Perceptual and physiological measures of auditory selective attention in normal-hearing and hearing-impaired listeners

Human listeners can direct top-down spatial auditory attention to listen selectively to one sound source amidst competing sounds. However, many listeners with hearing loss (HL) have trouble on tasks requiring selective auditory attention; even listeners with normal hearing thresholds (NHTs) differ in this ability. Selective attention depends on both top-down executive control and coding fidelity of the peripheral auditory system. Here we explore how low-level sensory perception and high-level attentional modulation interact to contribute to auditory selective attention for listeners with NHTs and HL. In the first study, we designed a paradigm to allow simultaneous measurement of envelope following responses (EFRs), onset event-related potentials (ERPs), and behavioral performance. We varied conditions to alter the degree to which the bottleneck limiting behavior was due to the coding of fine stimulus details vs. top-down control of attentional focus. We found attention modulated ERPs, from cortex, but not EFRs from the brainstem. Importantly, when coding fidelity limited the task, EFRs but not ERPs correlated with behavior; conversely, when sensory cues for segregation were robust, individual behavior correlated with both EFR strength and strength of attentional modulation of cortical responses. In the second study, we explored how HL affects control of auditory selective attention. Listeners with NHTs or with HL identified a simple melody presented simultaneously with two competing melodies, each from different spatial locations. Compared to NHT listeners, HL listeners both performed more poorly and showed less robust attentional modulation of cortical ERPs. While both groups showed some cortical suppression of distracting streams, this modulation was weaker in HL listeners, especially when spatial separation between attended and distracting streams was small. In the final study, we compared temporal coding precision in listeners with NHT and HL using both behavioral and physiological measures. We found that listeners with HL are more sensitive than listeners with NHT to amplitude modulation in both measures. Within the NHT listener group, we found a strong correlation between behavioral and electrophysiological measurements, consistent with cochlear synaptopathy. Overall, these studies demonstrate that everyday communication abilities depend jointly on both low-level differences in sensory coding and high-level ability to control attention

Contributions of Sensory Coding and Attentional Control to Individual Differences in Performance in Spatial Auditory Selective Attention Tasks

Listeners with normal hearing thresholds differ in their ability to steer attention to whatever sound source is important. This ability depends on top-down executive control, which modulates the sensory representation of sound in cortex. Yet, this sensory representation also depends on the coding fidelity of the peripheral auditory system. Both of these factors may thus contribute to the individual differences in performance. We designed a selective auditory attention paradigm in which we could simultaneously measure envelope following responses (EFRs, reflecting peripheral coding), onset event-related potentials from the scalp (ERPs, reflecting cortical responses to sound), and behavioral scores. We performed two experiments that varied stimulus conditions to alter the degree to which performance might be limited due to fine stimulus details vs. due to control of attentional focus. Consistent with past work, in both experiments we find that attention strongly modulates cortical ERPs. Importantly, in Experiment I, where coding fidelity limits the task, individual behavioral performance correlates with subcortical coding strength (derived by computing how the EFR is degraded for fully masked tones compared to partially masked tones); however, in this experiment, the effects of attention on cortical ERPs were unrelated to individual subject performance. In contrast, in Experiment II, where sensory cues for segregation are robust (and thus less of a limiting factor on task performance), inter-subject behavioral differences correlate with subcortical coding strength. In addition, after factoring out the influence of subcortical coding strength, behavioral differences are also correlated with the strength of attentional modulation of ERPs. These results support the hypothesis that behavioral abilities amongst listeners with normal hearing thresholds can arise due to both subcortical coding differences and differences in attentional control, depending on stimulus characteristics and task demands