Sensitivity to Interaural Time Differences Conveyed in the Stimulus Envelope: Estimating Inputs of Binaural Neurons Through the Temporal Analysis of Spike Trains

Abstract

Sound-source localization in the horizontal plane relies on detecting small differences in the timing and level of the sound at the two ears, including differences in the timing of the modulated envelopes of high-frequency sounds (envelope interaural time differences (ITDs)). We investigated responses of single neurons in the inferior colliculus (IC) to a wide range of envelope ITDs and stimulus envelope shapes. By a novel means of visualizing neural activity relative to different portions of the periodic stimulus envelope at each ear, we demonstrate the role of neuron-specific excitatory and inhibitory inputs in creating ITD sensitivity (or the lack of it) depending on the specific shape of the stimulus envelope. The underlying binaural brain circuitry and synaptic parameters were modeled individually for each neuron to account for neuron-specific activity patterns. The model explains the effects of envelope shapes on sensitivity to envelope ITDs observed in both normal-hearing listeners and in neural data, and has consequences for understanding how ITD information in stimulus envelopes might be maximized in users of bilateral cochlear implants-for whom ITDs conveyed in the stimulus envelope are the only ITD cues available.

Influence of envelope waveform on ITD sensitivity of neurons in the auditory midbrain

“…Even when a stage of peripheral adaptation is added to the cross-correlation model, the sensitivity difference is still underestimated ( Klein-Hennig et al 2011 ). In a parallel study ( Dietz et al 2016 ) using modulation cycle histograms of the same data set as in the current study and Hodgkin-Huxley-type model lateral superior olive neurons, we were able to demonstrate that only response onsets of each modulation cycle convey temporal information. Sustained activity, which is rate adapted but in many neurons still well above zero, conveys little, if any, temporal information and is little influenced by ITD.…”

Temporal Envelope Coding by Inferior Colliculus Neurons with Cochlear Implant Stimulation

“…Moreover, MTFs measured using SAM differ significantly from MTFs measured using short sound bursts separated by periods of silence (Sinex et al 2002;Krebs et al 2008;Zheng and Escabí 2008). Neural sensitivity to other stimulus parameters, such as interaural time differences, also depends on envelope shape and in general cannot be predicted from SAM responses alone (Dietz et al 2016).…”

A framework for testing and comparing binaural models

“…This is in contradiction to what is seen behaviorally (Klein-Hennig et al, 2011), in actual neurons (Greenberg et al, 2017), or in Hodgkin-Huxley type model neurons . This topic appears to be well suited and timely for comparative studies, as several datasets were published in recent years (Buell et al, 2008;Dietz et al, 2016Dietz et al, , 2015Dietz et al, , 2014Dietz et al, , 2013bJoris et al, 1994;Klein-Hennig et al, 2011;Stecker and Bibee, 2014), many of which included models. Furthermore, neither the biophysical binaural models (e.g., Cai et al, 1998;Zhou et al, 2005) nor the more recent spiking phenomenological models (e.g., Ashida et al, 2016;Takanen et al, 2014) have been compared with continuous waveform-based models on the datasets referenced above.…”

“…In addition, Carney and her colleagues have developed a long line of realistic auditory models (e.g., Zhang et al, 2001;Zilany et al, 2014Zilany et al, , 2009) that have also been widely distributed and used as inputs for models of binaural interaction (e.g., Dietz et al, 2016;Wang and Colburn, 2012 to name just a few). Some of the features of these models include a more detailed description of various nonlinear attributes of the response, including level-dependent amplitude compression, and a control path that varies the gain and frequency selectivity of the primary response path.…”