Effects of the Weight and Balance of Head-Mounted Displays on Physical Load

To maximize user experience in VR environments, optimizing the comfortability of head-mounted displays (HMDs) is essential. To date, few studies have investigated the fatigue induced by wearing commercially available HMDs. Here, we focus on the effects of HMD weight and balance on the physical load experienced by the user. We conducted an experiment in which participants completed a shooting game while wearing differently weighted and balanced HMDs. Afterwards, the participants completed questionnaires to assess levels of discomfort and fatigue. The results clarify that the weight of the HMD affects user fatigue, with the degree of fatigue varying depending on the center of mass position. Additionally, they suggest that the torque at the neck joint corresponds to the physical load imparted by the HMD. Therefore, our results provide valuable insights, demonstrating that, to improve HMD comfortability, it is necessary to consider both the balance and reduction of weight during HMD design.

The Impact of Control Interface on Features of Heart Rate Variability

Shared human-robot control for assistive machines can improve the independence of individuals with motor impairments. Monitoring elevated levels of workload can enable the assistive autonomy to adjust the control-sharing in an assist-as-needed way, to achieve a balance between user fatigue, stress and independent control. In this work, we aim to investigate how heart-rate variability features can be utilized to monitor elevated levels of mental workload while operating a powered wheelchair, and how that utilization might vary under different control interfaces. To that end, we conducted a 22 person study with three commercial interfaces. Our results show that the validity and reliability of using the ultra-short-term heart-rate variability features as predictors for workload indeed are affected by the type of interface in use.

A P300 brain-computer interface with a reduced visual field

A P300 brain-computer interface (BCI) is a paradigm, where text characters are decoded from visual evoked potentials (VEPs). In a popular implementation, called P300 speller, a subject looks at a display where characters are flashing and selects one character by attending to it. The selection is recognized by the strongest VEP. The speller performs well when cortical responses to target and non-target stimuli are sufficiently different. Although many strategies have been proposed for improving the spelling, a relatively simple one received insufficient attention in the literature: reduction of the visual field to diminish the contribution from non-target stimuli. Previously, this idea was implemented in a single-stimulus switch that issued an urgent command. To tackle this approach further, we ran a pilot experiment where ten subjects first operated a traditional P300 speller and then wore a binocular aperture that confined their sight to the central visual field. Visual field restriction resulted in a reduction of non-target responses in all subjects. Moreover, in four subjects, target-related VEPs became more distinct. We suggest that this approach could speed up BCI operations and reduce user fatigue. Additionally, instead of wearing an aperture, non-targets could be removed algorithmically or with a hybrid interface that utilizes an eye tracker. We further discuss how a P300 speller could be improved by taking advantage of the different physiological properties of the central and peripheral vision. Finally, we suggest that the proposed experimental approach could be used in basic research on the mechanisms of visual processing.

DESIGN, FABRICATION, AND TESTING OF A MOVABLE SOLAR OPERATED SPRAYER FOR FARMING OPERATION

Famers do spray seeds, fertilizers, pesticides, herbicides, etc. to protect crops from different insects, pests, diseases and have good harvests. Hand and fuel operated spray pumps are the most common sprayer used in Nigeria. The sprayer causes user fatigue due to excessive bulky and heavy construction, a user can't use it for more than five (5) hours without getting tired, the fuel sprayer is expensive to maintain, emits carbon dioxide and harmful to our environment. In this study, a movable solar operated sprayer for the farming operation was designed and fabricated to overcome these difficulties. The system operates in both direct mode and indirect mode. In the direct mode, the sprayer is operated from the electricity generated by 50W solar panel mounted on a movable frame and in the indirect mode it is operated on stored electrical energy in the lead-acid DC battery (12 V, 12 Ah). Priming diaphragm pump of 10W or mini DC reciprocating cycle motor of 5W is used to generate the required operating pressure to spray the liquid pesticide formulations. The capacity of the storage tank is 20 liters for uninterrupted operation of 25.1 minutes with the discharge rate of 0.79 L/min through the electric flexible mists high-pressure multiple sprayers with four (4) nozzles. Data generated from the theoretical formulae were used to fabricate the system using locally available and durable materials. The sprayer was tested in farmland on two different crops after charging the battery for 3 hours in sunlight. The results obtained were as follows: Power conversion efficiency 20.4%, the time required to charge the battery 2.88hrs, time taken to spray 1 acre of land 2.13hrs, backup time of spray 14.5hrs, application rate 0.04 𝐿/𝑚2 and operating time of the battery 8hrs. The results obtained show that solar sprayer was effective and will be useful in rural areas where there is no constant power supply. The system is incorporated with an energy bulb and charging kit to light up the farmyard and for the operator to charge his/her phone.

Fatigue-Aware Bandits for Dependent Click Models

As recommender systems send a massive amount of content to keep users engaged, users may experience fatigue which is contributed by 1) an overexposure to irrelevant content, 2) boredom from seeing too many similar recommendations. To address this problem, we consider an online learning setting where a platform learns a policy to recommend content that takes user fatigue into account. We propose an extension of the Dependent Click Model (DCM) to describe users' behavior. We stipulate that for each piece of content, its attractiveness to a user depends on its intrinsic relevance and a discount factor which measures how many similar contents have been shown. Users view the recommended content sequentially and click on the ones that they find attractive. Users may leave the platform at any time, and the probability of exiting is higher when they do not like the content. Based on user's feedback, the platform learns the relevance of the underlying content as well as the discounting effect due to content fatigue. We refer to this learning task as “fatigue-aware DCM Bandit” problem. We consider two learning scenarios depending on whether the discounting effect is known. For each scenario, we propose a learning algorithm which simultaneously explores and exploits, and characterize its regret bound.

Effect of Control-Display Gain and Mapping and Use of Armrests on Accuracy in Temporally Limited Touchless Gestural Steering Tasks

Touchless gestural controls are becoming an important natural input technique for interaction with emerging virtual environments but design parameters that improve task performance while at the same time reduce user fatigue require investigation. This experiment aims to understand how control-display (CD) parameters such as gain and mapping as well as the use of armrests affect gesture accuracy in specific movement directions. Twelve participants completed temporally constrained two-dimensional steering tasks using free-hand fingertip gestures in several conditions. Use of an armrest, increased CD gain, and horizontal mapping significantly reduced success rate. The results show that optimal transfer functions for gestures will depend on the movement direction as well as arm support features.