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Motivation

Motivation. Ability to localize sounds can deteriorate as we age. ITDs: rely on temporal processing at low frequencies ILDs: rely on high frequency hearing Previous cortical data gives insight into sound localization (see companion paper; Briley et al. , 2013).

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Motivation

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  1. Motivation • Ability to localize sounds can deteriorate as we age. • ITDs: rely on temporal processing at low frequencies • ILDs: rely on high frequency hearing • Previous cortical data gives insight into sound localization (see companion paper; Briley et al., 2013). • Quantified cortical representation of azimuthal space using EEG • Passive listening (i.e., no attentional or task dependence) • Pattern of responses fit well into a computational opponent-channel model

  2. Binaural Hearing • Interaural Time Differences (ITDs) • Dominant at Low Frequencies • Due to the difference in time a sound reaches one ear relative to the other ear • Interaural Level Differences (ILDs) • Dominant at High Frequencies • Due to the acoustic head shadow for short wavelengths

  3. Opponent-channel Model vs.Topographic Model • Opponent-channel model -Predicts greater activity for outward shifts • Topographic: Each location represented by an equal number of neurons -Predicts equal activity for shifts • Topographic: Larger number of neurons tuned to locations near midline -Predicts greater activity for inward shifts Briley et al., 2013; Fig 1.

  4. Method • 11 young adults (10 female) • Taken from Briley et al., 2013 • 11 older adults (4 female) • Sub-divided into young-old (n=6) and older-old (n = 5) • Both groups showed symmetric, sloping high-frequency hearing loss • Psychophysics: Minimum audible angle (MAA) measured around a fixed reference angle using simulated spatial locations (HRIR) of pink noise presented over headphones. Task was 3I3AFC and estimated 71% correct threshold. • EEG: 1.51s pink noise (48 dB SL) presented from 1 of 5 speakers in the free field then shifted to another speaker (10ms overlap). All combinations of shifts presented 120 times. • Modeling: 2 spatial channels, 1 maximally responsive to -90° and 1 maximally responsive to +90 ° (i.e., opponent-channel model)

  5. Results: Psychophysics • Young adults show good spatial acuity up to ~60° • Younger-old adults show similar MAA to young adults • Older-old adults start to lose spatial acuity as early as 45° (and possibly earlier) • Pure-tone thresholds show typical signs of presbycusis in the older adults

  6. Results: EEG Young Adults (n = 11; Briley et al., 2013 & Briley and Summerfield, 2014)

  7. Results: EEG Older Adults (n = 11; Briley and Summerfield, 2014)

  8. Results: Modeling • Tuning curves (2 channels) fitted to data • Summed gradients of the 2 channels • Reciprocals of the gradients • Predicted MAAs versus the data measured

  9. Discussion • There is deterioration in spatial acuity in the horizontal plane for older adults (seen from both cortical representations and psychophysical measurements). • Appears accelerate at later stages of aging, although more evidence would be needed to confirm this. • It’s likely that ITDs were the principal location cue in the current paradigm, and impaired neural coding of temporal fine structure has been shown extensively in older populations. • More work needed to tease apart peripheral and central impairments responsible for poor spatial acuity with age.

  10. Current work in this lab SCOOPED!

  11. Briley with a twist: The effects of attention • No-Attention: • Same as Briley and Summerfield, 2014 (ugh..) • Old vs Young • Passive listening (i.e., subtitled movie presented in direct view of listener) • Directed-Attention: • Same participants • Attend either to left or right hemifield • Respond when stimulus occurs in attended hemifield

  12. Schedule for summer? If you haven’t done so, please email unavailable weeks. Volunteer for next week?

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