Using Sound Awareness for Mobility with Vision Loss
Last updated: April 2021
It seems I get a fair number of page ideas while I am walking the dogs. Today I heard a car and started turning my head to locate where it was. Eureka! I can write about sound and orientation, mobility, and other such stuff for Health Union!
Tuning into sound
Do you remember when they came out with a stereo for home systems? I don’t exactly remember, but I was around and I imagine many of you were, too.
It was the late 50s - 1957/1958-ish when my mother started buying records for the new “stereo” system. Younger folks cannot imagine having a “flat” sound coming from only one speaker. (That is monaural, by the way). However, until the late 1950s that was the way things were.
I remember my parents moving speakers around the room so we could get the best stereo effects. Once we graduated from a record player to a stereo, we seemed to be immersed in the sounds coming from different directions.
The thing is, listening in stereo is more realistic and true to life. Sounds do not limit themselves to coming at us from one direction. Right now Maggie is barking to my left and Etta is barking from the other room. The printer is running off the article I need for this page over to my right. Sound is coming at me from all over the place! It comes at you the same way.
How do we hear space?
The article I am running off is entitled Directional Hearing: How to Listen to Stereo. Part 1 of the article is entitled How We Hear Space. The author tells us there are four sources of information that contribute to the perception of direction. Our brains combine these to tell us where a sound is coming from. These sources are listed as amplitude differences, phase differences, arrival-time differences and tonal balance.
I only have a clue what one of those actually is. We should probably, therefore, read on.
What are amplitude differences?
It appears amplitude differences signal where a sound is coming from by having that sound be louder in the ear that is pointed towards it. Sounds in front or behind us sound equally loud in both ears. Ergo, if I am trying to discern if a car is approaching me from the front or the rear, I turn my head. The sound of the car will be louder in the ear pointed towards it.2
Ok. Got that? Let’s move on.
What are arrival-time differences?
Phase differences seem to have to do with arrival-time difference so let’s do these out of sequence. Hard to believe but your brain can actually discern the differences in the times sounds take to reach one ear, wrap around your head and reach your second ear. Amazing! If the sound reaches your right ear a nanosecond before it reaches your left, it is coming from your right. 2
What are phase differences?
Now phase differences are a little murkier. Basically, it appears that your head is a more formidable obstacle to higher (high frequency) sounds than it is to lower (low frequency) sounds. Going around your head slows down the higher frequency sound and lowers the pitch as compared to what is being heard in the ear facing the sound. Your brain is able to decide which one is the more “true” pitch of the sound, compare the two sounds, and tell you where the sound is coming from... I think. Anyway, the bottom line on this: they sound different. So there! 2
What is tonal-balance shift?
The last one is tonal-balance shifts. If you think I confused the last one, just wait for this one!
Don’t trust me on this, but it appears the sound of a sound is changed by bouncing around in your ear on the way to the eardrum. Depending upon the direction from which the sound enters the ear, it “bounces” differently. According to my source, this particular mechanism not only gives us directionality but it also gives us information about the height of the sound source. 2
Hearing as a mobility aid for vision loss
Weird science? Yes, but also rather cool. It gives us justification for using our hearing as a mobility aid. I am not just cocking my head and looking like Big Bird. I am using amplitude differences, phase difference, arrival-time differences and tonal balance to locate sound and keep us from becoming roadkill!
So all together now...turn your heads! Use all that weird science to keep yourself safe, too.
Do you find that fear interferes with your ability to regularly go to eye specialist appointments?