BCS 221: Auditory Perception BCS 521 & PSY 221

Transcription

1 BCS 221: Auditory Perception BCS 521 & PSY 221 Time: MW 10:25 11:40 AM Recitation: F 10:25 11:25 AM Room: Hutchinson 473 Lecturer: Dr. Kevin Davis Office: 303E Meliora Hall Office hours: M 1 3 PM kevin_davis@urmc.rochester.edu vanderbilt.edu

2 Textbook: Fundamentals of Hearing by William A. Yost, 5 th ed Course website: learn.rochester.edu Exams: 4 midterms Course organization Grading: 25% for each exam A C A C B C B D B D 63-67

3 Syllabus 1. Physical Acoustics simple and complex sounds propagation and analysis 2. Sound Transduction peripheral auditory system 3. Perceptual Dimensions hearing threshold masking loudness and pitch binaural hearing 4. Auditory Scene Analysis sound localization speech, music hearing loss and restoration

4 Sound Sound constantly surrounds us and informs us about many objects in our world. The ability to locate food, avoid predators, find a mate, navigate, and communicate often depends on being able to locate and identify sounds. Sounds from various sources do not reach us as individual sounds, but are combined into one complex sound field. webneel.com

5 Hearing In order to locate and to identify sounds, the nervous system must first translate the various physical aspects of sound into a neural code. Then, it must extract useful information, combine it with that from other sensory modalities and experience (memory), and elicit the appropriate behavioral and emotional response. Hearing is the result of a complex interaction of physics, physiology, perception and cognition. en.wikipedia.org

6 Psychoacoustics is the scientific study of the perception of sound. More specifically, it studies relationships between perception and physical properties of sound. Psychoacoustics The field of psychoacoustics is multidisciplinary as it often involves acoustics, physiology and psychology.

7 Adequate Stimulus for Hearing Sound is a longitudinal pressure wave: a disturbance travelling through a medium (air/water) Particles do NOT travel, only the disturbance. Particles oscillate back and forth about their equilibrium positions

8 Pressure Amplitude Physical Dimensions of Sound Fundamental measures of a physical stimulus that can be detected with an instrument (e.g., spectrum analyzer) Longitudinal waves High One cycle Low Time or Distance from the source Time or Distance from the source

9 Natural sounds are complex patterns of vibrations. Fourier analysis breaks a natural sound down into its component sine waves. Natural Sounds are Complex

10 The Ear Sound propagation: wave enters auditory canal strike the eardrum (or tympanic membrane) ossicles (hammer, anvil and stirrup) vibrate oval window vibrates fluid in cochlea set in motion vibrations of fluid dissipated at round window

11 The Cochlea The cochlea is divided into three chambers (scala) by Reissner s membrane and the basilar membrane. The auditory receptor organ, the organ of Corti, sits on the basilar membrane in the middle scala.

12 Motion of the Basilar Membrane

13 Hair Cells: Mechanotransduction There are two types of hair cells in the Organ of Corti: inner hair cells, ~3,500 outer hair cells, ~14,000 All hair cells have stereocilia on their upper surfaces which are in or near the tectorial membrane. Up-down motion of basilar membrane converted to side-toside motion of stereocilia. Inner hair cells release transmitter onto axons of the auditory nerve that elicits action potentials that propagate towards the central auditory system.

14 From Ear to Primary Auditory Cortex The axons of each auditory nerve synapse in the cochlear nuclei on the same side (ipsilateral) From there, projections lead to the superior olives on both sides of the brain stem (binaural) Cochlear nuclei and superior olives inferior colliculi ipsilateral medial geniculate nuclei of the thalamus ipsilateral primary auditory cortex

15 Perceptual Dimensions of Sound The terms pitch, loudness, and timbre refer NOT to the physical characteristics of sound, but refer to the mental experiences that occur in the brains of listeners. Perceptual dimensions can be measured, but not with a meter.

16 Perception of Sound Dimensions Sensitivity Loudness Pitch

17 Auditory Scene Analysis The Problem of Hearing: Sound has no dimensions of space, distance, shape, or size; and the auditory periphery of all known vertebrates contains peripheral receptors that code for the parameters of the sound pressure wave rather than information about sound sources per se. William Yost (Perceiving Sounds in the Real World; 2007). Fan

18 Hearing Scientists Hearing scientists come from just about every field of science, including biology (neuroanatomy), chemistry (neurotransmitters), psychology (psychoacoustics, biopsychology), physics and engineering (hearing aids, cochlear implants), as well as audiology (diagnostic testing, rehabilitation) and otology (diagnosis, medical treatment).