Absolute Threshold
Level at which you can hear anything at all
- somewhat better when you test both ears together, rather than one at a time
- better (usually) in middle, speech sounds, 500-5000 ish
Intensity discrimination
- which interval was the intensity higher?
- equivalent to frequency discrimination - you can have a RIGHT or WRONG answer
(loudness is a correlate of pitch, there is no wrong answer, it can sound different to the person) - less selective of intensity on the extremes (has to be much louder to sound the same)
Weber’s Law
JND - Just noticeable difference
- for softer sounds the JND is higher, but once the sound is clearly audible (20-100dB) you can hear a smaller difference, at a pretty consistent rate between 1/2 and 1 dB change
- good ability to discriminate as the sound level goes up/JND goes down
- delta I/I = K -> JND over initial stimulus intensity = this remains constant despite variations in the I -> change in stimulus that will be JND is a constant ratio of the original stimulus
Ex. you can tell the difference between 10 and 11 inches - then you can tell the difference between 100 and 110 inches (10% in both) - but it flattens out because it is a logarithmic scale
How is intensity discrimination different for those with hearing loss?
- when amplified the brain is being trained to discriminate at that level - so they get better at it than they were before the aid
- auditory system is plastic, it can move around and the capacity to hear, discriminate between sounds, make judgements etc can get better or adapt
- can be improved through effort
What is loudness?
- corresponds to the subjective impression of the magnitude of a sound
- formal ef: the attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud
- subjective - (like pitch)
Loudness level: Phons
Phon: level of a 1000Hz tone in dB SPL that equals the loudness of a test sound
If X sounds the same loudness as 1000 Hz tone at 65 dB SPL, it has loudness of 65 phons
Equal Loudness Contours
Frequency Vs Sound Level dB SPL -> how many phons?
- relatively similar close to 1000 hz (duh) and gets more different the further you get away -> more so on the lower frequencies *GRAPH
- follow the line across (that is showing how many phons at 80 dB SPL 4000 Hz is hitting the 90 phone line
- can be equally intense (both playing at 50 dB) but one sounds louder because it is higher in phons
Loudness Summation
- graph opposite of band width -> flat to a point and then goes up with wider bandwidth
- the overall level (power) is the same for all the stimuli (low level wide bandwidth, or high level narrow bandwidth)
- as it is getting louder, the loudness system is paying attention to how many filters are engaged and as that increases, the loudness increases - as the bandwidth is getting wider you are engaging more auditory filters or critical bandwidths
SO really wide low level, sounds much louder than narrow at a higher level (activating more bands)
Loudness scaling: Sones
Sone: one sone is arbitrarily defined as the loudness of a 1000 Hz tone at 40 dB SPL
- ex. something is 2 sones if it sounds 2x as loud as a tone @ 1000 Hz 40 dB SPL
- perceived loudness (L) is a power function of physical intensity (I)
- Does it sound the same? Half as loud? Twice as loud?
- L=kl^.3 k is constant
Loudness scaling - magnitude estimation
- one way to measure sones
- sounds with various intensities are presented and the listener assigns a number to each according to its perceived loudness
- loudness grows very fast, doubles every 10 dB (ABOVE 40 dB)
- People are pretty good at this
Loudness recruitment
- abnormal growth of loudness associated with hearing loss
- limits dynamic range, because sounds near threshold sound soft, but more intense sounds as loud as in normal hearing
Temporary Threshold Shift
Hearing Level (HL): threshold specified relative to 0 dB HL, the average threshold at each frequency for young health listeners with "normal" hearing - temporary loss of hearing due to noise exposure (sometimes on purpose) goes back the next day to normal, usually only loss of like 10 dB in the experiments from class
Half-octave shift
TTS gets worse the longer the exposure
- hearing loss is above the frequency that you play, maximum loss in this case between 2000-4000 Hz, always above
- no loss under done, greatest loss at the half octave, ex: 4000 Hz tone, 4000-8000 is an octave - half that is 6000 Hz that will be the height of the loss
- don’t realize you are loosing your hearing because it is such high frequencies, and this isn’t where speech frequencies are so you don’t notice an impact until it becomes really big
- basal-ward, toward the base shift of maximal vibration as you increase sound intensity, loosing high frequencies that vibrate in the base
- HIT: high sound level that damages
- intensity goes up, shifts to the base
Long-term Consequence of TTS (Mice Example)
- Compound Action Potential: mice are much better at hearing high frequency sounds, they rebuild and replenish hair cells and their hearing goes back to normal by 2 weeks later and further maintained 8 weeks after that in testing
- hair cell response returns to normal
- synaptic loss does not recover
- neural amplitude loss (ABR wave 1) does not recover, same course as synaptic loss
- Ganglion (8th nerve) cell loss significantly delayed
Permanent hearing loss: ages 12-19 yrs
- noise induced threshold shift 15(+) dB higher at 3000 to 6000 than below 1000
- high frequency hearing loss *LESS than noise induced
- low frequency hearing loss *LESS than high
- low SES?
- HL gets worse as you age, what can you do to fix it, you get a hearing aid
Permanent Hearing Loss: Risk Factors
Non-modifiable: increasing age genetics male gender race Modifiable: voluntary exposure to loud sounds nonuse of hearing protection smoking lack of exercise poor diet tooth loss presence of diabetes & cardiovascular disease
