Auditory cortex activation linearly reflects perceived loudness rather than physical intensity

Evidence

Specifically, while changes in sound pressure level were reflected by a quadratic growth of activation magnitude, especially in cortical areas, the relation between activation and categorical loudness can be described as predominantly linear in all investigated auditory regions. This finding, in conjunction with the similarities between the growth of categorical loudness (Fig. 1 ) and BOLD signal changes (Fig. 2b ) with sound intensity, lends support to previous auditory fMRI studies suggesting that neural activation in AC might be more a direct linear reflection of perceived loudness rather than of physical sound pressure level (Langers et al. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610

Specifically, while changes in sound pressure level were reflected by a quadratic growth of activation magnitude, especially in cortical areas, the relation between activation and categorical loudness can be described as predominantly linear in all investigated auditory regions. This finding, in conjunction with the similarities between the growth of categorical loudness (Fig. 1 ) and BOLD signal changes (Fig. 2b ) with sound intensity, lends support to previous auditory fMRI studies suggesting that neural activation in AC might be more a direct linear reflection of perceived loudness rather than of physical sound pressure level (Langers et al. 2007 ; Röhl and Uppenkamp 2012 ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 2645

As expected from the strong relationship between sound intensity and loudness, a very similar pattern across auditory regions was found for the relationship between BOLD responses and individual loudness. Nonetheless, it was possible to identify distinct differences with regard to the representation of sensory stimulation and perception in the human auditory system. Specifically, while changes in sound pressure level were reflected by a quadratic growth of activation magnitude, especially in cortical areas, the relation between activation and categorical loudness can be described as predominantly linear in all investigated auditory regions. … 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. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2646

Our findings support the notion that neural activation in auditory cortex as well as in certain stages of the ascending auditory pathway is more a direct linear reflection of perceived loudness rather than of physical sound intensity. There are, however, systematic differences between the investigated auditory regions in terms of the strength of this relationship and the degree of lateralization. We therefore suggest that functional differentiation, both between cortical and subcortical regions as well as between regions of auditory cortex, is an important issue to consider in the pursuit of a complete and comprehensive understanding of the physiological correlates of loudness perception. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2649

Some auditory functional magnetic resonance imaging (fMRI) studies suggest that neural activation, at least in auditory cortex (AC), might be more a representation of perceived loudness rather than of physical sound pressure level (Hall et al. 2001 ; Langers et al. 2007 ; Röhl and Uppenkamp 2012 ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 2612

Some auditory functional magnetic resonance imaging (fMRI) studies suggest that neural activation, at least in auditory cortex (AC), might be more a representation of perceived loudness rather than of physical sound pressure level (Hall et al. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610

As expected from the strong relationship between sound intensity and loudness, a very similar pattern across auditory regions was found for the relationship between BOLD responses and individual loudness. Nonetheless, it was possible to identify distinct differences with regard to the representation of sensory stimulation and perception in the human auditory system. Specifically, while changes in sound pressure level were reflected by a quadratic growth of activation magnitude, especially in cortical areas, the relation between activation and categorical loudness can be described as predominantly linear in all investigated auditory regions. This finding, in conjunction with the similarities between the growth of categorical loudness (Fig. 1 ) and BOLD signal changes (Fig. 2b ) with sound intensity, lends support to previous auditory fMRI studies suggesting that neural activation in AC might be more a direct linear reflection of perceived loudness rather than of physical sound pressure level (Langers et al. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2638

As expected from the strong relationship between sound intensity and loudness, a very similar pattern across auditory regions was found for the relationship between BOLD responses and individual loudness. Nonetheless, it was possible to identify distinct differences with regard to the representation of sensory stimulation and perception in the human auditory system. Specifically, while changes in sound pressure level were reflected by a quadratic growth of activation magnitude, especially in cortical areas, the relation between activation and categorical loudness can be described as predominantly linear in all investigated auditory regions. This finding, in conjunction with the similarities between the growth of categorical loudness (Fig. 1 ) and BOLD signal changes (Fig. 2b ) with sound intensity, lends support to previous auditory fMRI studies suggesting that neural activation in AC might be more a direct linear reflection of perceived loudness rather than of physical sound pressure level (Langers et al. 2007 ; Röhl and Uppenkamp 2012 ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 2646

Categorization

• DEEPTHINKING: Decoupling physical intensity from neural response via the loudness transform — BOLD magnitude is quadratic in dB SPL but linear in loudness — directly implicates the cochlear/perceptual transform in cortical coding.
• QUESTION: Worth chasing: does the loudness transform (compressive cochlear I/O function) explain the quadratic-vs-linear distinction, and at what stage does it arise?
• XREF: Connects to the soundscape/loudness-perception theme, and to hearing-impaired loudness recruitment as a disruptive case. — connects to: The phon unit measures perceived loudness, not physical sound level; Distinct brain regions process sound intensity versus perceived loudness differently — Dijk, Pim van, Physiology, Psychoacoustics and…, 2607; Loudness perception requires a tenfold intensity increase to double — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 652 (+9 more)
• DEFINE: Distinguishes the quadratic intensity-activation versus linear loudness-activation relationship explicitly.
• corroborated: 14 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610; Dijk, Pim van, Physiology, Psychoacoustics and…, 2645; Dijk, Pim van, Physiology, Psychoacoustics and…, 2646 (+3 more)

Broader Connections

• Perceived loudness does not map one-to-one onto acoustic amplitude #corroborates (0.95) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 616
• Subcortical auditory structures encode sound intensity linearly while cortex compresses it. #qualifies (0.85) — Dijk, Pim van, Physiology, Psychoacoustics and…, 2645
• Loudness depends on more than physical sound intensity alone #corroborates (0.85) — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610
• Perceived loudness and physical sound intensity follow different, non-intuitive mathematical scales #corroborates (0.80) — George Michelsen Foy, Zero Decibels, 53
• Recruitment patients could disambiguate loudness from intensity encoding in fMRI #responds-to (0.78)
• Loudness perception requires a tenfold intensity increase to double #expands (0.75) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 652
• Primary auditory cortex shows the strongest intensity encoding along the auditory pathway #corroborates (0.75) — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610
• Perceived loudness grows nearly linearly with intensity until steepening near 90 dB SPL #contradicts (0.75) — Dijk, Pim van, Physiology, Psychoacoustics and…, 2626
• Spreading a sound’s energy across more critical bands increases perceived loudness without raising intensity #expands (0.72) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 665
• Loudness perception involves central mechanisms beyond cochlear vibration #expands (0.70)