The Auditory System

Question 1

What ist he stimuli for the auditory system?

Answer 1

Vibrating air molecules.

Question 2

What does the Pinna do?

Answer 2

Collects sound.

Question 3

What are the parts of the auditory system?

Answer 3

Pinna (collects sound); ear canal; ear drum; vibrates tiny bones which press on membrane, moving tiny hair cells (the receptors – frequency specific); transmission to brain

Question 4

What is sound comprised of?

Answer 4

Sound has frequency (pitch) and amplitude (loudness); usually a combination of frequencies

Question 5

What is the psychological correlation of frequency?

Answer 5

Pitch

Question 6

What is the range of sound intensity for human hearing (dB)

Answer 6

0 to 140 dB (note that after 140 vibrotactile interpretation, anything over 100 dB can result in permanent damage). Anything below 20dB the ear rapidly loses its ability to detect frequency changes.

120 dB – jet engine; 100 dB – manufacturing; 60 dB, conversation; 20 dB, whisper

Question 7

What is the psychological correlation of dB to sound intensity?

Answer 7

Loudness

Question 8

How is dB measured?

Answer 8

dB (a ratio) 20 log (P1/P2)

P1 (sound of interest, sound pressure); P2 (background/baseline)

Question 9

How is loudness related to dB?

Answer 9

Loudness (what you perceive) related to dB (actual stimuli value)

Question 10

What is loudness related to?

Answer 10

dB and frequency

Question 11

When does loudness double?

Answer 11

Doubles with each 10 dB increase

Question 12

What is threshold?

Answer 12

Threshold – minimum you can hear

Question 13

What is masking?

Answer 13

Masking – sounds can “hide” other sounds (e.g., similar frequencies; <15 dB difference)

Question 14

What is equal loudness for dB and frequency?

Answer 14

“equal loudness” – lower dB, higher frequency = to lower frequency, higher dB

Question 15

What are the three aspects of safety and hearing?

Answer 15

1. Noise can cause damage to hair cells – frequency dependent
2. Damage depends on intensity, frequency, and duration of exposure
3. Effect of continuous exposure can be cumulative

Question 16

What are two types of thresholds?

Answer 16

1. Temporary Threshold Shift (TTS)
2. Permanent Threshold shift (PTS)

Question 17

What are design implications related to safety?

Answer 17

• Equipment, tool selection
• Shielding (mufflers, equipment shields)
• Leave the area (e.g., reduce time of exposure)
• Hearing protection (compliance, comfort, properly worn/fit)

Question 18

What is temporary threshold shift (TTS)?

Answer 18

Loss in ability to hear after exposure to loud noise (shift in threshold dB 2 minutes after exposure ends); declines over time. E.g., TTS for 100 dB exposure for 100 minutes is 60 dB.

Repeated exposure to TTS producing sounds can cause PTS

Question 19

What is is permanent threshold shift (PTS)?

Answer 19

• Permanent loss of hearing.
• Time weighted average -> remediation required
• About 75 dBA (dB weighted by frequencies) or less, ok; after that, different limits based on time of exposure

Question 20

What are 5 aspects of the design of auditory displays (alarms, “earcons”)?

Answer 20

1. Not directional (you don’t have to look at them) but don’t persist in time (working memory limitations) 5 dB above background to be heard
2. Keep below 85, 90dB
3. Consider “rise time” in amplitude to avoid a startling effect
4. Make different signals easily discriminable, but not too many of them (pitch, rhythm, timbre)
5. Non-verbal audio messages that are used in the computer/user interface to provide information to the user about some computer object, operation or interaction“ (Blattner, 1989)