Suprathreshold Signals Research Articles

Diversity-induced resonance for optimally suprathreshold signals.

Recent research has revealed that a system of coupled units with a certain degree of parameter diversity can generate an enhanced response to a subthreshold signal compared to that without diversity, exhibiting a diversity-induced resonance. We here show that diversity-induced resonance can also respond to a suprathreshold signal in a system of globally coupled bistable oscillators or excitable neurons, when the signal amplitude is in an optimal range close to the threshold amplitude. We find that such diversity-induced resonance for optimally suprathreshold signals is sensitive to the signal period for the system of coupled excitable neurons, but not for the coupled bistable oscillators. Moreover, we show that the resonance phenomenon is robust to the system size. Furthermore, we find that intermediate degrees of parameter diversity and coupling strength jointly modulate either the waveform or the period of collective activity of the system, giving rise to the resonance for optimally suprathreshold signals. Finally, with low-dimensional reduced models, we explain the underlying mechanism of the observed resonance. Our results extend the scope of the diversity-induced resonance effect.

Suppression of switching errors in weakly damped Josephson junctions

The task of the Josephson junction switching is numerically solved in the framework of the classical RCSJ model with white Gaussian noise. In order to switch the junction to the resistive state a periodic supra-threshold signal is applied. The operational mode is similar to the single photon counter proposed earlier. Here we consider a purely classical situation in order to find out how far the typical aluminium Josephson junction is from the single photon operational mode. We have found that for the considered parameters, if the switching happens due to external periodic signal, it occurs mostly during the first two periods of driving, and the number of photons, needed for switching, is more than one hundred. Also we observe the double minima of the mean switching time and the standard deviation versus the driving frequency. This determines the parameter range, optimal for reliable switching, which can be used as a guidance in quasi-classical and quantum approaches.

Set-reset latch logic operation in a bistable system under suprathreshold and subthreshold signals.

A set-reset latch is a basic building block of computers and can be used to store state information. Here, by testing the influence of the two logical input signals on the reliable set-reset latch logic operation in the bistable system, we found that there are two types of input signals, namely, suprathreshold and subthreshold signals. For the suprathreshold signals, reliable set-reset logic operation can be achieved without any driving forces and exhibits certain anti-interference ability; for the subthreshold signals, a single harmonic could induce correct set-reset latch logic operation but with a narrow optimal parameter region. The introduction of biharmonic-induced set-reset latch logic operation (logical vibrational resonance) could greatly expand the parameter region. Explanations for the above results were provided by taking the logical inputs as the dynamic bias to analyze the dynamic changes in the system. Finally, the results were further verified by circuit simulation and actual hardware circuit.

Psychophysical changes in temporal processing in chinchillas with noise-induced hearing loss: A literature review.

It is well-established that excessive noise exposure can systematically shift audiometric thresholds (i.e., noise-induced hearing loss, NIHL) making sounds at the lower end of the dynamic range difficult to detect. An often overlooked symptom of NIHL is the degraded ability to resolve temporal fluctuations in supra-threshold signals. Given that the temporal properties of speech are highly dynamic, it is not surprising that NIHL greatly reduces one's ability to clearly decipher spoken language. However, systematic characterization of noise-induced impairments on supra-threshold signals in humans is difficult given the variability in noise exposure among individuals. Fortunately, the chinchilla is audiometrically similar to humans, making it an ideal animal model to investigate noise-induced supra-threshold deficits. Through a series of studies using the chinchilla, the authors have elucidated several noise-induced deficits in temporal processing that occur at supra-threshold levels. These experiments highlight the importance of the chinchilla model in developing an understanding of noise-induced deficits in temporal processing.

The Minimum Audible Movement Distance for Localization of Approaching and Receding Broadband Noise with a Reduced Fraction of High-Frequency Spectral Components Typical of Prebyscusis

The minimum audible movement distance was estimated for approaching and receding sound images with a reduced fraction of high-frequency spectral components which reflects an age-related deterioration of auditory perception (presbycusis). Such a reduction can lead to a partial shutdown of the high-frequency binaural auditory mechanism and changes in distance estimation for sound sources positioned at egocentric distances up to 5 m, i.e. in case of making a contact (collision) decision. This study was carried out in free-field conditions using a sound source movement model. The movement was modelled by noise bursts with linearly changing amplitudes, which were emitted by two loudspeakers spaced 3 m apart. The minimum audible movement distance in estimating moving sound images with a reduced fraction of high-frequency signal components was found to be twice as low as for sound images without such a reduction. The data obtained indicate that, provided that the suprathreshold signal encoding mechanisms remain intact, high-frequency level lowering does not increase the minimum audible movement distance.

Behavioral Assessment of Hearing in 2- to 7-Year-Old Children: Evaluation of a Two-Interval, Observer-Based Procedure Using Conditioned Play-Based Responses.

Purpose It is challenging to collect reliable behavioral data from toddlers and preschoolers. Consequently, we have significant gaps in our understanding of how auditory development unfolds during this time period. One method that appears to be promising is an observer-based procedure that uses conditioned, play-based responses (Bonino & Leibold, 2017). In order to evaluate the quality of data obtained with this method, this study presented a suprathreshold signal to determine the number of trials 2- to 7-year-old children could complete, as well as the associated hit rate and observer confidence. Method Participants were 23 children (2-7 years old). Children were taught to perform a play-based motor response when they detected the 1000-Hz warble tone signal (at 30 dB SPL). An observer evaluated children's behavior using a 2-interval, 2-alternative testing paradigm. Testing was terminated after 100 trials or earlier, if signs of habituation were observed. Results Data were successfully collected from 22 of the 23 children. Of the 22 children, all but 1 child completed 100 trials. Overall hit rate was high (0.88-1.0; M = 0.94) and improved with listener age. Hit rate was stable across the test session. Strong agreement was seen between the correctness of the response and the observer's confidence in the judgment. Conclusion Results of this study confirm that the 2-interval, observer-based procedure described in this article is a powerful tool for measuring detection and discrimination abilities in young children. Future research will (a) evaluate coder reliability and (b) examine stability of performance across a test session when the signal intensity is manipulated. Supplemental Material https://doi.org/10.23641/asha.8309273.

A patterned polystyrene-based microelectrode array for in vitro neuronal recordings.

Substrate-integrated microelectrode arrays (MEAs) are non-invasive platforms for recording supra-threshold signals, i.e. action potentials or spikes, from a variety of cultured electrically active cells, and are useful for pharmacological and toxicological studies. However, the MEA substrate, which is often fabricated using semiconductor processing technology, presents some challenges to the user. Specifically, the electrode encapsulation, which may consist of a variety of inorganic and organic materials, requires a specific substrate preparation protocol to optimize cell adhesion to the surface. Often, these protocols differ from and are more complex than traditional protocols for in vitro cell culture in polystyrene petri dishes. Here, we describe the fabrication of an MEA with indium tin oxide microelectrodes and a patterned polystyrene electrode encapsulation. We demonstrate the electrochemical stability of the electrodes and encapsulation, and show viable cell culture and in vitro recordings.

A hypothesis study on bionic active noise reduction of auditory organs

BackgroundNoise exposure can lead to hearing loss and multiple system dysfunctions. As various forms of noise exist in our living environments, and our auditory organs are very sensitive to acoustic stimuli, it is a challenge to protect our hearing system in certain noisy environments.Presentation of the hypothesisHerein, we propose that our hearing organ could serve as a noise eliminator for high intensity noise and enhance acoustic signal processing abilities by increasing the signal-noise ratio. For suprathreshold signals, the hearing system is capable of regulating the middle ear muscles and other structures to actively suppress the sound level to a safe range.Testing the hypothesisTo test our hypothesis, both mathematic model analyses and animal model studies are needed. Based on a digital 3D reconstructed model, every structure in the auditory system can be analyzed and tested for its contribution to the process of noise reduction. Products manufactured by this bionic method could be used and verified in animal models and volunteers.ImplicationsBy mimicking the noise-reduction effect of the sophisticated structures in the hearing system, we may be able to provide a model that establishes a new active-sound-suppression mode. This innovative method may overcome the limited capabilities of current noise protection options and become a promising possibility for noise prevention.

Energy-efficient population coding constrains network size of a neuronal array system.

We consider the open issue of how the energy efficiency of the neural information transmission process, in a general neuronal array, constrains the network size, and how well this network size ensures the reliable transmission of neural information in a noisy environment. By direct mathematical analysis, we have obtained general solutions proving that there exists an optimal number of neurons in the network, where the average coding energy cost (defined as energy consumption divided by mutual information) per neuron passes through a global minimum for both subthreshold and superthreshold signals. With increases in background noise intensity, the optimal neuronal number decreases for subthreshold signals and increases for suprathreshold signals. The existence of an optimal number of neurons in an array network reveals a general rule for population coding that states that the neuronal number should be large enough to ensure reliable information transmission that is robust to the noisy environment but small enough to minimize energy cost.

Novel disposable microelectrode array for cultured neuronal network recording exhibiting equivalent performance to commercially available arrays

Microelectrode arrays (MEAs) enable non-invasive recording of supra-threshold signals, i.e. action potentials or spikes, from a variety of cultured electrically active cells. While this label-free technology has been shown to be useful for pharmacological and toxicological studies, a major limitation has been the reliance on expensive recording substrates that have been manufactured with the intent of re-use. Prior work by our group has demonstrated an approach for fabricating MEAs using conventional liquid crystal display manufacturing techniques. Here, we describe and characterize the UT Dallas planar MEA which is fabricated with low cost materials and processes. We compare the performance of the UT Dallas MEAs, which consist of exposed gold microelectrodes with patterned parylene insulation over traces, with well-established commercially available MEAs using cultured murine cortical networks. Detailed electrophysiological comparisons show virtually identical performance between MEA types with respect to network metrics including recording yield across the array, network spike rate and burst rate, and virtually identical pharmacological responses to a diverse set of neuropharmacological agents.

Noise-Enhanced Information Systems

Noise, traditionally defined as an unwanted signal or disturbance, has been shown to play an important constructive role in many information processing systems and algorithms. This noise enhancement has been observed and employed in many physical, biological, and engineered systems. Indeed stochastic facilitation (SF) has been found critical for certain biological information functions such as detection of weak, subthreshold stimuli or suprathreshold signals through both experimental verification and analytical model simulations. In this paper, we present a systematic noise-enhanced information processing framework to analyze and optimize the performance of engineered systems. System performance is evaluated not only in terms of signal-to-noise ratio but also in terms of other more relevant metrics such as probability of error for signal detection or mean square error for parameter estimation. As an important new instance of SF, we also discuss the constructive effect of noise in associative memory recall. Potential enhancement of image processing systems via the addition of noise is discussed with important applications in biomedical image enhancement, image denoising, and classification.

Weaker signals induce more precise temporal-integration

It is well known that our perceptual system integrates local information to generate global percepts. Although events in the real world occur over time, it is still unclear how we integrate temporally dispersed information. Here, I systematically explore the relation between the intensity of local signals and the resultant of temporal-integration. Presented sequentially with two directions of variably coherent random dot patterns (40 degrees apart), participants were instructed to report a perceived motion direction by using a mouse driven cursor. As the strength of the motion signal was varied, the behavioral results and qualitative analyses indicate existence of two aspects of temporal-integration, subthreshold integration and suprathreshold integration. In subthreshold integration (when the local signals are subthreshold), stronger signals enhance integration. On the other hand, in suprathreshold integration (when the signals are above threshold), stronger signals decrease integration. As a result, relatively weaker, subthreshold or near threshold signals produce more precise temporal-integration than suprathreshold signals.

Role of subthreshold stimuli in task-performance and its underlying mechanism

Considerable evidence exists indicating that a stimulus which is subthreshold and thus consciously invisible, influences brain activity and behavioral performance. However, it is not clear how subthreshold stimuli are processed in the brain. We found that a task-irrelevant subthreshold coherent motion leads to stronger disturbance in task performance than suprathreshold motion. With the subthreshold motion, fMRI activity in the visual cortex was higher, but activity in the dorsolateral prefrontal cortex (DLPFC) was lower, than with suprathreshold motion. The results of the present study demonstrate two important points. First, a weak task-irrelevant stimulus feature which is below but near the perceptual threshold more strongly activates visual area (MT+) which is highly related to the stimulus feature and more greatly disrupts task performance. This contradicts the general view that irrelevant signals that are stronger in stimulus properties more greatly influence the brain and performance and that the influence of a subthreshold stimulus is smaller than that of suprathreshold stimuli. Second, the results may reveal important bidirectional interactions between a cognitive controlling system and the visual system. LPFC, which has been suggested to provide inhibitory control on task-irrelevant signals, may have a higher detection threshold for incoming signals than the visual cortex. Task-irrelevant signals around the threshold level may be sufficiently strong to be processed in the visual system but not strong enough for LPFC to “notice” and, therefore, to provide effective inhibitory control on the signals. In this case, such signals may remain uninhibited, take more resources for a task-irrelevant distractor, and leave fewer resources for a given task, and disrupt task performance more than a suprathreshold signal. On the other hand, suprathreshold coherent motion may be “noticed”, given successful inhibitory control by LPFC, and leave more resources for a task. This mechanism may underlie the present paradoxical finding that subthreshold task-irrelevant stimuli activate the visual area strongly and disrupt task performance more and could also be one of the reasons why subthreshold stimuli tend to lead to relatively robust effects.

Supra-threshold stochastic resonance in a population of stochastic Hogkin-Huxley neuron models with random ion channel gating

Supra-threshold stochastic resonance (SSR) refers to a phenomenon what an optimally added noise can enhance information transmission when a supra-threshold signal is driven into an array of non-linear systems with threshold [1]. The noise in neurons has been considered to come up from not only randomness of synaptic vesicle secretions (extrinsic fluctuations) but also stochasticity of ion channel gating (intrinsic fluctuations). However, it is still unclear whether and how those fluctuations help enhance information transmission in the case of supra-threshold input signals. The objective of this presentation was to see how randomness of ion channel gating could affect spike firing times and mutual information, and if SSR could be observed or not through computer simulations.

Sub-threshold task-irrelevant signals disrupt task performance more severely than supra-threshold signals

Sub-threshold task-irrelevant signals disrupt task performance more severely than supra-threshold signals

Suprathreshold stochastic resonance in visual signal detection

The present study aimed to demonstrate stochastic resonance (SR) for a visual signal above the threshold by using a two-alternative forced-choice protocol. The percent correct response enhanced at non-zero intensity of noise, while decreased with more intense noise. SR for the suprathreshold signals was found for signals with relatively low intensity above the threshold, and disappeared for more intense signals. These findings show the suprathreshold SR in the visual perception.

Suprathreshold Stochastic Resonance in Mechanoelectrical Transduction of Hair Cells

Haircell, the sound signal sensor in the auditory system, works in an environment full of noise. This noise has been demonstrated before to be a factor beneficial to the transfer of subthreshold weak signal. We further theoretically demonstrate that in suprathreshold signal situation, noise can still be a beneficial factor and enhance the haircell nonlinear transfer of suprathreshold signal. This reveals an additional constructive function of noise in hearing and provides theoretic foundation for relevant applications.

Stochastic resonance in a parallel array of nonlinear dynamical elements

In an uncoupled parallel array of bistable dynamical elements subject to a common noisy subthreshold rectangular signal, the signal-to-noise ratio (SNR) gain can be improved by tuning the internally added array noise. A SNR gain above unity is observed in certain regions of the array noise intensity. The maximum SNR gain is obtained as the size of the array goes to infinity. This form of stochastic resonance (SR), i.e., array SR, is analytically described by introducing a quasi-stationary probability density model, yielding expressions for the transition probability and the stationary autocorrelation function. The analytical results have interpretative value for the mechanism of array SR, and may be of heuristic interest for applying array SR to related signal processing problems. Additionally, the analytical descriptions of an isolated bistable system agree well with numerical results of both conventional SR for a subthreshold rectangular input and residual SR for a slightly suprathreshold signal.

Audiological evaluation and self-assessed hearing problems in subjects with single-sided congenital external ear malformations and associated conductive hearing loss

Previously, unilateral hearing impairment (UHI) has been considered of little consequence. However, a recent meta-analysis of children with UHI displayed educational and behavioural problems and possible delays of speech and language development. Further, patients with UHI consequently report hearing difficulties. Our study investigated hearing function, possible inner ear protection, and self-assessed hearing problems in 57 subjects aged between 3–80 years with single-sided congenital ear malformations and conductive UHI. Pure-tone thresholds and speech recognition (quiet, noise) were measured, and all patients completed a self-assessment questionnaire. Pure-tone thresholds corresponding to sensorineural function did not significantly differ between the normal (air conduction) and affected ear (bone conduction). However, speech recognition in both quiet and in noise was normal on the non-affected side but significantly worse on the malformed side. A moderate to high degree of self-assessed hearing problems were reported. In conclusion, hearing function in the affected ear was found to be subnormal in terms of supra threshold signal processing. Furthermore, a high degree of hearing difficulty was reported. Therefore, active treatment, surgery, or hearing amplification, might be considered.

Visual Warning Signals Optimized for Human Perception: What the Eye Sees Fastest

This study aimed to answer the question of how to design a visual warning signal that is most easily seen and produces the quickest reaction time. This is a classic problem of bionic optimization—if one knows the properties of the receiver one can most easily find a suitable solution. Because the peak of the spatio-temporal contrast sensitivity function of the human visual system occurs at non-zero spatial and temporal frequencies, it is likely that movement enhances the detectability of threshold visual signals. Earlier studies employing extended drifting sinewave gratings bear out this prediction. We have studied the ability of human observers to detect threshold visual signals for both moving and stationary stimuli. We used discrete, localized signals such as might be employed in aerospace or automotive warning signal displays. Moving stimuli show a superior detectability to non-moving stimuli of the same integrated energy. Moving stimuli at threshold detectability are seen faster than non-moving threshold stimuli. Under some conditions the speed advantage is over 0.25 seconds. Similar advantages have also been shown to occur for suprathreshold signals.