Human Senses: hearing Week 13 Dr. Belal Gharaibeh 1 Hearing the - - PowerPoint PPT Presentation

Human Senses: hearing

Week 13

• Dr. Belal Gharaibeh

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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.

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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.

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The Ear

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The Ear

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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

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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

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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.

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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.

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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.

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Noise Induced Hearing Loss

• Sufficient sound intensity and duration result

in

• temporary hearing loss
• permanent hearing loss.

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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

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Noise Induced Hearing Loss

• If exposed to sound levels of less than 100 dB,
• ften 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)

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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

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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)

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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

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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.

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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.

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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.

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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

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Hearing Protecting Devices

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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)

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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.

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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

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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”.

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• 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.

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Chapter 4: smelling, tasting, and touching

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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
• dors (feet)
• External:

– Atmospheric contaminants

• Odorless and colorless (CO2, CO)
• They can be strong and easily detectible (sulfur compounds).

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Psychological and Physiological reaction to Smell

• Smells can affect well being by producing physiological and

psychological reactions such as:

– Nausea – Vomiting – Headache – Shallow breathing – Coughing – Upset sleep, stomach, appetite – Irritate eyes, nose, throat – Disturbance – Annoyance – Depression – Disrupt ‘comfort’ and enjoyment of food

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Engineering use of smelling sense

• Addition of methyl mercaptan to render natural gas

detectable by smell.

• Adding pyridine to argon, to have odor.
• Smell can penetrate vast complex areas like

underground mines, where a “stench” bad smell can signal an emergency.

• Spraying sweetener in the ambient air. If the wearer of

a respiratory mask or hood smells the sweetener, the seal on the mask is proven inadequate.

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Factors affecting ability to smell

• Olfactory sense easily adapts and quit

different from one person to another.

• Smells changes with concentration and time
• Smoking and aging affects one’s ability to

smell.

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Tasting – The Gustation Sense

• Taste stimuli:

– Sour – Salty – Bitter – Sweet

• The sense of tasting is poorly understood.
• The sense of taste interacts strongly with

sensation of smell, that’s why food becomes tasteless if a cold causes a temporary loss of the sense of smell.

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The Tactile Sense- The Cutaneous Senses

• The sensory capability in skin is called the

cutaneous (from cutis, Latin for skin)

• Tactile sense – sense of touch. It is sensitive

to: –Pressure –Pain –Temperature

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Some design-relevant characteristics(1)

• Can only cope with limited complexity of

information

• As for auditory, sense is omni-directional
• Reaction times to stimuli can be very high
• Can sense a variety of tactile features (e.g. edges,

contours, textures)

• Touch sensitivity measured by two point threshold:

– smallest distance between two pressure points – Touch sensitivity varies across the body and between individuals and environments

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Some design-relevant characteristics(2)

• Tactile discrimination relatively resilient to the

effects of age

• Evidence that Active touch (e.g. fingers

moving across an object) more effective than passive touch (e.g. object being moved across fingers)

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Applications of ‘touch’ in Human Factors

Traditionally, sense of touch has been studied for the following applications:

• aids for those with visual impairments (Braille,

tactile maps/graphs, etc.)

• characteristics of different ‘basic’ controls
• Increasing research on Haptic, e.g.

– Virtual Reality (surgeon training)….. – racing video games

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