Chapter 7 Nonvisual Sensation and Perception Audition Sound processed by auditory system Audition is synonym for hearing Like vision acoustic information uniquely perceived by humans relative to other species Sound waves must travel through medium Sound Frequency Frequency refers to the cycles per unit of time or wavelength of a sound Frequency is measured in Hertz Hz Pitch is our perception of the frequency of a sound The Auditory World Across Species Sound Intensity Intensity loudness is a function of sound wave amplitude Intensity is measured in decibels dB Loudness is our experience of sound energy Sound Intensity Sound Ear Structure The Outer Ear The Pinna Collects focuses and localizes sound Acts like funnel Emotional states The Outer Ear The Auditory Canal The Middle Ear Boundaries of middle ear are formed by two membranes Tympanic membrane or eardrum Oval window The Middle Ear Ossicles transfer sound from air to fluid Malleus Hammer Incus Anvil Stapes Stirrup The Inner Ear Cochlea Responds to vibrations from middle ear The oval window initiates liquid pressure wave The round window relieves pressure The Inner Ear Cochlea Three parallel chambers Vestibular Canal Cohlear Duct contains Organ of Corti Tympanic Canal Perilymph like CSF Endolymph high K low Na The Inner Ear Cochlea Three parallel canals Vestibular Canal Cohlear Duct contains Organ of Corti Tympanic Canal Two membranes Reissner s membrane Basilar membrane The Cochlea Organ of Corti The Organ of Corti Contains hair cells inner hair cells act as receptor for auditory transduction Sits on the basilar membrane Inner hair cells are attached to the tectorial membrane via cilia Vibration of the basilar membrane bends and activates hair cells Sound Transduction Sound Frequency Organ of Corti Hair Cells Endolymph surrounds hair cells Contains high amount of K higher than inside hair cell Hair Cells Hair Cells Resting membrane potential 70 mV Cilia movement opens and closes mechanicallygated K channels Open channels lead to depolarization and glutamate release The Cochlea Organ of Corti Central Auditory Pathways Spiral ganglion cells form connections with hair cells of the cochlea Project to the inferior colliculi in midbrain Part of pathway connects bilaterally through the superior olive Central Auditory Pathways Central Auditory Pathways Axons from the inferior colliculi synapse in the medial geniculate nucleus of the thalamus MGN The MGN projects to primary auditory cortex A1 in the temporal lobe Primary Auditory Cortex Columns respond to frequencies Topographically organized with low frequencies at rostral end and high frequencies at caudal end Some neurons respond maximally to input from one ear others respond maximally to input from both ears Some neurons respond to intensity of sounds Auditory Cortex A2 Activated by more complex sounds including speech Wernicke s area specialized for speech sounds Courtesy Dr Dean Shibata Secondary Auditory Cortex Audition Auditory Perception Pitch Perception Due to frequency intensity and context of stimulus Tonotopic organization Frequency Theory Groups of neurons in auditory nerve fire at same frequency as original sound source Place Theory Identifying the frequency of a sound depends on the location of maximal vibration on the basilar membrane and which neurons are firing most Frequency Place theory Frequency follows individual neuronal firing up to 4 kHz Frequency Theory Higher frequencies 4 kHz represented by the patterns of neuronal firing Place Theory Audition Auditory Perception Pitch Perception Due to frequency intensity and context of stimulus Tonotopic organization Loudness Perception Decibel level describes physical qualities of sound stimulus Loudness is human perception of that stimulus Equal loudness contours Loudness Contours Loudness doubles with each 10 dB increase in stimulus intensity Higher frequency sounds perceived as louder at same level of intensity Audition Auditory Perception Pitch Perception Due to frequency intensity and context of stimulus Tonotopic organization Loudness Perception Decibel level describes physical qualities of sound stimulus Loudness is human perception of that stimulus Equal loudness contours Localization of Sound Comparison of arrival times of sounds at each ear and differences in intensities important in horizontal plane Pinna important for localizing sound in vertical plane Localizing Sound Arrival time of sound at each ear is analyzed by the superior olive Sound intensity at each ear also analyzed The pinna is essential to localization in the vertical plane Localizing Sound Arrival time of sound at each ear is analyzed by the superior olive Sound intensity at each ear also analyzed The pinna is essential to localization in the vertical plane