Relation between human alertness, velocity wave profile of saccade, and performance of visual activities

Transcutaneous trigeminal nerve stimulation modulates the hand blink reflex

The hand-blink reflex (HBR) is a subcortical response, elicited by the electrical stimulation of the median nerve, whose magnitude is specifically modulated according to the spatial properties of the defensive peripersonal space (DPPS) of the face. For these reasons, the HBR is commonly used as a model to assess the DPPS of the face. Little is known on the effects induced by the activation of cutaneous afferents from the face on the DPPS of the face. Therefore, we tested the effect of non-painful transcutaneous trigeminal nerve stimulation (TNS) on the amplitude of the HBR. Fifteen healthy participants underwent HBR recording before and after 20 min of sham- and real-TNS delivered bilaterally to the infraorbital nerve in two separate sessions. The HBR was recorded bilaterally from the orbicularis oculi muscles, following non-painful median nerve stimulation at the wrist. The HBR amplitude was assessed in the “hand‐far” and “hand‐near” conditions, relative to the hand position in respect to the face. The amplitudes of the hand-far and hand-near HBR were measured bilaterally before and after sham- and real-TNS. Real-TNS significantly reduced the magnitude of the HBR, while sham-TNS had no significant effect. The inhibitory effect of TNS was of similar extent on both the hand-far and hand-near components of the HBR, which suggests an action exerted mainly at brainstem level.

Analysis of cognitive fatigue using EEG parameters

Continuous and repetitive performance of a task is likely to induce a drop in alertness levels of an individual. Changes in Electroencephalogram (EEG) have been proposed in literature as a marker of alertness during repeated performance of a cognitive task set. The present paper investigates the increase in fatigue levels and resultant drop in alertness of subjects during continuous performance of cognitive tasks by analyzing changes in energy of EEG frequency bands. The trends reflected in the EEG parameters correspond to a gradual increase in fatigue levels of subjects with increase in cognitive loading.

A noncontact measurement of saccadic eye movement with two high-speed cameras

A noncontact method for measuring saccadic eye movement with two high-speed cameras is proposed. The method is based on image processing for acquiring the center gravity of one pupil of the subject and also on stereo photogrammetry for estimating three-dimensional coordinate of the pupil. The proposed method was examined through experiments using a imitated eye ball and using a real human subject. The results showed a possibility of the method for the measurement. Since dynamic characteristics of the saccadic eye movement is reported as a promising index for monitoring human vigilance level according to the author's previous research works, this method can be utilized for accident prevention system in the future. However, there is still room for improvement in measuring accuracy and stability to the body motion in terms of its practical use.

Acoustic feedback system with digital signal processor to alert the subject and quantitative visualization of arousal reaction induced by the sound using dynamic characteristics of saccadic eye movement: a preliminary study

A new system has been developed to assess human alertness and to alert the subject with acoustic stimulation in accordance with the assessed level of alertness. Dynamic characteristics of saccadic eye movement (saccade: SC) were used to calculate an alertness index. Digital signal processor was adopted for the calculation. The system was tested through eye tracking tasks. The results indicated that the developed system could awaken the subject by feeding sound back to the subject. Also, arousal reaction induced by the sound was visualized quantitatively by analyzing values of the alertness index after the stimulation. These results indicate applicability of the system not only to awakening device for accident prevention, but also to a tool for investigating effects of the stimulation.