Ch. 11 The Auditory Brain and Sound Localization Review

Azimuth

• – Measured in degrees 

  • 0°= straight ahead 

  • - 90° = straight left 

  • +90° = straight right 

  • 180° = straight behind

the angle of a sound source relative to the listener's head, measured horizontally around them in a 360-degree plane. It is a key component of spatial hearing, helping the brain determine the direction a sound is coming from, such as left, right, or straight ahead.

Example:

If a sound comes from directly to the right of a listener, it has an azimuth of 90 degrees, whereas a sound directly in front has an azimuth of 0 degrees.

Fill-in-the-Blank Example:

1. ________ is the horizontal angle that describes the direction of a sound source relative to a listener’s position.

Cochlear Nucleus

he first brainstem structure that receives auditory signals from the cochlea via the auditory nerve. It processes these signals and begins analyzing sound features like pitch, intensity, and timing before sending the information to higher auditory centers.

Example :

When a sound wave enters the ear and stimulates the cochlea, the auditory nerve carries the signal to the cochlear nucleus, which then helps differentiate the timing and intensity of the sound.

Fill-in-the-Blank Example:

1. The ________ is the first brainstem structure to receive auditory signals from the cochlea.
   

Directional Transfer Function (DTF)

• Each person has their own DTF (based on their own body) and uses it to help locate sounds

describes how the shape of the head, ears, and torso modify incoming sound waves depending on the direction they arrive from. It is crucial for spatial hearing, as it helps the brain localize sounds in three-dimensional space by analyzing these directional sound changes.

Example:

The DTF helps you distinguish whether a sound is coming from above or below because the unique shape of your ear alters the sound wave differently depending on its elevation.

Fill-in-the-Blank Example:

1. The ________ describes how the head, ears, and body affect sound waves arriving from different directions, aiding in spatial hearing.

Echolocation

the process of using reflected sound waves to determine the location, size, and shape of objects in the environment. Animals like bats and dolphins, as well as some humans with visual impairments, use this technique by emitting sound waves and analyzing the echoes that bounce back.

Example:

A bat flying in the dark emits high-pitched sounds and uses the returning echoes to avoid obstacles and catch flying insects.

Fill-in-the-Blank Example:

1. ________ is the process of using sound waves and their echoes to identify objects and navigate an environment.

Equal-Loudness Curve

a graphical representation of the varying sound intensities at different frequencies that are perceived as equally loud by the human ear. It shows that the human ear is more sensitive to certain frequencies (like mid-range sounds) and less sensitive to very low or high frequencies at the same perceived loudness level.

Example:

A 1000 Hz tone at 40 dB will sound equally as loud as a 100 Hz tone at 60 dB, according to the equal-loudness curve, though the latter requires more energy to reach the same perceived loudness.

Fill-in-the-Blank Example:

1. The ________ represents the different frequencies that are perceived as equally loud at various sound pressure levels.

Inattentional Deafness

• “The senses of hearing and vision share a limited neural resource.” 

• “the effects are driven by brain mechanisms at a very early stage of auditory processing”

when a person fails to hear an auditory stimulus because their attention is focused on a different task or sensory input. It is not due to any physical hearing loss but rather a limitation in cognitive processing of sound.

Example:

A person deeply focused on reading a book might not hear someone calling their name from the next room, even though their hearing is normal.

Fill-in-the-Blank Example:

1. ________ refers to the failure to hear sounds due to attention being focused elsewhere, rather than a hearing impairment.

Parabelt Area

a region in the auditory cortex that processes complex sounds and integrates auditory information with other sensory modalities. Located adjacent to the auditory belt areas, it plays a role in higher-order auditory functions, such as recognizing and interpreting sounds in context.

Example:

The parabelt area becomes active when someone identifies a familiar voice or interprets the emotional tone in speech.

Fill-in-the-Blank Example:

1. The ________ is a higher-order auditory region involved in processing complex sounds and integrating multisensory information.

Simple Cue

refers to a basic auditory signal or feature that provides straightforward information about a sound's properties, such as its pitch, loudness, or timing. It is often used in sound localization or recognition tasks, such as determining the direction of a sound based on its intensity or timing difference between ears.

Example:

A sound being louder in the right ear than the left provides a simple cue that the source is closer to the right side.

Fill-in-the-Blank Example:

1. A ________ is an auditory signal, like loudness or timing, that provides basic information about a sound's properties.

Superior Colliculus

• Located in the midbrain

• Deeper layers contain overlapping spatial maps of the visual, auditory and somatosensory modalities

a structure in the midbrain that plays a key role in integrating sensory information, particularly visual and auditory cues, to guide movements like orienting toward a sound or object. It is critical for spatial awareness and coordinating eye and head movements in response to stimuli.

Example:

When you hear a sudden sound to your left, the superior colliculus helps you reflexively turn your head and eyes in that direction.

Fill-in-the-Blank Example:

1. The ________ is a midbrain structure that integrates auditory and visual information to guide spatial attention and movement.

Temporal Integration

• Sound at a constant level is perceived as getting louder as duration increases

the process by which the auditory system combines sound energy over time to perceive the loudness or detect the presence of a sound. It explains why sounds of longer duration are often perceived as louder or easier to detect than shorter, equally intense sounds.

Example:

A brief 50-millisecond tone at low volume may be harder to hear than a 500-millisecond tone at the same volume, because the auditory system integrates the sound energy over time.

Fill-in-the-Blank Example:

1. ________ refers to how the auditory system combines sound energy over time to affect the perception of loudness or detectability.

Tonotopic Organization

• Neurons that respond to different frequencies are organized anatomically in order of frequency 

• Starts in the cochlea. 

• Maintained all the way through the primary auditory cortex (A1). 

the spatial arrangement of neurons in the auditory system that are specifically tuned to different sound frequencies. This organization is present in structures like the cochlea and auditory cortex, where low frequencies are processed in one region and high frequencies in another.

Example:

In the cochlea, high-frequency sounds are detected near the base, while low-frequency sounds are detected near the apex, reflecting its tonotopic organization.

Fill-in-the-Blank Example:

1. ________ describes how neurons in the auditory system are arranged to respond to specific sound frequencies.

Ventriloquist Effect

• Like going to the movie and the sounds are to the side of you or behind. If it sounds like its coming in front of you then it most likely is

a phenomenon where a person perceives a sound to come from a visual source rather than its actual origin, often due to visual cues that dominate auditory perception. This effect occurs when the brain integrates conflicting visual and auditory information, such as when a ventriloquist's voice seems to come from a puppet instead of the ventriloquist.

Example:

When a ventriloquist speaks, the audience perceives the voice as coming from the puppet rather than the ventriloquist, due to the alignment of visual and auditory cues.

Fill-in-the-Blank Example:

1. The ________ occurs when a person perceives a sound to come from a source based on visual cues, even if the sound originates elsewhere.