Neural correlates of binaural masking level difference in the inferior colliculus of the barn owl (Tyto alba)

Abstract

Humans and animals are able to detect signals in noisy environments. Detection improves when the noise and the signal have different interaural phase relationships. The resulting improvement in detection threshold is called the binaural masking level difference. We investigated neural mechanisms underlying the release from masking in the inferior colliculus of barn owls in low-frequency and high-frequency neurons. A tone (signal) was presented either with the same interaural time difference as the noise (masker) or at a 180 degrees phase shift as compared with the interaural time difference of the noise. The changes in firing rates induced by the addition of a signal of increasing level while masker level was kept constant was well predicted by the relative responses to the masker and signal alone. In many cases, the response at the highest signal levels was dominated by the response to the signal alone, in spite of a significant response to the masker at low signal levels, suggesting the presence of occlusion. Detection thresholds and binaural masking level differences were widely distributed. The amount of release from masking increased with increasing masker level. Narrowly tuned neurons in the central nucleus of the inferior colliculus had detection thresholds that were lower than or similar to those of broadly tuned neurons in the external nucleus of the inferior colliculus. Broadly tuned neurons exhibited higher masking level differences than narrowband neurons. These data suggest that detection has different spectral requirements from localization.

Inferring the basis of binaural detection with a modified autoencoder

“…Nodes tuned to smaller ITDs responded most to in-phase tones (So) and least to out-of-phase tones (Sπ), and vice-versa for nodes tuned to larger ITDs. studies have reported neural responses consistent with a cross-correlation mechanism 15,16,38,39 ( Fig. 3g-i).…”

“…Comparative outputs from a simple binaural cross-correlation algorithm (namely for signals in noise passed through narrow-band filters centered at 500 Hz) are shown in Figure 3d-f , and were found to resemble responses across the DNN’s layer 2 nodes (Pearson’s r=0.36, p≪0.0001). A number of physiology studies have reported neural responses consistent with a cross-correlation mechanism 15,16,38,39 ( Fig. 3g-i ).…”

“…Neural ITD tuning curves have been observed in a number of animal species ( a ), including cat 35 (inferior colliculus, IC), barnowl 39 (IC), and guinea pig 16 (auditory cortex, GP ACtx). ITD tuning emerged as a property of nodes within the early layers of the DNN and increased hierarchically between layer 1 ( b ) and layer 2 ( e ).…”

Language experience-dependent advantage in pitch representation in the auditory cortex is limited to favorable signal-to-noise ratios

“…In animals, BRM is observed in single neurons at the level of the inferior colliculus (Asadollahi et al, 2010; McAlpine et al, 1996; Palmer et al, 2000) and auditory cortex (Gilbert et al, 2015). In humans, EEG studies reveal larger magnitude for the S0Nπ condition relative to S0N0 for cortical transient components N1–P1–P2 (Fowler & Mikami, 1996; Kevanishvili & Lagidze, 1987), cortical steady-state response (Wong & Stapells, 2004) and brainstem frequency following response (Wilson & Krishnan, 2005).…”

The binaural masking level difference: cortical correlates persist despite severe brain stem atrophy in progressive supranuclear palsy

“…Single-cell recordings from a number of animal species have shown that the initial interaural processing important for the BMLD takes place in the medial superior olive and that an accurate representation of this processing is preserved at the level of the inferior colliculus (IC) ( Asadollahi et al 2010 ; Palmer and Shackleton 2002 ; Shackleton and Palmer 2010 ). Indeed, it has proven possible to provide a quantitative account of the BMLD based solely on changes in the firing rates in cells of the central nucleus of the IC ( Palmer and Shackleton 2002 ).…”