Adequate Stimulus: The energy form for which a receptor is specialized.

Agraphia: The inability to write due to brain damage.

Alexia: The inability to read due to brain damage.

Angular Gyrus: A gyrus at the border of the parietal and occipital lobes containing pathways that connect the visual area with auditory, visual, and somatosensory association areas in the temporal and parietal lobes. Damage results in alexia and agraphia.

Aphasia: Language impairment caused by damage to the brain.

Auditory Object: A sound that we recognize as having an identity that is distinct from other sounds.

Basilar Membrane: The membrane in the cochlea that separates the cochlear canal from the tympanic canal and on which the organ of Corti is located.

Broca’s Aphasia: Language impairment caused by damage to Broca’s area and surrounding cortical and subcortical areas.

Cochlea: The snail-shaped structure where the ear’s sound-analyzing structures are located.

Cochlear Canal: The middle canal in the cochlea, which contains the organ of Corti.

Cocktail Party Effect: The ability to sort out meaningful auditory messages from a complex background of sounds.

Coincidence Detectors: Neurons that fire most when they receive input from both ears at the same time; they are involved in sound localization.

Complex Sound: A sound composed of more than one pure tone.

Dyslexia: An impairment of reading, which can be developmental or acquired through brain damage.

Eustachian Tube: The connection between the middle ear and the oral cavity, the function of which is to equalize air pressure differences between the outside of the head and the middle ear.

Frequency: A characteristic of sound; the number of cycles or waves of alternating compression and decompression of the vibrating medium that occur in a second. For the psychological perception of frequency, see pitch.

Frequency-Place Theory: The hypothesis that frequency following individual neurons accounts for the discrimination of frequencies up to about 200 Hz, and higher frequencies are represented by the place of greatest activity on the basilar membrane.

Frequency Theory: Any one of several hypotheses of auditory frequency analysis that state that the frequency of a sound is represented in the firing rate of each neuron or a group of neurons.

Grammar: The consistent set of rules of a particular language.

Head-Related Transfer Function (HRTF): Spectral frequency alterations to a sound as it passes through the pinna and auditory canal, as well as through the head and other parts of the body. One of the cues for localizing the direction of a sound source.

Inner Hair Cells: A single row of about 3,500 hair cells located on the basilar membrane toward the inside of the cochlea’s coil; they produce most, if not all, of the auditory signal.

Intensity: In audition, the physical energy in a sound; the sound’s amplitude. For the psychological perception of intensity, see loudness.

Interaural Level Difference: A binaural cue to the location of a sound coming from one side that results from the sound shadow created by the head; most effective above 2000 to 3000 Hz.

Interaural Timing Difference (ITD): A binaural cue to the location of a sound coming from one side due to the time the sound requires to travel the distance between the ears; most effective for low-frequency sounds.

Language: A structured system of communication with a common set of grammatical, lexical, and organizational rules.

Language Acquisition Device: A part of the brain hypothesized to be dedicated to learning and controlling language.

Loudness: The term for our experience of sound intensity.

Organ of Corti: The sound-analyzing structure on the basilar membrane of the cochlea; it consists of four rows of hair cells, their supporting cells, and the tectorial membrane.

Ossicles: Tiny bones in the middle ear that operate in lever fashion to transfer vibration from the tympanic membrane to the cochlea; they also produce a slight amplification of the sound.

Outer Hair Cells: Three rows of about 12,000 cells located on the basilar membrane toward the outside of the cochlea’s coil; they amplify the cochlea’s output and sharpen frequency tuning, possibly by adjusting the tension of the tectorial membrane.

Perception: The interpretation of sensory information.

Phonological Hypothesis: The idea that the fundamental problem in dyslexia is impaired phoneme processing.

Pinna: The ear flap on each side of the head; the outer ear.

Pitch: The experience of the frequency of a sound.

Place Theory: A theory that states that the frequency of a sound is identified by the location of maximal vibration on the basilar membrane and which neurons are firing most.

Planum Temporale: The area in each temporal lobe that is the location in the left hemisphere of Wernicke’s area and that is larger on the left in most people.

Prosody: The use of intonation, emphasis, and rhythm to convey meaning in speech.

Pure Tone: A sound consisting of a single frequency.

Receptor: A cell, often a specialized neuron, that is suited by its structure and function to respond to a particular form of energy, such as sound.

Sensation: The acquisition of sensory information.

Tectorial Membrane: A shelf-like membrane overlying the hair cells and the basilar membrane in the cochlea.

Telephone Theory: A theory of auditory frequency analysis, which stated that the auditory neurons transmit the actual sound frequencies to the cortex.

Tonotopically Organized: A term that means that neurons from adjacent receptor locations project to adjacent cells in the auditory cortex, forming a tonotopic map.

Tympanic Membrane: The eardrum, a very thin membrane stretched across the end of the auditory canal; its vibration transmits sound energy to the ossicles.

Volley Theory: A hypothesis of auditory frequency analysis that states that groups of neurons follow the frequency of a sound when the frequency exceeds the firing rate capability of a single neuron.

Wernicke’s Aphasia: Language impairment resulting from damage to Wernicke’s area; the person has difficulty understanding and producing spoken and written language.