that two factors can predict at least some part of the variation in speech understanding: (1) duration of deafness between onset and the implant operation and (2) preoperative speechreading skill. These results indicate that a shorter, as opposed to longer, duration of deafness might result in a greater number of surviving auditory nerve fibers and more complete memory for sounds (Gantz, Woodworth, Ab- bas, Knutson, & Tyler, 1993; Summerfield & Marshall, 1994). Preoperative skill in visual speechreading is as- sumed to reflect a verbal cognitive capacity necessary to transfer sensory data into meaningful units (Sum- merfield & Marshall, 1994). However, the interpreta- tion of these observations must be regarded as rather indirect since the inferences about the underlying ca- pability derive from another test or observation. In this study, we examine subjects' performance in clusters of tasks that more directly assess verbal cogni- tive functioning and are assumed to be related to post- operative performance following a cochlear implant. More precisely, we employ tests of working memory capacity (Baddeley, 1990), speed of verbal information processing (Hunt, 1985), internal speech functioning (Baddeley & Wilson, 1985; Conrad, 1979), and visual speechreading performance. The first three tasks have previously proved to account for varying proportions of the variance in visual, audio-visual, and tactually supported speechreading (Lyxell, 1989). 192 Journal of Deaf Studies and Deaf Education matching, Posner & Mitchell, 1967; or semantic deci- sion making, Shoben, 1982). Thus, the data suggest that the deterioration of deafened adults' internal speech functioning is not complete, but occurs under specific conditions. Further examination of the perfor- mance of the deafened adults suggests that the is localized at the representational level, rather than the transformational. Performance for deafened adults in rhyme judgment tasks is further correlated with speechreading performance and also with the number of years that an individual has been deaf. Well- functioning internal speech should, at least intuitively, be important for individuals receiving cochlear im- plants. That is, a cochlear implant gives the some sense of hearing, and it is important that impressions can be matched against existing internal auditory representations. Clinical observations support this assumption, as one determinant of postoperative level of speech understanding is the time elapsed be- tween the onset of deafness and the point when the in- dividual receives an implant (Tyler, in press). In this study we focus on the type of spoken com- munication that the individual can manage after six to eight months of experience with a cochlear implant. The subjects were classified in one of four categories with respect to their functional communicative ability: the lowest level of this scale was awareness of environ- mental acoustical stimuli; the next was improvement in speechreading with the implant; next was the ability to understand speech when the speaker is out of sight; and, finally, the highest level was the ability to under- stand speech transmitted by the telephone. Data also include clinical observations from members of cochlear implant teams and self-reports from the implant pa- tients themselves. Method Subjects. Eleven cochlear implant candidates (mean age = 51.6 years, standard deviation [SD] = 10, range = 28-70; see Table 4 for data on each individual) participated in our study. Seven of the 11 individuals received their cochlear implantation at the University hospital in Linkoping, Sweden, and four at Sodersjuk- huset, Stockholm. They were given the cognitive tests when they were candidates for implantation and visited the clinics for medical examination. Ten of the eleven three groups on one index of verbal ability. No signifi- cant difference among the groups emerged (/> > .05). Tests. The tests used in this study have previously been used to examine speechreading and tactile-supported speechreading under conditions similar to those exam- ined here. Therefore, a condensed description of the tests will be presented here, and readers can consult Lyxell (1994), Ronnberg, Arlinger, Lyxell, & (1989), or Ronnberg (1993) for more detailed descrip- tions. 1. Sentence-based speechreading test. To measure subjects' sentence-based speechreading ability, 24 different sentences-to-be-speechread were presented (i.e., same test as in Ronnberg, et al., 1989; Ronnberg, 1989, 1992; Ronnberg, 1990, 1993). The 24 sentences were divided into three blocks, each ing eight sentences. All eight sentences in were presented together before any sentence from an- other block was presented. Prior to the presentation the sentences in each of the three blocks, the were instructed to read a context-creating script, which was printed on an answer-sheet and informed the subjects about a scenario in which a hypothetical conversation took place. Three different scenarios used (i.e., a "train scenario"; a "restaurant and a "shop scenario"), each with a unique frame- history. In half of the sentences, the subjects were offered an extra contextual cue, which informed them about the semantic content of the sentence-to-be- speechread. A JVC VHS videotape recorder was used to pres- ent the material on a 66-cm Tandberg TV-monitor in the following way. First, the videoscreen was red for a period of five seconds; following this, a male actor (JA) appeared on the videoscreen. The actor was silent for a period of three seconds, before and after presentation of a sentence. After the presentation, the response in- terval started (25 seconds), during which the TV- screen was gray. This procedure,was repeated for all sentences in the test. The subjects were placed at a dis- tance of three meters from the screen during the test session and were instructed to write all words that they had been able to speechread and to guess the rest of the message (cf, Lyxell & Ronnberg, 1991, 1992). Scoring of the responses was carried out with re- spect to both correctness of the word and their correct 194 Journal of Deaf Studies and Deaf Education test, half being real words and half not. Twenty-five items that were not a real word sounded like a real word when pronounced (i.e., homophone), whereas the re- maining 25 did not sound like real words (i.e., nonho- mophones). The real words used in the present test were all, according to Allen (1970), familiar Swedish words. 4. Semantic decision-making. The subjects' task was to decide whether a word belonged to a certain predefined semantic category or not (cf., Shoben, 1982). Four trials were used with 24 to-be-categorized items, of which 12 items belonged to a semantic cate- gory and 12 items were foils. The four trials were "col- ors," "occupations," "diseases," and "parts of the body." For all long-term memory access tests, latency data were based on the average of each subject's yes/no re- sponses. Rhyme judgment test of internal speech. The subjects were given a rhyme judgment test in which they had to de- cide whether two simultaneously presented words rhymed. The subjects were to respond by pressing pre- defined buttons for "yes" and "no" answers. Half of the pairs rhymed and half did not. Four experimental conditions were created in the rhyme judgment test (cf., Lyxell et al., 1994). The first condition involved word-pairs which rhymed and were orthographically similar in spelling (e.g., KATT- HATT), the second by words that rhymed, but were orthographically dissimilar in spelling (e.g., DAGS- LAX). In the third condition the words did not rhyme, but were orthographically similar in spelling (e.g., STAL-STEL); in the final condition the words did not rhyme and were orthographically dissimilar in spelling (e.g., CYKEL-SPADE). Results The results will be presented in two parts. The first part examines the performance of the implanted group of deafened adults, the nonimplanted deafened adults, and normal hearing adults on the verbal cognitive tasks. The second examines the pattern of verbal cog- nitive performance of the 11 implanted patients and re- lates performance to the individuals' levels of speech understanding with their implants. Table 2 Mean performance for the three groups Deafened adults, Cochlear implants Speechreading (proportion .48 correct) Tests of short-term/working memory (proportion correct) Reading span .38 Word span .53 Tests of information- processing speed (in seconds) Physical matching .85 Name matching .87 Semantic decision making .73 Lexical decision making Yes .78 No: homophones 1.03 No: nonhomophones .73 Rhyme-judgement: word- pairs (in seconds) Yes: visually similar 1.15 Yes: visually dissimilar 1.71 No: visually similar 1.62 No: visually dissimilar 1.36 Table 3 Accuracy level for the tests of verbal judgement for the three groups Deafened adults, Cochlear implants Test of information- processing speed Physical matching .89 Name matching .92 Semantic decision making .96 Lexical decision making Yes .93 No: homophones .80 No: nonhomophones .93 Rhyme-judgement word- pairs Yes: visually similar .98 Yes: visually dissimilar .65 No: visually similar .63 No: visually dissimilar .89 *p < .05. 196 Journal of Deaf Studies and Deaf Education Table 4 Age, duration of deafness, and mean Speech reception Telephone performance conversation Individuals 2 3 8 Age 28 39 Duration of deafness 4 4 Speechreading (proportion .65 .68 correct) Tests of short-term working memory (proportion correct) Reading span .52 .56 Word span .58 .52 Test of information- processing speed (in seconds) Physical matching .51 .70 Name matching .57 .70 Semantic decision making .53 .50 Lexical decision making Yes .59 .61 No: homophones .68 .78 No: nonhomophones .55 .55 Rhyme-judgement: word- pairs (in seconds) Yes: visually similar .88 .96 Yes: visually dissimilar 1.22 1.36 No: visually similar 1.45 1.42 No: visually dissimilar .99 1.21 1991; Mogford, 1987), the subjects in all three groups performed comparably in the speechreading task, al- though the range of performance was larger in both groups of deafened adults than in the group of normal hearing controls. This indicates that these two groups include both proficient and less proficient speechread- ers (see Table 4, for the group of implanted deaf adults). A similar pattern of results with respect to the accuracy level in the deafened adults' performance on the rhyme judgment task has recently been observed in our own laboratory (Lyxell & Ronnberg, 1994; Lyxell et al., 1995; Lyxell et al., 1994; all three studies with somewhat larger number of subjects). These results are also in line with results from other studies in which in- ternal phonological abilities of other groups of deaf (i.e., prelingually deaf children and adults) have been examined (although with a different methodology than municative ability. The lowest level on this scale was awareness of environmental acoustical stimuli; the next highest was improvement in speechreading with the implant; next was the ability to understand speech when the speaker is out of sight; and the highest was the ability to understand speech transmitted by the telephone. The subjects were classified in the four categories as follows: Three individuals (i.e., the individuals 2, 3, and 8) can communicate quite effortlessly with other individuals by means of telephone. More specifically, two of the three report no problem in telephone use even if the speaker and the topic of the conversation are unfamiliar to them; one can quite easily follow a conversation if the speaker and the topic are familiar. Two individuals (i.e., 1, 10) can without effort follow a conversation when an unfamiliar speaker is out of sight and when the topic is unfamiliar. These individuals can sometimes understand a few words spoken over the telephone, but they cannot manage a telephone conver- sation in a functional sense. Three (i.e., individuals 4, 5, 6) report that their speechreading is substantially improved with the implant or less effortful (i.e., 7 and 9). Similar to the previous group, this group of subjects can hear some words when the speaker is out of sight, but the speaker must be visible before they can use the Table 5 Accuracy level for the tests of verbal implant patient Speech reception Telephone performance conversation Individuals 2 3 8 1 Test of information- processing speed Physical matching 1.0 .91 .94 .75 Name matching .94 .86 1.0 .95 Semantic decision making 1.0 .98 .99 .96 Lexical decision making Yes .90 .94 .98 .96 No: homophones 1.0 1.0 .96 .71 No: non-homophones .96 .92 .96 .92 Rhyme-judgement: word- pairs Yes: visually similar 1.0 1.0 1.0 1.0 Yes: visually dissimilar .92 .92 1.0 1.0 No: visually similar 1.0 .38 1.0 .92 No: visually dissimilar 1.0 1.0 .92 1.0 198 Journal of Deaf Studies and Deaf Education the reading span task and above on the word-span task. Thus, this individual possesses an excellent working memory capacity when the task demand in the memory task only emphasizes storage (i.e., word-span), whereas his capacity to deal with tasks emphasizing both pro- cessing and storage (i.e., reading span) is poor. The second individual within this category possesses a nor- mal working memory capacity. Both perform on par with the controls on the tasks assessing verbal informa- tion-processing speed. For speed of rhyme judgment, subject 1 proves to be faster than the control group, whereas subject 10 is considerably slower. The accu- racy level for subject 1 is on par with the controls for the tests of verbal information-processing speed and rhyme judgement, with two exceptions: the physical matching and one condition in lexical decision task. Subject 10 has a similar rate of accuracy for the verbal information-processing tasks as the control group, but performs substantially lower on the rhyme judgment task. Three individuals (i.e., 4, 5, and 6) improved in their speechreading substantially and two (i.e., 7 and 9) did not improve in their speechreading but report that their speechreading is less effortful with the implant. The subjects who improved in their speechreading performance (two cases) on average are somewhat be- low the control group or substantially below in one case. As for the working memory span tasks and the tests of verbal information-processing speed, one sub- ject performs comparably to the controls, and two are inferior to them. In the rhyme judgment task, all three perform slower than the normal hearing controls. On verbal information-processing tasks, the three subjects' accuracy level is in one case on par with the controls and in two somewhat below both controls. However, when rhyme judgment is considered, the accuracy level is clearly below that of normal hearing subjects. Two subjects cannot follow a conversation when the speaker is out of sight and did not increase their speechreading performance with the implant. How- ever, both are skilled speechreaders and, compared to the other three within this category, there might be less room for improvement. Subject 7 performs on par on some of the verbal information-processing tasks and less well on the rhyme judgment task. Parenthetically, subject 7 is the only deafened adult that we have ob- that the individual must possess a capacity that is at least similar to or better than that of normal hearing individuals in each of these three tasks in order to understand speech without visual contact with the speaker. If it is the case that the performance level in one of the three components does not resemble that of the normal hearing subjects, understanding of speech without seeing the speaker is not possible after six to eight months' experience with the implant. The results are partly in line with results presented by Summerfield and Marshall (1994), who demon- strated that better performance in speech understand- ing could be explained by (a) duration of deafness (where shorter periods lead to better results), (b) pos- session of some usable residual hearing, and (c) preop- erative skill in lipreading. Implications for the first two factors above are reflected in this study by the fact that relatively intact internal speech is found only among individuals with the most successful outcome (i.e., ca- pable of following a conversation when the speaker is out of sight). Performance on tasks measuring phono- logical capabilities or internal speech is further nega- tively correlated with the number of years that the indi- vidual has been deaf (see also, Lyxell et al., 1994; Conrad, 1979). Our data suggest that the role of pre- served internal speech in cochlear implantees is that the individual must possess the ability to match the ex- perience of external sound with an existing internal representation of sounds. Given that this possibility does not exist, the individual will inevitably suffer from difficulties in interpreting the sounds from the external world. Other independent support for such a hypothe- sis comes from studies using PET-scan methodology, which has demonstrated that the metabolic activity in the primary auditory cortex declines progressively with time as a function of auditory deprivation (Ito, Iwasaki, Sakakibara, & Yonekura, 1993; Soderfeldt, 1994). A question for further research is whether this deteriora- tion is irreversible or whether a cochlear implantation possibly can alter this state of affairs. An implication for the latter possibility was demonstrated in a recent study with six subjects (with varying experience of the implant) in which their metabolic rate returned to an almost normal level after receiving an implant (Naito et al., 1995). In clinical practice, duration of deafness is often 200 Journal of Deaf Studies and Deaf Education derstanding at levels above gain in speechreading is still critically dependent on the quality of the individu- al's internal speech. In sum, the results from this study indicate that it might be possible to predict what level of speech un- derstanding the individual will reach six to eight months after cochlear implantation, by means of pre- operative testing of verbal cognitive abilities. Measures of duration of deafness and preoperative skill reading are indirect predictors as they are assumed to tap abilities such as memory for sounds and general cognitive abilities (Summerfield & Marshall, 1994; Tyler, in press). In clinical practice we can dividuals with a relatively long duration of deafness and with intact internal speech functions and, simi- larly, individuals with a high level of preoperative lip- reading skill whose level of speech understanding low the expected. The results from our study suggest that higher prediction-accuracy is obtained if these abilities are tested directly. However, any prediction must take into account that, given the individual pos- sesses a perfect verbal cognitive architecture, there must also be optimal anatomical and technical condi- tions for a successful outcome of the implantation. this study, this is illustrated by subject 9, who possesses almost the same verbal cognitive abilities as the indi- viduals with the most successful outcomes. Further ex- amination of her case suggests that her lack ment in speech understanding may be due to technical problems with the implant, not anatomical problems or, as indicated by her results, verbal cognitive diffi- culties. Collecting preoperative data of cognitive function- ing thus serves two purposes: to allow predictions about the outcome with the implant and to provide preoperative information that can allow determination of possible problems with the implant due to the indi- vidual's capacity to process verbal spoken informatio or other factors (i.e., medical or technical). References Alegria, J., Leybaert, J., Charlier, B., & origin of phonological representations in the deaf: Hearing lips and hands. In J. Alegria, D. Holender, Lyxell, B., Andersson, J., & Ronnberg, J. functioning and speechreading of a connected discourse. Manuscript, Department of Education and Psychology, Linkoping University, Linkoping, Sweden. Lyxell B., Ronnberg, J., & Samuelsson, S. (1994). Internal speech functioning and speechreading in deafened and nor- mal hearing adults. Scandinavian Audiology, 23, 179-185. Mogford, K. (1987). Lipreading in the prelingually deaf. In B. Dodd, & R. CampbeU (Eds.), Hearing by eye (pp. 191-211). London: LEA. Naito, Y., Okazawa, H., Honjo, I., Hirano, S., Takahashi, H., Shiomi, Y., Hoji, W., Kawano, M., Ishizu, K., & Yonekura, Y. (1995). Cortical activation with sound stimulation in co- chlear implant users demonstrated by Positron Emission Topography. Cognitive Brain Research, 2, 207—214. Osberger, M. J., Todd, S. L., Berry, S. W., Robbins, A. M., & Miyamoto, R. T. (1991). Effect of age at onset of deafness on children's speech perception abilities with a cochlear im- plant. Annals of Otology, Rhinology and Laryngology, 100, 883-S88. Posner, M. I., & Mitchell, R. F. (1967). classification. Psychological Review, 74, 392-409. Ronnberg, J. (1990). Cognitive and communicative function: The effects of chronological age and "handicap-age." Euro- pean Journal of Cognitive Psychology, 2, 253—274. Ronnberg, J. (1993). Cognitive characteristics The case of GS. European Journal of Cognitive Psychology, 5, 19-33. processing components (Lyxell, 1994; Ronnberg, 1995). Cochlear Implants and Information Processing 191 Tests of working memory are included because when part of the spoken signal is missing or ambigu- ous, the individual must temporarily store information to be able to fill in information (by means of infer- ences). Exceptional working memory capacity is one key feature in cases of high visual speechreading skill (Lyxell, 1994; the case of SJ), audio-visual speech un- derstanding (Ronnberg et al., 1995; the case of MJ), and in tactually supported speechreading (Ronnberg, 1993; the case of GS). Also, Knutson et al. (1991), us- ing a visual monitoring task in which short-term stor- age of information was a task demand, demonstrated a significant relationship between auditory and audio- visual performance with the implant. Verbal information-processing speed is the speed with which lexical information can be accessed from long-term memory (Hunt, 1985; Sternberg, 1985). This speed accounts for the variability in a number of tasks such as general verbal ability (Hunt, 1978; 1980; Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 1985), reading comprehension (Baddeley, Logie, Nimmo-Smith, & Brereton, 1985), chronological age (Salthouse, 1982), and, relevant in this context, sentence-based speechreading (Lyxell & Ronnberg, 1992). The importance of a relatively fast access of ver- bal information in speechreading is evident, as the spo- ken stimuli are degraded and short-lived. A relatively slow access to verbal information would create a "pro- cessing bottle-neck" and inhibit the allocation* of resources to other necessary processes (cf. Lyxell & Ronnberg, 1992). Previous studies have demonstrated the involve- ment of an internal speech code in visual speechread- ing (Conrad, 1979; Lyxell, Ronnberg, & Samuelsson, 1994). Recent results suggest that postlingually deaf adults perform worse than normal hearing controls in tasks demanding usage of internal speech (Lyxell, An- dersson, & Ronnberg, 1995; Lyxell et al., 1994). Prob- lems encountered by adults in using an internal speech code could be tied to (a) distortions in the transforma- tion process (i.e., the internal representation of sounds is intact), to (b) representational aspects (i.e., the trans- formation process is intact), or some possible combina- tion of (a) and (b). However, Lyxell and his colleagues have found that these results hold only for tasks that require some explicit form of internal speech (e.g., rhyme judgment tasks), and not when the require- ments on internal speech are less explicit (e.g., name 1:3 Summer 1996 Table 1 Hearing threshold levels determined by sound field testing with cochlear implants for each subject 250 Hz 500 Hz 1KHz 2KHz 4KHz Individuals 1 30 30 40 30 30 2 30 25 30 25 25 problem 3 35 30 30 30 35 4 25 20 30 30 30 5 35 30 35 30 30 6 45 40 40 35 40 7 40 40 35 30 30 8 55 45 40 45 45 9 30 35 35 35 45 10 55 45 35 40 55 11 50 35 35 35 50 individual auditory implant candidates received the Nucleus 22-channel implant and one the Ineraid implant. Their mean du- ration of deafness was 13.1 years (SD = 14.8, range = 1-51; see Table 4 for data for each individual). Their Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 postoperative hearing threshold levels 6—8 months after the implantation were determined by sound field testing with the cochlear implant, using warble tones and calibrating in terms of dB HL with data according to ISO 226 (1987) as reference. The mean hearing threshold levels were for 250 Hz 39 dB (SD = 10.7, range = 25-55), for 500 Hz 34 dB (SD = 8.0, range = 20-45), for 1 kHz 35 dB (SD = 3.9, range = 30-40), for 2 kHz 33 dB (SD = 5.6, range = 25-45) and, fi- nally, for 4 kHz 37 dB (SD = 9.8, range = 25-55). Using the average sound field hearing threshold levels as a basis, the application of simple Articulation Index (Killion, Mueller, Pavlovic, & Humes, 1993) calcula- tions would estimate a perceptual speech intelligibility on the order of 4O%-50%. The Articulation Index can be considered a measure of the proportion of speech cues that are audible and thus theoretically available for the implantees. Threshold values for each implant pa- tient are displayed in Table 1. Ten nonimplanted deafened adults (mean age = 57.4 years, SD = 8, range = 22-67) and 10 normal hearing individuals (mean age = 56.8, SD = 8, range = 22-70) participated in our study on a volun- tary basis. None of the nonimplanted deafened adults had any functional residual hearing with hearing aids according to their most recent medical records. A test of vocabulary size (antonyms; F-testet, Psykologi forla- get, Stockholm) was given to match the subjects in the Cochlcar Implants and Information Processing 193 position in the sentence. The number of correctly re- called words per sentence was expressed as a propor- tion for each sentence and subject for the purpose of data analysis. Short-term /working memory tests. 1. Reading span test. The subjects' task was to comprehend sentences and to recall either the first or Kinnefors the final words of a presented sequence of sentences in correct serial order (cf., Baddeley et al., 1985). The words were presented in a word-by-word fashion, at a rate of one word per .80 sec with an interstimulus in- terval of .07 sec Half of the sentences were absurd (e.g., "The train sang a song"), and half were normal senten- Lyxell & ces (e.g., "The girl brushed her teeth"). The subjects' task was to respond "yes" (for a normal sentence) or includ- "no" (for an absurd sentence) during a 1.75 sec inter- a given block val. After a sequence of sentences (3-6 sentences), the experimenter pointed at the words "First" or "Final" Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 of written on a piece of paper, indicating that the subjects subjects should start to recall either the first or the final words of each presented sentence in the sequence in their cor- rect serial order. The order ("First" or "Final") was randomized. were 2. Word span. The subjects' task was to recall in scenario"; correct serial order a string of words, which were pre- sented one at a time on the computer screen. The first span size employed (after a practice session) was three words, the next was four and so on up to eight words. Tests ofverbal information processing speed. 1. Physical matching. The subjects' task was to judge whether two simultaneously presented letters had the same physical shape (e.g., A-A) or not (A-a). The subjects were to respond by pressing predefined buttons for "yes" and "no" answers. Half of the pairs were identical and half were not. 2. Name matching. Instead of matching letter- pairs for their physical identity, the subjects were asked to match letter-pairs for their name. Sixty-four re- sponses were collected in four trials of 16 responses. The same letter-pairs were used as in the test of physi- cal matching. 3. Lexical decision-making. The subjects' task was to judge whether a string of three letters constituted a real word or not. One hundred items were used in the 1:3 Summer 1996 Preoperative level of verbal cognitive performance. Tables 2 and 3 give descriptive data for the three groups in this study. Performance on tasks assessing working mem- ory/short-term memory is comparable for all three groups and replicates previous results, both with re- spect to mean performance and to performance level on tests, where groups of deafened adults and normal hearings have been compared (Lyxell & Ronnberg, 1989; Ronnberg, 1990). A similar pattern of results emerges when verbal information processing speed and accuracy level are examined: no differences (with one exception) between the groups in any of the tests (or test conditions) occurred. The performance levels closely resemble previously reported levels when simi- lar (cf, Hunt, 1980) or the same tests have been used (Lyxell, 1994; Lyxell & Ronnberg, 1992; Ronnberg, 1990). In one condition of the lexical decision test, the deafened adults (i.e., both the implanted and the non- implanted individuals) proved to have a significantly Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 lower level of accuracy (t(18) = 2.95, p < .01, and t(19) = 2.16 , p < .05) than the normal hearing sub- jects: when the string of letters did not constitute a word but when pronounced sounded like a real word (i.e., pseudohomophones). In the rhyme judgment test, no differences between the groups occurred when speed of judgment was ex- amined, which is in line with previous results (although tested here with slightly different rhyme judgment tasks; cf. Lyxell et al., 1994). The accuracy level was significantly lower for the two groups of deafened adults in two conditions: when the words in the word- pair rhymed and were orthographically dissimilar (t(18) = 2.35,/) < .05, t(19) = 2.33,/> < .05), and when the words did not rhyme but were orthographically sim- ilar (t( 18) = 2.15,/) < .05, t(19) = 2.15,/) < .05). No differences occurred in the two conditions wherein words rhymed and were orthographically similar or did not rhyme and were orthographically dissimilar (ps > .05). Taken together, the results at the group level can be summarized by two points: First, the two groups of deafened adults performed comparably in all cognitive tasks used in this study, suggesting that the group of implant patients does not differ from other populations of deafened adults. Second, similar to other studies (Cowie & Douglas-Cowie, 1993; Lyxell & Ronnberg, Cochlear Implants and Information Processing 195 on the tests used in the study Deafened adults, nonimplanted Normal hearing .38 .34 .38 .39 .46 .48 .82 .73 .89 .83 .75 .69 .80 .74 1.07 .92 .72 .69 Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 1.17 ' 1.13 1.84 1.65 1.86 1.59 1.28 1.20 information-processing speed and rhyme- Deafened adults, nonimplanted Normal hearing .96 .98 .96 .97 .98 .98 .94 .94 .82 .93* .96 .96 .98 .97 .67 .92* .59 .87* .96 1.00 1:3 Summer 1996 performance for the cochlear implant patients on the tests used in the study Listening Speechreading improvement Sound awareness 1 10 4 5 6 7 9 11 58 70 61 29 70 58 57 42 59 10 10 12 1 10 5 51 1 27 .68 .27 .69 .36 .04 .22 .77 .80 .25 .57 .28 .44 .41 .19 .06 .33 .39 .17 .74 .81 .52 .54 .63 .19 .47 .60 .31 .83 .87 .86 .65 1.65 1.26 .71 .76 .68 .89 .88 .87 .74 1.12 1.38 .78 .87 .78 .83 .74 .74 .59 .76 1.19 .81 .68 .72 Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 .95 .70 .78 .64 .76 1.17 .85 .80 .78 1.03 1.16 1.0 .99 .90 1.45 1.27 1.13 1.03 .76 .81 .77 .55 .65 1.15 .85 .73 .73 1.17 1.01 1.40 1.18 1.13 1.30 1.46 1.06 1.16 1.65 1.56 2.58 1.71 1.26 1.98 2.32 1.20 2.00 1.19 1.27 2.03 1.76 1.85 1.62 1.82 1.23 2.26 1.22 1.02 1.40 1.34 1.94 1.60 2.04 1.10 1.11 in this study; Alegria, Leybaert, Charlier, & Hage, 1992; Hanson & McCarr, 1989). The novel finding from this study is that we can extend our observation of a deterioration in internal speech functioning to tasks other than rhyme judgment tasks (i.e., lexical de- cision tasks). Relation between preoperative measures and postoperative speech understanding. Postoperative clinical observations by the members of the implant teams and self-reports reveal individual differences in type and quality of gain in speech understanding with the implant. This is by no means a new finding; rather, it is observed each time a population of implanted individuals has been exam- ined (Knutson et al., 1991; Osberger et al., 1991). The subjects were classified into one of four categories on an ordinal scale with respect to their functional com- Cochlear Implants and Information Processing 197 implant in a functional communicative sense. Finally, one subject (i.e., 11) has only sound awareness and some ability to identify enviromental sounds. Further examination of the individuals' verbal cog- nitive capacity reveals a correspondence between their preoperative verbal cognitive performance and postop- erative level of speech understanding. The three sub- jects who can communicate by means of telephone can be characterized as skilled speechreaders (i.e., they outperform the controls by approximately a factor of two); they have a relatively large working memory ca- pacity (i.e., they outperform the normal hearing con- trols by approximately a factor of 1.5). Furthermore, when verbal information-processing speed and speed of performance in the rhyme judgment tasks are con- sidered, their performance is faster (subjects 2 and 3) or comparable to the controls (subject 8). All three sub- jects demonstrate an accuracy level somewhat higher than that for the control group on the verbal informa- Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 tion-processing tasks. They perform on par with the normal hearing control for the rhyme judgment tasks. The two subjects who can follow an oral communi- cation when the speaker is out of sight are in one case skilled in speechreading (i.e., 10) and in the other slightly below the average (i.e., 1). As for the memory tests, one subject is considerably below the average for information-processing speed and rhyme-judgement for each cochlear Listening Speechreading improvement Sound awareness 10 4 5 6 7 9 11 .94 .97 .50 .94 .94 1.0 .94 .97 .97 .88 .67 .91 .94 .98 1.0 1.0 .90 .91 .89 .99 .95 .90 .92 .90 .98 .92 .92 .96 .96 .75 .65 .54 .54 .88 .83 .89 .96 .96 .92 .92 .96 .92 1.0 1.0 .83 1.0 1.0 1.0 1.0 .50 .58 .42 .17 .42 .92 .33 .77 .23 .31 .63 .15 1.0 .54 1.0 1.0 .15 1.0 .92 1.0 1.0 1:3 Summer 1996 served who is a skilled speechreader without well- functioning internal speech. Subject 9 performs simi- larly to the normal hearing controls on most of the tasks and should, at least in comparison with the other subjects in this study, reach a higher level of speech un- derstanding. However, further medical examination re- vealed that the absence of improvement in this case may be due to a combination of technical and medical problems. Finally, one subject can discriminate only between conditions of sound and nonsound in the acoustic environment. An examination of his verbal cognitive profile reveals that his performance is below or substantially below compared to normal hearing subjects on most tasks in the study. The results from this study can be summarized based on the observed data-pattern: Implanted indi- viduals who are able to communicate with others over the telephone perform better or on par with the normal hearing controls on verbal information-processing Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 measures. Individuals who can follow a conversation when the speaker is out of sight perform at the same level as the normal hearing subjects on most tasks with one exception (in each of the two cases). Individuals who improve only their speechreading or receive acoustical orientation are inferior to the controls on most tasks. Similar to previous studies, we can observe that skill in speechreading is a feature among those im- plant patients who are most proficient in interpreting spoken acoustic stimuli, but we can also observe skilled speechreaders among those individuals who are less proficient. This finding further suggests that in order to preoperatively predict success with a cochlear im- plant, verbal cognitive capacity of the individual must be properly understood as well. Discussion Our study was designed to examine the possibility that the preoperative characteristics of some verbal cogni- tive components could be related to the level of speech understanding six to eight months after operation. Here, we can identify three verbal cognitive factors that can serve as predictors of the level of speech understanding following a cochlear implantation: working memory capacity, speed of verbal information- processing, and internal speech. Our results suggest Cochlear Implants and Information Processing 199 used as a predictor of the outcome. The rationale for using duration of deafness as a predictor is that it is "a reflection of number of surviving hair cells and neu- rones" (Tyler, in press) or the ability "to interpret audi- tory sensations" (Summerfield & Marshall, 1994). These are indirect indicators of the functions of inter- nal speech. Even if there is a correlation between dura- tion of deafness and outcomes, however, the correlation is far from perfect, and a large variability exists among the individuals (Tyler, in press). Although the popula- tion in this study is relatively small, this variability is to some extent present. The clinical suggestion from this study is, thus, that a more appropriate approxima- tion of the functioning of the individuals' internal speech is achieved by testing the ability directly (e.g., by means of rhyme judgment tests). Similar to previously reported results (Sum- merfield & Marshall, 1994; Tyler, in press), as well as clinical observations, we found that better skill in visual Downloaded from jdsde.oxfordjournals.org by guest on July 13, 2011 speechreading is characteristic of those subjects who reach the highest levels of speech understanding. How- ever, proficiency above the level in the control groups is also observed in individuals who do not reach higher levels in speech understanding. Visual speechreading may constitute an ability that is necessary but not sufficient for success with the implant. The reason for this relation is that some of the verbal cognitive abilities that are critical determinants for skill in speechreading are also critical for the outcome of an implant opera- tion, whereas other verbal cognitive abilities, also criti- cal for speechreading performance, might be less criti- cal for performance with the implant (e.g., visual decoding skill; Gailey, 1987; Lyxell & Ronnberg, 1989). Speed of verbal information processing and working memory capacity (Lyxell, 1994; Ronnberg, 1990) are two abilities critical for performance in both visual speechreading and with implants. Common to individ- uals who can communicate with a speaker who is out of sight is their performance above or on a par with that of the control groups. This level of performance serves as a performance threshold, indicating that the thresh- old must at least be reached before gains in speech un- derstanding other than mere acoustic orientation are achieved. However, even if the individuals possess a ca- pacious working memory and are fast in accessing in- formation from their long-term memory, speech un- 1:3 Summer 1996 Radeau (Eds.), Analytic approaches to human cognition. Am- sterdam: North-Holland. Allen, S. (1970). Frequency dictionary ofpresent-day Swedish. (In Swedish: Nusvensk frekvensordbok.). Stockholm: Alm- quist & Wiksell. Baddeley, A. (1990). Human memory: Theory and practice. Hills- dale: LEA. Baddeley, A., Logic, R., Nimmo-Smith, I., & Brereton, N. (1985). Components of fluent reading. Journal of Memory ami Language, 24, 119-131. Baddeley, A., & Wilson, B. (1985). 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