Hearing in Complex Environments

75 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 mechanism for determining the elevation of sound sources. In simpler terms, HRTF helps figure out where sounds come from. This process is monaural, meaning it takes place in one ear at a time, independently. The brain analyzes subtle differences in arrival time and intensity of the sound between the two ears, deducing the elevation of said sound with reasonable accuracy.

Central to the HRTF is the intricate structure of the pinnae, which is the outer visible part of the ear. Every person has their own HRTF because their ears are shaped and sized differently. These anatomical differences change how sounds of different pitches weaken at various elevations. Consequently, the HRTF provides essential cues for accurately perceiving sound elevation.

A seminal study conducted by Hofman et al. (1996) highlighted the HRTF’s adaptability. In their experiment, subjects underwent alterations to the shape of their pinnae, leading to intriguing findings:

  1. Initially, subjects experienced difficulty determining sound elevation when presented with artificial pinnae.
  2. Subjects adapted over time and learned to interpret the new HRTF. This shows the brain’s remarkable ability to adjust to changes in sensory input.
  3. Even after acquiring a new HRTF, subjects were able to revert to their original perceptual framework once the artificial pinnae were removed, highlighting the persistence of their innate HRTF.

An essential concept in auditory perception is the “cone of confusion,” which is an area extending outward from the head where interaural time differences (ITD) and interaural level differences (ILD) are the same in each ear across different sound source locations. This phenomenon makes sound localization difficult, particularly when discerning between front/back and left/right orientations. However, the HRTF is key in resolving such confusions by giving us clues about the height of sounds. Moreover, research suggests that head movements aid in disambiguating sound localization cues and breaking down the cone of confusion.

To summarize, the HRTF, shaped by the unique features of the pinnae, is instrumental in providing elevation cues necessary for accurate sound localization. Its adaptability and role in resolving perceptual confusion emphasize its importance in understanding human auditory perception.

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
Refereces:

Hofman, P., Van Riswick, J. & Van Opstal, A. Relearning sound localization with new ears. Nat Neurosci 1, 417–421 (1998). https://doi.org/10.1038/1633

Brungart DS. Informational and energetic masking effects in the perception of two simultaneous talkers. J Acoust Soc Am. 2001 Mar;109(3):1101-9. doi: 10.1121/1.1345696. PMID: 11303924.

Blauert, J. (1997). Spatial hearing: The psychophysics of human sound localization. MIT press. https://books.google.com/books/about/Spatial_Hearing.html?id=ApMeAQAAIAAJ

Wightman FL, Kistler DJ. Resolution of front-back ambiguity in spatial hearing by listener and source movement. J Acoust Soc Am. 1999 May;105(5):2841-53. doi: 10.1121/1.426899. PMID: 10335634.

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Introduction to Sensation and Perception Copyright © 2022 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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