Study

Children with severe to profound unilateral hearing loss (UHL) 9.2.1 -Language Lateralization Indices

At the time of fTCD and clinical evaluation the mean chronological age of the experimental sample was 8.4 (SD 3.4) and of the controls was 8.5 y (SD 3.4 y) and did not significantly differ (t=0.069, p=0.9).

Mean laterality indices in patients with UHL was 1.1 (SD 4.1) and in controls 2.1 (SD 2.3), indicative of a prevalent left hemispheric activation during the language task but the difference between the two groups wasn’t statistically significant (t=0.7, p=0.5).

LI variability in the experimental and control group appeared comparable (Levene’s test F 3.5 SD 0.073.).

With regard to the side of hearing loss, children with right UHL had a mean LI value of 2.43 (SD 2.5) , while in subjects with left UHL it was -0.31 (SD 3.38).

On a categorical level, 54,5% (6/11) of children with UHL showed a positive LI, indicative of left hemispheric dominance (LH), 36,4% (4/11) had right hemispheric dominance (RH) and 9% (1/11) were uncertain.

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Figure 22. Distribution of hemispheric dominance in patients with UHL.

Legend: LH=Left Hemisphere Activation; RH= Right Hemisphere Activation; LI=Lateralization Index

Hemispheric activation was controlateral to the ear with normal hearing threshold in 4/11 (36.4%), ipsilateral in 6/11 (54,5%) children, and uncertain in one.

With regard to LI direction, we didn’t found any statistically significant difference between patients and controls in distribution of LIs (Pearson Chi square 2.3). However, 4/11 children with UHL, but only 1/11 of controls showed right hemisphere lateralization.

The distribution of LIs in subjects with right UHL was 66.7% (4/6) left and 33.3% (2/6) right. The distribution of LIs in subjects with left UHL was 40% (2/5) left, 40% (2/5) right, and 20% (1/5) uncertain.

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Figure 23a-23b. Distribution of hemispheric dominance in right- and left- unilateral hearing loss.

Legend: HL= Hearing Loss; LH=Left Hemisphere Activation; RH= Right Hemisphere Activation; LI=Lateralization Index

9.2.2 -Linguistic and Cognitive Outcome

Evaluation of language outcome revealed that subjects with UHL performed significantly lower than normal controls (t test t=2.09, df 20, p=0.049).

Within UHL subjects, the composite score of children with left hemisphere activation was higher (M 7.5, sd 0.8, range 7–8) than the composite score of patients with right hemisphere activation (M 6.5, sd 1.9, range 4–8), but the difference wasn’t statistically significant (t=1.16, df 8, p = 0.27).

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Figure 24. Mean language composite score in subjects with left and right hemisphere activation.

Legend: LH=Left Hemisphere Activation; RH= Right Hemisphere Activation; LI=Lateralization Index. Bars represent SD.

For what concerns cognitive performances in UHL subjects, no statistically significant differences were found between subjects with left and right LI hemisphere activation, either when computing mean values for each cognitive test or when comparing absolute frequencies of subjects obtaining a standard score less or more than 90 in each single test.



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Figure 25a-25b. Mean values and distribution of test in subjects with left and right hemispheric dominance.

Legend: IQ=Intelligence Quotient; PRI=Perceptual reasoning Index; WMI=Working Memory Index; PSI=Processing Speed Index; VCI=Verbal Comprehension Index; VMI= Visual Motor Integration; LI=Lateralization Index.

Furthermore language composite scores varied in relation to side of hearing loss (right ear: M 6.5, SD 1.51; left ear: M 8, SD 0.0) for a significantly lower language performance in right - compared to - left hearing loss subjects (U=5, p = 0.034).

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Figure 26. Mean language composite score in subjects wit left and right hearing loss (HL). Bars represent SD.

Subjects with right UHL scored lower than left UHL in each single test of cognitive abilities (table 9), but the differences were statistically significant only for WMI (t=-3.2 p=0.0094) and IQ (t=-2.8 p= 0.021).

This data was confirmed also taking into consideration the absolute frequency of right and left UHL subjects obtaining a standard score more or less than 90 on each test. Left UHL subjects showed more frequently than right UHL scores above 90 for WMI (χ2=7.6, p=0.0057), IQ (χ2=5.23, p=0.02) and VCI (χ2=5.23, p=0.02), but, interestingly, not for non verbal tests such as VMI (χ2 = 0.917, p=0.33), PSI (χ2=2.3, p=0.12) and PRI (χ2 =2.101, p=0.07).

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ϳϯ Right HL Left HL mean (SD) mean (SD) WMI 75.67 (17.6) 103 (6) VCI 89.17 (21.8) 108.2 (12.8) PRI 89.67 (17.6) 102.4 (11.9) IQ 83.5 (17.8) 108.8 (9.5) VMI 92.17 (17.4) 107.8 (7.6) PSI 93.4 (20.4) 105.67 (16.7)

Table 9. Legend: IQ=Intelligence Quotient; PRI=Perceptual reasoning Index; WMI=Working Memory Index; PSI=Processing Speed Index; VCI=Verbal Comprehension Index; VMI= Visual Motor Integration; LI=Lateralization Index.

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Figure 27a-27b. Mean values and distribution of test scores in subjects with left and right hearing loss

Legend: IQ=Intelligence Quotient; PRI=Perceptual reasoning Index; WMI=Working Memory Index; PSI=Processing Speed Index; VCI=Verbal Comprehension Index; VMI= Visual Motor Integration; LI=Lateralization Index.

Finally, the language composite score was significantly correlated with verbal subtests of cognitive evaluation, in particularly WMI (Spearman’s rho = 0.9, p<0.01) and VCI (Spearman’s rho = 0.7, p=0.015).     DĞĂŶ ǀĂůƵĞƐ EŽĨ ƐƵďũĞĐƚƐ

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Subject

N. Hearing _Loss Side standard PPVT _score LCS IQ total PRI WMI PSI VCI VMI value SD LI side LI

1 Right 94 7 87 111 82 85 80 96 8,69 0,9 Left 2 Left 8 119 122 112 126 102 118 1,29 1,4 Uncertain 3 Right 74 6 75 65 75 -2,86 2 Right 4 Right 6 77 76 73 126 66 101 1,95 0,3 Left 5 Right 118 8 110 111 85 103 122 117 6,32 0,8 Left 6 Left 103 8 96 93 106 85 102 98 1,68 0,7 Left 7 Right 115 8 94 85 100 85 110 96 2,56 0,8 Left 8 Right 57 4 58 69 49 68 82 59 -2,1 0,8 Right 9 Left 120 8 115 100 100 115 3,32 1,2 Left 10 Left 100 8 100 104 97 106 94 110 -3,89 1,1 Right 11 Left -- 8 114 93 100 128 103 -3,97 1 Right

Table 10. Language and cognitive assessment of children with UHL and LI value and side. Legend: Ppvt= Peabody Picture Vocabulary; TROG= Test for Reception of Gramma-Version 2; LCS= Language composite score; IQ=Intelligence Quotient; PRI=Perceptual reasoning Index; WMI=Working Memory Index; PSI=Processing Speed Index; VCI=Verbal Comprehension Index; VMI= Visual Motor Integration; LI=Lateralization Index; na= not available; ne= not evaluable.

It’s interesting to remark that the effect of side of acoustic afference on language composite score was maintained when UHL and CI subjects were grouped together (right ear CI and left UHL: M 6.48 SD 1.6; left ear CI and right UHL: M 5.37 SD 1.45), with a difference between right and left ear afference that approached statistical significance (U =178, p =0.078).

In contrast, the effect of side of hemispheric activation (LI) on language composite score was not significant (U=186, p=0.38).

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