Enhancement of a genuine visual mismatch negativity correlates with the facilitation of perceptual alternation of a bistable image.

By focusing on the automatic visual change detection process, the present study attempted to clarify neural processing relevant to the exogenously driven perceptual alternation (ePA) of a bistable image. In our recent electroencephalographic study, the oddball paradigm was adopted to the continuous presentation of a bistable image to record visual mismatch negativity (vMMN, a relative enhancement in the brain response to a deviant over a repetitively presented standard, reflecting the visual change detection process and prediction error to the deviant over the standard). In terms of interindividual differences in behavioral and neural data, a correlation was reported previously between the enhancement of vMMN and facilitation of perceptual alternation, suggesting the involvement of the visual change detection process in ePA. However, the vMMN recorded was expected to be confounded by neural adaptation to the repetitively presented standard; thus, it currently remains unclear whether visual change detection not dependent on neural adaptation, reflected in a 'genuine vMMN', is relevant to ePA. To examine this issue, the present study used a new stimulation paradigm, based on the so-called equiprobable paradigm, to mitigate neural adaptation. The results showed that a genuine vMMN significantly emerged and correlated with an increase in the proportion of perceptual alternation across participants. This supports the involvement of the automatic visual change detection process, not dependent on neural adaptation, in facilitating perceptual alternation. The present results provide a deeper understanding of the involvement of the visual change detection process in ePA.

Temperature Distribution and Thermal Conductivity Measurements of Chirality-Assigned Single-Walled Carbon Nanotubes by Photoluminescence Imaging Spectroscopy.

It is expected that single-walled carbon nanotubes (SWCNTs) have high thermal conductivity along the tube axis and that the thermal conductivities depend on their structure, such as length, diameter, chirality (n, m), and so forth. Although many experimental measurements of the thermal conductivity have been reported, the SWCNT structure was not characterized sufficiently. In particular, the chirality was not assigned, and it was not confirmed whether SWCNT was isolated or not (bundled with multiplicate SWCNTs). Therefore, measured values widely vary (101 to 104 W/(m·K)) so far. Here, we measured the thermal conductivity of chirality-assigned SWCNTs, which were individually suspended, by using photoluminescence (PL) imaging spectroscopy. The temperature distribution along the tube axis was obtained, and the temperature dependence of the thermal conductivity was measured in a wide-temperature range (from 350 to 1000 K). For (9, 8) SWCNTs with 10-12 µm in length, the thermal conductivity was 1166 ± 243 W/(m·K) at 400 K. The proposed PL imaging spectroscopy enables to measure the thermal conductivity of SWCNTs with high precision and without any contacts, and it is an effective method in the temperature distribution measurements of nanomaterials.