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This study aimed to observe the impact of pure Binaural Beats (BB) stimulation in the inaudible frequency range, excluding the influence of sound, on visuospatial memory. Additionally, we investigated whether the brainwave changes induced by BB stimulation directly affect brain activation. The experiment involved 17 participants (12 males with a mean age of 23.2 ± 1.7 and 5 females with a mean age of 21.0 ± 0.7) in their 20s. Each participant received 10 Hz BB stimulation by presenting frequencies of 18,000 Hz and 18,010 Hz to the left and right ears, respectively. The experiment consisted of Rest phase (5 min), Task phase (5 min), and Rest phase (5 min). The Task phase included conditions where participants performed the task either without BB stimulation “Task only” or with BB stimulation “Task + BB”. Visuospatial memory was evaluated using the 3-back task. To observe brain activation, functional Near Infrared Spectroscopy (fNIRS) was employed to measure hemodynamic responses in all phases. The cognitive task performance (Accuracy, Reaction time) and oxyhemoglobin (HbO) concentration during the Task phase were compared between conditions with and without BB stimulation using paired t-tests. Results indicated a significantly shorter Reaction time in the Task + BB condition compared to the Task only condition. Moreover, an increase in HbO concentration was observed in the F1-F3, F2-F4, and P2-P4 regions during the Task + BB condition. In conclusion, the observed increase in HbO concentration suggests a positive influence on task performance. This study is meaningful in objectively demonstrating the impact of inaudible BB stimulation on visuospatial memory, utilizing both behavioral data and direct neural activation reflected in hemodynamic responses.

Humans mostly perceive tactile sensations in daily life as a combination of warmth, vibration, and pressure. To understand the complex tactile perception and cognitive processes, in this study, we aimed to develop a multimodal stimulator and investigate changes in neuronal activity. An actuator that can display warmth (W), vibration (V), and pressure (P) on the distal region of the index finger has been developed. Preliminary experiments were conducted with nine subjects. Electroencephalograms were measured for six tactile stimuli—three single stimuli (W, V, and P) and three combination stimuli (W + V, V + P, and W + V + P)—and event-related desynchronization/synchronization (ERD/S) analysis were performed. The actuator can present all kinds of stimuli in the same location and control stimulation parameters quantitatively. For all experiments, there was an ERD in the α and β bands about 0.5 s after stimulation followed by ERS was observed in the C3 area. The change in the peak-to-peak value was the largest for warmth and the smallest for pressure. In contrast, in the duration of the ERD, W was the shortest and P was the longest. As stimulus presented simultaneously, the ERD became longer in both the alpha and beta bands. In the beta band, the peak of ERD became larger. The developed system was confirmed to be capable of providing valid tactile stimulation, inducing appropriate neuronal activation, and enabling multimodal tactile research.

This study was examined the effective connectivity between brain areas activated during driving. Using a driving simulator, the subjects controlled a wheel with both of their hands as well as an accelerator and brake pedal with their right foot. Of the areas activated during driving, three areas from each hemisphere were analyzed for effective connectivity using dynamic causal modeling. In the right hemisphere, bidirectional connectivity was prominent between the inferior temporal gyrus, precuneus, and lingual gyrus, which provided driving input . In the left hemisphere, the superior temporal gyrus provided driving input, and bidirectional connectivity was prominent between the superior temporal gyrus, inferior parietal lobule, and inferior frontal gyrus. The visual attention pathway was activated in the right hemisphere, whereas the inhibitory control movement and task-switching pathways, which are responsible for synesthesia, were activated in the left hemisphere. In both of the hemispheres, the visual attention, inhibitory control movement, and episodic memory retrieval pathways were prominent. The activation of these pathways indicates that driving requires multi-domain executive function in addition to vision. Moreover, pathway activation is influenced by the driving experience and familiarity of the driver. This study elucidated the overall effective connectivity between brain areas related to driving.

While the perception of stickiness serves as one of the fundamental dimensions for tactile sensation, little has been elucidated about the stickiness sensation and its neural correlates. The present study investigated how the human brain responds to perceived tactile sticky stimuli using functional magnetic resonance imaging (fMRI). To evoke tactile perception of stickiness with multiple intensities, we generated silicone stimuli with varying catalyst ratios. Also, an acrylic sham stimulus was prepared to present a condition with no sticky sensation. From the two psychophysics experiments-the methods of constant stimuli and the magnitude estimation-we could classify the silicone stimuli into two groups according to whether a sticky perception was evoked: the group that evoked sticky perception and the group that did not. In the vs. contrast analysis of the fMRI data using the general linear model (GLM), the contralateral primary somatosensory area (S1) and ipsilateral dorsolateral prefrontal cortex (DLPFC) showed significant activations in subjects, whereas no significant result was found in the vs. contrast. This result indicates that the perception of stickiness not only activates the somatosensory cortex, but also possibly induces higher cognitive processes. Also, the contrast analysis revealed significant activations in several subcortical regions, including the pallidum, putamen, caudate and thalamus, as well as in another region spanning the insula and temporal cortices. These brain regions, previously known to be related to tactile discrimination, may subserve the discrimination of different intensities of tactile stickiness. The present study unveils the human neural correlates of the tactile perception of stickiness and may contribute to broadening the understanding of neural mechanisms associated with tactile perception.

This study aimed to investigate the effect of inaudible-frequency binaural beats (BB), excluding the influence of audible sound, on visuospatial working memory performance (VSWMP). In particular, the effects were examined in relation to the stimulation timing of the stimulus and the task performance level of participants. Thirty adults in their 20 s (20 males, 25.7 ± 1.8 years; 10 females, 24.3 ± 1.6 years) participated in the experiment. A 10 Hz BB stimulus was generated by simultaneously presenting 18,000 Hz and 18,010 Hz tones to the left and right ears, respectively. The experiment employed a within-participant design consisting of a rest phase (5 min) and a task phase (5 min), with four BB stimulation conditions: Control (no BB), Exp1 (BB during both rest and task phases), Exp2 (BB during rest only), and Exp3 (BB during task only). VSWMP was assessed using corrected hit rate and reaction time in a 3-back task. Results indicated that all BB conditions (Exp1, Exp2, Exp3) significantly improved VSWMP compared to the Control condition, regardless of the stimulation timing. When participants were grouped based on task performance level into high- and low-performing groups (HPG, LPG), significant improvements in VSWMP were particularly evident in the LPG across all BB conditions compared to the Control. Notably, in Exp3, LPG participants demonstrated VSWMP comparable to that of the HPG. In conclusion, while BB stimulation enhances VSWMP regardless of its stimulation timing, its effectiveness may vary depending on the task performance level.

Humans process a plethora of sensory information that is provided by various entities in the surrounding environment. Among the five major senses, technology for touch, haptics, is relatively young and has relatively limited applications largely due to its need for physical contact. In this article, we suggest a new way for non-contact haptic stimulation that uses laser , which has potential advantages such as mid-air stimulation, high spatial precision and long working distance. We demonstrate such tactile stimulation can be enabled by laser-induced thermoelastic effects by means of physical and perceptual studies, as well as simulations. In the physical study, the mechanical effect of laser on a human skin sample is detected using low-power radiation in accordance with safety guidelines. Limited increases (< ~2.5 °C) in temperature at the surface of the skin, examined by both thermal camera and the Monte Carlo simulation, indicate that laser does not evoke heat-induced nociceptive sensation. In the human EEG study, brain responses to both mechanical and laser stimulation are consistent, along with subjective reports of the non-nociceptive sensation of laser stimuli.

Perceptual sensitivity to tactile roughness varies across individuals for the same degree of roughness. A number of neurophysiological studies have investigated the neural substrates of tactile roughness perception, but the neural processing underlying the strong individual differences in perceptual roughness sensitivity remains unknown. In this study, we explored the human brain activation patterns associated with the behavioral discriminability of surface texture roughness using functional magnetic resonance imaging (fMRI). First, a whole-brain searchlight multi-voxel pattern analysis (MVPA) was used to find brain regions from which we could decode roughness information. The searchlight MVPA revealed four brain regions showing significant decoding results: the supplementary motor area (SMA), contralateral postcentral gyrus (S1), and superior portion of the bilateral temporal pole (STP). Next, we evaluated the behavioral roughness discrimination sensitivity of each individual using the just-noticeable difference (JND) and correlated this with the decoding accuracy in each of the four regions. We found that only the SMA showed a significant correlation between neuronal decoding accuracy and JND across individuals; Participants with a smaller JND (i.e., better discrimination ability) exhibited higher decoding accuracy from their voxel response patterns in the SMA. Our findings suggest that multivariate voxel response patterns presented in the SMA represent individual perceptual sensitivity to tactile roughness and people with greater perceptual sensitivity to tactile roughness are likely to have more distinct neural representations of different roughness levels in their SMA.

This study demonstrates the feasibility of a mid-air means of haptic stimulation at a long distance using the plasma effect induced by laser. We hypothesize that the stress wave generated by laser-induced plasma in the air can propagate through the air to reach the nearby human skin and evoke tactile sensation. To validate this hypothesis, we investigated somatosensory responses in the human brain to laser plasma stimuli by analyzing electroencephalography (EEG) in 14 participants. Three types of stimuli were provided to the index finger: a plasma stimulus induced from the laser, a mechanical stimulus transferred through Styrofoam stick, and a sham stimulus providing only the sound of the plasma and mechanical stimuli at the same time. The event-related desynchronization/synchronization (ERD/S) of sensorimotor rhythms (SMRs) in EEG was analyzed. Every participant verbally reported that they could feel a soft tap on the finger in response to the laser stimulus, but not to the sham stimulus. The spectrogram of EEG evoked by laser stimulation was similar to that evoked by mechanical stimulation; alpha ERD and beta ERS were present over the sensorimotor area in response to laser as well as mechanical stimuli. A decoding analysis revealed that classification error increased when discriminating ERD/S patterns between laser and mechanical stimuli, compared to the case of discriminating between laser and sham, or mechanical and sham stimuli. Our neurophysiological results confirm that tactile sensation can be evoked by the plasma effect induced by laser in the air, which may provide a mid-air haptic stimulation method.

We studied the laser-induced thermoelastic effects in an elastic medium that can be used for indirect laser stimulation, depending on the position of the absorbing layer. The displacement of the front and rear surface centers of the medium was simulated numerically by solving the heat transfer and thermoelastic wave equations. It was observed that by changing the position of the absorbing layer in the medium, the magnitude and more importantly, the direction of displacement can be controlled. In particular, pushing (displacement into the skin) was expected for an absorbing layer near the rear surface of the medium, whereas pulling (displacement away from the skin) was observed for an absorbing layer near the front surface.

The purpose of this study is to analyze the cognitive characteristics that can be induced by vibration stimuli at two intensities, three frequencies, and five presentation periods. The experiment was conducted on 20 right-handed adult males, and a subjective evaluation was performed using a questionnaire. Regression analysis was performed to observe the parameters affecting cognitive characteristics according to changes in intensity, frequency, and stimulation duration. The regression analysis results showed that the cognitive characteristics affected by changes in intensity, frequency, and stimulation duration were “heavy”, “bold”, “thick”, and “light”. The cognitive characteristics affected by two-variable combinations were “deep”, “clear”, “vibrating”, “dense”, “numb”, “blunt”, “shallow”, “fuzzy”, and “soft”. Cognitive characteristics affected by either intensity, frequency, or stimulation duration were “fast”, “pungent”, “skinny”, “thin”, “slow”, “ticklish”, “tingling”, “prickling”, “tap”, and “rugged”. By observing the cognitive characteristics that can be induced by the combination of intensity, frequency, and stimulation duration, we confirmed that in addition to intensity and frequency, the stimulation duration is an important factor that influences the induction of various cognitive characteristics. The results presented in the study can be used to enhance the utility of haptic surfaces for extended reality applications.