In a three-dimensional (3D) virtual environment (VE), proper collaboration between vibrotactile and force cues - two cues of the haptic modality - is important to facilitate task performance of human users. Many studies report that collaborations between multi-sensory cues follow maximum likelihood estimation (MLE). However, an existing work finds that MLE yields a mean and an amplitude mismatches when interpreting the collaboration between the vibrotactile and force cues. We thus proposed mean-shifted MLE and conducted a human study to investigate the mismatches. For the study, we created a VE to replicate the visual scene, the 3D interactive task, and the cues from the existing work. Our participants were biased to rely on the vibrotactile cue for their tasks, departing from unbiased reliance on both cues in the existing work. Assessments of task completion time and task accuracy validated the replication. We found that based on task accuracy MLE explained the cue collaboration to certain degrees, agreed with the existing work. Mean-shifted MLE remedied the mean mismatch, but maintained the amplitude mismatch. Further examinations revealed that the collaboration between both cues may not be entirely additive. This sheds an insight for proper modeling of the collaboration between the vibrotactile and force cues to aid interactive tasks in VEs.

Vibrotactile and force cues of the haptic modality is increasing used to facilitate interactive tasks in three-dimensional (3D) virtual environments (VE). While maximum likelihood estimation (MLE) explains the integration of multi-sensory cues in many studies, an existing work yielded mean and amplitude mismatches when using MLE to interpret the integration of vibrotactile and force cues. To investigate these mismatches, we proposed mean-shifted MLE and conducted a study of comparing MLE and mean-shift MLE. Mean-shifted MLE shared the same additive assumption of the cues as MLE, but took account mean differences of both cues. In a VE, the study replicated the visual scene, the 3D interactive task, and the cues from the existing work. All human participants in the study were biased to rely on the vibrotactile cue for their task, departing from unbiased reliance towards both cues in the existing work. After validating the replications, we applied MLE and mean-shifted MLE to interpret the integration of the vibrotactile and force cues. Similar to the existing work, MLE failed to explain the mean mismatch. Mean-shifted MLE remedied this mismatch, but maintained the amplitude mismatch. Further examinations revealed that the integration of the vibrotactile and force cues might violate the additive assumption of MLE and mean-shifted MLE. This sheds a light for modeling the integration of vibrotactile and force cues to aid 3D interactive tasks within VEs.

Multiuser collaboration within virtual environments (VEs) need effective means of communication. A real-world collaboration benefits from verbal and nonverbal communication channels. To promote the nonverbal communication within VEs, some research studies have explored various forms of vibrotactile cues that are either spatially co-located with an interaction device held by a user's hand, or dislocated from the device. These studies are focused on VEs that are established on a leader and a follower paradigm. A multiuser collaborative VE is however governed by an interaction model to handle the simultaneous interactive commands issued by multiple peer users. Proposed in our earlier work, the dynamic priority model (DP) is an interaction model that yields perceived equality in interaction and promotes the multiuser collaboration when peer users communicate through verbal dialogue. As a key means of nonverbal communication in VEs, co-located and dislocated vibrotactile cues might affect the perceived equality in interaction, and how users collaborate under the DP model. In this study, we have thus investigated the role of vibrotactile cues on multiuser collaboration under the DP model. We undertook this investigation in two cue settings: co-located and dislocated. We observed that the DP model yields perceived equality in interaction both in the absence and presence of vibrotactile cues. Also, the co-located cues significantly enhanced the multiuser collaboration compared to the dislocated cues. These observations imply a potential application of co-located vibrotactile cues to enhance multiuser collaboration within VEs.

Proper integration of sensory cues facilitates 3D user interaction within virtual environments (VEs). Studies showed that the integration of visual and haptic cues follows maximum likelihood estimation (MLE). Little effort focuses however on the mechanism of integrating force and vibrotactile cues. We thus investigated MLE's suitability for integrating these cues. Within a VE, human users undertook 3D interaction of navigating a flying drone along a high-voltage transmission line for inspection. The users received individual force or vibrotactile cues, and their combinations in collocated and dislocated settings. The users' task performance including completion time and accuracy was assessed under each individual cue and setting. The presence of the vibrotactile cue promoted a better performance than the force cue alone. This agreed with the applicability of tactile cues for sensing 3D surfaces, herein setting a baseline for using MLE. The task performance under the collocated setting indicated a degree of combining the individual cues. In contrast, the performance under the dislocated setting was alike under the individual vibrotactile cue. These observations imply a possible role of MLE in integrating force and vibrotactile cues for 3D user interaction within VEs.

Collaborative virtual environments (VEs) require interaction models for resolving conflicts and promoting multiuser collaboration. Common models, such as the first-come-first-serve (FCFS) model, which grants interaction opportunities to the most agile user, and the static priority model, which gives interaction opportunities to the user with the highest predefined priority, disregard the importance of perceiving equality in interaction (EII) among all users. One exception is the dynamic priority (DP) model, as proposed in our earlier work, which grants interaction opportunities to a user based on the recency of his/her gained opportunities. To date, few research efforts have investigated the effect of interaction models on multiuser satisfaction. This paper hence presents an assessment of the DP model's effect on multiuser satisfaction within a collaborative VE. We first verified that the DP model allowed multiple users to perceive EII. We then conducted an experiment to examine the effect of the DP and FCFS models on multiuser satisfaction under a quasi-practical scenario that mimicked a decision-making meeting of experts. The framework of the examination was based on several metrics, which we proposed for the components of the ISO/IEC 25010:2011 standard. This framework resolved issues with existing metrics that measure user satisfaction by analyzing individual experience, thus omitting EII desired by multiple users. The results of the experiment indicated that the DP model fulfilled the metrics of the framework significantly better than the FCFS model. This observation implies a potential application of the DP model in collaborative VEs where multiuser satisfaction is the key to productive collaboration.

Multi-user efficacy is a key factor of genuine collaboration among multiple users towards a common goal. To assess multi-user efficacy, social scientists have traditionally applied subjective measurements from a theoretical perspective. Researchers in human-computer interaction have developed combined metrics of objective and subjective measurements. Nevertheless, the combined metrics fall short to fully cover the theoretical perspective of social scientists. To remedy this shortfall, we have developed a set of objective and subjective metrics to complete the theoretical perspective. Utilizing the metrics, we present in this paper a study to verify the robustness of our dynamic priority (DP) model, which under a quasi-practical scenario resolves command conflicts and promotes perceived equality in interaction among multiple users. In the study, we utilized a realistic scenario which differs from the quasi-practical scenario in the allowance of verbal communication among users. The results of the study revealed that the DP model yielded a significantly higher degree of multi-user efficacy under the realistic scenario than the quasi-practical scenario. Moreover, there was no significant difference of the perceived equality in interaction between both scenarios. These observations confirm the robustness of the DP model, and imply the potential application of the model for genuine collaboration within multi-user VEs.

Multi-user usability of collaborative virtual environments (VEs) require the consideration of users’ socio-human needs. However, most investigations of the usability have focused on either the technologies involved or individual user experience. Few have examined the effect of interaction models o

Multi-user collaborative virtual environments (VEs) need strategies of conflict resolution to handle simultaneous interaction with shared objects. Current strategies are first-come-first-serve (FCFS) and predefined static priority of each user. These strategies cannot provide each user with a perc