Biology subjects

Van Opstal, J.

Publications and source records attributed to Van Opstal, J..

3 recordsLinked to original sources

bioRxiv2021

The what and where of synchronous sound perception

AO_SCPLOWBSTRACTC_SCPLOWSound localization and identification are challenging in acoustically rich environments. The relation between these two processes is still poorly understood. As natural sound-sources rarely occur exactly simultaneously, we wondered whether the auditory system could identify ("what") and localize ("where") two spatially separated sounds with synchronous onsets. While listeners typically report hearing a single source at an average location, one study found that both sounds may be accurately localized if listeners are explicitly being told two sources exist. We here tested whether simultaneous source identification (one vs. two) and localization is possible, by letting listeners choose to make either one or two head-orienting saccades to the perceived location(s). Results show that listeners could identify two sounds only when presented on different sides of the head, and that identification accuracy increased with their spatial separation. Notably, listeners were unable to accurately localize either sound, irrespective of whether one or two sounds were identified. Instead, the first (or only) response always landed near the average location, while second responses were unrelated to the targets. We conclude that localization of synchronous sounds in the absence of prior information is impossible. We discuss that the putative cortical what pathway may not transmit relevant information to the where pathway. We examine how a broadband interaural correlation cue could help to correctly identify the presence of two sounds without being able to localize them. We propose that the persistent averaging behavior reveals that the where system intrinsically assumes that synchronous sounds originate from a single source. SO_SCPLOWIGNIFICANCEC_SCPLOW SO_SCPLOWTATEMENTC_SCPLOWIt is poorly understood whether identification ( what) of sounds and their localization ( where) are inter-related, or independent neural processes. We measured sound-localization responses towards synchronous sounds to examine potential coupling of these processes. We varied the spatial configurations of two sounds and found that although identification improved considerably with larger spatial separation, their localization was unaffected: responses were always directed towards the average location. This shows absence of mutual coupling of information between the what and where streams in the auditory system. We also show how broadband interaural correlation could explain the improved identification results, without affecting localization performance, and explain how the persistent spatial averaging could be understood from strong internal priors regarding sound synchronicity.

neuroscience↗

bioRxiv2021

A spiking neural network model of the Superior Colliculus that is robust to changes in the spatial-temporal input

Previous studies have indicated that the location of a large neural population in the Superior Colliculus (SC) motor map specifies the amplitude and direction of the saccadic eye-movement vector, while the saccade trajectory and velocity profile are encoded by the population firing rates. We recently proposed a simple spiking neural network model of the SC motor map, based on linear summation of individual spike effects of each recruited neuron, which accounts for many of the observed properties of SC cells in relation to the ensuing eye movement. However, in the model, the cortical input was kept invariant across different saccades. Electrical microstimulation and reversible lesion studies have demonstrated that the saccade properties are quite robust against large changes in supra-threshold SC activation, but that saccade amplitude and peak eye-velocity systematically decrease at low input strengths. These features are not accounted for by the linear spike-vector summation model. Here we show that the models input projection strengths and intra-collicular lateral connections can be tuned to generate saccades that follow the experimental results. Author statementThe midbrain SC generates fast saccadic eye movements through a large population of cells within a topographically organized motor map, in which the location, spike count and temporal firing patterns of recruited cells determine saccade metrics and kinematics. According to the dynamic ensemble-coding model, each recruited SC cell contributes to the saccade by linear vector summation of all its spike contributions. Our previous spiking neural network model used invariant cortical inputs to the SC cells for all saccades. We here improved the robustness of the model to large spatial-temporal variations in the input patterns, by tuning its top-down and lateral synaptic connections, to generate saccades with properties observed in electrophysiological experiments.

neuroscience↗

bioRxiv2020

Changes in Sound Localization Performance of Single-Sided Deaf Listeners after Visual Feedback Training in Azimuth

Chronic single-sided deaf (CSSD) listeners lack the availability of binaural difference cues to localize sounds in the horizontal plane. Hence, for directional hearing they have to rely on different types of monaural cues: loudness perceived in their hearing ear, which is affected in a systematic way by the acoustic head shadow, on spectral cues provided by the low-pass filtering characteristic of the head, and on high-frequency spectral-shape cues from the pinna of their hearing ear. Presumably, these cues are differentially weighted against prior assumptions on the properties of sound sources in the environment. The rules guiding this weighting process are not well understood. In this preliminary study, we trained three CSSD listeners to localize a fixed intensity, high-pass filtered sound source at ten locations in the horizontal plane with visual feedback. After training, we compared their localization performance to sounds with different intensities, presented in the two-dimensional frontal hemifield to their pre-training results. We show that the training had rapidly readjusted the contributions of monaural cues and internal priors, which resulted to be imposed by the multisensory information provided during the training. We compare the results with the strategies found for the acute monaural hearing condition of normal-hearing listeners, described in an earlier study [1].

biophysics↗