for a complete beginner's intro to the fascinating world of neuroscience.
Was Rayleigh correct?
Lord Rayleigh is credited for developing the "duplex theory" for sound localization, which states that the brain relies heavily on ITDs for low frequency sounds, and on ILDs for high frequency sounds.
Final Question: In your own words, do the results you have obtained in this practical agree with the duplex theory?
This concludes this practical.
Unlike ILDs, ITDs are generally thought not to vary much with frequency. The graph below shows ITDs as a function of sound source direction measured in an adult male with small microphones inserted in the ear canal.
Question: Use the graph to work out what MAAs the ITD thresholds you have obtained would correspond to. How do these MAAs compare to those you obtained for ILDs?
Once you have collected, interpreted and evaluated your ILD data, go back to the software's main screen, and collect ITD data by clicking on the "ITD" button
When you have completed your trials the program will generate a plot of your results for you, which should look more or less like this:
If you are doing these exercises as part of a taught class, you should consider making a print-out of these result graphs so that you can show them to your instructors if necessary. (There should be a File | Print menu on the top left above the figure).
When you launch Experiment.m you should obtain a window which looks like this:
Using the methods described in the previous sections, you should by now have obtained estimates of your own ILD sensitivity at two different test frequencies (500 and 2,000 Hz if you ran with the suggested values). Your ILD thresholds in dB may or may not have been very similar for the two frequencies. However, ILDs are a cue to sound source direction. Source directions are not specified in dB! To localize sounds in space, your brain needs to "translate" ILD values to angles relative to the inter-aural axis.
Here below you can find the Matlab source code for a program authored by Matthieu Lesburgueres and Jan Schnupp which you can use to run a psychoacoustic experiment to measure your own sensitivity to ITDs and ILDs.
This podcast by science journalist Dr Carinne Piekema explores how hearing loss affects people, in particular how it affects musicians, and what modern prosthetic devices such as hearing aids or cochlear implants can and cannot do for these patients. It contains insightful interviews with inspirational deaf musicians, some of the UKs leading hearing researchers, as well as simulations designed to show to normal listeners what it would be like to have to rely on a hearing aid or a cochlear implant.
You can listen to the podcast here,
The numbered squares signify the sound directions corresponding to a series of "virtual acoustic space" stimuli, which were generated by convolving a stimulus - in this case, a series of tapping sounds - with the head-related transfer function of one of the authors of this book.