Towards Decoding Selective Attention Through Cochlear Implant Electrodes as Sensors in Subjects with Contralateral Acoustic Hearing

Objectives: Focusing attention on one speaker in a situation with multiple background speakers or noise is referred to as auditory selective attention. Decoding selective attention is an interesting line of research with respect to future brain-guided hearing aids or cochlear implants (CIs) that are designed to adaptively adjust sound processing through cortical feedback loops. This study investigates the feasibility of using the electrodes and backward telemetry of a CI to record electroencephalography (EEG). Approach: The study population included 6 normal-hearing (NH) listeners and 5 CI users with contralateral acoustic hearing. Cortical auditory evoked potentials (CAEP) and selective attention were recorded using a state-of-the-art high-density scalp EEG and, in the case of CI users, also using two CI electrodes as sensors in combination with the backward telemetry system of these devices (iEEG). Main results: The peak amplitudes of the CAEPs recorded with iEEG were lower and the latencies were higher than those recorded with scalp EEG. In the selective attention paradigm with multi-channel scalp EEG the mean decoding accuracy across subjects was 92.0 and 92.5% for NH listeners and CI users, respectively. With single-channel scalp EEG the accuracy decreased to 65.6 and to 75.8% for NH listeners and CI users, respectively, and was above chance level in 9 out of 11 subjects. With the single-channel iEEG, the accuracy for CI users decreased to 70% and was above chance level in 3 out of 5 subjects. Significance: This study shows that single-channel EEG is suitable for auditory selective attention decoding, even though it reduces the decoding quality compared to a multi-channel approach. CI-based iEEG can be used for the purpose of recording CAEPs and decoding selective attention. However, the study also points out the need for further technical development for the CI backward telemetry regarding long-term recordings and the optimal sensor positions.

Infants' Preference for Child-Directed Speech Over Time-Reversed Speech in On-Channel and Off-Channel Masking

Purpose This study aims to examine the development of auditory selective attention to speech in noise by examining the ability of infants to prefer child-directed speech (CDS) over time-reversed speech (TRS) presented in “on-channel” and “off-channel” noise. Method A total of 32 infants participated in the study. Sixteen typically developing infants were tested at 7 and 11 months of age using the central fixation procedure with CDS and TRS in two types of noise at +10 dB signal-to-noise ratio. One type of noise was an “on-channel” masker with a spectrum overlapping that of the CDS (energetic masking), and the second was an “off-channel” masker with frequencies that were outside the spectrum of the CDS (distractive masking). An additional group of sixteen 11-month-old infants were tested in quiet and served as controls for the “off-frequency” masker condition. Results Infants preferred CDS over TRS in both age groups, but this preference was more pronounced with “off-channel” masker regardless of age. Also, older infants demonstrated longer looking time for the target stimuli when presented with an “off-channel” masker compared to the “on-channel” masker. Looking time in quiet was similar to looking time in the “off-channel” condition, and looking time for CDS was longer in quiet compared to the “on-channel” condition. Conclusions These findings support the notion that (a) infants as young as 7 months of age are already showing preference for speech in noise, regardless of type of masker; (b) by 11 months of age, listening with the “off-channel” condition did not yield different results than in quiet. Thus, by 11 months of age, infants' cognitive–attentional abilities may be more developed.

Cochlear activity in silent cue-target intervals shows a theta-rhythmic pattern and is correlated to attentional alpha and theta modulations

BackgroundA long-standing debate concerns where in the processing hierarchy of the central nervous system (CNS) selective attention takes effect. In the auditory system, cochlear processes can be influenced via direct and mediated (by the inferior colliculus) projections from the auditory cortex to the superior olivary complex (SOC). Studies illustrating attentional modulations of cochlear responses have so far been limited to sound-evoked responses. The aim of the present study is to investigate intermodal (audiovisual) selective attention in humans simultaneously at the cortical and cochlear level during a stimulus-free cue-target interval.ResultsWe found that cochlear activity in the silent cue-target intervals was modulated by a theta-rhythmic pattern (~ 6 Hz). While this pattern was present independently of attentional focus, cochlear theta activity was clearly enhanced when attending to the upcoming auditory input. On a cortical level, classical posterior alpha and beta power enhancements were found during auditory selective attention. Interestingly, participants with a stronger release of inhibition in auditory brain regions show a stronger attentional modulation of cochlear theta activity.ConclusionsThese results hint at a putative theta-rhythmic sampling of auditory input at the cochlear level. Furthermore, our results point to an interindividual variable engagement of efferent pathways in an attentional context that are linked to processes within and beyond processes in auditory cortical regions.

Auditory selective attention under working memory load

Can cognitive load enhance concentration on task-relevant information and help filter out distractors? Most of the prior research in the area of selective attention has focused on visual attention or cross-modal distraction and has yielded controversial results. Here, we studied whether working memory load can facilitate selective attention when both target and distractor stimuli are auditory. We used a letter n-back task with four levels of working memory load and two levels of distraction: congruent and incongruent distractors. This combination of updating and inhibition tasks allowed us to manipulate working memory load within the selective attention task. Participants sat in front of three loudspeakers and were asked to attend to the letter presented from the central loudspeaker while ignoring that presented from the flanking ones (spoken by a different person), which could be the same letter as the central one (congruent) or a different (incongruent) letter. Their task was to respond whether or not the central letter matched the letter presented n (0, 1, 2, or 3) trials back. Distraction was measured in terms of the difference in reaction time and accuracy on trials with incongruent versus congruent flankers. We found reduced interference from incongruent flankers in 2- and 3-back conditions compared to 0- and 1-back conditions, whereby higher working memory load almost negated the effect of incongruent flankers. These results suggest that high load on verbal working memory can facilitate inhibition of distractors in the auditory domain rather than make it more difficult as sometimes claimed.