SSD Flashcards
Define SSD
A term used to describe individuals with an aidable hearing loss in their better ear and no usable hearing and poor word recognition in the poorer ear.
Define spatial hearing
“A listener’s ability to receive, process, and utilize directionally specific auditory signals from the two ears, working independently and in concert” (Murphy et al., 2011)
Describe spatial hearing for normal hearing individuals
Individuals with normal hearing use interaural time differences (ITDs), interaural level differences (ILDs), and spectral differences as part of spatial hearing. The person utilizes all these cues to determine where the signal is coming from.
What are ITDs?
They are evaluated for low frequency sounds (<1500 Hz)
They compare the time difference of sounds between the two ears.
The sound will arrive first to the ear on the side which it is presented
Envelope of the signal.
What are ILDs?
They are evaluated for higher frequency sounds (>1500 Hz).
They compare the level difference of sounds between the two ears
The sound will be louder in the ear on side which it is presented. This is affected by the head shadow effect.
What is the head shadow effect?
A phenomenon that describes the degradation of a speech signal (particularly the high frequency sounds) by up to 15 dB as they travel from one ear to the other in space. (Staab, 1988)
What frequencies are affected by the head shadow effect? Low frequencies or high frequencies?
High frequency sounds because they have shorter wavelengths
What happens in the presence of noise for normal hearing individuals?
They are able to spatially separate the signal and the noise resulting in binaural unmasking and a louder signal relative to the noise. (Murphy et al., 2011)
What happens with individuals with SSD in terms of spatial hearing?
The individual is unable to use the head shadow effect for localization which is a safety concern.
Speech understanding, especially in the presence of noise, declines due to the inability to take advantage of binaural unmasking (binaural squelch) in the way that normal hearing individuals are able to (Murphy et al., 2011). This binaural squelch, in addition to binaural summation requires two ears.
Define auditory scene analysis (ASA)
“The ability to disentangle the mixture of sound input, integrating sensory inputs that belong together and segregating those inputs that originate from different sources”. (Sussman, 2005)
In other words, it is how we organize the incoming sounds into various streams through integration and segregation.
Why is ASA important?
It allows the listener to identify the sound and either integrate the signal or segregate it into what is important.
Integration is important for music perception as it allows for harmony in a band.
Segregation is important for speech understanding as it involves picking one sound among a variety of inputs.
Why is speech understanding a difficult task?
It requires temporal and spectral cues
How do normal hearing individuals complete ASA?
Inherently and without any difficulty.
They are able to classify input into different streams and integrate or segregate these streams.
What happens with ASA for patients with hearing loss?
As the level of the background noise increases, speech recognition performance deteriorates and a breakdown occurs in separating and integrating the sources of input.
What happens with ASA for patients with SSD?
Binaural unmasking (squelch) does not occur and the patient is unable to complete auditory scene analysis because of their inability to accurately disentangle the sound input.
Why do patients with SSD have poor ASA?
Poor temporal and spectral resolution in these patients may result in the dysfunction in ASA. (Edwards, 2007)
Why are temporal and spectral resolution important?
They affect the envelope and pitch cues.
