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J Am Acad Audiol 12 : 506-513 (2001) Distortion-Product Otoacoustic Emissions in Schoolchildren : Effects of Ear Asymmetry, Handedness, and Gender Tegan Keogh* Joseph Kei* Carlie Driscoll* Veronica Smyth* Abstract The present study examined effects of ear asymmetry, handedness, and gender on distortionproduct otoacoustic emissions (DPOAEs) obtained from schoolchildren . A total of 1003 children (528 boys and 475 girls), with a mean age of 6.2 years (SD = 0.4, range = 5.2-7 .9 years), were tested in a quiet room at their schools using the GSI-60 DPOAE system . A distortion-product (DP)-gram was obtained for each ear, with f2 varying from 1 .1 to 6 .0 kHz and the ratio of f2/f1 at 1 .21 . The signal-to-noise ratios (SNRs) (DPOAE amplitude minus the mean noise floor) at the tested frequencies 1 .1, 1 .5, 1 .9, 2.4, 3 .0, 3.8, 4 .8, and 6.0 kHz were measured . The results revealed a small but significant difference in SNR between ears, with right ears showing a higher mean SNR than left ears at 1 .9, 3.0, 3.8, and 6.0 kHz. At these frequencies, the difference in mean SNR between ears was less than 1 dB . A significant gender effect was also found. Girls exhibited a higher SNR than boys at 3.8, 4.8, and 6.0 kHz. The difference in mean SNR, as a result of the gender effect, was about 1 to 2 dB at these frequencies . There was no significant difference in mean SNR between left-handed and right-handed children for all tested frequencies . Key Words : Children, distortion-product otoacoustic emissions, ear asymmetry, gender, handedness, hearing screening Abbreviations : DPOAE = distortion-product otoacoustic emission, OAE = otoacoustic emission, SNR = signal-to-noise ratio, SOAE = spontaneous otoacoustic emission, TEOAE _ transient evoked otoacoustic emission tudies of auditory function in the general population revealed an ear asymmetry effect . Right ears consistently demonstrate better responses than left ears . For example, Chung et al (1983) found that the mean pure-tone threshold for right ears was significantly better than that for left ears . Investigations have also shown that objective tests of hearing, such as auditory brainstem responses, reveal larger amplitudes and shorter latencies for the right ear in comparison with the left ear (Levine et al, 1988). In speech perception or dichotic listening tasks, right-handed subjects S *Department of Speech Pathology and Audiology, The University of Queensland, St . Lucia, Queensland, Australia Reprint requests : Joseph Kei, Department of Speech Pathology and Audiology, The University of Queensland, St . Lucia, Queensland 4072, Australia 506 report more accurately words presented to the right than to the left ear (Kimura, 1967 ; Bryden, 1986). The ear asymmetry effect is also evident in the objective measurement of spontaneous otoacoustic emissions (SOAEs), with the right ear producing stronger emissions than the left ear (Bilger et al, 1990 ; Burns et al, 1992 ; Khalfa et al, 1997). Studies of transient evoked otoacoustic emissions (TEOAEs) have also shown significantly larger emissions in the right in comparison with the left ear (Khalfa and Collett, 1996 ; Aidan et al, 1997 ; Kei et al, 1997 ; Khalfa et al, 1997 ; Newmark et al, 1997 ; Driscoll et al, 1999). Although the presence of an ear asymmetry effect in SOAEs and TEOAEs is widely accepted, its existence in distortion-product otoacoustic emissions (DPOAEs) has not been confirmed. To date, studies have revealed no asymmetry in DPOAEs between the ears (e .g ., LonsburyMartin et al, 1997, p. 96). However, these studies DPOAEs: Ear Asymmetry, Handedness, and Gender Effects/Keogh et al involved small sample sizes . Given the small effect size and inadequate power of statistical tests used in the analyses, the results may not have been conclusive . The exact cause of ear asymmetry in otoacoustic emissions (OAEs) is as yet undetermined. At present, there are only speculations about the phenomenon . For example, Previc (1991) suggested that the asymmetry was a result of a prenatal asymmetry occurring in the auditory system during the first trimester of pregnancy. McFadden (1993) speculated that the influence of efferent activity, specifically concerning efferent auditory inhibition, was a cause of ear asymmetry, with the efferent system exerting a stronger influence on the left than the right ear . This theory has been evaluated in a few studies that have focused on whether the medial olivocochlear bundle, which is an efferent system affecting the motility of outer hair cells, is responsible for the greater OAEs in the right ear (Morlet et al, 1993 ; Khalfa and Collet, 1996 ; Khalfa et al, 1997, 1998 ; Maison et al, 1997) . In summary, these studies suggest that ear asymmetry might be a product of the efferent system and/or a result of a prena- tal asymmetry. The possibility that ear asymmetry is a genetically determined function, similar to that of handedness, cannot be excluded . Handedness is the most easily observed expression of cerebral lateralization (Peters, 1995) . The estimate for people in the United States writing with the left hand is about 12 percent (10 .5% for females and 13% for males) (Gilbert and Wisocki, 1992) . Handedness is related to other behavioral asymmetries such as footedness, eyedness, and ear dominance . In general, lateral preference for the eyes and the ears is less clearly expressed than hand preference . Studies on footedness (Searleman, 1980 ; Peters, 1988) and eyedness (Porac and Coren, 1976) have shown that righthanded persons tend to have a right foot preference and a right-sided visual preference . In contrast, left-handed persons have either a left foot or eye preference, or a right preference that is far less pronounced than that evidenced in right-handers . Investigations of the effect of handedness on auditory tasks (e .g., a dichotic listening task and pure-tone audiometry) show that the right ear advantage is reversed or less pronounced for left-handed persons (Demarest and Demarest, 1980 ; Emmerich et al, 1988 ; Pirila et al, 1991) . However, there have been no reports in the literature that compare DPOAEs between left-handed and right-handed persons . Gender differences are found for almost all measures of auditory function, including OAEs . The studies by Driscoll et al (1999), Kei et al (1997), and various other investigators (eg, Aidan et al, 1997 ; Newmark et al, 1997 ; Driscoll et al, 2000) have revealed that females have stronger TEOAEs than males across many age groups from infancy to adulthood . Gender differences are also observed for DPOAE measures obtained from adults (e .g., Gaskill and Brown, 1990 ; Lonsbury-Martin et al, 1990 ; Cacace et al, 1996) . For instance, the study by Lonsbury-Martin et al (1990), based on the data from 79 female ears and 70 male ears, found that DPOAE amplitudes (especially in the high frequencies) were greater for women than for men . Supporting evidence for this effect in children, however, has not been established . The present study aimed to examine the effects of ear asymmetry, handedness, and gender on DPOAEs obtained from schoolchildren . METHOD Subjects A total of 1003 schoolchildren (528 boys and 475 girls), with a mean age of 6 .2 years (range = 4 .1-7 .9 years, SD = 0 .4), participated in the present study. They were recruited from Grade 1 children who were enrolled in 23 primary schools in Brisbane, Australia . No particular selection criteria were required for participation in this study, apart from full written consent from the children's parents . Although the data from all 1003 children were included for the initial statistical analysis, the data for 819 (426 boys and 393 girls) of the 1003 children, who had passed tympanometry and the pure-tone screening test (pass/fail criteria to be described later), were used for a subsequent analysis . From among the 1003 children, 159 lefthanded children (94 boys and 65 girls) were identified . Children who wrote with their left hand were classified as left-handers . This classification was adopted because in Australia, where pressures against the use of the left hand are restricted to religious and ethnic minorities, the choice of writing hand should provide the single most stable indicator of a bias toward the left hand (Peters, 1995). The percentage of left-handers (15.9%) in this cohort of schoolchildren is comparable to the figure reported by Gilbert and Wisocki (1992) . Of these 159 lefthanded children, only 128 (69 boys and 59 girls) 507 Journal of the American Academy of Audiology/Volume 12, Number 10, November/December 2001 Table 1 Mean DPOAE SNR (in dB) and SD Values for the Left and Right Ears for 1003 Children (528 Boys and 475 Girls) Mean DPOAE SNR (SD) Left Ear f2 Frequency (kHz) 1 .1 1 .5 1 .9 2.4 Boys Girls 1 .7 (10 .9) 16 .4 (7 .0) 9.9 (8 .7) 2 .5 (11 .8) 16 .5 (7 .0) 10 .9 (8 .4) 12 .5 13 .3 14 .6 11 .6 13 .4 14 .8 15 .8 13 .3 14 .3 3 .0 3 .8 4 .8 6 .0 Right Ear (6 .7) (5 .6) (5 .5) (6 .4) (6 .9) 14 .9 Boys 1 .7 (11 .1) 16 .6 (7 .1) 14 .6 (7 .3) 11 .2 14 .9 13 .0 13 .9 (6 .8) (5 .1) (5 .8) (7 .1) (7 .0) 12 .5 Procedures Subjects were tested individually, in a seated position, in non-sound-treated rooms within each school . Ambient noise levels, measured with a CEL-254 sound level meter, ranged from 34 to 51 dBA. An otoscopic examination was conducted by an audiologist prior to all testing to ensure that all tests were not affected by conditions of the external auditory meatus such as collapsing ear canals or excessive cerumen. Pure-tone screening, tympanometry, and DPOAE test were randomly administered in the six possible permutations . Tympanometry was performed using a Madsen Zodiac 901 Middle Ear Analyzer . Tympanometry is essential to detect middle ear dysfunction, which reduces or obliterates OAEs (Owens et al, 1993 ; Nozza et al, 1997). Failure in tympanometry was defined as any result that could be classified as a type B or C2 tympanogram based on the modified version of Jerger's (1970) classification system (refer to the Appendix for further details) . Pure-tone screening was performed using the Madsen Micromate 304 Screening Audiometer, fitted with ME70 noise-excluding audiocups . 508 3 .2 (11 .5) 16 .5 (7 .3) 15 .8 (7 .4) (8 .0) (6 .6) (5 .0) (5 .6) 11 .2 15 .1 13 .0 15 .1 (6 .5) 13 .5 DPOAE = distortion-product otoacoustic emission ; SNR = signal-to-noise ratio, passed the pure-tone screening and tympanometry. Their mean age was 6.2 years (range = 5.4-7 .3 years, SD = 0.39) . The data from these 128 left-handed children were compared with those for 128 right-handed children who were selected from among the same pool of 1003 children to match the left-handed children for age (within 1 month) and gender. These right-handed children also passed the pure-tone screening and tympanometry. Girls (9 .0) (6 .6) (6 .0) (6 .1) (7 .0) Pure tones of frequencies 0 .5, 1, 2, and 4 kHz were presented to each ear at 20 dB HL. If a child failed to respond twice to three consecutive presentations at any frequency at 20 dB HL, the threshold for that frequency was determined . Failure in pure-tone screening was indicated if the hearing threshold at any frequency exceeded 25 dB HL . DPOAEs were obtained from all 1003 children using the GSI-60 DPOAE System . Adequacy of probe fit was inspected prior to the commencement of data acquisition . A series of simultaneous pure-tone pairs, of frequencies fl and f2, at intensities of 65 dB SPL (L1) and 55 dB SPL (L2), respectively, were delivered to the test ear and produced a DP-gram. These stimulus intensity levels were chosen based on recommendations concerning optimal results in humans (Harris et al, 1989 ; Whitehead et al, 1995 ; Stover et al, 1996). The test frequency ratio (f2/fl) was set at 1.21 to ensure optimal DPOAE results (Harris et al, 1989). All other aspects of the test protocol were set in default mode . In the event of high ambient noise (levels exceeding 50 dBA), testing was temporarily paused . Measurement parameters included amplitude of the distortion product (DP-amp), noise floor, and SNR (defined as DP-amp minus noise floor) at f2 frequencies of 1.1, 1.5, 1.9, 2.4, 3.0, 3 .8, 4.8, and 6 .0 kHz. RESULTS T able 1 shows the mean DPOAE SNR and standard deviation values for the ear and gender conditions for all 1003 children . As shown in Table 1, the mean SNR attains its maximum value at 1.5 kHz, with a dip at 1.9 kHz. DPOAEs: Ear Asymmetry, Handedness, and Gender Effects/Keogb et al Table 2 Summary of ANOVA Results for DPOAE SNR at Various f2 Frequencies for 1003 Children (528 Boys and 475 Girls), Showing the Main Effects and Interactions Ear Effect Gender Effect Ear x Gender 11 1 .5 1,9 2,4 NS NS r NS NS NS NS NS NS NS NS NS 3 .8 4 .8 6,0 * NS * * * NS NS NS f2 Frequency (kHz) 3.0 NS NS DPOAE = distortion-product otoacoustic emission, SNR = signal-to-noise ratio : NS = not significant at 95% con fid ence level . *Significant at p < .05 . Table 3 Summary of ANOVA Results for DPOAE SNR at Various f2 Frequencies for 819 Children (426 Boys and 393 Girls) Who Passed Pure-Tone Screening (<_ 25 dB HL from 0 .5-4 kHz) and Tympanometry (Only Type A and C1 Tympanograms) Ear Effect Gender Effect Ear x Gender 2 .4 3 .0 3 .8 NS NS * NS NS * NS NS NS NS NS * NS NS NS NS NS NS 6 .0 * f2 Frequency (kHz) 1 .1 1 .5 1 .9 4.8 NS * NS NS DPOAE = distortion-product otoacoustic emission ; SNR = signal-to-noise ratio ; NS = not significant at 95% confidence level *Significant at p < .05 The mean SNR ranges from 11 .6 to 15 .8 dB between 2 .4 and 6 .0 kHz . The standard deviation values below 2 kHz are generally greater than those above 2 kHz . A factorial model, which included two factors (ear and gender) and all interactions, was fitted to the data with SNR as the dependent variable . The significance of any term was assessed using the analysis of variance (ANOVA) for each of the f2 frequencies tested (1 .1, 1 .5, 1 .9, 2 .4, 3 .0, 3 .6, 4 .8, and 6 .0 kHz) . Table 2 shows a summary of the ANOVA results for DPOAE SNR at these frequencies for all 1003 children . The main effect for ear was significant at 1 .9, 3 .0, 3 .8, and 6 .0 kHz (with respective values of F = 8 .11, df = 1, 1002, p = .004 ; F = 7 .14, df = 1, 1002, p = .008 ; F = 7 .21, df = 1, 1002, p = .007 ; and F = 5 .85, df = 1, 1002, p = .016), with right ears showing a higher SNR value than left ears . The results also revealed a gender effect at 3 .8, 4 .8, and 6 .0 kHz (with values of F = 7 .21, df = 1, 1002, p = .007 ; F = 9 .98, df = 1, 1002, p = .002 ; and F =11 .52, df =1, 1002, p = .001, respectively) . The difference in mean SNR was about 1 to 2 dB at these frequencies . Girls displayed a higher SNR value than boys . The ear x gender interaction did not reach significance for any of the test frequencies . One of the possible confounding factors in the above analysis is children's hearing loss . To minimize the effect of hearing loss on the DPOAE analysis, the above statistical analysis was repeated only for children who passed pure-tone screening and tympanometry . The results of the analysis are shown in Table 3. When compared with Table 2, the results from Table 3 show essentially the same pattern of results, except for the disappearance of the significant ear effect at 3 kHz . Table 4 shows the mean DPOAE SNR and standard deviation values for 128 left-handed and 128 right-handed children matched to the left-handers for age and gender. All children passed pure-tone screening and tympanometry. As shown in Table 4, the mean SNR exceeds 11 dB for all ears irrespective of handedness at all frequencies except for 1.1 kHz . To investigate whether left-handed and right-handed children display different patterns of results for DPOAE SNRs, a three-factor ANOVA (with ear as within-subject factor and gender and handedness as between-subject factors) was performed on SNR data . The results showed a significant main effect for ear at 1.9 (F = 8 .23, df = 1, 252, p = .004) and at 6.0 kHz (F = 5.27, df = 1, 252, p = .022), with the right ears showing a higher SNR value than the left ears . However, the main effect for handedness and handedness x ear interaction for all tested frequencies did not reach significance . A significant handedness x gender interaction was present at 1 .1 (F = 5 .15, df = 1, 252, p = .023) and at 1 .9 kHz (F = 4 .66, df = 1, 252, p = .032) . These significant interactions are graphically illustrated in Figure 1 . In essence, Figure 1 indicates that the mean DPOAE SNR for right-handed girls is greater than that for right-handed boys . However, this phenomenon is reversed for the left-handed children . As noise contamination might be a confounding factor 509 Journal of the American Academy of Audiology/Volume 12, Number 10, November/December 2001 Table 4 Mean DPOAE SNR (in dB) and SD Values (Italics) for the Left and Right Ears for 128 Lefthanded Children (69 Boys and 59 Girls) and 128 Right-handed Children Matched to the Left-handers for Age and Gender Left-handers Boys f2 Frequency 1 .1 1 .5 1 .9 2 .4 3 .0 3.8 4 .8 6 .0 Mean SD Mean SD Mean SD Mean SD Girls LE RE LE RE LE RE 3 .8 9 .9 18 .1 6 .1 5 .4 10.2 18 .5 5.7 3 .1 11 .3 16 .2 7.1 4 .1 9.8 16 .7 7.0 12 .6 6.8 16 .0 1 .8 10.5 17 .9 7.1 3 .2 10.2 18 .0 6.3 6 .4 9 .0 17 .6 7.1 6 .2 10 . 1 18 . 4 5.2 16 .2 17 .5 16 .6 16 .7 12 .8 7.4 15 .8 4.5 SD Mean 4 .2 16 .7 Mean SD Boys RE 14 .0 4 .8 SD Girls LE Mean SD Mean Right-handers 15 .0 4.5 12 .9 5.1 15 .1 5.2 11 .4 7.2 4 .9 8.4 16 .7 15 .6 14 .9 3.8 13 .4 4 .5 3.9 17 .2 14 .3 5 .0 15 .9 4.2 7.2 11 .5 8.7 5.7 14 .1 13 .1 7.0 6.2 14 .3 4.8 16 .8 14 .4 6 .6 15 .8 6.4 17 .2 4.0 15 .1 3.9 17 .4 3.7 15 .9 4 .6 17 .4 13 .7 5 .9 14 .7 5.4 13 .5 6 .5 14 .3 5.4 15 .2 5.7 6.0 4.7 5.5 13 .4 7.1 13 .8 7.6 5.9 14 .9 5.9 14 .6 5.0 6. 2 14 .9 4 .5 16 .6 5 .2 17 .9 14 .9 4.8 5 .3 16 .1 5 .0 17.5 5.5 All children passed pure-tone screening (<_25 dB HL from 0.5-4 kHz) and tympanometry (only type A and C1 tympanograms) . DPOAE = distortion-product otoacoustic emission ; SNR = signal-to-noise ratio; LE = left ear ; RE = right ear, in DPOAE recordings at low frequencies, further analysis of the noise floor was performed using a three-factor (ear, handedness, and gender) ANOVA with noise (noise floor recorded on the DP-gram) as the dependent variable. The results showed no significant main effect for all independent variables and their interactions (p > .05) at both 1.1 and 1.9 kHz. DISCUSSION T he findings from the present study revealed an ear asymmetry effect on DPOAEs in schoolchildren . Right ears were found to produce stronger DPOAEs than left ears mainly in the higher frequencies (1 .9, 3.0, 3 .8, and 6.0 kHz) . This pattern of results remained practically unchanged (except for the results at 3 .0 kHz only) even when children who failed pure-tone screening and tympanometry were excluded from the statistical analysis . However, despite the significance of this ear asymmetry effect, the mean difference in DPOAE SNR between ears was small. The mean differences in SNR between the ears were less than 1 dB . Given these small differences, it is not surprising to find that previous studies based on a small sample size (e .g ., Lonsbury-Martin et al, 1997) did not report an ear asymmetry effect in DPOAEs . In compari- 510 son, the ear asymmetry effect that exists in DPOAEs is not as large an effect as that seen in studies of TEOAEs in which the mean difference between ears was about 1 to 2 dB (Kbalfa and Collet, 1996 ; Aidan et al, 1997 ; Kei et al, 1997 ; Khalfa et al, 1997; Newmark et al, 1997 ; Driscoll et al, 1999). The contribution of the SOAEs, which are more frequently found in females and in right ears, to the TEOAE recordings may account for the greater difference in TEOAEs between ears than in DPOAEs (Kulawiec and Orlando, 1995). However, the contribution of SOAEs to DPOAE recordings is negligible unless the frequency of SOAE coincides with the DPOAE frequency (2f1-f2) . The reasons for the ear asymmetry effect in DPOAEs are, as yet, unclear. It is possible that the slightly poorer hearing sensitivity in the left than in the right ear could result in an ear asymmetry effect . However, the pure-tone screening test in the present study did not provide hearing threshold data for each ear. The speculations that ear asymmetry in DPOAEs could be a product of the efferent system (McFadden, 1993), a result of a prenatal asymmetry before birth (Previc, 1991), and/or cerebral lateralization (Peters, 1995) still stand . But more evidence is needed to confirm such possible causes of ear asymmetry. DPOAEs : Ear Asymmetry, Handedness, and Gender Effects/Keogh et al 16U N 0 r z rn W a O a 1412 10 8 J 6 42 0 LH/Boy ~~ i- I LH/Girl RH/Boy RH/Girl Handed ness/Gender 01 .1 kHz E1 .9 kHZ LH = left handed, RH = right handed Figure l Mean DPOAE SNR at 1.1 and 1.9 kHz for 69 left-handed boys and 59 left-handed girls and 128 righthanded children matched to the left-handers for age and gender. The mean age for the left-handed children is 6.2 years (SD = 0.39) . All children passed pure-tone screening (25 dB HL from 0.5-4 kHz) and tympanometry (only type A and C1 tympanograms). LH and RH represent lefthanded and right-handed, respectively. Vertical bars indicate 1 SD from the mean . The present study also revealed a significant gender effect in DPOAEs in schoolchildren, predominantly in the high frequencies . Again, this effect remained unchanged when children who failed pure-tone screening and tympanometry were excluded from the present study. The magnitude of this gender effect was greater than that of the ear asymmetry effect and ranged from 1 to 2 dB between the two genders (see Table 1) . This gender effect in schoolchildren is in keeping with the findings of Gaskill and Brown (1990), Moulin et al (1993), and Cacace et al (1996) for adults . The possible confounding factor that SOAEs, which occur more frequently in females (Kulawiec and Orlando, 1995), might have contributed to DPOAEs is regarded as minimal in view of the rare coincidence of the SOAE and DPOAE frequencies . In contrast, this gender effect was not observed below 3 .8 kHz . This finding is consistent with that of Lonsbury-Martin et al (1990), who found that the difference in DPOAEs between males and females in the low frequencies was small . The other reason for the absence of the gender effect in the low frequencies is the possibility of the interference of environmental and subject noise (e .g ., from breathing and jaw movements) with the DPOAE recording process . Such noise interference is reflected in the higher standard deviation values of the SNR in the lower-frequency region (see Table 1) . These noises, being more intense in the lower-frequency region, raised the noise floor and decreased the SNR (e .g ., at 1 .1 kHz) at these frequencies . Possible reasons for the gender effect on DPOAEs are numerous . It is possible that the hearing sensitivity of the boys was poorer than that of the girls . However, since the pure-tone screening test in the present study did not provide hearing threshold data for each child, this claim is only tentative . The gender effect might be attributed to the anatomic and physiologic dif- ferences at the cochlear level (Don et al, 1993) between the boys and girls. It is also possible that different body temperature between boys and girls may give rise to gender differences in DPOAEs because the length and electromotility of outer hair cells have been found to be temperature dependent (Ashmore and Holley, 1988 ; Gitter, 1992) . The difference in efferent inhibition to individual cochleas may be relatively less in females than in males (McFadden, 1993) . An interesting finding of the present study is the absence of the effect of handedness on DPOAE SNR since the main effect for handedness and handedness x ear interaction for all tested frequencies did not reach significance . There was no difference in the ear asymmetry effect on SNR between left-handed and right- handed children . Although the literature shows that left-handers have either less pronounced or reversed lateralizations in footedness (Searleman, 1980 ; Peters, 1988), eyedness (Porac and Coren, 1976), and speech perception (Demarest and Demarest, 1980 ; Emmerich et al, 1988), the case for DPOAEs obtained from schoolchildren cannot be established . However, the generalization of this result should be made with caution in view of the small effect size and relatively small sample size (256 children) . With this small sample size, the pattern of results from the three-factor (ear, handedness, and gender) ANOVA is different from the pattern of results obtained previously (see Tables 2 and 3) in that the gender effect has disappeared altogether for all frequencies . The main effect for ear was significant only at 1.9 and 6.0 kHz, with right ears showing more robust DPOAEs than left ears . The handedness x gender interaction was significant for DPOAE SNR at 1.1 and 1 .9 kHz. The graphic representation of these results, shown in Figure 1, indicates a greater mean DPOAE SNR for righthanded girls than for right-handed boys at both 1 .1 and 1 .9 kHz. However, this phenomenon is reversed for the left-handed children . 511 Journal of the American Academy of Audiology/Volume 12, Number 10, November/December 2001 It is not clear why such a reversal has occurred at these frequencies . Further analysis of the noise at these frequencies did not show any significant difference in noise floor across the two genders and handedness . In summary, the present study revealed an ear asymmetry effect in DPOAEs obtained from 1003 schoolchildren . Right ears exhibited stronger DPOAEs at 1.9, 3.0, 3.8, and 6.0 kHz than left ears, but the difference in SNR was small. A gender effect was observed only in the high frequencies (3 .8, 4.8, and 6 .0 kHz), with girls consistently displaying stronger DPOAEs compared with boys . However, no difference in DPOAE SNR between 128 left-handed and 128 right-handed children (matched for age and gender) was found . This means that although reversed lateralization of functions such as eyedness, footedness, and speech perception is seen in left-handers, they are not evidence in DPOAE SNR measures in this cohort of schoolchildren . Acknowledgment. This article was presented at the 17th Biennial Symposium of the International Evoked Response Audiometry Study Group, July 22-27, 2001, University of British Columbia, Vancouver, Canada . The current investigation was supported by a very generous bequest from Mrs. Julie Luttrell in memory of her daughter, Suzanne Luttrell, and supplemented by a research grant from the University of Queensland . The authors would like to thank Queensland Health, Queensland Education, Queensland Catholic Education, and participating schools for their cooperation and assistance during the course of this study. 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