Wk3b - Channels: Interactions and Psychophysics Flashcards
T/F: Electrodes have an independent effect on neurons
False - there is overlap
____ _____ results in significant Inferior Colliculus activity when 2 monopolar electrodes are stimulated at sub-threshold levels simultaneously
Channel Interaction
T/F: Having 2 electrodes active at the same time means the response is the sum of response 1 and response 2 (linear assumption)
False - because of this, it is difficult to generate the desired Spiral Ganglion stimulation with simultaneous stimulation
In present CI systems, electrodes are stimulated _____ (simultaneously/in trains of current pulses)
In trains of current pulses (meaning they are interleaved in time/non-simultaneous) which reduces channel interactions
What pulse parameters in CIs influence loudness perception?
Current Amplitude
Pulse Period
Positive Duration
What is the typical phase duration of a biphasic pulse train?
20-60 microseconds
What is a typical pulse rate?
1/T, typically 250-1000 Hz (on each channel)
What 2 terms did Ioan not want us to mix up?
Bipolar and biphasic
Why are biphasic pulses a critical safety feature?
Monophasic would result in a buildup of charge on the electrodes
- it is important to “sink” as much charge as was “sourced” to avoid corrosion and production of toxins through electrochemical reactions
- each pulse should be charge-balanced to reverse any local reactions
Why do we use biphasic pulses?
- to charge-balance pulses to reverse local reactions
- to increase chances of stimulating nearby SG neurons
Detection is equivalent to _____
Threshold
Discrimination is usually tested at _______ levels
Suprathreshold
Scaling has to do with categorization. What information does the patient use to categorize information?
Previous experience
What is the ACOUSTIC threshold limited by?
The minimal mechanical vibration that can be picked up by the hair cells and nerve via an active mechanical mechanism (or amplifier)
What 4 things does the electric threshold reflect? (I.e what 4 electrical and anatomical aspects will influence threshold?) (NOT current)
- the type of electrode used
- the electrode-tissue interface
- the distance b/w the electrode and the nerve
- the degree and pattern of the nerve survival
What is the electric threshold?
The minimal amount of current that can stimulate the AN
What two things were shown in the 70’s to influence electric threshold?
Phase duration and pulse rate
- the lowest thresholds were obtained with the longest phase duration and highest pulse rate
How does polarity affect electric threshold?
Monopolar has significantly lower thresholds compared to bipolar and especially tripolar
- also shown to be higher threshold variability b/w channels of bi- and tri-polar
Since CI electrodes do not stimulate independently, how does this change perception (compared to acoustic hearing)?
The electric fields add up - stimulating 2 separate electrodes simultaneously below threshold may cause a perception, whereas this would not be the case with acoustic hearing
When comparing thresholds for simultaneous stimulation, a larger negative shift (lower threshold) indicates a ____ (lower/higher) channel interaction
Higher
Which array had the highest channel interaction: mono, bi, or tri-polar?
Monopolar
Which had a greater threshold shift: simultaneous interaction or temporally adjacent presentation?
Simultaneous
When a time gap was introduced (symmetrically interleaved), there was a(n) _____ (increased/decreased) interaction compared to simultaneous presentation
Decreased
What are two ways to reduce channel interaction?
Choose bipolar or tripolar Temporal Offset (signal)
The dynamic range for electric hearing is defined as what?
The difference b/w the threshold current (T) and current producing max comfortable loudness (C)
What does the electric dynamic range depend on?
- electrode configuration
- anatomy
- simulation parameters
Which type has a smaller dynamic range: monopolar or bipolar?
Monopolar
Which type requires more current to reach threshold levels: monopolar or bipolar?
Bipolar
As pulse rates increase, thresholds _______ (decrease/increase) and dynamic range ______ (decreases/increases)
Decrease; Increases
How does electric dynamic range compare to acoustic dynamic range (according to the pulse train study)?
Electric: 10-30 dB (3x - 30x current)
Acoustic: 100-120 dB
Non-impaired acoustic hearing loudness doubles every ___ dB over a wide range
10 dB - almost linear
How does electric loudness growth increase compared to acoustic hearing?
Very rapid increase (small dynamic range)
- even more rapidly than hearing-impaired
Does the steep loudness growth mean CI patients have better intensity discrimination than NH listeners?
No - JNDs are similar (~0.5-2 dB)
How many steps of intensity increase can CI users generally hear? NH listeners?
7-30 steps (CI)
50-150 steps (NH)
What did the JND study conclude regarding those with limited number of steps?
Those with limited # of steps showed lower abs. thresholds, wider Dynamic Ranges, and poorer electrode speech ranking (associated with more gradual neural rate intensity functions and sparse dendritic survival)
What did the JND study conclude regarding those with higher # of steps?
Those with higher # of steps showed high abs thresholds, small dynamic ranges, and excellent electrode speech ranking - associated c/ steep neuro rate intensity functions and dense axonal survival
