Biology subjects

Kopco, N.

Publications and source records attributed to Kopco, N..

6 recordsLinked to original sources

bioRxiv2022

Timescales of adaptation to context in horizontal sound localization

Psychophysical experiments explored how the repeated presentation of a context, consisting of an adaptor and a target, induces plasticity in the localization of an identical target presented alone on interleaved trials. The plasticity, and its time course, was examined both in a classroom and in an anechoic chamber. Adaptors and targets were 2-ms noise clicks and listeners were tasked with localizing the targets while ignoring the adaptors (when present). The context had either a fixed temporal structure, consisting of a single-click adaptor and a target, or its structure varied from trial to trial, either containing a single-click or an 8-click adaptor. The adaptor was presented either from a frontal or a lateral location, fixed within a run. The presence of context caused responses to the isolated targets to be displaced up to 14{degrees} away from the adaptor location. This effect was stronger and slower if the context was variable, growing over the 5-minute duration of the runs. Additionally, the fixed-context buildup had a slower onset in the classroom. Overall, the results illustrate that sound localization is subject to slow adaptive processes that depend on the spatial and temporal structure of the context and on the level of reverberation in the environment.

neuroscience↗

bioRxiv2021

A model of the reference frame of the ventriloquism aftereffect

The ventriloquism aftereffect (VAE), observed as a shift in the perceived locations of sounds after audio-visual stimulation, requires reference frame alignment since hearing and vision encode space in different reference frames (head-centered vs. eye-centered). Previous experimental studies reported inconsistent results, observing either a mixture of head-centered and eye-centered frames, or a predominantly head-centered frame. Here, a computational model is introduced to examine these inconsistencies. Based on experimental data, the model uses the measured size of the ventriloquism effect to predict the VAE adaptation in the auditory spatial map. Versions of the model examine whether the adaptation is induced by visual signals in head-centered frame, eye-centered frame, by eye-gaze direction-dependent signals, or their combination, and whether some biases are induced by the saccade-to-auditory-target response method used in the experiments. The model is first evaluated on three separate data sets. It can predict them well even without explicit need for an eye-centered signals influencing VAE, suggesting that the reference frame of VAE is mainly head-centered. The model predictions are qualitatively similar but less accurate when all three data sets are combined, suggesting that interactions between individual neural mechanisms are more complex than the simple linear combination assumed in the model.

neuroscience↗

bioRxiv2020

Calibration of consonant perception to room reverberation

PurposeWe examined how consonant perception is affected by a preceding speech carrier simulated in the same or a different room, for a broad range of consonants. Carrier room, carrier length, and carrier length/target room uncertainty were manipulated. A phonetic feature analysis tested which phonetic categories are most influenced by the acoustic context of the carrier. MethodTwo experiments were performed, each with 9 participants. Targets consisted of vowel-consonant (VC) syllables presented in one of 2 strongly reverberant rooms, preceded by a VC carrier presented either in the same room, a different reverberant room, or an anechoic room. In Experiment 1 the carrier length and the target room randomly varied from trial to trial while in Experiment 2 they were fixed within blocks of trials. ResultsCompared to the no-carrier condition, a consistent carrier provided only a small advantage for consonant perception, whereas inconsistent carriers disrupted performance significantly. For a different-room carrier, carrier length had an effect; performance dropped significantly in the 2-VC compared to the 4-VC carrier length. The only effect of carrier uncertainty was an overall drop in performance. Phonetic analysis showed that an inconsistent carrier significantly degraded identification of the manner of articulation, especially for stop consonants, and, in one of the rooms, also of voicing. ConclusionsCalibration of consonant perception to strong reverberation is exhibited through disruptions in perception when the room is switched. The strength of calibration varies across different consonants and phonetic features, as well as across rooms and durations of exposure to a given room.

neuroscience↗

bioRxiv2020

Audio-visual interactions in egocentric distance perception: Ventriloquism effect and aftereffect1

The processes of audio-visual integration and of visually-guided re-calibration of auditory distance perception are not well understood. Here, the ventriloquism effect (VE) and aftereffect (VAE) were used to study these processes in a real reverberant environment. Auditory and audio-visual (AV) stimuli were presented, in interleaved trials, over a range of distances from 0.7 to 2.04 m in front of the listener, whose task was to judge the distance of auditory stimuli or of the auditory components of AV stimuli. The relative location of the visual and auditory components of AV stimuli was fixed within a session such that the visual component was presented from distance 30% closer (V-closer) than the auditory component, 30% farther (V-farther), or aligned (V-aligned). The study examined the strength of VE and VAE as a function of the reference distance and of the direction of the visual component displacement, and the temporal profile of the build-up/break-down of these effects. All observed effects were approximately independent of target distance when expressed in logarithmic units. The VE strength, measured in the AV trials, was roughly constant for both directions of visual-component displacement such that, on average, the responses shifted in the direction of the visual component by 72% of the audio-visual disparity. The VAE strength, measured on the interleaved auditory-only trials, was stronger in the V-farther than the V-closer condition (44% vs. 31% of the audio-visual disparity, respectively). The VAE persisted to post-adaptation auditory-only blocks of trials, however it was weaker and the V-farther/V-closer asymmetry was reduced. The rates of build-up/break-down of the VAE were also asymmetrical, with slower adaptation in the V-closer condition. These results suggest that, on a logarithmic scale, the AV distance integration is symmetrical, independent of the direction of induced shift, while the visually-induced auditory distance re-callibration is asymmetrical, stronger and faster when evoked by more distant visual stimuli.

animal behavior and cognition↗

bioRxiv2019

Cortical auditory distance representation based on direct-to-reverberant energy ratio

Auditory distance perception and its neuronal mechanisms are poorly understood, mainly because 1) it is difficult to separate distance processing from intensity processing, 2) multiple intensity-independent distance cues are often available, and 3) the cues are combined in a context-dependent way. A recent fMRI study identified human auditory cortical area representing intensity-independent distance for sources presented along the interaural axis (Kopco et al., PNAS, 109, 11019-11024). For these sources, two intensity-independent cues are available, interaural level difference (ILD) and direct-to-reverberant energy ratio (DRR). Thus, the observed activations may have been contributed by not only distance-related, but also direction-encoding neuron populations sensitive to ILD. Here, the paradigm from the previous study was used to examine DRR-based distance representation for sounds originating in front of the listener, where ILD is not available. In a virtual environment, we performed behavioral and fMRI experiments, combined with computational analyses to identify the neural representation of distance based on DRR. The stimuli varied in distance (15-100 cm) while their received intensity was varied randomly and independently of distance. Behavioral performance showed that intensity-independent distance discrimination is accurate for frontal stimuli, even though it is worse than for lateral stimuli. fMRI activations for sounds varying in frontal distance, as compared to varying only in intensity, increased bilaterally in the posterior banks of Heschl's gyri, the planum temporale, and posterior superior temporal gyrus regions. Taken together, these results suggest that posterior human auditory cortex areas contain neuron populations that are sensitive to distance independent of intensity and of binaural cues relevant for directional hearing.\n\nHighlightsO_LIPosterior auditory cortices (AC) are sensitive to frontally presented distance cues\nC_LIO_LIThese effects are independent of intensity- and direction-related binaural cues\nC_LIO_LIfMRI activations to frontal distance cues are found in the right and left AC\nC_LIO_LIThe frontal reverberation-related auditory distance cues are behaviorally relevant\nC_LI

neuroscience↗

bioRxiv2019

Hemisphere-Specific Properties of the Ventriloquism Aftereffect in Humans and Monkeys

Visual calibration of auditory space requires re-alignment of representations differing in 1) format (auditory hemispheric channels vs. visual maps) and 2) reference frames (head-centered vs. eye-centered). Here, a ventriloquism paradigm from Kop[c]o et al. (J Neurosci, 29, 13809-13814) was used to examine these processes in humans and monkeys for ventriloquism induced within one spatial hemifield. Results show that 1) the auditory representation is adapted even by aligned audio-visual stimuli, and 2) the spatial reference frame is primarily head-centered in humans but mixed in monkeys. These results support the view that the ventriloquism aftereffect is driven by multiple spatially non-uniform processes.\n\nPACS numbers: 43.66.Pn, 43.66.Qp, 43.66.Mk

neuroscience↗