Hearing Assistive Technologies in the Classroom

The issue

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When listening is the student’s primary mode for learning, the ability to hear and understand speech is critical for ensuring successful learning.  As a result, a deaf or hard-of-hearing student’s hearing loss (HL), as well as the classroom environment can significantly disrupt access to the teacher’s voice, and thus, the student’s ability to learn.

Hearing Assistive Technologies (HAT) can greatly improve a student’s ability to hear the instructor.  HAT improves listening by addressing the negative effects of HL, classroom environment, and the limitations of hearing aids (HAs) and/or cochlear implants (CIs) alone.

What we know

The following national guidelines promote favorable listening environments to foster children’s education and learning in the classroom:

  • Background noise levels in unoccupied classrooms should be <35dBA,
  • Reverberation time (time for reflected sounds to become inaudible) in unoccupied classrooms should be <0.4 seconds,
  • Overall occupied classroom sound levels should be <70dBA, and
  • Signal-to-noise ratio (SNR) should be >+15dB, meaning the teacher’s voice must be 15 dB louder than the noise level when it arrives at the student’s ears.

However, these guidelines are essentially unenforceable, and typically are not met.  This issue puts students with HL at a severe disadvantage in the classroom – obtaining significantly poorer scores on speech recognition tasks compared to students with normal hearing.

HAT solutions are the most effective tools to overcome these barriers.  HAT may be obtained for the student with a hearing loss by the school system through a service or educational plan.  Although in some cases the student would obtain the technology independently.

There are three HAT configurations used to improve the SNR in the classroom – Classroom Audio Distribution Systems (CADS), induction loop systems, and personal systems.  Each HAT type aims to collect the desired signal (e.g., teacher’s voice) from a microphone or direct audio feed (e.g., Smart Board, TV, or computer) and transmit that signal wirelessly to the listener at a volume that is well above the noise level. The wireless transmission method is either traditional frequency modulation (FM), digital radio frequency (RF), infrared, or magnetic induction signal.

CADS, which generally use infrared transmission (some use FM/RF), can provide between 5-10dB SNR benefit to all students by amplifying and distributing the desired signal evenly throughout the classroom via strategically placed loudspeaker(s).  One drawback to this technology is that the signal projected by the CADS raises the overall classroom noise levels.  Once the dB level in the classroom exceeds 70dBA, speech recognition for all students declines.  The use of CADS is generally ideal when the teaching style is a lecture format to improve access to the teacher’s voice for all students in the classroom, including those without HAs or CIs.

Induction loop systems deliver the desired signal directly to HAs, CIs, or other hearing devices equipped with telecoil features via a magnetic induction generated by wires installed in the perimeter of the classroom.  The looped output does not raise the overall noise levels and also removes the effect that distance has on the signal.  Because the signal is delivered directly into the student’s ears, the signal is not subject to deterioration due to distance or background noise.

Personal systems can deliver ~15-25 dB of SNR benefit, providing superior signal quality compared to CADS.  They are ideal for individuals who use HAs, CIs, desktop speakers, or other hearing devices.  In most cases, the personal systems can be equipped with receivers that are compatible with a FM/RF transmitter.  Unlike CADS and induction loops, personal systems can travel with the student between classes and to extracurricular activities.  With the signal being delivered to the student’s ear(s), the output does not raise the overall noise levels and also removes the effects of distance.

What we don’t know

On an individual basis, it is known that a thorough assessment of each student’s HL and listening abilities is needed to determine the most appropriate accommodation.  However, it is unclear how to best accommodate multiple students with diverse levels of HL within the same classroom. Another unknown is the long-term needs of individual students.  The most appropriate accommodations can change year by year based on the student’s progress and new classroom environments.  An issue that needs further research is how to best monitor the performance and effectiveness of HAT for each student.

Implications

HAT solutions for students with HL can help mitigate delays in academic progress, literacy, and incidental learning.  It is critical for the education team to identify the appropriate HAT type based on each individual student and classroom environment in order to overcome the effects of hearing deficits.

Posted on Jan 11, 2016 by
Zachary S. La Fratta
District of Columbia Public Schools
zachary.lafratta {at} dc.gov

Further reading