J Am Acad Audiol 16:205–218 (2005)

Differential Attention Effects on Dichotic Listening Jennifer B. Shinn*† Jane A. Baran‡ Deborah W. Moncrieff* Frank E. Musiek*

Abstract The role of attention in the differentiation of auditory processing disorders from attention deficit disorders is gaining considerable interest in both the clinical and research arenas. It has been well established that when attention is directed to one ear or the other on traditional dichotic tests, performance can be altered. However, preliminary studies in our laboratory have shown that dichotic fusion paradigms are resistant to shifts in ear performance associated with changes in attention. The purpose of this study was to assess the performance of normal listeners on a dichotic consonant-vowel and a dichotic rhyme (fusion) test. Both test procedures were administered to 20 young adults in three different listening conditions (free recall, attention directed to the left ear, and attention directed to the right ear). Results from this study supported the hypothesis that dichotic rhyme tests are resistant to alterations in the laterality of attention and have implications for the development of test paradigms that can be used to segregate attention from pure auditory deficits in the clinical domain. Key Words: Attention, auditory processing, consonant vowel, dichotic consonant-vowel, dichotic listening, ear advantage Abbreviations: ADHD = attention deficit-hyperactivity disorder; APD = auditory processing disorder; CV = consonant vowel; DCV = dichotic consonant-vowel; DL = directed left; DR = directed right; DRT = dichotic rhyme test; FR = free recall; LEA = left ear advantage; NEA = no ear advantage; REA = right ear advantage; SRT = speech recognition threshold

Sumario El papel de la atención al diferenciar entre un trastorno de procesamiento auditivo y un trastorno de deficiencia de la atención está ganando considerable interés tanto en el campo clínico como en el de la investigación. Se ha establecido claramente que cuando se dirige la atención a uno u otro oído durante las pruebas dicóticas tradicionales, el desempeño puede alterarse. Sin embargo, los estudios preliminares en nuestro laboratorio han mostrado que los paradigmas de fusión dicótica son resistentes a cambios en el desempeño auditivo asociados con cambios en la atención. El propósito de este estudio fue evaluar el desempeño de sujetos normo-oyentes en una prueba dicótica de consonante-vocal y una de rima dicótica. Ambos pruebas fueron administradas a 20 adultos jóvenes en tres diferentes condiciones de escucha (audición libre, con atención dirigida al oído izquierdo, y con atención dirigida al oído derecho). Los resultados de este estudio apoyan la hipótesis de que las pruebas dicóticas de rima son resistentes a las alteraciones en la lateralidad

*University of Connecticut, Storrs, Connecticut; †Currently at the University of Kentucky College of Medicine; ‡University of Massachusetts Amherst, Amherst, Massachusetts Jennifer B. Shinn, Department of Surgery, Otolaryngology-Head and Neck Surgery, University of Kentucky College of Medicine, 800 Rose Street, C236, Lexington, Kentucky 40536-0293; Phone: 859-257-3390, ext. 82173; Fax: 859-257-5096 This paper was presented at the American Academy of Audiology convention, April 3, 2004, in Salt Lake City, Utah.

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de la atención, y tienen implicaciones en el desarrollo de paradigmas de evaluación que puede usarse, en el campo clínico, para segregar los trastornos de atención de los trastornos auditivos puros. Palabras Clave: Atención, procesamiento auditivo, audición dicótica, oído con ventaja Abreviaturas: ADHD = trastorno de hiperactividad y deficiencia en la atención; ADP = trastorno de procesamiento auditivo; CV = consonante-vocal; DCV = consonante-vocal dicótica; DL = dirigido a la izquierda; DR = dirigido a la derecha; DRT = prueba dicótica de rima; FR = audición libre; LEA = ventaja del oído izquierdo; NEA = sin ventaja de oído; REA = ventaja del oído derecho; SRT = umbral de reconocimiento del lenguaje

T

he concept of dichotic listening was first introduced by Broadbent in 1954. Dichotic listening occurs when different auditory stimuli are presented to each ear simultaneously. It has been used historically to assess hemispheric dominance and lateralization, as well as hemispheric asymmetries (Kimura, 1961a, 1961b, 1967; Zattore, 1989), with diminished scores on these types of listening tasks suggesting auditory and/or cognitive dysfunction or pathology (Kimura, 1961a, 1961b). Kimura is credited as the first researcher to investigate the association between lateralization of speech and its relationship to the right ear advantage (REA). Her early work has been the foundation for the widely accepted theory that in man, the contralateral (or crossed) auditory pathway has more neural connections than the ipsilateral pathway and is considered the dominant pathway. On dichotic listening tasks, individuals will generally show an ear advantage in the ear contralateral to the hemisphere dominant for language. For most individuals this will result in an REA, which is believed to be the result of the left hemisphere’s dominance for language and the auditory perception of speech stimuli (Kimura, 1967). Although most individuals will tend to demonstrate an REA, this ear advantage is by no means a universal finding. The variability in performance on dichotic tasks with respect to ear advantage has been extensively studied in the past (Pizzamiglio et al, 1974; Ryan and McNeil, 1974; Blumstein et al, 1975; Speaks and Niccum, 1977). Results of these studies have demonstrated considerable variability in both the numbers of individuals demonstrating REAs, the size or extent of the ear advantage, and the stability of the REA

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across test sessions (i.e., test-retest correlation). One potential explanation for the differences noted in these measures is that attention effects may be operating to bias responses on several of these tests. A number of studies have demonstrated that some dichotic tests are vulnerable to shifts in attentional focus (Keith et al, 1985; Hugdahl and Andersson, 1986; Asbjørnsen and Hugdahl, 1995; Asbjørnsen and Bryden, 1996; Wiens and Emmerich, 1999; Hugdahl et al, 2000, 2001; Vingerhoets and Luppens, 2001; Voyer and Flight, 2001; Foster et al, 2002; Hugdahl et al, 2003). For example, Asbjørnsen and Hugdahl (1995) assessed the performance of normal subjects on a dichotic consonant-vowel (DCV) task in a non-forced (NF) condition (attention divided between ears) in which the normal subjects were instructed to freely repeat what they heard, and two forced conditions in which the subjects were instructed to direct their attention to either the left or right ear (i.e., attention forced right and forced left paradigms). These researchers demonstrated that the size and/or the direction of the ear advantage could be altered based on the focus of the subjects’ attention in the forced attention conditions. When attention was directed to the right ear, the expected REA was enhanced, whereas a reversal of the ear advantage from an REA to a left ear advantage (LEA) was commonly observed when the subjects were instructed to direct their attention to the left ear. Hugdahl and colleagues (2000) subsequently studied the effects of attention by measuring brain activation through the use of a 15O-PET study using dichotic consonant vowels (CVs) or short musical instrument passages as the stimuli. The subjects were

D i f f e r e n t i a l A t t e n t i o n E f f e c t s o n D i c h o t i c L i s t e n i n g /Shinn et al

evaluated using a paradigm in which they were directed to detect a target stimulus in either ear, in the left ear only, or in the right ear only. Their results indicated that when attention was focused on either the right or left ear, there was a significant decrease in brain activation bilaterally in certain areas of the temporal lobes when compared to the activation patterns observed in the NF condition. For the forced attention conditions, brain activation migrated from the temporal lobes to the right posterior and inferior superior parietal lobes. These areas have been identified previously as being active during attentional tasks (Cabeza and Nyberg, 1997). Although CVs are often the stimuli utilized in research on dichotic listening, there are many alternative stimuli that have been employed. These include words (Niccum et al, 1981; Wexler and Halwes, 1983; Speaks et al, 1985), digits (Kimura, 1961a, 1961b, 1967; Milner et al, 1968), chords (Efron, 1977; Efron et al, 1979), and sentences (Jerger et al, 1972; Speaks, 1975). A less frequently used dichotic test is the dichotic rhyme task (DRT). This task was first introduced by Wexler and Halwes (1983) and then later modified by Musiek et al (1989). The DRT uses temporally aligned consonant-vowelconsonant pairs that vary only in their initial consonants. Although subjects are presented two words (one word to each ear), the precise alignment of the words, as well as the fact that the final vowel-consonant elements in each pair of words are identical, result in the subjects perceiving only one word the vast majority of the time. As a result of these test features, normal right-handed subjects tend to demonstrate test scores that are slightly greater than 50% in the right ear and slightly less than 50% in the left ear (Musiek et al, 1989). This unique pattern of performance is presumed to be the result of some type of dichotic “fusion” of the signals, which occurs low within the central auditory nervous system. Such a phenomenon had been described earlier by Repp (1976) as a fusion of stimulus pairs resulting from a “low-level cross-correlated mechanism.” The DRT was originally developed to address the limitations of many of the traditional dichotic tasks, including low testretest correlations, the presence of an LEA in some right-handed subjects, and high error rates (Wexler and Halwes, 1983). Wexler and Halwes reported LEA rates in the literature

of 25 to 30% on dichotic speech tests for righthanded subjects. However, in an earlier study utilizing a sodium amytal procedure to investigate brain lateralization, Rasmussen and Milner (1975) reported that 97% of righthanded individuals exhibited left hemisphere dominance for language. Therefore, these REA statistics reflect a possible 22 to 27% discrepancy between results of traditional behavioral dichotic testing and true hemispheric language lateralization. Concerned by these findings, Wexler and Halwes (1983) investigated the utility of their DRT as an alternative dichotic tool. Using this test, these investigators demonstrated an REA in 85% of right-handed subjects versus the 70 to 75% they had previously reported in their review of the literature. These results met more closely the expected validity criterion with respect to REA in right-handed subjects as well as left-handed subjects. In addition, their results demonstrated better intrasubject reliability, and they found that the DRT was resistant to shifts or changes in attention (Wexler and Halwes, 1985). This latter finding becomes important particularly when evaluating individuals with attentional disorders since it is unlikely that focus of attention may result in an artificial ear asymmetry on this test. Zattore’s (1989) work that investigated speech lateralization using the carotid sodium amytal test supports the validity claims of the DRT made by Wexler and Halwes (1983, 1985). Zattore examined the DRT in 61 patients (35 subjects with left hemispheric representation, 4 with right hemispheric representation, and 22 subjects with bilateral representation as determined by the results of the carotid sodium amytal test). Those patients who had a significant REA on the DRT exhibited left hemispheric speech representation, whereas the reverse was true for those patients with right hemispheric speech dominance. Those patients who showed no significant ear asymmetry demonstrated bilateral speech representation. This study clearly demonstrated the sensitivity of the DRT test to hemispheric dominance for speech. Asbjørnsen and Bryden (1996) examined the effects of biased attention on a dichotic fused word test in comparison to the DCV test. Although they did not test a free recall (FR) condition, they did study the effects of attention in forced right and forced left conditions. Their overall findings indicated

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that attention significantly affected performance on both the DCV test and the dichotic fusion test, with the effects being much greater on the DCV test than on the dichotic fusion test. These findings were consistent with previous attention research on DCVs; however, the finding of significant attention effects on the dichotic fusion test was contrary to earlier claims made by Wexler and Halwes (1985), which indicated that dichotic fusion tasks were resistant to shifts in attention. The DRT was also used in studying dichotic listening performance in split-brain patients (Musiek et al, 1989). In this study, two significant observations were made for this population of patients. The first of these was that the subjects in this investigation consistently demonstrated the “expected” left ear deficit due to the compromise of the normal interhemispheric pathways, and the second was that the subjects not only showed the expected REA but that the size of this advantage was noticeably greater than that noted for normal subjects. The results of this study demonstrated that in addition to being clinically feasible for use with patients with compromise of the central auditory nervous system, this test was highly sensitive in assessing the integrity of interhemispheric transfer of auditory information. The unique nature of dichotic fusion tasks leads to the hypothesis that this dichotic task may be uniquely resistant to the effects of attention. Moreover, preliminary work by Baran and Musiek (1987) has demonstrated that the DRT is highly resistant to shifts in attention. Therefore, the purpose of the present study was to expand upon this earlier investigation by increasing the number of subjects tested and to additionally investigate the effects of directing attention to one ear versus the other on a DCV as well as the DRT test. Due to overwhelming evidence regarding the instability of dichotic CVs with respect to attentional demands, the need to compare these two tests of dichotic listening was apparent. In addition, the current pressure being placed upon professionals to differentially diagnose attentional deficits associated with auditory processing disorders (APD) from those associated with attention deficit-hyperactivity disorder (ADHD) renders this investigation both appropriate and timely.

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METHODS

Subjects A total of 20 college students recruited from the University of Connecticut participated in the present study. Subjects ranged in age from 20 to 27 years with a mean age of 22.5 years (SD ± 2.25). All subjects were righthand dominant based on results obtained from the Annette (1970) handedness questionnaire and were native speakers of English. All subjects reported negative histories of audiologic, neurological, and otologic involvement, and all subjects denied any of history of learning disabilities. In addition, each subject was screened for ADHD using the Brown ADD Scale™ (Brown, 1996) prior to participation in this study, and all 20 subjects tested negative for ADHD. Prior to participating in the experimental protocols, each subject underwent an otoscopic and audiological examination. Criteria for inclusion in this study included (1) a normal otoscopic exam; (2) pure-tone air-conduction thresholds of 20 dB HL or better bilaterally with no significant asymmetries (