Neural Correlates of Spatial Processing in Older Individuals

Abstract

Background: In everyday listening situations, older individuals often have difficulty understanding speech, especially in the presence of background noise. In such complex environments, spatially separating the masker from the target results in spatial release from masking, which aids in better speech comprehension by reducing the amount of masking. The extent to which older individuals benefit from spatial separation is evaluated in this study. Aim: To explore the neural correlates of spatial release from masking (SRM) in older individuals using the electrophysiological method and compare it to a behavioral correlate of spatial release from masking. Method: A total of 30 participants were divided into two groups. Group 1 comprised of younger individuals in the age range of 18 to 30 years, and Group 2 comprised of older individuals in the age range of 55 to 70 years. Frequency Following Responses (FFR) and Speech Identification Scores (SIS) in noise in spatially separated and collocated conditions were used to objectively assess spatial release from masking. A spatial subsection of the SSQ questionnaire was also administered to understand their spatial processing difficulties. Statistical analyses were performed to compare the findings in group-wise and pair-wise manner. Results: Younger individuals obtained higher scores than older individuals in all the measures. There were significant differences between F0 amplitude of FFRs in spatially co-located and separated conditions in both younger and older individuals, whereas there was no difference in the SIS scores. The group-wise comparison revealed significantly higher FFR F0 amplitude, SIS scores, and SSQ scores in Group 1. However, the amount of SRM was not significantly different between groups. No correlation was found between the measures. Conclusion: Higher F0 amplitude in FFR and higher SIS scores in younger individuals indicate better brainstem encoding and better speech perception in noise in the group. The lack of significant difference in SRM (in FFR F0 amplitude and SIS scores) between the groups indicates a relative decrease in the measures studied with aging. It also indicates that the cues are still encoded relatively well in the older age group. The scores from SSQ, however, revealed that the age-related changes occurring in the auditory system in older individuals resulted in a reduced ability to access spatial cues and less benefit from spatial separation due to a reduced amount of SRM. This is reflected in the lesser F0 amplitude of FFR and poorer SIS scores in older individuals.