Subcortical auditory structures encode sound intensity linearly while cortex compresses it.

Evidence

By contrast, in the previous study by Röhl and Uppenkamp ( 2012 ) no significant relationship between the BOLD signal strength and categorical loudness was found at the level of the IC or MGB. One interpretation in that study was that at the level of the IC, “neural activation might be more a reflection of physical sound intensity”. The current results are different, given that activity in subcortical regions was—albeit only slightly—more closely related to individual loudness as compared to sound pressure. However, the interpretation of BOLD fMRI results from these regions appears difficult, given the poor signal-to-noise ratio caused by the small size of the structures and their susceptibility to cardiac-related, pulsatile motion effects. Taking measures to improve the signal quality in subcortical regions, such as cardiac gated image acquisition (Guimaraes et al. 1998 ), is therefore strongly advised for future investigations. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2645

Categorization

• QUESTION: Is the subcortical-vs-cortical encoding difference real, or an fMRI SNR artifact? The cardiac gating fix is worth researching further.
• corroborated: 2 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 2645
• XREF: connects to: Single auditory neurons encode only a narrow 20-40 dB dynamic range — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 785; Distinct brain regions process sound intensity versus perceived loudness differently — Dijk, Pim van, Physiology, Psychoacoustics and…, 2607; Auditory cortex activation linearly reflects perceived loudness rather than physical intensity — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610 (+4 more)

Broader Connections

• Hearing integrates sound intensity over a fixed 200 ms window #expands (0.72)