Abstract
Traditionally, the auditory system is thought to serve reliable sound localization. Stimulus-history driven feedback circuits in the early binaural pathway, however, contradict this canonical concept and raise questions about their functional significance. Here we show that stimulus-history dependent changes in absolute space perception are poorly captured by the traditional labeled-line and hemispheric-difference models of auditory space coding. We therefore developed a new decoding model incorporating recent electrophysiological findings in which sound location is initially computed in both brain hemispheres independently and combined to yield a hemispherically balanced code. This model closely captures the observed absolute localization errors caused by stimulus history, and furthermore predicts a selective dilation and compression of perceptional space. These model predictions are confirmed by improvement and degradation of spatial resolution in human listeners. Thus, dynamic perception of auditory space facilitates focal sound source segregation at the expense of absolute sound localization, questioning existing concepts of spatial hearing.
Highlights
The auditory system is thought to serve reliable sound localization
It was shown that binaural processing in medial superior olive (MSO) and Lateral Superior Olive (LSO) is subject to short-term adaptation based on feed-back loops in the mammalian auditory brainstem[18,20,21], through which the neuronal firing rate is modulated by recent stimulus history (Fig. 1a,b)
Motivated by reports that a unilateral lesion of the midbrain still allows for sound localization in the hemisphere contralateral to the lesion[28,29,30], and the fact that the low-frequency limb of the LSO is ITD sensitive[31,32], we developed a new hierarchical decoding model in which sound source azimuth is estimated based on population vector analysis for both hemispheres independently
Summary
The auditory system is thought to serve reliable sound localization. Stimulus-history driven feedback circuits in the early binaural pathway, contradict this canonical concept and raise questions about their functional significance. We developed a new decoding model incorporating recent electrophysiological findings in which sound location is initially computed in both brain hemispheres independently and combined to yield a hemispherically balanced code This model closely captures the observed absolute localization errors caused by stimulus history, and predicts a selective dilation and compression of perceptional space. It was shown that binaural processing in MSO and LSO is subject to short-term adaptation based on feed-back loops in the mammalian auditory brainstem[18,20,21], through which the neuronal firing rate is modulated by recent stimulus history (Fig. 1a,b) In both nuclei, the inhibitory transmitter GABA (gamma-Aminobutyric acid) is released in activity-dependent manner and binds to pre-synaptic GABA-B receptors to mediated gain adaptation on the time scale of seconds. Changes in absolute localization were not tracked by these studies, rendering a conclusion about the causal role of compromised absolute sound localization for the observed improvement impossible
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