Limits...
Ubiquitous crossmodal Stochastic Resonance in humans: auditory noise facilitates tactile, visual and proprioceptive sensations.

Lugo E, Doti R, Faubert J - PLoS ONE (2008)

Bottom Line: Specifically, we show that the effective auditory noise significantly increased tactile sensations of the finger, decreased luminance and contrast visual thresholds and significantly changed EMG recordings of the leg muscles during posture maintenance.We conclude that crossmodal SR is a ubiquitous phenomenon in humans that can be interpreted within an energy and frequency model of multisensory neurons spontaneous activity.The result is an integrated activation that promotes sensitivity transitions and the signals are then perceived.

View Article: PubMed Central - PubMed

Affiliation: Visual Psychophysics and Perception Laboratory, School of Optometry, University of Montreal, Montreal, Quebec, Canada.

ABSTRACT

Background: Stochastic resonance is a nonlinear phenomenon whereby the addition of noise can improve the detection of weak stimuli. An optimal amount of added noise results in the maximum enhancement, whereas further increases in noise intensity only degrade detection or information content. The phenomenon does not occur in linear systems, where the addition of noise to either the system or the stimulus only degrades the signal quality. Stochastic Resonance (SR) has been extensively studied in different physical systems. It has been extended to human sensory systems where it can be classified as unimodal, central, behavioral and recently crossmodal. However what has not been explored is the extension of this crossmodal SR in humans. For instance, if under the same auditory noise conditions the crossmodal SR persists among different sensory systems.

Methodology/principal findings: Using physiological and psychophysical techniques we demonstrate that the same auditory noise can enhance the sensitivity of tactile, visual and propioceptive system responses to weak signals. Specifically, we show that the effective auditory noise significantly increased tactile sensations of the finger, decreased luminance and contrast visual thresholds and significantly changed EMG recordings of the leg muscles during posture maintenance.

Conclusions/significance: We conclude that crossmodal SR is a ubiquitous phenomenon in humans that can be interpreted within an energy and frequency model of multisensory neurons spontaneous activity. Initially the energy and frequency content of the multisensory neurons' activity (supplied by the weak signals) is not enough to be detected but when the auditory noise enters the brain, it generates a general activation among multisensory neurons of different regions, modifying their original activity. The result is an integrated activation that promotes sensitivity transitions and the signals are then perceived. A physiologically plausible model for crossmodal stochastic resonance is presented.

Show MeSH

Related in: MedlinePlus

Unimodal and crossmodal SR architecture.The scheme represents the physical paths through which the signals combine in the brain.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2481403&req=5

pone-0002860-g008: Unimodal and crossmodal SR architecture.The scheme represents the physical paths through which the signals combine in the brain.

Mentions: From unimodal SR studies it can be inferred that 70 dBSPL is much louder than the noise required for auditory SR [25]–[26]. This may make the SR label we have used here problematic. However the auditory unimodal SR works in a simpler architecture than the crossmodal SR as shown in figure 8, where more neuronal networks are necessarily involved between modalities. Since the crossmodal architecture is vaster, and complex, one would expect more energy losses in such network and according with the model we have developed it is possible to have SR with these conditions. The aforementioned studies have shown that auditory unimodal SR happens between 5 dB [25] and 3–5 dB [26] below a point defined as noise threshold [26]. The noise threshold is the point where the noise hinders the signal detection and the sensitivity worsens to levels above threshold (the crossing point in the inverse u-shape curve). If we use this level as our reference instead of the SPL absolute scale (we will call this level the noise ceiling level that defines a ceiling decibel dBc) then we found that crossmodal SR threshold minima occur approximately in the same experimental range as the ones mentioned above. Figure 9 shows the crossmodal SR threshold minima for the four experiments presented and it is clear that for visual experiments the minima are localized at −6±1 dBc (first order) and −5±1 dBc (second order). In the proprioception experiments the minima occurs around −6±1 dBc and for tactile experiments at −8±1 dBc. The theoretical model can be used to estimate noise ceiling levels as follows: since conditions (14) and (15) are equivalent we only used condition (14). Condition (14) with parameter values γ− = 0.095, β− = 0.316, α+ = 49, α− = 1, ω0 = 0.6283 (0.1 Hz), N = 500, c = 0.02, and ωcut = 3 gave a firing threshold of σ− = 0.147. Computer simulations gave a bigger value of σ− = 0.209. We increased σ− up to the SR peak (by analyzing the 0.1 Hz signal spectrum amplitude) and we kept increasing σ− until the 0.1 Hz signal spectrum amplitude was the same as at threshold (noise ceiling level). The SR peak was found at σ− = 0.22 and the noise ceiling level at σ− = 0.25. We know that the crossmodal peaks occur at approximately 70 dB therefore σ− = 0.22 is proportional to 70 dB. This means that the noise ceiling level would be around 79 dB. This implies that the SR peak is located at −9 dBc which is the same order of magnitude than the experimental values found for unimodal and crossmodal SR with the above parameters. These results underscore the very important fact that independently of the unimodal or crossmodal SR the energy transfer from signal plus noise is approximately fixed, which correlates with our theoretical model. Note that for measuring the noise ceiling level we have used a similar approach than the one presented in [26].


Ubiquitous crossmodal Stochastic Resonance in humans: auditory noise facilitates tactile, visual and proprioceptive sensations.

Lugo E, Doti R, Faubert J - PLoS ONE (2008)

Unimodal and crossmodal SR architecture.The scheme represents the physical paths through which the signals combine in the brain.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2481403&req=5

pone-0002860-g008: Unimodal and crossmodal SR architecture.The scheme represents the physical paths through which the signals combine in the brain.
Mentions: From unimodal SR studies it can be inferred that 70 dBSPL is much louder than the noise required for auditory SR [25]–[26]. This may make the SR label we have used here problematic. However the auditory unimodal SR works in a simpler architecture than the crossmodal SR as shown in figure 8, where more neuronal networks are necessarily involved between modalities. Since the crossmodal architecture is vaster, and complex, one would expect more energy losses in such network and according with the model we have developed it is possible to have SR with these conditions. The aforementioned studies have shown that auditory unimodal SR happens between 5 dB [25] and 3–5 dB [26] below a point defined as noise threshold [26]. The noise threshold is the point where the noise hinders the signal detection and the sensitivity worsens to levels above threshold (the crossing point in the inverse u-shape curve). If we use this level as our reference instead of the SPL absolute scale (we will call this level the noise ceiling level that defines a ceiling decibel dBc) then we found that crossmodal SR threshold minima occur approximately in the same experimental range as the ones mentioned above. Figure 9 shows the crossmodal SR threshold minima for the four experiments presented and it is clear that for visual experiments the minima are localized at −6±1 dBc (first order) and −5±1 dBc (second order). In the proprioception experiments the minima occurs around −6±1 dBc and for tactile experiments at −8±1 dBc. The theoretical model can be used to estimate noise ceiling levels as follows: since conditions (14) and (15) are equivalent we only used condition (14). Condition (14) with parameter values γ− = 0.095, β− = 0.316, α+ = 49, α− = 1, ω0 = 0.6283 (0.1 Hz), N = 500, c = 0.02, and ωcut = 3 gave a firing threshold of σ− = 0.147. Computer simulations gave a bigger value of σ− = 0.209. We increased σ− up to the SR peak (by analyzing the 0.1 Hz signal spectrum amplitude) and we kept increasing σ− until the 0.1 Hz signal spectrum amplitude was the same as at threshold (noise ceiling level). The SR peak was found at σ− = 0.22 and the noise ceiling level at σ− = 0.25. We know that the crossmodal peaks occur at approximately 70 dB therefore σ− = 0.22 is proportional to 70 dB. This means that the noise ceiling level would be around 79 dB. This implies that the SR peak is located at −9 dBc which is the same order of magnitude than the experimental values found for unimodal and crossmodal SR with the above parameters. These results underscore the very important fact that independently of the unimodal or crossmodal SR the energy transfer from signal plus noise is approximately fixed, which correlates with our theoretical model. Note that for measuring the noise ceiling level we have used a similar approach than the one presented in [26].

Bottom Line: Specifically, we show that the effective auditory noise significantly increased tactile sensations of the finger, decreased luminance and contrast visual thresholds and significantly changed EMG recordings of the leg muscles during posture maintenance.We conclude that crossmodal SR is a ubiquitous phenomenon in humans that can be interpreted within an energy and frequency model of multisensory neurons spontaneous activity.The result is an integrated activation that promotes sensitivity transitions and the signals are then perceived.

View Article: PubMed Central - PubMed

Affiliation: Visual Psychophysics and Perception Laboratory, School of Optometry, University of Montreal, Montreal, Quebec, Canada.

ABSTRACT

Background: Stochastic resonance is a nonlinear phenomenon whereby the addition of noise can improve the detection of weak stimuli. An optimal amount of added noise results in the maximum enhancement, whereas further increases in noise intensity only degrade detection or information content. The phenomenon does not occur in linear systems, where the addition of noise to either the system or the stimulus only degrades the signal quality. Stochastic Resonance (SR) has been extensively studied in different physical systems. It has been extended to human sensory systems where it can be classified as unimodal, central, behavioral and recently crossmodal. However what has not been explored is the extension of this crossmodal SR in humans. For instance, if under the same auditory noise conditions the crossmodal SR persists among different sensory systems.

Methodology/principal findings: Using physiological and psychophysical techniques we demonstrate that the same auditory noise can enhance the sensitivity of tactile, visual and propioceptive system responses to weak signals. Specifically, we show that the effective auditory noise significantly increased tactile sensations of the finger, decreased luminance and contrast visual thresholds and significantly changed EMG recordings of the leg muscles during posture maintenance.

Conclusions/significance: We conclude that crossmodal SR is a ubiquitous phenomenon in humans that can be interpreted within an energy and frequency model of multisensory neurons spontaneous activity. Initially the energy and frequency content of the multisensory neurons' activity (supplied by the weak signals) is not enough to be detected but when the auditory noise enters the brain, it generates a general activation among multisensory neurons of different regions, modifying their original activity. The result is an integrated activation that promotes sensitivity transitions and the signals are then perceived. A physiologically plausible model for crossmodal stochastic resonance is presented.

Show MeSH
Related in: MedlinePlus