Abstract
Stochastic Resonance (SR) is a phenomenon, mainly present in nonlinear detection systems, in which the addition of certain amount of noise, called optimal noise, has proven to enhance detection performance of subthreshold stimuli. When added noise is present only during the stimulus, an additional enhancement can be reached. This phenomenon was called time Coincidence Enhanced Stochastic Resonance (CESR). The aim of this study was to study the effect of spatially distributed vibrotactile noise in subthreshold stimuli detection. The correct response rates from two different stimuli conditions were compared, using four tactile stimulator systems to excite four different spatial locations on the fingertip. Under two different conditions, the stimuli were present in only one randomly chosen stimulator. For the first condition, all stimulators contain optimal noise level. In the second condition, the optimal noise was present only at the stimulator with the stimulus. SR threshold principle should not produce different correct response rates between the two conditions, since in both cases the noise enables the subthreshold stimulus to go above threshold. The stimulus signal used was a rectangular displacement controlled pulse that lasted 300ms within a 1.5s attention interval, applied to the exploratory zone of the index finger of 13 human subjects. For all subjects it was found that detection rates were better (p<0.0003) when noise was spatially coincident with the stimulus, compared to the condition in which noise was present simultaneously in all the stimulators. According to our literature review this is the first report of SR being influenced by the spatial location of the noise. These results were not found previously reported, so represent the discovery of a new phenomenon. We call this phenomenon Spatial-Coincidence-Enhanced Stochastic Resonance (SCESR). As results show, the optimal noise level is dependent on the relative position between stimulus and noise.
Highlights
Stochastic resonance (SR) is a counterintuitive phenomenon in which the addition of certain amount of noise increases detection of weak signals in some nonlinear systems such as touch [1], [2], [3], [4], [5], [6]
The objective of the present study is to test predictions made from the SR model under two different conditions: In the first condition, the noise was applied at the stimulus location and at the other three locations, and the other with the noise coincident at the same spatial location as that of the rectangular pulse stimulus
Optimal noise levels which produce stochastic resonance with correct response rates above chance were measured for all 13 subjects, for two different conditions: noise only in the same stimulator that contains the rectangular stimuli and noise in all
Summary
Stochastic resonance (SR) is a counterintuitive phenomenon in which the addition of certain amount of noise increases detection of weak signals in some nonlinear systems such as touch [1], [2], [3], [4], [5], [6]. There is multiple experimental evidence that SR occurs in the human tactile system [2], [3], [7], [8], [9]. Authors used a subthreshold mechanical stimulus in the form of pulse and mechanical noise in the form of random. Coincident vibrotactile noise improves subthreshold stimulus detection vibrations. They demonstrated that true positive detection rates were higher for certain levels of noise added to the subthreshold stimuli signal. SR phenomena are commonly explained assuming that noise works as a pedestal allowing weak signals to exceed sensory thresholds [2], [8], [10]
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