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1.
Nat Commun ; 12(1): 4839, 2021 08 10.
Artigo em Inglês | MEDLINE | ID: mdl-34376673

RESUMO

The ability to maintain a sequence of items in memory is a fundamental cognitive function. In the rodent hippocampus, the representation of sequentially organized spatial locations is reflected by the phase of action potentials relative to the theta oscillation (phase precession). We investigated whether the timing of neuronal activity relative to the theta brain oscillation also reflects sequence order in the medial temporal lobe of humans. We used a task in which human participants learned a fixed sequence of pictures and recorded single neuron and local field potential activity with implanted electrodes. We report that spikes for three consecutive items in the sequence (the preferred stimulus for each cell, as well as the stimuli immediately preceding and following it) were phase-locked at distinct phases of the theta oscillation. Consistent with phase precession, spikes were fired at progressively earlier phases as the sequence advanced. These findings generalize previous findings in the rodent hippocampus to the human temporal lobe and suggest that encoding stimulus information at distinct oscillatory phases may play a role in maintaining sequential order in memory.


Assuntos
Potenciais de Ação/fisiologia , Epilepsia/fisiopatologia , Aprendizagem/fisiologia , Neurônios/fisiologia , Ritmo Teta/fisiologia , Adolescente , Adulto , Epilepsia/diagnóstico , Feminino , Hipocampo/citologia , Hipocampo/fisiologia , Humanos , Masculino , Modelos Neurológicos , Neurônios/citologia , Estimulação Luminosa/métodos , Lobo Temporal/citologia , Lobo Temporal/fisiologia , Adulto Jovem
2.
J Neurosci ; 41(31): 6714-6725, 2021 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-34183446

RESUMO

An indispensable feature of episodic memory is our ability to temporally piece together different elements of an experience into a coherent memory. Hippocampal time cells-neurons that represent temporal information-may play a critical role in this process. Although these cells have been repeatedly found in rodents, it is still unclear to what extent similar temporal selectivity exists in the human hippocampus. Here, we show that temporal context modulates the firing activity of human hippocampal neurons during structured temporal experiences. We recorded neuronal activity in the human brain while patients of either sex learned predictable sequences of pictures. We report that human time cells fire at successive moments in this task. Furthermore, time cells also signaled inherently changing temporal contexts during empty 10 s gap periods between trials while participants waited for the task to resume. Finally, population activity allowed for decoding temporal epoch identity, both during sequence learning and during the gap periods. These findings suggest that human hippocampal neurons could play an essential role in temporally organizing distinct moments of an experience in episodic memory.SIGNIFICANCE STATEMENT Episodic memory refers to our ability to remember the what, where, and when of a past experience. Representing time is an important component of this form of memory. Here, we show that neurons in the human hippocampus represent temporal information. This temporal signature was observed both when participants were actively engaged in a memory task, as well as during 10-s-long gaps when they were asked to wait before performing the task. Furthermore, the activity of the population of hippocampal cells allowed for decoding one temporal epoch from another. These results suggest a robust representation of time in the human hippocampus.

3.
PLoS Biol ; 19(2): e3001142, 2021 02.
Artigo em Inglês | MEDLINE | ID: mdl-33635855

RESUMO

Rhythmic sensory or electrical stimulation will produce rhythmic brain responses. These rhythmic responses are often interpreted as endogenous neural oscillations aligned (or "entrained") to the stimulus rhythm. However, stimulus-aligned brain responses can also be explained as a sequence of evoked responses, which only appear regular due to the rhythmicity of the stimulus, without necessarily involving underlying neural oscillations. To distinguish evoked responses from true oscillatory activity, we tested whether rhythmic stimulation produces oscillatory responses which continue after the end of the stimulus. Such sustained effects provide evidence for true involvement of neural oscillations. In Experiment 1, we found that rhythmic intelligible, but not unintelligible speech produces oscillatory responses in magnetoencephalography (MEG) which outlast the stimulus at parietal sensors. In Experiment 2, we found that transcranial alternating current stimulation (tACS) leads to rhythmic fluctuations in speech perception outcomes after the end of electrical stimulation. We further report that the phase relation between electroencephalography (EEG) responses and rhythmic intelligible speech can predict the tACS phase that leads to most accurate speech perception. Together, we provide fundamental results for several lines of research-including neural entrainment and tACS-and reveal endogenous neural oscillations as a key underlying principle for speech perception.


Assuntos
Encéfalo/fisiologia , Percepção da Fala/fisiologia , Adulto , Relógios Biológicos , Eletroencefalografia , Feminino , Humanos , Magnetoencefalografia , Masculino , Pessoa de Meia-Idade , Estimulação Transcraniana por Corrente Contínua
4.
J Cogn Neurosci ; 32(2): 226-240, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-31659922

RESUMO

Several recent studies have used transcranial alternating current stimulation (tACS) to demonstrate a causal role of neural oscillatory activity in speech processing. In particular, it has been shown that the ability to understand speech in a multi-speaker scenario or background noise depends on the timing of speech presentation relative to simultaneously applied tACS. However, it is possible that tACS did not change actual speech perception but rather auditory stream segregation. In this study, we tested whether the phase relation between tACS and the rhythm of degraded words, presented in silence, modulates word report accuracy. We found strong evidence for a tACS-induced modulation of speech perception, but only if the stimulation was applied bilaterally using ring electrodes (not for unilateral left hemisphere stimulation with square electrodes). These results were only obtained when data were analyzed using a statistical approach that was identified as optimal in a previous simulation study. The effect was driven by a phasic disruption of word report scores. Our results suggest a causal role of neural entrainment for speech perception and emphasize the importance of optimizing stimulation protocols and statistical approaches for brain stimulation research.


Assuntos
Córtex Cerebral/fisiologia , Percepção da Fala/fisiologia , Estimulação Transcraniana por Corrente Contínua , Adulto , Feminino , Humanos , Masculino , Placebos , Desempenho Psicomotor/fisiologia , Fatores de Tempo , Adulto Jovem
5.
Curr Biol ; 29(24): R1318-R1320, 2019 12 16.
Artigo em Inglês | MEDLINE | ID: mdl-31846682

RESUMO

Previous research has demonstrated that auditory perception fluctuates rhythmically after a cue. New research shows that these 'behavioural oscillations' critically depend on expectations from preceding stimulation.


Assuntos
Percepção Auditiva , Estimulação Acústica
6.
Neuroimage ; 202: 116175, 2019 11 15.
Artigo em Inglês | MEDLINE | ID: mdl-31499178

RESUMO

Research on whether perception or other processes depend on the phase of neural oscillations is rapidly gaining popularity. However, it is unknown which methods are optimally suited to evaluate the hypothesized phase effect. Using a simulation approach, we here test the ability of different methods to detect such an effect on dichotomous (e.g., "hit" vs "miss") and continuous (e.g., scalp potentials) response variables. We manipulated parameters that characterise the phase effect or define the experimental approach to test for this effect. For each parameter combination and response variable, we identified an optimal method. We found that methods regressing single-trial responses on circular (sine and cosine) predictors perform best for all of the simulated parameters, regardless of the nature of the response variable (dichotomous or continuous). In sum, our study lays a foundation for optimized experimental designs and analyses in future studies investigating the role of phase for neural and behavioural responses. We provide MATLAB code for the statistical methods tested.


Assuntos
Encéfalo/fisiologia , Modelos Neurológicos , Neurônios/fisiologia , Percepção/fisiologia , Simulação por Computador , Interpretação Estatística de Dados , Eletroencefalografia , Humanos , Magnetoencefalografia , Estimulação Transcraniana por Corrente Contínua
7.
Curr Biol ; 28(18): R1102-R1104, 2018 09 24.
Artigo em Inglês | MEDLINE | ID: mdl-30253150

RESUMO

It has been hypothesized that stimulus-aligned brain rhythms reflect predictions about upcoming input. New research shows that these rhythms bias subsequent speech perception, in line with a mechanism of prediction.


Assuntos
Percepção da Fala , Fala , Estimulação Acústica , Encéfalo , Audição
8.
Front Neurosci ; 12: 95, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29563860

RESUMO

It is undisputed that presenting a rhythmic stimulus leads to a measurable brain response that follows the rhythmic structure of this stimulus. What is still debated, however, is the question whether this brain response exclusively reflects a regular repetition of evoked responses, or whether it also includes entrained oscillatory activity. Here we systematically present evidence in favor of an involvement of entrained neural oscillations in the processing of rhythmic input while critically pointing out which questions still need to be addressed before this evidence could be considered conclusive. In this context, we also explicitly discuss the potential functional role of such entrained oscillations, suggesting that these stimulus-aligned oscillations reflect, and serve as, predictive processes, an idea often only implicitly assumed in the literature.

9.
Curr Biol ; 28(3): 401-408.e5, 2018 02 05.
Artigo em Inglês | MEDLINE | ID: mdl-29358073

RESUMO

Due to their periodic nature, neural oscillations might represent an optimal "tool" for the processing of rhythmic stimulus input [1-3]. Indeed, the alignment of neural oscillations to a rhythmic stimulus, often termed phase entrainment, has been repeatedly demonstrated [4-7]. Phase entrainment is central to current theories of speech processing [8-10] and has been associated with successful speech comprehension [11-17]. However, typical manipulations that reduce speech intelligibility (e.g., addition of noise and time reversal [11, 12, 14, 16, 17]) could destroy critical acoustic cues for entrainment (such as "acoustic edges" [7]). Hence, the association between phase entrainment and speech intelligibility might only be "epiphenomenal"; i.e., both decline due to the same manipulation, without any causal link between the two [18]. Here, we use transcranial alternating current stimulation (tACS [19]) to manipulate the phase lag between neural oscillations and speech rhythm while measuring neural responses to intelligible and unintelligible vocoded stimuli with sparse fMRI. We found that this manipulation significantly modulates the BOLD response to intelligible speech in the superior temporal gyrus, and the strength of BOLD modulation is correlated with a phasic modulation of performance in a behavioral task. Importantly, these findings are absent for unintelligible speech and during sham stimulation; we thus demonstrate that phase entrainment has a specific, causal influence on neural responses to intelligible speech. Our results not only provide an important step toward understanding the neural foundation of human abilities at speech comprehension but also suggest new methods for enhancing speech perception that can be explored in the future.


Assuntos
Encéfalo/fisiologia , Inteligibilidade da Fala/fisiologia , Percepção da Fala/fisiologia , Adulto , Compreensão , Feminino , Humanos , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Estimulação Transcraniana por Corrente Contínua , Adulto Jovem
10.
Lang Cogn Neurosci ; 32(7): 910-923, 2017 Aug 09.
Artigo em Inglês | MEDLINE | ID: mdl-28670598

RESUMO

Transcranial electric stimulation (tES), comprising transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), involves applying weak electrical current to the scalp, which can be used to modulate membrane potentials and thereby modify neural activity. Critically, behavioural or perceptual consequences of this modulation provide evidence for a causal role of neural activity in the stimulated brain region for the observed outcome. We present tES as a tool for the investigation of which neural responses are necessary for successful speech perception and comprehension. We summarise existing studies, along with challenges that need to be overcome, potential solutions, and future directions. We conclude that, although standardised stimulation parameters still need to be established, tES is a promising tool for revealing the neural basis of speech processing. Future research can use this method to explore the causal role of brain regions and neural processes for the perception and comprehension of speech.

11.
Front Neurosci ; 11: 296, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28603483

RESUMO

All sensory systems need to continuously prioritize and select incoming stimuli in order to avoid overflow or interference, and provide a structure to the brain's input. However, the characteristics of this input differ across sensory systems; therefore, and as a direct consequence, each sensory system might have developed specialized strategies to cope with the continuous stream of incoming information. Neural oscillations are intimately connected with this selection process, as they can be used by the brain to rhythmically amplify or attenuate input and therefore represent an optimal tool for stimulus selection. In this paper, we focus on oscillatory processes for stimulus selection in the visual and auditory systems. We point out both commonalities and differences between the two systems and develop several hypotheses, inspired by recently published findings: (1) The rhythmic component in its input is crucial for the auditory, but not for the visual system. The alignment between oscillatory phase and rhythmic input (phase entrainment) is therefore an integral part of stimulus selection in the auditory system whereas the visual system merely adjusts its phase to upcoming events, without the need for any rhythmic component. (2) When input is unpredictable, the visual system can maintain its oscillatory sampling, whereas the auditory system switches to a different, potentially internally oriented, "mode" of processing that might be characterized by alpha oscillations. (3) Visual alpha can be divided into a faster occipital alpha (10 Hz) and a slower frontal alpha (7 Hz) that critically depends on attention.

12.
Neuroimage ; 150: 344-357, 2017 04 15.
Artigo em Inglês | MEDLINE | ID: mdl-28188912

RESUMO

Neural entrainment, the alignment between neural oscillations and rhythmic stimulation, is omnipresent in current theories of speech processing - nevertheless, the underlying neural mechanisms are still largely unknown. Here, we hypothesized that laminar recordings in non-human primates provide us with important insight into these mechanisms, in particular with respect to processing in cortical layers. We presented one monkey with human everyday speech sounds and recorded neural (as current-source density, CSD) oscillations in primary auditory cortex (A1). We observed that the high-excitability phase of neural oscillations was only aligned with those spectral components of speech the recording site was tuned to; the opposite, low-excitability phase was aligned with other spectral components. As low- and high-frequency components in speech alternate, this finding might reflect a particularly efficient way of stimulus processing that includes the preparation of the relevant neuronal populations to the upcoming input. Moreover, presenting speech/noise sounds without systematic fluctuations in amplitude and spectral content and their time-reversed versions, we found significant entrainment in all conditions and cortical layers. When compared with everyday speech, the entrainment in the speech/noise conditions was characterized by a change in the phase relation between neural signal and stimulus and the low-frequency neural phase was dominantly coupled to activity in a lower gamma-band. These results show that neural entrainment in response to speech without slow fluctuations in spectral energy includes a process with specific characteristics that is presumably preserved across species.


Assuntos
Córtex Auditivo/fisiologia , Sincronização de Fases em Eletroencefalografia/fisiologia , Percepção da Fala/fisiologia , Estimulação Acústica , Animais , Eletroencefalografia , Feminino , Macaca mulatta , Processamento de Sinais Assistido por Computador
13.
Neuroimage ; 124(Pt A): 16-23, 2016 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-26341026

RESUMO

Phase entrainment of neural oscillations, the brain's adjustment to rhythmic stimulation, is a central component in recent theories of speech comprehension: the alignment between brain oscillations and speech sound improves speech intelligibility. However, phase entrainment to everyday speech sound could also be explained by oscillations passively following the low-level periodicities (e.g., in sound amplitude and spectral content) of auditory stimulation-and not by an adjustment to the speech rhythm per se. Recently, using novel speech/noise mixture stimuli, we have shown that behavioral performance can entrain to speech sound even when high-level features (including phonetic information) are not accompanied by fluctuations in sound amplitude and spectral content. In the present study, we report that neural phase entrainment might underlie our behavioral findings. We observed phase-locking between electroencephalogram (EEG) and speech sound in response not only to original (unprocessed) speech but also to our constructed "high-level" speech/noise mixture stimuli. Phase entrainment to original speech and speech/noise sound did not differ in the degree of entrainment, but rather in the actual phase difference between EEG signal and sound. Phase entrainment was not abolished when speech/noise stimuli were presented in reverse (which disrupts semantic processing), indicating that acoustic (rather than linguistic) high-level features play a major role in the observed neural entrainment. Our results provide further evidence for phase entrainment as a potential mechanism underlying speech processing and segmentation, and for the involvement of high-level processes in the adjustment to the rhythm of speech.


Assuntos
Ondas Encefálicas , Córtex Cerebral/fisiologia , Inteligibilidade da Fala/fisiologia , Percepção da Fala/fisiologia , Estimulação Acústica , Adulto , Eletroencefalografia , Potenciais Evocados Auditivos , Feminino , Humanos , Masculino , Ruído , Acústica da Fala , Adulto Jovem
14.
Front Hum Neurosci ; 9: 651, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26696863

RESUMO

Constantly bombarded with input, the brain has the need to filter out relevant information while ignoring the irrelevant rest. A powerful tool may be represented by neural oscillations which entrain their high-excitability phase to important input while their low-excitability phase attenuates irrelevant information. Indeed, the alignment between brain oscillations and speech improves intelligibility and helps dissociating speakers during a "cocktail party". Although well-investigated, the contribution of low- and high-level processes to phase entrainment to speech sound has only recently begun to be understood. Here, we review those findings, and concentrate on three main results: (1) Phase entrainment to speech sound is modulated by attention or predictions, likely supported by top-down signals and indicating higher-level processes involved in the brain's adjustment to speech. (2) As phase entrainment to speech can be observed without systematic fluctuations in sound amplitude or spectral content, it does not only reflect a passive steady-state "ringing" of the cochlea, but entails a higher-level process. (3) The role of intelligibility for phase entrainment is debated. Recent results suggest that intelligibility modulates the behavioral consequences of entrainment, rather than directly affecting the strength of entrainment in auditory regions. We conclude that phase entrainment to speech reflects a sophisticated mechanism: several high-level processes interact to optimally align neural oscillations with predicted events of high relevance, even when they are hidden in a continuous stream of background noise.

15.
Neuroreport ; 26(13): 773-8, 2015 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-26164609

RESUMO

Evidence for rhythmic or 'discrete' sensory processing is abundant for the visual system, but sparse and inconsistent for the auditory system. Fundamental differences in the nature of visual and auditory inputs might account for this discrepancy: whereas the visual system mainly relies on spatial information, time might be the most important factor for the auditory system. In contrast to vision, temporal subsampling (i.e. taking 'snapshots') of the auditory input stream might thus prove detrimental for the brain as essential information would be lost. Rather than embracing the view of a continuous auditory processing, we recently proposed that discrete 'perceptual cycles' might exist in the auditory system, but on a hierarchically higher level of processing, involving temporally more stable features. This proposal leads to the prediction that the auditory system would be more robust to temporal subsampling when applied on a 'high-level' decomposition of auditory signals. To test this prediction, we constructed speech stimuli that were subsampled at different frequencies, either at the input level (following a wavelet transform) or at the level of auditory features (on the basis of LPC vocoding), and presented them to human listeners. Auditory recognition was significantly more robust to subsampling in the latter case, that is on a relatively high level of auditory processing. Although our results do not directly demonstrate perceptual cycles in the auditory domain, they (a) show that their existence is possible without disrupting temporal information to a critical extent and (b) confirm our proposal that, if they do exist, they should operate on a higher level of auditory processing.


Assuntos
Reconhecimento Psicológico , Percepção da Fala , Estimulação Acústica , Adulto , Feminino , Humanos , Masculino , Fatores de Tempo , Adulto Jovem
16.
J Neurosci ; 35(5): 1954-64, 2015 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-25653354

RESUMO

Perceptual phase entrainment improves speech intelligibility by phase-locking the brain's high-excitability and low-excitability phases to relevant or irrelevant events in the speech input. However, it remains unclear whether phase entrainment to speech can be explained by a passive "following" of rhythmic changes in sound amplitude and spectral content or whether entrainment entails an active tracking of higher-level cues: in everyday speech, rhythmic fluctuations in low-level and high-level features always covary. Here, we resolve this issue by constructing novel speech/noise stimuli with intelligible speech but without systematic changes in sound amplitude and spectral content. The probability of detecting a tone pip, presented to human listeners at random moments during our speech/noise stimuli, was significantly modulated by the rhythmic changes in high-level information. Thus, perception can entrain to the speech rhythm even without concurrent fluctuations in sound amplitude or spectral content. Strikingly, the actual entrainment phase depended on the tone-pip frequency, with tone pips within and beyond the principal frequency range of the speech sound modulated in opposite fashion. This result suggests that only those neural populations processing the actually presented frequencies are set to their high-excitability phase, whereas other populations are entrained to the opposite, low-excitability phase. Furthermore, we show that the perceptual entrainment is strongly reduced when speech intelligibility is abolished by presenting speech/noise stimuli in reverse, indicating that linguistic information plays an important role for the observed perceptual entrainment.


Assuntos
Acústica da Fala , Inteligibilidade da Fala , Percepção da Fala , Estimulação Acústica/métodos , Adulto , Encéfalo/fisiologia , Feminino , Humanos , Masculino , Ruído , Periodicidade
18.
Philos Trans R Soc Lond B Biol Sci ; 369(1641): 20130214, 2014 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-24639585

RESUMO

Does our perceptual awareness consist of a continuous stream, or a discrete sequence of perceptual cycles, possibly associated with the rhythmic structure of brain activity? This has been a long-standing question in neuroscience. We review recent psychophysical and electrophysiological studies indicating that part of our visual awareness proceeds in approximately 7-13 Hz cycles rather than continuously. On the other hand, experimental attempts at applying similar tools to demonstrate the discreteness of auditory awareness have been largely unsuccessful. We argue and demonstrate experimentally that visual and auditory perception are not equally affected by temporal subsampling of their respective input streams: video sequences remain intelligible at sampling rates of two to three frames per second, whereas audio inputs lose their fine temporal structure, and thus all significance, below 20-30 samples per second. This does not mean, however, that our auditory perception must proceed continuously. Instead, we propose that audition could still involve perceptual cycles, but the periodic sampling should happen only after the stage of auditory feature extraction. In addition, although visual perceptual cycles can follow one another at a spontaneous pace largely independent of the visual input, auditory cycles may need to sample the input stream more flexibly, by adapting to the temporal structure of the auditory inputs.


Assuntos
Percepção Auditiva/fisiologia , Conscientização/fisiologia , Audição/fisiologia , Modelos Neurológicos , Periodicidade , Visão Ocular/fisiologia , Percepção Visual/fisiologia , Atenção , Eletroencefalografia , Humanos , Fatores de Tempo
19.
Front Psychol ; 4: 262, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23717293

RESUMO

Low-frequency oscillations in the electroencephalogram (EEG) are thought to reflect periodic excitability changes of large neural networks. Consistent with this notion, detection probability of near-threshold somatosensory, visual, and auditory targets has been reported to co-vary with the phase of oscillations in the EEG. In audition, entrainment of δ-oscillations to the periodic occurrence of sounds has been suggested to function as a mechanism of attentional selection. Here, we examine in humans whether the detection of brief near-threshold sounds in quiet depends on the phase of EEG oscillations. When stimuli were presented at irregular intervals, we did not find a systematic relationship between detection probability and phase. When stimuli were presented at regular intervals (2-s), reaction times were significantly shorter and we observed phase entrainment of EEG oscillations corresponding to the frequency of stimulus presentation (0.5 Hz), revealing an adjustment of the system to the regular stimulation. The amplitude of the entrained oscillation was higher for hits than for misses, suggesting a link between entrainment and stimulus detection. However, detection was independent of phase at frequencies ≥1 Hz. Furthermore, we show that when the data are analyzed using acausal, though common, algorithms, an apparent "entrainment" of the δ-phase to presented stimuli emerges and detection probability appears to depend on δ-phase, similar to reports in the literature. We show that these effects are artifacts from phase distortion at stimulus onset by contamination with the event-related potential, which differs markedly for hits and misses. This highlights the need to carefully deal with this common problem, since otherwise it might bias and mislead this exciting field of research.

20.
Hear Res ; 296: 83-95, 2013 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-23268356

RESUMO

Detection thresholds for pairs or multiple copies of sounds are better than those for a single sound, an observation commonly interpreted as indicating temporal integration by the auditory system. Detection thresholds for pairs of brief tones depend on the delay between the tones (if short) and on frequency, suggesting frequency-dependent temporal overlap of auditory-filter responses elicited by the two successive stimuli (Krumbholz and Wiegrebe, 1998). The model presented by Krumbholz and Wiegrebe did not account for all aspects of their data, despite its complexity. This study shows that a simple probabilistic model based on Neubauer and Heil (2008) predicts the increase in threshold for short temporal delays as well as the asymptotic behaviour towards longer delays. The model entails (i) a 4th-order gammatone filter with a brief impulse response and thus broad bandwidth (shorter and broader than those of a filter normally assumed), (ii) the formation of stochastic 'spikes' or 'events' whose probability of occurrence is proportional to the filter output (half-wave rectified fine-structure or amplitude envelope), raised to a power of 3, and (iii) probability summation. The same model with the same front-end filter also predicts thresholds for pairs of clicks presented in band-reject noise, measured by Hall and Lummis (1973). The model accurately predicts the magnitudes and the decay of the alternating increase and decrease of thresholds as the delay between the click varies, the small effects of click polarity, and the dependence of thresholds for pairs of clicks with unequal intensities on their temporal order. Finally, we show that this model also correctly predicts the decrease in threshold with increasing number of temporally separated brief sounds, reported in several studies. While the latter data do not constrain the characteristics of the front-end filter, they do confirm the exponent of 3 in the model. Our paper stresses the viability of the model and raises the possibility that the bandwidths of filters estimated with psychophysical techniques may depend more strongly on the experimental paradigms and stimuli than hitherto thought.


Assuntos
Vias Auditivas/fisiologia , Limiar Auditivo , Modelos Neurológicos , Modelos Estatísticos , Detecção de Sinal Psicológico , Estimulação Acústica , Animais , Gatos , Humanos , Ruído/efeitos adversos , Mascaramento Perceptivo , Espectrografia do Som , Fatores de Tempo
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