Module 12: CROS and BICROS

Question 1

List some hearing problems associated with unilateral hearing loss (3)

Answer 1

-Speech & communication issues when sound is arriving to the poor ear
-Background noise and group situations–increased challenges
-Sound localization challenges

Question 2

What is a CROS device overcoming?

Answer 2

The head shadow effect

Question 3

What is the head shadow effect?

Answer 3

Frequency-specific decrease in SPL when sound is presented to the contralateral side of the skull (greatest decrease in the high frequencies, above 1500 Hz)

Question 4

What does CROS stand for?

Answer 4

Contralateral Routing of Signals

Question 5

What are CROS devices?

Answer 5

-CROS devices appear to look like conventional hearing instruments, but they are only transmitting sound to be delivered to the better ear to a receiver device
-Communicate though wireless transmission
-Select manufacturers have solutions

Question 6

What kind of patient is a good candidate for CROS devices?

Answer 6

-Normal or near normal hearing in one ear
-Other ear is “unaidable”:
·Not enough residual hearing
·Extremely poor WRS
·Binaural interference
·Medical condition preventing the use of an aid

Question 7

For CROS devices, mic transmitter goes on the __ side, while the amplifier and receiver go on the __ side (good/bad)

Answer 7

poor, good

Question 8

What kind of tip/earmold should go on the normal ear in a CROS device?

Answer 8

Open

Question 9

Benefits and Limitations of CROS

Answer 9

-Benefits: easier to hear speech originating from the poor side, most helpful when noise is on good side and when speech is on poor side
-Limitations: least helpful when noise is on poor side and speech is on good side, not helpful with localization

Question 10

What is BiCROS?

Answer 10

Bilateral Contralateral Routing of Signals

Question 11

What kind of patient is a good candidate for BiCROS?

Answer 11

Bilateral hearing loss with one unaidable ear

Question 12

For BiCROS devices, the hearing aid is on the ___ ear and there’s an additional mic on the ___ ear (better/unaidable)

Answer 12

better, unaidable

Question 13

For BiCROS devices, both mics send signal to one ___ on the ___ ear

Answer 13

receiver, better

Question 14

CROS/BiCROS arrangements

Answer 14

-Wire along neck (ancient technology)
-Wireless transmission (commonly used)
·Transmitter-mic on poor side and receiver on good side
·Radio frequency transmission
-Transcranial CROS (not commonly used)
·One normal ear & absolutely no residual hearing in other ear
·One powerful HA on ‘dead’ ear to provide crossover hearing to normal ear via bone conduction

Question 15

For CROS fittings, the target is ___

Answer 15

REUR

Question 16

For BiCROS fittings, targets for better ear are the __ targets when the test signal is delivered to the poorer side

Answer 16

Same (DSL, NAL-NL2)

Question 17

What is the purpose of CROS and BiCROS verification?

Answer 17

To measure the effectiveness in overcoming the head shadow effect by measuring the response in the better ear receiving input from the transmitter side

Question 18

Key rules for CROS and BiCROS verification

Answer 18

-The probe tube/mic is always in the better ear
-Coupling to the “better” ear is key (we need to ensure that with CROS systems, the ear is not occluded)
-The system being used requires a way to separate the probe mic system from the reference mic

Question 19

What is the probe mic responsible for?

Answer 19

Measuring response of sound delivered to the microphone (better ear)

Question 20

What is the reference mic responsible for?

Answer 20

Making sure the sound you’re playing is the sound being delivered to the ear

Question 21

What are the steps for verifying CROS devices with an insertion gain approach?

Answer 21

-Have patient sit at a 45 or 90 degree angle relative to speaker
-Probe mic and reference mic goes on the better ear to start to measure the SPL in the unaided response
-Next, we have the patient switch so that the poorer ear is now facing the speaker. The reference mic is now on the poorer ear with the probe mic still on the better ear. This is done so that we can see if we overcame the head shadow effect

Question 22

Insertion gain approach advantages and disadvantages

Answer 22

-Advantages: easy to run and perform with verifit
-Disadvantages: pink noise isn’t real world (not conversational speech)

Question 23

T/F: speech mapping (along with REIG) can be used as a verification measure for CROS and BiCROS

Answer 23

True: this will also confirm if we are overcoming the head shadow effect

Question 24

Speech mapping advantages and disadvantages

Answer 24

-Advantages: can verify how much gain they’re getting
-Disadvantages: NONE

Question 25

CROS verification with REM steps

Answer 25

-Probe mic in good ear and reference mic on side of louspeaker location (Verifit: probe modules with reference mic on each ear with probe mic only in good ear)
-Set Verifit to BTE and position speaker 45-90º to good ear: response is measured
-Position CROS transmitter on patient
-Set Verifit to CROS and position speaker at 45-90º to poor ear: response is measured with device turned off, then on
-We are verifying that we have overcome the head shadow effect

Question 26

BiCROS verification with REM steps

Answer 26

-Probe mic in better (aidable) ear & reference mic on side of loudspeaker location
-Verify the HA in the better ear using standard REM, as if verifying a monaural fit (REAR1). We’re matching targets. Verifit set to device configuration, and match targets accordingly
-Set Verifit to CROS
-Then verify the BiCROS system by positioning the speaker 45-90º to poor ear with the CROS transmitter: REAR2 should match REAR1 obtained with the HA alone
-We are verifying that we have overcome the head shadow effect, and that the hearing aid (also the CROS receiving device) is meeting targets

Question 27

CROS verification with speech tests

Answer 27

-Speech ~50 dB HL; noise ~45 dB (+5 S/N)
-Speech on poor side; noise on good side:
·Unaided: challenging
·Aided: should show some improvement

Question 28

Additional program considerations in BiCROS fittings

Answer 28

-HA only mode (no BiCROS) so that noise coming predominantly from the poor side is not routed to the better side
-CROS mode for situations where noise is on the side of the better ear and speech on the side of the unaidable ear

Question 29

Patient satisfaction with CROS or BiCROS devices is ___

Answer 29

Generally high (one study showed a satisfaction rate of over 70%)