The Impoverished Brain: Disparities in Maternal Education Affect the Neural Response to Sound

Erika Skoe; Jennifer Krizman; Nina Kraus

doi:10.1523/JNEUROSCI.2102-13.2013

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Figure 1.
Adolescents with low maternal education (black) have less consistent auditory brain responses (ABRs) than adolescents with high maternal education (red). A, For the low-MaternalEd group (top) and high-MaternalEd group (bottom), the ABR during the first half of the recording (black/red, respectively) is compared with the response during the second half of the recording (gray). For the high group, the two waveforms align more closely in morphology than for the low group (p = 0.01). B, The average correlation (r value) between the first and second halves of the recording is 0.44 for the low group versus 0.57 for the high group (r = 1, when the two halves are identical). Mean + 1 SEM are plotted.
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Figure 2.
Adolescents with lower maternal education (black) have smaller auditory brainstem responses (ABRs) to the speech stimulus than adolescents with higher maternal education (red). A, The speech frequency spectrum is plotted. The band of energy in the 264–656 Hz range corresponds to the first formant of the speech syllable. The first formant carries important phonological information regarding the identity of the speech sound. B, Bottom, The frequency spectrum of the ABR is plotted for the two groups. For the response to the first formant, the average energy is reduced in the low-MaternalEd group compared with the high-MaternalEd group (p = 0.03), suggesting that the speech stimulus is encoded less robustly in the low group. Mean + 1 SEM are plotted for both groups.
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Figure 3.
Adolescents with lower maternal education (black) have more spontaneous neural activity than those with higher maternal education (red). A, Neural activity is plotted for each participant in the low-MaternalEd (top) and high-MaternalEd (bottom) groups during the 15 ms of silence preceding each stimulus presentation. Time 0 refers to when the stimulus starts playing. B, The average energy is greater in the low group compared with the high group (p = 0.01). Increased energy during the absence of auditory input is argued to be indicative of greater neural noise.

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Table 1.

Distribution of maternal educational achievement within the low-MaternalEd and high-MaternalEd groups

Maternal education	Number of participants
Low-MaternalEd	33
Less than high school diploma	6
High school diploma/GED	27
High-MaternalEd	33
Some college, no degree	3
Vocational degree	2
College degree (level not specified)	4
Associate's degree	12
Bachelor's degree	5
Master's degree	6
Doctoral degree	1

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Table 2.

The low- and high-MaternalEd groups were matched with respect to age, hearing thresholds (pure tone average for right and left ear), and birth weight

	Low-MaternalEd	High-MaternalEd	t	Significance (two-tailed)
Age (years)	Mean, 14.52; SD, 0.51	Mean, 14.58; SD, 0.50	−0.49	0.63
Hearing thresholds, (dB hearing level)	Mean, 6.79; SD, 4.55	Mean, 5.55; SD, 4.77	1.08	0.28
Birth weight (lb)^{^a}	Mean, 7.15; SD, 1.22	Mean, 7.47; SD, 1.48	−0.85	0.40

↵^aInformation not available on 11 participants.

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Table 3.

Self-reported age of acquisition and extent of current exposure to English and Spanish for the low-MaternalEd and high-MaternalEd groups^{^a}

	English		Spanish
	Age of acquisition (years)	Current exposure	Age of acquisition (years)	Current exposure
Low-MaternalEd	3.13 (SD, 2.35)	75.75% (SD, 1.21%)	3.28 (SD, 2.42)	20.33% (SD, 20.39%)
High-MaternalEd	2.31 (SD, 2.35)	81.84% (SD, 1.17%)	3.74 (SD, 2.96)	14.67% (SD, 17.63%)

↵^aLanguage background was assessed using the Language Experience and Proficiency Questionnaire (LEAP-Q; Marian et al., 2007). The low and high groups did not differ in terms of their current daily exposure to English or Spanish, nor did they differ in the age that English and/or Spanish was acquired. All comparisons, p > 0.05.

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Table 4.

Group comparisons for the low- and high-MaternalEd groups on reading and cognitive measures^{^a}

	Low-MaternalEd	High-MaternalEd	F	Significance (two-tailed)	Effect size (η²)
IQ	Mean, 96.36; SD, 8.76	Mean, 100.09; SD, 8.52	3.071	0.084	0.005
TOSWRF	Mean, 97.12; SD, 11.50	Mean, 103.06; SD, 11.29	4.482	0.038^*	0.065
TOWRE	Mean, 92.03; SD, 12.56	Mean, 99.00; SD, 10.53	5.965	0.017^*	0.085
Basic Reading	Mean, 95.21; SD, 7.39	Mean, 100.97; SD, 9.23	7.830	0.007^*	0.109
Spelling	Mean, 103.06; SD, 7.84	Mean, 106.67; SD, 10.09	2.630	0.110	0.04
Working Memory
Numbers Reversed	Mean, 95.82; SD, 11.38	Mean, 99.27; SD, 10.79	1.601	0.210	0.024
Auditory Working Memory	Mean, 100.55; SD, 9.71	Mean, 106.76; SD, 10.47	6.244	0.015^*	0.090

↵^aTests are reported as age-normed standard scores with 100 corresponding to 50th percentile.
↵*p < 0.05.

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Table 5.

Correlations among brainstem, cognitive, and years of maternal education variables^{^a}

	Response Consistency	Speech Encoding	Spontaneous Activity	IQ	TOSWRF	TOWRE	Basic Reading	Spelling	Digits Reversed	Auditory Working Memory	Years of maternal education (n = 46)
Response Consistency		0.718^**	−0.445^**	0.069	0.009	0.107	0.071	0.153	0.127	−0.031	0.430^**
Speech Encoding	0.718^**		−0.093	−0.051	−0.003	0.108	0.011	0.001	0.154	0.022	0.336^*
Spontaneous Activity	−0.445^**	−0.093		−0.046	−0.119	0.045	−0.075	−0.175	−0.073	0.012	−0.24
IQ	0.069	−0.051	−0.046		0.219	0.346^**	0.512^**	0.399^**	0.293^*	0.374^**	−0.053
TOSWRF	0.009	−0.003	−0.119	0.219		0.432^**	0.380^**	0.433^**	0.006	0.156	0.022
TOWRE	0.107	0.108	0.045	0.346^**	0.432^**		0.699^**	0.641^**	0.151	0.265^*	0.047
Basic Reading	0.071	0.011	−0.075	0.512^**	0.380^**	0.699^**		0.743^**	0.248^*	0.399^**	0.133
Spelling	0.153	0.001	−0.175	0.399^**	0.433^**	0.641^**	0.743^**		0.155	0.350^**	0.063
Digits Reversed	0.127	0.154	−0.073	0.293^*	0.006	0.151	0.248^*	0.155		0.608^**	0.026
Auditory Working Memory	−0.031	0.022	0.012	0.374^**	0.156	0.265^*	0.399^**	0.350^**	0.608^**		−0.074
Years of maternal education	0.430^**	0.336^*	−0.24	−0.053	0.022	0.047	0.133	0.063	0.026	−0.074

↵^aComparisons with years of maternal education was performed on a subset of the group (n = 46). All other comparisons included the full dataset (n = 66).
↵*p < 0.05;
↵**p < 0.01.

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Table 6.

Binary logistic regression

	Independent variable(s)	Standardized regression coefficients	Overall model, χ²	Correct classification (%)
	Independent variable(s)	Standardized regression coefficients	Overall model, χ²	Low-MaternalEd	High-MaternalEd	Total
Model 1^{^a}	Response Consistency	B = −0.130, SE = 2.085, p = 0.950
	Speech Encoding	B = 121.576, SE = 88.739, p = 0.171
	Spontaneous Activity	B = −66.152, SE = 34.298, p = 0.054
	Combined		χ²₍₃₎ = 10.905, p = 0.012	60.6	69.7	65.2
Model 2^{^a}	Brainstem^*: Response Consistency	B = 3.553, SE = 1.409, p = 0.019
	Reading: Test of Sight Word Reading	B = 0.047, SE = 0.026, p = 0.067
	Working memory^*: Auditory Working Memory	B = 0.070, SE = 0.031, p = 0.022
	Combined		χ²₍₃₎ = 17.118, p = 0.001	78.8	72.7	75.8
Model 3^{^a}	Brainstem^*: Response Consistency	B = 3.683, SE = 1.464, p = 0.012
	Reading∼: Test of Sight Word Reading	B = 0.047, SE = 0.027, p = 0.082
	Working memory^*: Auditory Working Memory	B = 0.069, SE = 0.032, p = 0.029
	Hearing threshold: pure tone averages for left and right ear	B = −0.034, SE = 0.072, p = 0.966
	English exposure: current exposure to English	B = 0.018, SE = 0.015, p = 0.225
	Combined		χ²₍₅₎ = 18.926, p = 0.002	80	75	77.4

↵^aDependent variable: maternal education category. ∼ p <0.1;
↵* p <0.05