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.

Subthreshold noise facilitates the detection and discrimination of visual signals.

It has recently been shown that noise can facilitate signal detection in the sensory systems. We have previously shown that contrast detection sensitivity in the visual perception is improved in the presence of noise by measuring the detection threshold (Sasaki et al. Effect of noise on the contrast detection threshold in visual perception, Neurosci. Lett. 408 (2006) 94-97). In the present study, we reexamined the previous findings by measuring the percent correct detection rates in a two-alternative forced-choice (2AFC) paradigm and examined further whether the addition of noise improved the discrimination of the visual patterns. In the first experiment, the addition of weak noise facilitated the detection rate, thus confirming the previous findings. Furthermore, a significant correlation between the control detection rate without noise and the noise intensity that induced the maximum facilitation of the detection rate was found. In the second experiment, the addition of a subthreshold noise facilitated the discrimination of visual patterns. These results showed that the effect of noise that induces facilitation in signal detection is robust regardless of the methods used for measuring the detection sensitivity, and that pattern discrimination can also be improved by the addition of noise.

Effect of noise on the contrast detection threshold in visual perception.

It has recently been shown that noise can improve the detection of stimuli in several sensory modalities. We herein investigated whether visual contrast detection sensitivity can be improved by adding a certain amount of noise. The contrast detection thresholds of a light changing brightness periodically were measured either with or without overlapping noise in 22 normal participants. Sinusoidal modulating light at 1 or 15 Hz was used as a signal. White noise was used to produce random flickering light as the noise. Participants were required to detect any changes in the brightness of the signal with or without noise. The contrast detection threshold, which was measured using a psychophysical method, decreased at around the threshold level of the noise intensity. The maximum facilitatory effect was obtained at a noise intensity of 5 dB. This effect was consistently observed regardless of the frequency of the signal (1 and 15 Hz). These findings indicate that noise can improve the signal detection in human visual perception.

Periodic buckling of smectic-A tubular filaments in an isotropic phase.

Periodic buckling of smectic-A tubular filaments in an isotropic phase has been investigated both experimentally and theoretically in the binary mixture of octyloxycyanobiphenyl and dodecyl alcohol. As the mixture is cooled, straight filaments become unstable and continuously buckle by elongating at a constant periodicity. An analytical solution to the minimization of the curvature elastic energy of the smectic-A filament has been shown, and is consistent with the shapes of the buckled filaments. In addition, the dependence of the load on the length of the filament has been numerically calculated, and the critical buckling load of the smectic-A filament has been found to be of the order of 1 pN.