Auditory Neuroscience 1 Spatial Hearing

1. Auditory Neuroscience 1 Spatial Hearing Systems Biology Doctoral Training Program Physiology course Prof. Jan Schnupp jan.schnupp@dpag.ox.ac.uk HowYourBrainWorks.net

2. Hearing: an impossible task!

3. http://auditoryneuroscience.com/foxInSnow

4. ITD Interaural Time Difference (ITD) Cues ITDs are powerful cues to sound source direction, but they are ambiguous (“cones of confusion”)

5. Front-Back Ambiguity and Phase Ambiguity http://auditoryneuroscience.com/ear/bm_motion_2

6. Interaural Level Cues (ILDs) Unlike ITDs, ILDs are highly frequency dependent. At higher sound frequencies ILDs tend to become larger, more complex, and hence potentially more informative. ILD at 700 Hz ILD at 11000 Hz

7. Spectral (Monaural) Cues

8. Adapting to Changes in Spectral Cues Hofman et al. made human volunteers localize sounds in the dark, then introduced plastic molds to change the shape of the concha. This disrupted spectral cues and led to poor localization, particularly in elevation. Over a prolonged period of wearing the molds, (up to 3 weeks) localization accuracy improved.

9. EI neuron

10. Phase locking improves in the cochlear nucleus Sphericalbushycell Endbulbof Held Auditory nervefiber

11. EE neuron

12. The Jeffress model: mapping ITDs in the brain? http://auditoryneuroscience.com/topics/jeffress-model-animation

13. McAlpine and colleagues ITD tuning varies with sound frequency: no map?

14. The Auditory Pathway CN, cochlear nuclei; SOC, superior olivary complex; NLL, nuclei of the lateral lemniscus; IC, inferior colliculus; MGB, medial geniculate body.

15. Lesion Studies Suggest Important Role for A1 Jenkins & Merzenich, J. Neurophysiol, 1984

16. Binaural Frequency-Time Receptive Field

17. Linear Prediction of Responses FTRF “w matrix” Input“i vector” r(t) = i1(t-1) w1(1) + i1(t-2) w1(2)+ ...+ i2(t-1) w2(1) + i2(t-2) w2(2)+ ... + i3(t-1) w3(1) + i2(t-2) w3(2)+ ... Frequency [kHz] Latency

18. Predicting Space from Spectrum a Left and Right Ear Frequency-Time Response Fields Virtual Acoustic Space Stimuli d Frequency [kHz] Elev [deg] b e c f Schnupp et al Nature 2001

19. “Higher Order” Cortical Areas • In the macaque, primary auditory cortex(A1) is surrounded by rostral (R), lateral (L), caudo-medial (CM) and medial “belt areas”. • L can be further subdivided into anterior, medial and caudal subfields (AL, ML, CL)

20. Are there “What” and “Where” Streams in Auditory Cortex? AnterolateralBelt • Some reports suggest that anterior cortical belt areas may more selective for sound identity and less for sound source location, while caudal belt areas are more location specific. • It has been hypothesized that these may be the starting positions for a ventral “what” stream heading for inferotemporal cortex and a dorsal “where” stream which heads for postero-parietal cortex. CaudolateralBelt

21. A “Panoramic” Code for Auditory Space? • Middlebrooks et al.found neural spike patterns to vary systematically with sound source direction in a number cortical areas of the cat (AES, A1, A2, PAF). • Artificial neural networks can be trained to estimate sound source azimuth from the neural spike pattern. • Spike trains in PAF carry more spatial information than other areas, but in principle spatial information is available in all auditory cortical areas tested so far.

22. Artificial Vowel Sounds • Bizley et al J Neurosci 2009 29:2064

23. Vowel type (timbre) Pitch (Hz) Responses to Artificial Vowels in Space • Bizley et al J Neurosci 2009 29:2064

24. Azimuth, Pitch and Timbre Sensitivity in Ferret Auditory Cortex • Bizley et al J Neurosci 2009 29:2064