Animals and ICE: meaning, origin, and diversity.

Area of Science:

• Acoustics
• Auditory Neuroscience
• Bioacoustics

Background:

• Internally coupled ears (ICE) are found in over half of terrestrial vertebrates and many insects, featuring an air-filled cavity connecting the eardrums.
• ICE significantly modifies auditory signals, creating distinct low- and high-frequency regimes governed by the fundamental tympanic frequency.

Discussion:

• The low-frequency regime exhibits an internal time difference (iTD) 2-5 times greater than the external interaural time difference (ITD), with a plateau where iTD/ITD remains constant.
• The high-frequency regime shows an amplified internal level difference (iLD) compared to the external interaural level difference (ILD).
• A key debate centers on the neural exploitation of these ICE-generated auditory cues for sound source localization.

Key Insights:

• ICE provides amplified auditory cues for sound localization, crucial for many vertebrate species.
• The system demonstrates frequency-dependent amplification of both temporal and amplitude differences between the ears.
• Understanding the neural basis of ICE function is critical for explaining auditory perception in diverse animals.

Outlook:

• Further research into the neurobiological mechanisms underlying ICE processing is needed.
• Investigating the evolutionary advantages and diversity of ICE systems across species will provide deeper insights.
• This special issue highlights the interdisciplinary approach required to fully understand internally coupled ears.