Biology subjects

Alamatsaz, N.

Publications and source records attributed to Alamatsaz, N..

3 recordsLinked to original sources

bioRxiv2023

Increased reliance on temporal coding when target sound is softer than the background

Everyday environments often contain multiple concurrent sound sources that fluctuate over time. Normally hearing listeners can benefit from high signal-to-noise ratios (SNRs) in energetic dips of temporally fluctuating background sound, a phenomenon called dip-listening. Specialized mechanisms of dip-listening exist across the entire auditory pathway. Both the instantaneous fluctuating and the long-term overall SNR shape dip-listening. An unresolved issue regarding cortical mechanisms of dip-listening is how target perception remains invariant to overall SNR, specifically, across different tone levels with an ongoing fluctuating masker. Equivalent target detection over both positive and negative overall SNRs (SNR invariance) is reliably achieved in highly-trained listeners. Dip-listening is correlated with the ability to resolve temporal fine structure, which involves temporally-varying spike patterns. Thus the current work tests the hypothesis that at negative SNRs, neuronal readout mechanisms need to increasingly rely on decoding strategies based on temporal spike patterns, as opposed to spike count. Recordings from chronically implanted electrode arrays in core auditory cortex of trained and awake Mongolian gerbils that are engaged in a tone detection task in 10 Hz amplitude-modulated background sound reveal that rate-based decoding is not SNR-invariant, whereas temporal coding is informative at both negative and positive SNRs.

neuroscience↗

bioRxiv2020

Hemodynamic responses link individual differences in informational masking to the vicinity of superior temporal gyrus

Suppressing unwanted background sound is crucial for aural communication. A particularly disruptive type of background sound, informational masking (IM), often interferes in social settings. However, IM mechanisms are incompletely understood. At present, IM is identified operationally: when a target should be audible, based on suprathreshold target/masker energy ratios, yet cannot be heard because perceptually similar background sound interferes. Here, functional near infrared spectroscopy recordings show that task-evoked blood oxygenation changes near the superior temporal gyrus (STG) covary with behavioral speech detection performance for high-IM but not low-IM background sound, suggesting that the STG is part of an IM-dependent network. Moreover, listeners who are more vulnerable to IM show increased hemodynamic recruitment near STG. In contrast, task-evoked responses near another auditory region of cortex, the caudal inferior frontal sulcus (cIFS), do not predict behavioral sensitivity, suggesting that the cIFS belongs to an IM-independent network. Results are consistent with the idea that cortical gating shapes individual vulnerability to IM.

neuroscience↗

bioRxiv2018

Human Sound Localization Depends on Sound Intensity: Implications for Sensory Coding

A fundamental question of human perception is how we perceive target locations in space. Through our eyes and skin, the activation patterns of sensory organs provide rich spatial cues. However, for other sensory dimensions, including sound localization and visual depth perception, spatial locations must be computed by the brain. For instance, interaural time differences (ITDs) of the sounds reaching the ears allow listeners to localize sound in the horizontal plane. Our experiments tested two prevalent theories on how ITDs affect human sound localization: 1) the labelled-line model, encoding space through tuned representations of spatial location; versus 2) the hemispheric-difference model, representing space through spike-rate distances relative to a perceptual anchor. Unlike the labelled-line model, the hemispheric-difference model predicts that with decreasing intensity, sound localization should collapse toward midline reference, and this is what we observed behaviorally. These findings cast doubt on models of human sound localization that rely on a spatially tuned map. Moreover, analogous experimental results in vision indicate that perceived depth depends upon the contrast of the target. Based on our findings, we propose that the brain uses a canonical computation of location across sensory modalities: perceived location is encoded through population spike rate relative to baseline.

neuroscience↗