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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.

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Related in: MedlinePlus

Auditory stimuli representation.Frequency-time representation of auditory noise (left) and the 3D sound (right).
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pone-0002860-g010: Auditory stimuli representation.Frequency-time representation of auditory noise (left) and the 3D sound (right).

Mentions: This study obtained ethics approval from the CERSS (Comité d'éthique de la recherche des sciences de la santé) of Université de Montréal where all the testing took place. Informed written consent was obtained from all participants of the study. The experiments took place in a dark room for vision testing and illuminated for tactile and posture testing. The auditory stimuli were presented binaurally by means of a pair of headphones (Grado Lab SR80) plugged in an amplifier (Rolls RA62b). We used a calibrated high fidelity capacitor microphone (Behringer ECM8000) to verify the frequency response of the headphones inside an acoustically isolated chamber. A computer provided auditory white noise to the amplifier and the intensity range of the noise generator was calibrated to supply white noise with an intensity of 60 to 95 dBSPL with a systematic error of 3.5 dBSPL. The testing room sound disturbances (e.g., computer fans and low power sounds coming from outside the testing room) were recorded by using the same microphone as before and their cut-off frequency was 2.5 kHz with intensity of 50±3.5 dBSPL. Although the noise generation band and the electronic amplification bandpass are wider than the auditory spectrum, the acoustic transducer of the headphones drastically modifies the noise spectrum density because of mechanic and electric resonances. The most limiting factors at successive stages are the headphones that cannot reproduce the full white noise spectrum but still have an effective acoustic noise spectrum. Common transducers have a high cut-off frequency between 10 and 12 kHz but the human auditory noise thresholds are best for a noise spectrum between 5 and 12 kHz (ITU-R 468 noise weighting standard) partially compensating each other. The different processing stages required for the original noise to finally reach the cortex inevitably modify the original white noise spectrum. This implies that the cortex interprets only a limited noise band with a cut-off frequency of about 12 to 15 kHz (where its spectrum is attenuated) instead of a full white noise spectrum. We evaluated the subjects' hearing, from 250 Hz to 8 KHz, in A 6′×10′ double wall IAC audiometric sound suite that met the ANSI standard (Standard 3.1-1991) for permissible ambient noise levels (in one-third octave bands) for testing in free-field and under headphones. We used an audiometer (Midimate 602). All the subjects had normal hearing with a group minimum of 8±4.5 dBSPL at 1200±200 Hz. Figure 10 (left) shows a time-frequency spectrogram example of auditory noise and The figure 10 (right) shows a time-frequency spectrogram example of the 3D sound stimuli.


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

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

Auditory stimuli representation.Frequency-time representation of auditory noise (left) and the 3D sound (right).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0002860-g010: Auditory stimuli representation.Frequency-time representation of auditory noise (left) and the 3D sound (right).
Mentions: This study obtained ethics approval from the CERSS (Comité d'éthique de la recherche des sciences de la santé) of Université de Montréal where all the testing took place. Informed written consent was obtained from all participants of the study. The experiments took place in a dark room for vision testing and illuminated for tactile and posture testing. The auditory stimuli were presented binaurally by means of a pair of headphones (Grado Lab SR80) plugged in an amplifier (Rolls RA62b). We used a calibrated high fidelity capacitor microphone (Behringer ECM8000) to verify the frequency response of the headphones inside an acoustically isolated chamber. A computer provided auditory white noise to the amplifier and the intensity range of the noise generator was calibrated to supply white noise with an intensity of 60 to 95 dBSPL with a systematic error of 3.5 dBSPL. The testing room sound disturbances (e.g., computer fans and low power sounds coming from outside the testing room) were recorded by using the same microphone as before and their cut-off frequency was 2.5 kHz with intensity of 50±3.5 dBSPL. Although the noise generation band and the electronic amplification bandpass are wider than the auditory spectrum, the acoustic transducer of the headphones drastically modifies the noise spectrum density because of mechanic and electric resonances. The most limiting factors at successive stages are the headphones that cannot reproduce the full white noise spectrum but still have an effective acoustic noise spectrum. Common transducers have a high cut-off frequency between 10 and 12 kHz but the human auditory noise thresholds are best for a noise spectrum between 5 and 12 kHz (ITU-R 468 noise weighting standard) partially compensating each other. The different processing stages required for the original noise to finally reach the cortex inevitably modify the original white noise spectrum. This implies that the cortex interprets only a limited noise band with a cut-off frequency of about 12 to 15 kHz (where its spectrum is attenuated) instead of a full white noise spectrum. We evaluated the subjects' hearing, from 250 Hz to 8 KHz, in A 6′×10′ double wall IAC audiometric sound suite that met the ANSI standard (Standard 3.1-1991) for permissible ambient noise levels (in one-third octave bands) for testing in free-field and under headphones. We used an audiometer (Midimate 602). All the subjects had normal hearing with a group minimum of 8±4.5 dBSPL at 1200±200 Hz. Figure 10 (left) shows a time-frequency spectrogram example of auditory noise and The figure 10 (right) shows a time-frequency spectrogram example of the 3D sound stimuli.

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