Harper [D.W. Harper, Signal detection analysis of effect of white noise intensity on sensitivity to visual flicker, Percept. Mot. Skills 48 (1979) 791-798] demonstrated that the visual flicker sensitivity was an inverted U-like function of the intensity of different levels of auditory noise from 50 to 90dB (SPL), without concomitant changes in the response bias. The aim of the present study was to extend these observations in the context of the stochastic resonance, a counterintuitive phenomenon in which a particular level of noise enhances the response of a nonlinear system to a weak input signal. We show psychophysical evidence in a yes-no paradigm for the existence of a stochastic resonance-like phenomenon in the auditory-visual interactions. We show that the detection of a weak visual signal was an inverted U-like function of the intensity of different levels of auditory noise. Nevertheless, for a strong visual signal the auditory noise acts in detriment of the ability of visual detection. Our results suggest that auditory noise could be employed in vision rehabilitation interventions in order to improve the detection of weak visual signals.

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Stochastic resonance (SR) is commonly understood to be the enhancement, by noise, of the response of a system to a weak input signal. The aim of this study was to demonstrate the occurrence of SR in spinal and cortical evoked field potentials (EFPs) elicited by periodic tactile stimuli in the anesthetized cat. The electrodes were positioned in spinal and cortical somatosensory regions in which the largest negative EFPs were detected. The periodic tactile stimuli consisted of local skin displacements on the central pad of the hindpaw. Two series of experiments were performed. First, periodic tactile stimuli and the noisy tactile stimuli were applied with the same indenter. Second, noisy tactile stimuli were applied with an additional indenter placed on the glabrous skin of the third hindpaw digit. This last protocol ensured that the signal and noise were mixed not in the skin but in the somatosensory regions of the CNS. All cats showed distinct SR behavior at the spinal and cortical stages of the sensory encoding. Such SR was abolished in the cortical but not in the spinal recording after sectioning of the dorsal columns and the ipsilateral dorsolateral funiculus. This suggests that the spinal neurons may also contribute to the SR observed at the cortical level. To the best of our knowledge, this is the first documented evidence that such a remarkable phenomenon embodies electrical processes of the spinocortical somatosensory system itself.

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