The Naked Scientists

The Naked Scientists Forum

Author Topic: boop-beep-boop, boop-beep-boop, etc. (2 streams heard)  (Read 2205 times)

Offline David Cooper

  • Neilep Level Member
  • ******
  • Posts: 1505
    • View Profile
Experiment involving two lots of beeps on different notes:-

The lower note is repeated about 14 times every 5 seconds while the higher note is repeated seven times in 5 seconds and occurs in the gaps between two of the lower beeps, thereby giving a "boop beep boop gap boop beep boop gap" pattern. When you listen to it for a while you soon start to hear the lower beeps as a seperate stream of sound, so it becomes a "boop gap boop gap boop gap boop gap" stream, while the higher sound becomes a "gap beep gap gap gap beep gap gap" stream. When you move your head, or when the speaker moves, you tend to go back to hearing "boop beep boop gap boop beep boop gap" as a single stream again and have to wait for it to divide out into two streams again. Conclusion of the scientists: your brain monitors how your head moves and how the sounds arrive at your ears and both of these things affect whether your hearing of the sound as two streams will be disrupted.

I've just copied the beep part of the programme from i-player into Audacity and copy-&-pasted it to get a reasonable length of beeps to try it out properly, and when listening to it through headphones I have found that head movement has no impact on things - I continue to hear the beeps as two separate streams without the expected disruption. What this reveals is that if you're listening to it without headphones, moving your head or moving the source of the sound are not two separate things, but just different ways of doing exactly the same thing - the disruption is entirely caused through what's heard and not by paying attention to where your head is moving. The scientists have got it wrong.

For anyone else who wants to test this, you'll have to be quick to get it: http://www.bbc.co.uk/iplayer/episode/b01g4sv7/Up_All_Night_16_04_2012/ (and jump to 2 hours 5 minutes in.)


 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8126
  • Thanked: 53 times
    • View Profile
Re: boop-beep-boop, boop-beep-boop, etc. (2 streams heard)
« Reply #1 on: 17/04/2012 01:04:24 »
I'm not familiar with this experiment, but if you listen to a monotone via two speakers, small movements of your head produce big changes in volume because of the spatial pattern of constructive and destructive interference.


http://www.physicsclassroom.com/class/sound/u11l3a.cfm

http://techtv.mit.edu/videos/14839-sound-wave-interference

Listening to the same monotone sound via headphones does not produce this effect.
« Last Edit: 17/04/2012 01:13:49 by RD »
 

Offline David Cooper

  • Neilep Level Member
  • ******
  • Posts: 1505
    • View Profile
Re: boop-beep-boop, boop-beep-boop, etc. (2 streams heard)
« Reply #2 on: 17/04/2012 21:10:31 »
Listening to the same monotone sound via headphones does not produce this effect.

That's exactly why I did the experiment with headphones - I wanted to test their claim that the brain is monitoring head movements in addition to analysing the audio input through the ears and that the head movements were interfering with your ability to hear the boops/beeps as two distinct streams. By eliminating the changes to the sound input I was able to test whether head movement by itself had any such effect, but it clearly didn't. The only effect head movement has is in changing the audio input in a way which is exactly equivalent to moving the source of the sound (ignoring reflections).
« Last Edit: 17/04/2012 21:12:32 by David Cooper »
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8126
  • Thanked: 53 times
    • View Profile
Re: boop-beep-boop, boop-beep-boop, etc. (2 streams heard)
« Reply #3 on: 17/04/2012 22:21:50 »
freaky video of the experiment, and example tones, here ... http://www.wired.com/wiredscience/2012/04/robotic-head-hearing/
« Last Edit: 17/04/2012 22:25:37 by RD »
 

Offline David Cooper

  • Neilep Level Member
  • ******
  • Posts: 1505
    • View Profile
Re: boop-beep-boop, boop-beep-boop, etc. (2 streams heard)
« Reply #4 on: 19/04/2012 19:57:59 »
Thanks for that link - it gives a clearer idea of what they were trying to do.

“If you move your head such that the acoustic stimulus at the ears changes, but the environment itself doesn’t, you wouldn’t have thought you would need to restart the process of interpretation,”

Oh yes you would! We've only got two ears each, so turning your head a bit in a noisy room is going to shift the whole set of possible locations for the origins of all the sounds you're hearing, and they'll shift in different directions depending on whether they're coming from behind you or in front, while not moving at all if directly overhead or underneath (if your head rotates horizontally). It's obvious that it isn't going to be able to predict all the changes and has to start analysing from scratch.
 

The Naked Scientists Forum

Re: boop-beep-boop, boop-beep-boop, etc. (2 streams heard)
« Reply #4 on: 19/04/2012 19:57:59 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length