Human Senses: hearing Week 13 Dr. Belal Gharaibeh 1
Hearing the Auditory Sense • Acoustics: is the science and technology of sound, including production, transmission and effects. • The acoustics design goal is to establish an environment that: – Transmit desired sounds reliably and pleasantly to the hearer – Is satisfactory to the human regarding noise – Minimize sound related annoyance and stress – Minimize disruptions of speech and – Prevent hearing loss. 2
The Ear • The ear has two functions: hearing and balance (equilibrium). • The sensory receptors for both of these are located in the inner ear. • In both cases the sensory receptors are hair cells that respond to mechanical stimulation, thus they are called mechano-receptors . 3
The Ear 4
The Ear 5
What is sound? • Sound: is any vibration that stimulates an auditory sensation: • Physical characteristics of sound: – Intensity or pressure (measured in dB) – Frequency (measured in Hz) – Duration 6
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What is sound? • Psychological characteristics of sound: – Tone is a single frequency oscillation – Pitch and frequency are synonymous – Loudness – Noise: unwanted sound – Understanding of speech 9
Human Response to Music • Making music has long accompanies activities. Eg. Singing during field work, marching. • Background and industrial music . – Background music is like acoustical wallpaper in shops, hotels, waiting rooms. To create a welcoming atmosphere, to relax customers, to reduce boredom and to cover other disturbing sounds. – Background music may produce a monotonous environment for those continuously exposed to it, while it may appear pleasant to the transient customer. • Industrial music – Music while work is opposite of background music. – It’s meant to break up monotony to generate mild excitement and an emotional impetus to demanding physical effort or labor in boring impersonal environment. 10
Human Response to Noise • Noise is defined as any unwanted, or unaccepted sound. • Noise is psychological and subjective . • Effects: Any sound may be annoying and thus conceived as noise. The threshold for noise annoyance varies, depending on the conditions, including the sensitivity and mental state of the individual. 11
Effects of Noise on Human Performance • A number of effects on the performance of tasks have been observed by (NASA): – As noise becomes more intense, we become more awaken and our performance of certain tasks can improve. – Beyond certain level of intensity, however task performance degrades: complex tasks, such as visual tracking; performance is diminished with increasing noise levels – Sudden, unexpected noise can produce a startle response that interrupts one’s concentration and physical performance of a task. • Psychological effects of noise includes anxiety, narrowed attention and other adverse effects that degrade task performance. 12
Noise Induced Hearing Loss • Sufficient sound intensity and duration result in • temporary hearing loss • permanent hearing loss. 13
Permanent threshold shift • Sound of high intensity and brief duration , such as that produced by a an explosion, can damage any or all the structures of the ear. • This type of trauma results in immediate, severe and permanent hearing loss, with permanent threshold shift (PTS). • If the nervous structure is damaged, the condition is not treatable with current knowledge and technology 14
Noise Induced Hearing Loss • If exposed to sound levels of less than 100 dB , often over a period of hours , that may initially cause only short term hearing loss, measured as a temporary threshold shift (TTS). • During quiet periods, hearing returns to its normal level. • Repeated exposure to sounds that cause TTSs may gradually bring about PTS , that is a Noise Induced hearing loss (NIHL) 15
Sounds that can Damage Hearing • 85 dBA of sound level is potentially hazardous. • It appears that sound below 75 dBA do not produce permanent hearing loss, even at about 4,000Hz 16
Physiological Effects of Sound 1. Hearing loss 2. Continuous exposure to noise is correlated with: – changes in the liver and kidneys – The production of gastro-intestinal ulcers. – Blood glucose levels change – Changes in cardiac muscles, fluctuations in blood pressure, and vaso-constriction have been reported with 70 dB SPL (Sound Pressure Level) 17
Shouting in Noise • People have a tendency to raise their voices to speak over noise and to return to normal when the noise subsides. This tendency is called the Lombard reflex , although it is probably not a reflex, but a conditioned response. • Speech communication has 5 components: – The message itself (clear and to the point) – The speaker (should speak slowly, use common and simple vocabulary, with limited number of terms) – The means of transmission (by a high fidelity system with no distortion in frequency, amplitude or time) – The environment (is affected by noise, wearing Hearing Protective Devices HPD) – The listener 18
Intelligibility • The ability to understand the meaning of the word, phrases, sentences, and entire speeches. – Psychological process that depends on acoustical conditions. – Direct face-to-face communication provides visual cues that enhance the intelligibility of speech. • For satisfactory communication at least 75% intelligibility is required. • Speech to noise ratio (S/N): intensity of speech signal relative to the level of ambient noise is the fundamental determinant of the intelligibility of speech. • S/N is not a ratio but a signed difference. 19
Speech to Noise “Ratio” • For a speech of 80 dBA in noise of 70 dBA, the S/N ratio is simply +10 dB. • With an S/N of +10 dBA normal people should understand at least 80% of spoken words. • As S/N falls, intelligibility drops to about 70% at 5 dB, to 50% at 0 dB and to 25% at -5dB. 20
Preventing NIHL • Avoid generation: by properly designing machine parts such as gears or bearings, reducing rotational velocities, changing the flow of air, or replacing a noisy apparatus with a quieter one. “Active countermeasures” • Impede transmission: from the source, i.e. mufflers on the exhaust side, encapsulate noise source, put sound absorbing surfaces and physically increase the distance. • Leave the area. 21
Hearing Protective Devices (HPD) • Part of Impeding the transmission is wearing HPD, either externally (sound isolating helmets or muffs, caps or plugs inserted into the ear canal. • The fit of the devise is important for effectiveness. • HRD are used in noisy environment, are mandated by OSHA (Occupational Safety and Health Administration) in the US, in the military, at auto races, etc. – Earplugs – Canal caps – Earmuffs – Helmets 22
Hearing Protecting Devices 23
Hearing Protective Devices (HPD) • Infrasound and Ultrasound Infrasound : – Below regular hearing limits, – though inaudible may still have vibration effects (exposed for 24 hours) on the human body. – Warning signs should be specifically designed to penetrate the device by using low frequencies (below 500Hz) 24
Passive HPDs • In the past HPD were “passive”, • conventional HPDs do not selectively pass speech versus noise at given frequencies, thus they do not improve S/N ratio. • Most passive devices reduce high frequency sound more than low frequency sound. 25
Active HPDs • New active HPDs incorporate electronics to improve communication and the reception of signals by the wearer. These devices can: • Provide increased protection during loud noises. • Reduce noise by destructive interference at selected frequency bands – Let pass or boost desired critical bands, especially those needed for speech 26
Reverberation • Reflection of sound from surfaces is called reverberation. • Reverberation time in a room is defined as the time it takes the SPL to decrease by 60dB after the source of sound is shut off. • A certain amount of reverberation is desirable because it makes the sound look natural and gives it enough time to reach the audience. • A “dead” room : room with little or no reverberation. • If reverberation time is more than 6 seconds intelligibility is cut in half, • a highly reverberate room is “live” or “hard”. 27
• The European Agency for Safety and Health at Work (EU-OSHA, 2006) recognizes that noise- related hearing loss is the most common professional disease seen in Europe, • it suggests greater focus should be placed on combined risk factors in workers exposed to high noise levels. 28
Chapter 4: smelling, tasting, and touching 29
Smelling- Olfactory Sense • Smells affect us – we describe smells by how they make us feel – Intoxicating (exciting) – Delightful (calming) – Revolting (disgusting) Smells can be internal or external • Internal – apocrine glands produce sweat, and other body odors (feet) • External: – Atmospheric contaminants • Odorless and colorless (CO 2 , CO) • They can be strong and easily detectible ( sulfur compounds). 30
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