Representation of Instantaneous and Short-Term Loudness in the Human Cortex

Abstract

Acoustic signals pass through numerous transforms in the auditory system before perceptual attributes such as loudness and pitch are derived. However, relatively little is known as to exactly when these transformations happen, and where, cortically or sub-cortically, they occur. In an effort to examine this, we investigated the latencies and locations of cortical entrainment to two transforms predicted by a model of loudness perception for time-varying sounds: the transforms were instantaneous loudness and short-term loudness, where the latter is hypothesized to be derived from the former and therefore should occur later in time. Entrainment of cortical activity was estimated from electro- and magneto-encephalographic (EMEG) activity, recorded while healthy subjects listened to continuous speech. There was entrainment to instantaneous loudness bilaterally at 45, 100, and 165 ms, in Heschl's gyrus, dorsal lateral sulcus, and Heschl's gyrus, respectively. Entrainment to short-term loudness was found in both the dorsal lateral sulcus and superior temporal sulcus at 275 ms. These results suggest that short-term loudness is derived from instantaneous loudness, and that this derivation occurs after processing in sub-cortical structures.

Tonotopic representation of loudness in the human cortex

“…In a previous study (Thwaites et al., 2016), we investigated whether the time-varying instantaneous loudness or short-term loudness predicted by the loudness model of Glasberg and Moore (2002) is ‘tracked’ by cortical current, a phenomenon known as cortical entrainment. The extent of cortical entrainment was estimated from electro- and magneto-encephalographic (EMEG) measures of cortical current, recorded while normal-hearing participants listened to continuous speech.…”

“…It is the loudness derived from auditory filters with CFs spanning a 1-Cam range. To obtain the overall instantaneous loudness, the specific instantaneous loudness is summed for filters with CFs between 1.75 and 39.0 Cams (corresponding to 47.5 Hz and 15,108 Hz, respectively), as described by Glasberg and Moore (2002) and Thwaites et al. (2016).…”

“…The overall short-term loudness was calculated from the overall instantaneous loudness, as described by Glasberg and Moore (2002) and Thwaites et al. (2016), by taking a running average of the instantaneous loudness.…”

“…Glasberg and Moore (2002) proposed a model in which transformations and processes that are assumed to occur at relatively peripheral levels in the auditory system (i.e. the outer, middle, and inner ear) are used to construct a quantity called “instantaneous loudness” that is not available to conscious perception, although it appears to be represented in the brain (Thwaites et al., 2016). At later stages in the auditory system the neural representation of the instantaneous loudness is assumed to be transformed into the short-term loudness and long-term loudness, via processes of temporal integration.…”

Single-channel in-ear-EEG detects the focus of auditory attention to concurrent tone streams and mixed speech

“…Several approaches to extraction of the broad-band temporal envelope from a speech signal have been proposed (Biesmans et al 2016, Thwaites et al 2016. In case of the oddball task, the envelope was extracted by a direct calculation of the absolute values of the Hilbert-transform.…”