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Many cells in the inferior colliculus (IC) are excited by contralateral and inhibited by ipsilateral stimulation and are thought to be important for sound localization. These excitatory-inhibitory (EI) cells comprise a diverse group, even though they exhibit a common binaural response property. Previous extracellular studies proposed specific excitatory and/or inhibitory events that should be evoked by each ear and thereby generate each of the EI discharge properties. The proposals were inferences based on the well established response features of neurons in lower nuclei, the projections of those nuclei, their excitatory or inhibitory neurochemistry, and the changes in response features that occurred when inhibition was blocked. Here we recorded the inputs, the postsynaptic potentials, discharges evoked by monaural and binaural signals in EI cells with in vivo whole cell recordings from the inferior colliculus (IC) of awake bats. We also computed the excitatory and inhibitory synaptic conductances from the recorded sound evoked responses. First, we showed that a minority of EI cells either inherited their binaural property from a lower binaural nucleus or the EI property was created in the IC via inhibitory projections from the ipsilateral ear, features consistent with those observed in extracellular studies. Second, we showed that in a majority of EI cells ipsilateral signals evoked subthreshold EPSPs that behaved paradoxically in that EPSP amplitudes increased with intensity, even though binaural signals with the same ipsilateral intensities generated progressively greater spike suppressions. These ipsilateral EPSPs were unexpected since they could not have been detected with extracellular recordings. These additional responses suggested that the circuitry underlying EI cells was more complex than previously suggested. We also proposed the functional significance of ipsilaterally evoked EPSPs in responding to moving sound sources or multiple sounds. Third, by computing synaptic conductances, we showed the circuitry of the EI cells was even more complicated than those suggested by PSPs, and we also evaluated how the binaural property was produced by the contralateral and ipsilateral synaptic events. / text

A perceptual sound field synthesis approach for music is presented. Its signal processing implements critical bands, the precedence effect and integration times of the auditory system by technical means, as well as the radiation characteristics of musical instruments. Furthermore, interaural coherence, masking and auditory scene analysis principles are considered. As a result, the conceptualized sound field synthesis system creates a natural, spatial sound impression for listeners in extended listening area, even with a low number of loudspeakers. A novel technique, the “precedence fade”, as well as the interaural cues provided by the sound field synthesis approach, allow for a precise and robust localization.Simulations and a listening test provide a proof of concept. The method is particularly robust for signals with impulsive attacks and long quasi-stationary phases, as in the case of many instrumental sounds. It is compatible with many loudspeaker setups, such as 5.1 to 22.2, ambisonics systems and loudspeaker arrays for wave front synthesis. The perceptual sound field synthesis approach is an alternative to physically centered wave field synthesis concepts and conventional, perceptually motivated stereophonic sound and benefits from both paradigms.

When presented with two identical sounds from different locations separated by a short onset asynchrony, listeners report hearing a single source at the location of the lead sound, a phenomenon called the precedence effect (Wallach et al., 1949; Haas, 1951). When the onset asynchrony is above echo threshold, listeners report hearing the lead and lag sounds as separate sources with distinct locations. Event-related potential (ERP) studies have shown that perception of separate sound sources is accompanied by an object-related negativity (ORN) 100-250 ms after onset and a late posterior positivity (LP) 300-500 ms after onset (Sanders et al., 2008; Sanders et al., 2011). The current study tested whether these ERP effects are modulated by attention. Clicks were presented in lead/lag pairs at and around listeners’ echo thresholds while in separate blocks they 1) attended to the sounds and reported if they heard the lag sound as a separate source, and 2) performed a difficult 2-back visual task. Replicating previous results, when attention was directed to the sounds, an ORN and LP were observed for click pairs 1 ms above compared to 1 ms below echo threshold. In contrast, when attention was directed away from the sounds to the visual task, neither the ORN nor the LP was evident. Instead, click pairs 1 ms above echo threshold elicited an anterior positivity 250-450 ms after onset. In addition, an effect resembling an ORN was found in comparing ERPs elicited by unattended click pairs with SOAs below attended echo threshold. These results indicate that attention modulates early perceptual processes in the precedence effect and may be critical for auditory object formation under these conditions.