Benefit from spatial separation of multiple talkers in bilateral hearing-aid users: Effects of hearing loss, age, and cognition

Abstract

Abstract

To study the spatial hearing abilities of bilateral hearing-aid users in multi-talker situations, 20 subjects received fittings configured to preserve acoustic cues salient for spatial hearing. Following acclimatization, speech reception thresholds (SRTs) were measured for three competing talkers that were either co-located or spatially separated along the front-back or left-right dimension. In addition, the subjects’ working memory and attentional abilities were measured. Left-right SRTs varied over more than 14 dB, while front-back SRTs varied over more than 8 dB. Furthermore, significant correlations were observed between left-right SRTs, age, and low-frequency hearing loss, and also between front-back SRTs, age, and high-frequency aided thresholds. Concerning cognitive effects, left-right performance was most strongly related to attentional abilities, while front-back performance showed a relation to working memory abilities. Altogether, these results suggest that, due to raised hearing thresholds and aging, hearing-aid users have reduced access to interaural and monaural spatial cues as well as a diminished ability to ‘enhance’ a target signal by means of top-down processing. These deficits, in turn, lead to impaired functioning in complex listening environments.

Sumario

Para estudiar las habilidades auditivas espaciales de usuarios de audífonos bilaterales en situaciones de hablantes múltiples, 20 sujetos recibieron auxiliares configurados para preservar las más destacadas claves acústicas de la audición espacial. Después de un período de adaptación, se midieron los umbrales de recepción del habla (SRTs) con tres hablantes en competencia que fueron colocados cerca o espacialmente separados en las dimensiones frente-atrás o izquierda-derecha. Además, se midieron las habilidades de memoria activa y atención. Los SRTs izquierda-derecha variaron más de 14 dB mientras que los SRTs frente-atrás, variaron más de 8 dB. Más aún, se observaron correlaciones significativas entre SRTs frente-atrás, edad y pérdida auditiva en las frecuencias graves y también entre SRTs frente-atrás, edad y umbrales con auxiliares auditivos en las frecuencias agudas. En relación con los efectos cognitivos, el rendimiento izquierda-derecha se relacionó más firmemente con habilidades de atención, mientras que el rendimiento frente-atrás, mostró relación con habilidades de memoria activa. En general, estos resultados sugieren que, debido a la elevación de los umbrales auditivos y el envejecimiento, los usuarios de auxiliares auditivos tienen un acceso reducido a las claves espaciales interaurales y monoaurales así como una habilidad disminuida para “mejorar” una señal blanco por medio del procesamiento arriba-abajo. Estos déficits, a su vez, conducen a un funcionamiento disminuido en ambientes de escucha complejos.

Key Words:

• Spatial hearing
• Spatial release from masking
• Speech-on-speech masking
• Hearing aids
• Hearing loss
• Age
• Cognition
• Attention
• Working memory

Acknowledgements

Ethical approval for the study reported in this manuscript was obtained from ‘de videnskabsetiske komiteer for region hovedstaden’. The authors would like to thank three anonymous reviewers for their useful comments to an earlier version of this manuscript. Preliminary analyses of the data from this study were presented at the ASA EAA Aoustics'08 conference, Paris, France, 29 June–4 July 2008, the International Hearing Aid Research Conference, Lake Tahoe, California, 13–17 August 2008, and the British Society of Audiology Short Papers Meeting on Experimental Studies of Hearing and Deafness, York, UK, 18–19 September 2008.

Declaration of interest: The authors report no conflicts of interest.

Appendix

This appendix provides details with respect to the tasks given to the subjects when performing the various cognitive measurements as well as the types of scores obtained. Note that, in order to ease interpretation of the correlation results (cf. sub-section ‘Effects of age and cognition’, above), the signs of the data points stemming from three TEA sub-tests (i.e. sub-tests 4 ‘timing’, 6 and 7) were inverted, so that for all cognitive tests higher scores corresponded to better cognitive performance.

The reading span test

The reading span test (Daneman & Carpenter, 1980; Hällgren et al, 2001) involves the following: On a computer screen, words are displayed one at a time at a rate of one word per 0.8 seconds. After the presentation of three words there is a pause of 1.75 seconds, during which the subject is asked to respond ‘yes’ if the previous three words made up a semantically correct sentence (e.g. ‘Pigen børstede håret’ – ‘The girl brushed the hair’). If the previous three words made up a semantically absurd sentence (e.g. ‘Toget sang sangen’ – ‘The train sang the song’), the test person has to respond ‘no’. Following a sequence of sentences (three, four, five or six, in ascending order), either ‘first’ or ‘final’ is displayed on the screen. The subject's task is then to recall either the first or the final words of all the three, four, five or six previous sentences. The performance measure used for this study was the number of correctly recalled first and final words presented.

The test of everyday attention (TEA)

Sub-test 1: Map search

In this visual sub-test of the TEA, the subject is asked to search for and circle as many restaurant symbols on a color map of a metropolitan area as possible. The score obtained is the number out of 80 found within two minutes. According to Robertson et al (1994), this sub-test probes into abilities of selective attention.

Sub-test 2: Elevator counting

As mentioned in the sub-section ‘Effects of age and cognition’ above, this sub-test was found to be affected by ceiling effects in Robertson et al's (1994) evaluation of the TEA with ‘normal’ (non-brain-damaged) subjects. Nevertheless, since it could serve as an introduction to the following sub-tests, a shortened version of it was included in this study, but the scores obtained were not used in the analyses.

Sub-test 2 is an auditory test, as part of which subjects have to imagine being in an elevator whose floor indicator is not working. To establish which floor they are on, they have to listen to and count some strings of tones. According to Robertson et al (1994), this sub-test probes into abilities of sustained attention.

Sub-test 3: Elevator counting with distraction

This auditory sub-test of the TEA builds on the previous one in that strings of tones have to be counted again. This time, however, there are also some distracting, higher-pitched tones. The subject has to ignore the higher tones and only count the lower ones. The score obtained is how many out of ten strings were counted correctly. According to Robertson et al (1994), this sub-test probes into working memory abilities.

Sub-test 4: Visual elevator

In this visual sub-test of the TEA, subjects are presented with some series of pictures that show either an elevator or an arrow pointing up or down. Each elevator picture represents a separate floor, and the arrows indicate the direction the elevator is moving in. The subjects have to keep track of which floor they are on, reversing the counting direction as necessary. The sub-test is self-paced, and the time taken to complete each picture series is noted. Two types of scores are obtained from the results: (1) an accuracy score reflecting how many (out of 10) final floor numbers the subject got right and (2) a timing score reflecting the total time taken for all correctly counted floor numbers divided by the total number of arrows (directional switches) contained in those series. According to Robertson et al (1994), this sub-test probes into abilities of switching attention.

Sub-test 5: Elevator counting with reversal

Basically, this TEA sub-test is the auditory equivalent of the previous sub-test. The test subject has to count tones, which are presented at a fixed speed, to determine the final floor number. This time, going up is signaled by a high-pitched tone and going down by a low-pitched tone. The tones that represent the different floors and that should therefore be counted have an intermediate pitch. The score obtained is an accuracy score reflecting how many (out of 10) final floor numbers the subject got right. According to Robertson et al (1994), this sub-test probes into working memory abilities.

Sub-test 6: Telephone search

This visual TEA sub-test involves searching a telephone directory for certain entries such as plumbers, restaurants or hotels. Next to each entry, there are two symbols (stars, squares, circles or crosses). The subjects’ task is to search for certain entries (e.g. plumbers) and circle the two symbols next to them if they are of the same type (e.g. two stars). Moreover, they are told to work as quickly and accurately as possible and to indicate when they are finished. The score obtained is a timing score, corresponding to the total time taken by the subject divided by the number of correctly circled symbol pairs. According to Robertson et al (1994), this test probes into abilities of selective attention.

Sub-test 7: Telephone search while counting

In this audio-visual TEA sub-test, the subject completes the same task as in the previous test. In addition to that, strings of tones have to be counted. Both the timing score from the telephone directory search as well as the proportion of tone strings counted correctly are then computed. By combining these data with the timing scores from the previous sub-test, dual-task decrement scores are obtained, i.e. scores that reflect the cost of having to complete two tasks in parallel. According to Robertson et al (1994), this test probes into abilities of sustained attention, but has aspects of attentional switching to it, too.