The goal of this study was to investigate the relationship between the psychophysical vibrotactile thresholds of the Pacinian (P) channel and the mechanical properties of the skin at the fingertip. Seven healthy adult subjects (age: 23–30) participated in the study. The mechanical stimuli were 250-Hz sinusoidal bursts and applied with cylindrical contactor probes of radii 1, 2, and 3.5 mm on three locations at the fingertip. The duration of each burst was 0.5 s (rise and fall time: 50 ms). The subjects performed a two-interval forced-choice task while the stimulus levels changed for tracking the threshold at 75% probability of detection. There were significant main effects of contactor radius and location (two-way ANOVA, values of p < 0.001). The thresholds decreased as the contactor radius increased (i.e., spatial summation effect) at all locations. The thresholds were lowest near the whorl at the fingertip. Additionally, we measured the mechanical impedance (specifically, the storage and loss moduli) at the contact locations. The storage moduli did not change with the contactor location, but the loss moduli were lowest near the whorl. While the loss moduli decreased, the storage moduli increased (e.g., more springiness) as the contactor radius increased. There was moderate and barely significant correlation between the absolute thresholds and the storage moduli (r = 0.650, p = 0.058). However, the correlation between the absolute thresholds and the loss moduli was high and very significant (r = 0.951, p < 0.001). The results suggest that skin mechanics may be important for locally shaping psychophysical detection thresholds, which would otherwise be expected to be constant due to uniform Pacinian innervention density at the fingertip.

In this study, a lorenz-like chaotic system was developed to encrypt the dorsal hand patterns on a microcomputer. Firstly, the dorsal hand vein images were taken from the subjects via an infrared camera. These were subjected to two different processes called as contrast enhancement and segmentation of vein regions. Secondly, the pre-and post-processed images were encrypted with a new encryption algorithm in the microcomputer environment. For the encryption process, random numbers were generated by the chaotic system. These random numbers were subjected to NIST-800-22 test which is the most widely accepted statistical test suite. The Speeded Up Robust Feature (SURF) matching algorithm was utilized in the initial condition sensitivity analysis of the encrypted images, The results of the analysis has shown that the proposed encryption algorithm can be used in identification and verification systems. The encrypted images were analysed with histogram, correlation, entropy, pixel change rate (NPCR), initial condition sensitivity, data loss and noise attacks which are frequently used for security analyses in the literature. In addition, the images were analyzed after noise attacks by means of peak signal-to-noise ratio (PSNR), mean square error (MSE) and the structural similarity index (SSIM) tests. It has been shown that dorsal hand vein images can be used in identification systems safely with the help of proposed method on microcomputers.

We investigated the gating effect of passive and active movement on the vibrotactile detection thresholds of the Pacinian (P) psychophysical channel and forward masking. Previous work on gating mostly used electrocutaneous stimulation and did not allow focusing on tactile submodalities. Ten healthy adults participated in our study. Passive movement was achieved by swinging a platform, on which the participant’s stimulated hand was attached, manually by a trained operator. The root-mean-square value of the movement speed was kept in a narrow range (slow: 10–20 cm/s, fast: 50–60 cm/s). Active movement was performed by the participant him-/herself using the same apparatus. The tactile stimuli consisted of 250-Hz sinusoidal mechanical vibrations, which were generated by a shaker mounted on the movement platform and applied to the middle fingertip. In the forward-masking experiments, a high-level masking stimulus preceded the test stimulus. Each movement condition was tested separately in a two-interval forced-choice detection task. Both passive and active movement caused a robust gating effect, that is, elevation of thresholds, in the fast speed range. Statistically significant change of thresholds was not found in slow movement conditions. Passive movement yielded higher thresholds than those measured during active movement, but this could not be confirmed statistically. On the other hand, the effect of forward masking was approximately constant as the movement condition varied. These results imply that gating depends on both peripheral and central factors in the P channel. Active movement may have some facilitatory role and produce less gating. Additionally, the results support the hypothesis regarding a critical speed for gating, which may be relevant for daily situations involving vibrations transmitted through grasped objects and for manual exploration.