The effect of an active transcutaneous bone conduction device on spatial release from masking

Figures & data

Figure 1. Audiograms of the 12 study subjects: (A and B) Seven subjects with bilateral hearing loss; and (C and D) five subjects with unilateral hearing loss. Median values are indicated in bold line. Bi: bilateral; Uni: unilateral; AC: air conduction; BC: bone conduction.

Table 1 . Information about the study subjects.

Subject ID	Age (yrs)	Sex	BCI use (yrs)	Aetiology	PTA4 at implant side, AC (dB HL)	PTA4 at implant side, BC (dB HL)	PTA4 at non-implant side, BC (dB HL)	PTA4 at non-implant side, AC (dB HL)	Interferers pres. level unaided (dB SPL)
3	23	M	4.1	Uni cond	39	5	3	3	63
7	22	M	1.6	Uni cond	53	1	3	5	63
201	45	F	1.0	Uni mixed	50	24	–	9	63
9	21	F	0.9	Uni cond	90	21	16	21	63
202	29	M	0.8	Uni mixed	76	21	20	25	63
6	52	M	2.9	Bi cond	78	16	13	39	70
10	22	F	0.7	Bi mixed	61	13	14	45	75
204	75	M	0.8	Bi mixed	53	19	24	46	70
5	51	F	3.0	Bi mixed	81	30	31	61	80
4	71	F	3.3	Bi cond	51	23	20	63	80
8	50	M	1.3	Bi cond	70	23	16	63	75
2	52	M	4	Bi mixed	56	25 (*)	30	73	70

Yrs: years; M: male; F: female; Bi: bilateral; Uni: unilateral; cond: conductive hearing loss; mixed: mixed hearing loss; PTA4 : Pure Tone Average (average at 500, 1000, 2000 and 4000 Hz); AC: air conduction; BC: bone conduction. (*) This value represents the BC threshold at 3000 Hz as thresholds for the remaining frequencies could not be determined due to issues related to masking. The rightmost column shows the presentation levels of the interferers used for testing in unaided conditions.

Figure 2. Schematic representation of the measurement set-up in the two different spatial conditions: (A) Target signal (S) and noise (N) from the same loudspeaker co-located in front of the test subject (0° azimuth); (B) signal from frontal loudspeaker, noise from four loudspeakers at ± 30° and ± 150° around the test subject.

Figure 3. Spatial Release from Masking (SRM) measured in unaided and aided condition: (A) histogram, unaided condition, (B) histogram, aided condition, (C) Unaided and aided SRM, with data from the same subject connected by a dotted line. Subjects with unilateral and bilateral hearing loss are distinguishable by the different markers, dot and triangle respectively. One aided data point (−4.5 dB) has been omitted in order to have a more suitable scale on the y-axis.

Figure 4. Boxplot of SRT (co-located and separated condition) and SRM, shown separately for patients with bilateral and unilateral hearing loss. Mean values are indicated with a green asterisk, medians with a red horizontal line. Individual data points are plotted in grey colour for patients with unilateral and bilateral hearing loss in circles and triangles, respectively. The y-axis in the right panel is limited between −1 and 5 dB, and one bilateral aided SRM data point (−4.5 dB) is therefore not shown. SRT: Speech Recognition Threshold; SRM: Spatial Release from Masking; uni: unilateral hearing loss; bi: bilateral hearing loss.

Table 2. Results of pair comparisons of aided and unaided conditions as well as distractor placement conditions are shown.

	Comparison	Unadjusted p-value	Unadjusted significance	Holm/Hochberg threshold	Corrected significance
1	SRM unaided vs 0	0.00049	Significant	0.0100	Significant
2	SRM aided vs unaided	0.03564	Significant	0.0125
3	SRT co-located, aided vs unaided	0.04053	Significant	0.0167
4	SRM aided vs 0	0.06689		0.0250
5	SRT separated, unaided vs aided	0.25830		0.0500

Adjusted significance levels taking into account corrections for multiple comparisons are given in the rightmost column. Only SRM obtained in unaided condition was found to be statistically significant as compared to zero.

Table 3. Speech Recognition Thresholds (SRT) obtained from measurements in co-located and separated configuration for all the study subjects.

Subject ID	SRT unaided (dB)		SRT aided (dB)
	Co-located	Separated	Co-located	Separated
3	−12.8	−15.1	−13.1	−14.2
7	−7.9	−12.6	−10.3	−12.7
201	−11.3	−12.8	−10.2	−11.4
9	−7	−7.8	−6.4	−8.3
202	−8.5	−8.9	−9.4	−10.1
6	−3.9	−7.1	−4.8	−6.2
10	−3.1	−5	−6.3	−8.3
204	−7.4	−10.1	−5.8	−10.3
5	−1.9	−3.9	−8.5	−4.1
4	0	−1.2	−5.5	−4.8
8	2	−0.2	−6.4	−8.3
2	−7.2	−6.9	3.6	2.8

Figure 5. Post-hoc linear regression analyses of the aided SRT as a function of average hearing thresholds for low frequencies (LF; left column) high frequencies (HF; middle column), and pure tone average (PTA4; right column) in co-located and separated target-interferer spatial configurations. SRT: Speech Recognition Threshold.

Figure 6. Correlation between separated SRT and PTA4 for the non-implanted ear for patients with unilateral and bilateral hearing loss separately. PTA4 is the average of tone thresholds at 500, 1000, 2000, and 4000 Hz. SRT is the speech recognition threshold when 40% of the target speech is correctly understood.

Figure 7. Correlation between SRT aided benefit and PTA4 at the contralateral ear. PTA4 is the average of tone thresholds at 500, 1000, 2000, and 4000 Hz. SRT aided benefit is calculated as the difference between aided and unaided SRT in the same spatial configuration. A positive benefit corresponds to a lower SRT in aided condition compared to the unaided one. Patients are divided in two groups, with unilateral and bilateral hearing loss. SRT: Speech Recognition Threshold.

Figure 8. Speech Recognition Thresholds (SRT) obtained in the four measurement conditions: target and interferer from the same loudspeaker (coloc) or from spatially separated ones (sep), without (unaided) and with the BCI device (aided). The boxplot shows how the data is distributed, with mean and median values marked by a black star and a red horizontal bar, respectively. Individual data points are plotted as orange circles and green triangles for patients with unilateral and bilateral hearing loss, respectively.

Figure 9. Speech Recognition Threshold (SRT) in co-located and separated configuration. The origins of the arrows represent the unaided result, the heads point at aided results. Values for normal hearing subjects estimated from a previous study (Asp and Reinfeldt Forthcoming) are marked with an asterisk. SRTs from patients with unilateral and bilateral hearing loss are marked with orange circles and green triangles, respectively. SRM (Spatial Release from Masking) is positive above the unity line (SRT separated: SRT co-located, dotted line) and negative below.