Hearing in Complex Environments

65 Head-related Transfer Function

Learning Objectives

Know that head-related transfer function (HRTF) is a monaural cue related to pinnae and why HRTF can provide information about elevation.

Understand that people can learn new HRTF but still have their old HRTF.

Know what the cone of confusion is.

The head-related transfer function (HRTF) is an auditory function that gives information about elevation. This function is monaural, meaning it takes place in each individual ear. By using information from both ears, one should be able to roughly identify the elevation of an external auditory cue. The speeds and intensities of the auditory cue are compared and contrasted at each ear, giving enough information for the brain to perceive the sound at the correct spot.

Each of us has a customized HRTF because of the shape of our pinnae: different frequencies are attenuated differently at different elevations. Thus, the HRTF provides information about elevation. It’s a complicated function and one that we’ve learned after years of living in our heads. A study by Hofman et al. (1998) changed the shape of subjects pinnae and discovered:

  1. Subjects lost the ability to determine the elevation of sounds when the first received some fake pinnae.
  2. Subjects learned a new HRTF after a few weeks.
  3. Subjects still had their old HRTF (were immediately accurately determining elevation) when the artificial pinnae were removed.

There’s a thing called the cone of confusion, which is the cone-shaped region pointing out from the side of your head in which ITD and ILD are the same for all locations. This often leads to front/back confusions as well as left-right confusions (although less often). Elevation information provided by the HRTF is needed to break this up. Head movements have also been shown to help break up the cone of confusion.

 

The image shows how sound from a given direction reaches both ears. The sound will approach the closer ear in a direct path. The sound will bend around the head to reach the farther ear.
Fig 7.4.1. Each person has an individualized head-related transfer function, which helps with detection of elevation information. The above image shows how there are multiple factors that go into auditory perception. The height of the sound’s location and the speed at which it is received at each ear are important factors. (Credit: Soumyasch. Provided by: Wikipedia. License: CC-BY 4.0)

 

Exercises

  1. Which one of the five senses comes into play when we need to identify the elevation of an external auditory cue?
    A. Hearing (Ears)
    B. Seeing (Eyes)
    C. Touch (Hands)
    D. Taste (Tongue)
    E. Smell (Nose)
  2. True/False: We all have the same HRTF and HRTF provides information about why we lose our sense of smell as we age?
  3. Which one of the following correctly defines cone of confusion?
    A. Cone of confusion is what causes confusion after a concussion
    B. Cone of confusion is the cone-shaped region pointing out from the side of your nose in which ITD and ILD are the same for all locations
    C. Cone of confusion is the cone-shaped region pointing out from the side of your head in which ITD and ILD are the same for all locations

Answer Key:

  1.  A (Explanation: You need to use the information from both ears to evaluate external auditory cues.)
  2.  False (Explanation: We all have customized HRTF because of the shape of our pinnae. And HRTF provides information about elevation.)
  3. C

 

CC LICENSED CONTENT, SHARED PREVIOUSLY
Cheryl Olman PSY 3031 Detailed Outline
Provided by: University of Minnesota
Download for free at http://vision.psych.umn.edu/users/caolman/courses/PSY3031/
License of original source: CC Attribution 4.0
Adapted by: Cameron Kennedy & Kori Skrypek

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Introduction to Sensation and Perception by Students of PSY 3031 and Edited by Dr. Cheryl Olman is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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