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So today I'm going to be discussing uh
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an introduction to psycho acoustics.
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What is it? Why are we studying this?
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And what does it mean for
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us? So to start off, psychopysics is a
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branch of perceptual sciences or
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psychology that deals with the
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relationship between a physical stimulus
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and its perception. It explores how we
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experience and interpret the physical
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world through our
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senses. One important set of
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psychophysics especially for aiologists
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is psycho acoustics which focuses
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specifically on sound and
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hearing. Psycho acoustics studies how we
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perceive different sounds, how we
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differentiate between them, how our
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auditory system processes these
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sounds. By understanding the
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psychopysics and psycho
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acoustics, we can know how to use it for
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various applications such as the design
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of audio equipment, hearing aid and
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improving acoustics of listening
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environments. Sound is processed by the
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auditory system which leads to
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perception.
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Measuring this perception allows us to
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understand auditory
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processing. This is crucial for our
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understanding because it
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changes because changes to sounds can
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alter what we
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hear. But acoustics and perception are
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not
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equivalent. Additionally, changes to the
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auditory pathway can also affect what we
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hear.
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Therefore, to truly understand hearing,
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we must measure
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perception. So, the sound here could
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change, which would change what we
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hear, or we could have the same sound,
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but an altered auditory system, which
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changes what we
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hear. We need to measure the perception
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of hearing.
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Measuring sound or physiology alone does
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not measure hearing. Psycho acoustics is
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what we're looking at is a comp. It's
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important to note that measuring sound
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or physiologic responses alone does not
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measure hearing. Hearing encompasses
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more than the physical aspects of the
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sound and it's more than just how it's
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processed. It's the complex process of
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those two things interacting in
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perception.
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Understanding psycho physics and psycho
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acoustics is crucial for various
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applications including the design of
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audio equipment, hearing aids, and
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improving the acoustics of
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environments. When we measure
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perception, there's four different
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levels of perception we can use. They
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are from the bottom down here up to the
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top.
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detection, discrimination,
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identification, and
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comprehension. These are four critical
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levels in the process of auditory
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perception. Each has a distinct role in
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how we understand and interpret
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sounds. So, detection down here is the
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basic level of auditory perception. It
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involves our ability to hear the
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presence of a sound. At this stage, it's
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just awareness that the sound
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exists. It doesn't mean we have any
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specific details about it. It's the
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lowest sound that is audible. So, we can
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say, "Oh, yep. I can detect that
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sound." The next level up is
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discrimination where we differentiate
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between sounds. This would involve us
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recognizing two sounds that are distinct
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from one another. for example,
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distinguishing between a high pitch
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sound and a low pitch sound. Um, and
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that would be what discrimination is.
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And we could come and see what that
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what's the minimum difference
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needed. Identification goes a step
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further by not only recognizing that
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they're different, but by saying that is
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a high pitch sound, that is a low pitch
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sound.
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This means being able to label them or
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name them. So you could also do like
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bell versus
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whistle. Comprehension is the highest
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level of auditory processing. It
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involves understanding the meaning or
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significance of the sounds we hear.
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This could mean understanding spoken
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language, interpreting the emotional
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tone of a voice or recognizing the
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significance of a specific sound in a
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given
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context. So together it forms this
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hierarchy of auditory processing from
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simply detecting sound to fully
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comprehending the meaning. Each level is
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necessary for us to understand what is
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going on, what we're hearing.
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Aometric testing evaluates the hearing
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ability and auditory processing by
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examining the different levels of
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auditory perception that we just talked
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about. Each of these levels plays a
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specific role in assessing hearing
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function.
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Detection is the most fundamental level
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tested
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in in audiometry overall using pure tone
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audiometry to determine the quietest
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sound a person can hear at the various
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aometric
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frequencies. The patient responds
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whenever they hear sound and establish
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their threshold. So down here this is
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where the aiogram is. It's one of our
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most basic tools as
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aologists. The next level up is
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discrimination. Uh this testing would
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assess the ability to distinguish
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between different
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sounds. So this might be where you're
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presented two different sounds and asked
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if they're the same or different. So it
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could be like two different phone names.
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It could be two different words.
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And you would essentially try and bring
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them as close as possible to find the
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just noticeable difference. So this
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would be that point at
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which if you go below this
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point you can't tell the difference. So
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for example you are not going to be able
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to tell the difference between a th00and
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hertz tone and a 101 hertz tone. But
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around 1,03 hertz you can start telling
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those sorts of
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differences. The next layer up is
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identification. So this would involve
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recognizing and naming the sound. So
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speech aometry for example just repeat
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back the word requires them to recognize
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the word.
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Um this could also be
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uh this would this really helps to
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determine the clarity of hearing and the
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ability to recognize and identify speech
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sounds
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accurately. At the top we have
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comprehension. Now this is not typically
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used in psycho acoustics but it is used
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in aometric testing. It evaluates the
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ability to understand and make sense of
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the sounds. It is assessed through more
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complex tasks such as spoken sentences
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or following verbal instructions.
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It could also be trying to determine
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someone's speech and noise
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uh threshold using a test such as the
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quicksen which so this would really be
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assessing the practical ability to
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comprehend speech in everyday listening
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situations. Each level of testing
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provides valuable information for us to
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be able to assess how the patient is
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actually
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um processing sounds and how it's going
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through their head. And so these will
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help us to diagnose uh impairments in
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the auditory system and determine the
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appropriate interventions.
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So psycho acoustics uh the study of
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perceiving sound
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has various important applications in
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multiple fields. So obviously I'm going
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to start off with aiology because that's
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why you're here in this program.
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uh these psycho acoustic
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um testing is going to be used to
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diagnose and treat uh impairments to the
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auditory system. So understanding how
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sounds are perceived helps aiologists
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develop better hearing tests and decide
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which hearing aids are going to be more
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effective for individual
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patients. For audio engineering, they
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apply psycho acoustic principles to
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create high quality sound recordings and
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playback systems. This includes
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optimizing sound for different
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environments and improving the clarity
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and fidelity of
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audio. Psychologists are going to use it
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to see how the brain processes auditory
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information and can provide insights
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into human cognition and behavior and
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inform treatments for auditory
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processing disorders. Though aiologists
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can engage in those sorts of treatments
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with auditory processing
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disorder in speech synthesis, psycho
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acoustics is used to create artificial
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speech that sounds natural. This
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technology is essential for applications
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such as virtual assistants like Siri or
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uh text to speech systems and
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communication
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aids. Telephone and stereo
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[Music]
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designers of stereo systems use psycho
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acoustics to enhance sound qualities and
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ensure that speech and music are
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transmitted clearly and accurately. And
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this involves optimizing the frequency
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response, reducing noise and reducing
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distortion. Hearing a design uh
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obviously has a lot of psycho acoustics
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involved with it because we want to
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understand how different sounds are
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perceived by individuals with hearing
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loss. So we can create devices that
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amplify the sounds in a way that's
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effective and comfortable and hopefully
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natural. Uh a lot of times people won't
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wear their hearing aids because it just
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sounds too weird. So if
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we can use psycho acoustic principles to
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design hearing aids to improve or make
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it sound more natural that can also
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help. And then basic science now when I
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say basic science that means people who
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do science for science's sake. So
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psychoacusticians uh do research to
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expand our knowledge of auditory
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perception and the functioning of the
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auditory system. This fundamental
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research lays groundwork for
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advancements in all of the applied
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fields mentioned
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above. Audibility refers to the range of
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sounds that can be heard by the human
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ear. Several key concepts and historical
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contributions have shaped our
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understanding of audibility.
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Fletcher and his colleagues Wel and
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Fowler made significant contributions to
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the study of hearing and audibility in
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the early 20th century. The research
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helped establish the basic principles of
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how we perceive sound and the thresholds
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of hearing.
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So if we look down here
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at this graph along the x- axis you can
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see the frequency along the y-axis you
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can see the RMS or the root mean square
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pressure change in dimes per square
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centimeter. So this
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uh is going to have two different
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u curves on it. The bottom curve is
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what's known as the threshold of
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hearing. The threshold of hearing is the
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quietest sound that can be detected by
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the average human ear. It's typically
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measured at different frequencies to
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create an aiogram showing the
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sensitivity of hearing across the
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audible spectrum. The threshold of
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hearing can vary among individuals and
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can be affected by factors such as age
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and hearing health. But this particular
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line here is the normative values. So
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this is what would be later set as 0
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dBHL. On the other side of the scale,
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you have this curve up here, which is
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maximal
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audibility. So it refers to the range of
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frequencies and sound levels that can be
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heard most clearly by the human ear.
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And so you can see that between
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about 2,000 and 5,000 hertz it has the
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widest dynamic range there. Um once you
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get up past this maximum audibility it
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is going to
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be this point of the threshold of
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feeling. So this is going to be the also
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known as the point of discomfort. So
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this is where the sound has become
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uncomfortably loud for the listener.
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Typically it's around 120 to 140 dB in
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people with normal aometric
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thresholds.
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However, it's going to vary based on the
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frequency of the sound and if someone
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has hearing loss that's going to have
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even greater
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effect. So Fowler and Wgle found what
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they called a dynamic range. So this is
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the number of logarithmic steps between
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the minimum and the
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maximum of liability. So between the
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normal threshold and the threshold of of
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feeling. They then determined the
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patient's threshold based on the root
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mean square
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pressure of the sound.
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They then took that and divided that by
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then the dynamic range for that
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particular frequency and calculated it
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as a percentage of normal hearing as you
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can see here. So basically they
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took this dynamic range they found this
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threshold they took this divided by that
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and said
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okay it is this much percentage of
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hearing and that's probably why you can
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hear people say oh I have this much
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percent of
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hearing
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Fletcher built on this and changed it
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from being
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uh percentage of normal hearing to the
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amount of sensation loss. So 100 up here
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would become zero and then these would
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become sensation loss as you go further
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and that's where the aiogram came from.
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Now at the time decibb was not something
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that had been thought of. It's not
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something that had been uh developed
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yet, but that later changed. And this is
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really where the aiogram comes
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from. So here we have a chart that shows
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the uh reference threshold levels of
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dBSPL for each one of the frequencies.
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So this is where we're going from SPL to
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dBHL. And so these
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frequencies, you don't have to have them
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memorized. You don't have to
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uh know these super well. Just know that
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the middle frequencies from, you know,
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around a thousand
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to two or 3,000 or so are going to be
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the most closely
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uh consistent with these uh DBSPL scale.
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But this is more for your uh
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reference. Uh that's it for this lecture
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and
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uh feel free to move on with the other
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psycho acoustic lectures at your own
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pace.
