D.G. Bouwhuis

Perceived depth and the feeling of presence in 3DTV

The present study investigates the subjective feeling of presence elicited by 3DTV and its relationship to perceived depth and image content. Subjective methods of assessing presence that have been used or proposed to date do not provide a measure of temporal variation. To overcome this limitation, we have applied the continuous assessment methodology (ITU-R, BT 500-7) to the assessment of presence, perceived depth and naturalness of depth. Twelve observers continuously rated their instantaneous perception of presence, depth and naturalness of depth when viewing stereoscopic footage. The results indicate that subjective presence ratings are subject to considerable temporal variation depending on the image content and camera techniques used. The correlations between the different attributes suggest that an increase in depth may lead to an enhanced sense of presence, provided depth is perceived as natural. A qualitative analysis of the data in relation to the image content provides evidence for the hypothesis that the extent of sensory information available to an observer is a determinant of presence, as proposed by T.B. Sheridan, Musings on telepresence and virtual presence, Presence: Teleoperators and Virtual Environments 1 (1992) 120‐125. q 1998 Elsevier Science B.V.

The Structure of Multimodal Dialogue

That the terms “dialogue” (e.g., between humans) and “interaction” (e.g., between user and computer) can be used interchangeably is implicitly assumed throughout this collection of papers edited by Taylor, Néel, and Bouwhuis. That a dialogue typically involves the use of multiple “modes” of communication and that it has its own internal structure are of obvious import to those who work in application domains that require the collaboration of human users either with software systems or with one another through the use of mediating software systems. This collection, therefore, will be of interest to researchers who want to know about early attempts to apply the metaphor of multimodal human-human communication to collaborative domains such as these. This volume is a long-delayed follow-up publication from a workshop held under the same title in Aquafredda di Maratea, Italy, in 1991. The material in this volume is clearly not recent—the editors report that the authors were requested to bring the papers up to date, but since practically all of the works referenced by the papers in this volume predate 1994, it seems that their request was not made in the years prior to publication. This is also reflected in the absence of the notion of a communicative agent (although, due to its now-rampant overuse, some might welcome this) and the lack of reference to the work on embodied agents that emerged in the last decade and is clearly relevant (for exam-

The effects of errors on system trust, self-confidence, and the allocation of control in route planning

The concept of trust is believed by some to compensate for feelings of uncertainty. Therefore, trust is considered to be crucial in peoples decision to rely on a complex automated system to perform tasks for them. This experiment aimed to study the effects of errors on control allocation, and the mediating role of trust and self-confidence in the domain of route planning. Using a computer-based route planner, participants completed 10 route-planning trials in manual mode, and 10 in automatic mode, allowing participants to become equally experienced in operating both modes. During these so-called fixed trials, the numbers of errors in automatic as well as manual mode were systematically varied. Subsequently, participants completed six free trials, during which they were free to choose between modes. Our results showed that high automation error rates (AERs) decreased levels of system trust compared to low AERs. Conversely, high manual error rates (MERs) resulted in lower levels of self-confidence compared to low MERs, although to a lesser extent. Moreover, the difference between measures of trust and self-confidence proved to be highly predictive of the number of times automatic mode was selected during the six free trials. Additionally, results suggest a fundamental bias to trust ones own abilities over those of the system. Finally, evidence indicating a relationship between trust and self-confidence is discussed.

Evaluation of Stereoscopic Images: Beyond 2D Quality

Perceived image quality is a standard evaluation concept for 2D imaging systems. When applied to stereoscopic 3D imaging systems, however, it does not incorporate the added value of stereoscopic depth. Higher level evaluation concepts (naturalness and viewing experience) are proposed that are sensitive to both image quality and stereoscopic depth. A 3D Quality Model is constructed in which such higher level evaluation concepts are expressed as a weighted sum of image quality and perceived depth. This model is validated by means of three experiments, in which stereoscopic depth (camera base distances and screen disparity) and image quality (white Gaussian noise and Gaussian blur) are varied. The resulting stimuli are evaluated in terms of naturalness, viewing experience, image quality and depth percept. Analysis revealed that viewing experience and naturalness incorporated variations in image quality to a similar extent, yet the added value of stereoscopic depth is incorporated significantly more by naturalness. This result classifies naturalness as the most appropriate concept to evaluate 3D quality of stereoscopic stills. The 3D Quality Model based on naturalness as evaluation concept is validly applicable to stereoscopic stills and the naturalness score is determined for approximately 75% by image quality and for approximately 25% by the added value of stereoscopic depth.

Identifying usability and fun problems in a computer game during first use and after some practice

This paper describes an experiment to discover the change in the types of detected problems and the attitude of children towards a game when user testing a computer game for young children during first use and after they have practiced with a game. Both the numbers of different types of identified problems and the severity of the problems are investigated. Based on this knowledge, practitioners could adapt the set up of their user tests to effectively find as many aspects of the game as possible that merit change, according to the aims of the developers. The study shows that usability problems caused by a lack of knowledge were more often identified during first use. Furthermore, fun problems related to a too-high challenge level may disappear after some practice, whereas fun problems caused by the game taking over control for too long while the user wants to proceed playing the game were identified more often after some practice. The study shows that the impact severity of problems detected during first use was higher than when children had more practice with a game. As a result of these changes in experienced problems the commonly used measures efficiency, effectiveness and satisfaction increased when children had practiced with the game. Finally, the study also shows that the set of most severe problems identified during first use may be radically different from the set of most severe problems identified after some practice.

Toward a better understanding of the relation between music preference, listening behavior, and personality

Previous research relating personality and music preferences has often measured such reported preferences according to genre labels. To support previous research, the current paper has expanded investigation of the relation between personality and music preferences to include direct measurement of music listening behavior. A study (N = 395) measured participants’ personality, reported music preferences, and their listening behavior, which was tracked while using a music database for a minimum period of three months. Results indicated that reported music preferences were correlated to listening behavior, and indicated robust positive relations between Neuroticism and Classical music preference, and between Openness to Experience and Jazz music preference. Results also indicated issues when using genre labels to measure music preferences, which are discussed.

Visual word recognition of three-letter words as derived from the recognition of the constituent letters

Word recognition is one of the basic processes involved in reading. In this connection, a model for word recognition is proposed consisting of a perceptual and a decision stage. It is supposed that, in the perceptual stage, the formation of possible words proceeds by separate identification of each of the letters of the stimulus word in their positions. Letter perception is taken to be conditional on position because of interaction effects from neighboring letters. These effects are dependent on both position in the word and retinal eccentricity, which are of particular relevance in reading. The letter-based approach rests on the strong relationship between the results from single-letter recognition in meaningless strings and in real words. Next, in the decision step, the many alternatives generated in the perceptual stage are matched with a vocabulary of real words. It is supposed that the final choice from among the remaining words is made in accordance with the constant ratio rule; frequency effects are not separately incorporated in the model. All predictions of the model are generated by means of data from earlier experiments. Despite being not optimally suited for this purpose, the predictions compare favorably with responses in word-recognition experiments.

Melodic cues to the perceived ‘‘finality’’ of utterances

One of the possible functions of intonation is its capacity to clarify textual structure. It may indicate, for instance, that a sentence is likely to be the last one in a sequence of statements that build a discourse unit. In order to investigate the perception of melodic cues to ‘‘finality,’’ a series of three listening experiments was performed with short sentences, the intonation of which was manipulated with respect to different melodic variables. The actual testing was done in two ways (1) by pairwise comparison and (2) by absolute rating. A linear least‐squares estimation method brought to light that in both tests finality judgments were influenced significantly by differences in pitch register (experiment 1), pitch range (experiment 1), and shape of the pitch contour (experiments 1, 2, and 3). The results of the data analysis suggest strongly that these different variables generally combine additively in producing finality judgments, though the effect of one is sometimes conditional on the value of...

Individual differences in the rubber-hand illusion: predicting self-reports of people's personal experiences.

Can we assess individual differences in the extent to which a person perceives the rubber-hand illusion on the basis of self-reported experiences? In this research, we develop such an instrument using Rasch-type models. In our conception, incorporating an object (e.g., a rubber hand) into ones body image requires various sensorimotor and cognitive processes. The extent to which people can meet these requirements thus determines how intensely people experience and, simultaneously, describe the illusion. As a consequence, individual differences in peoples susceptibility to the rubber-hand illusion can be determined by inspecting reports of their personal experiences. The proposed model turned out to be functional in its capability to predict self-reports of peoples experiences and to reliably assess individual differences in susceptibility to the illusion. Regarding validity, we found a small, but significant, correlation between individual susceptibility and proprioceptive drift. Additionally, we found that asynchrony, and tapping rather than stroking the fingers constrain the experience of the illusion.

Programming and enjoying music with your eyes closed

Design and user evaluation of a multimodal interaction style for music programming is described. User requirements were instant usability and optional use of a visual display. The interaction style consists of a visual roller metaphor. User control of the rollers proceeds by manipulating a force feedback trackball. Tactual and auditory cues strengthen the roller impression and support use without a visual display. The evaluation investigated task performance and procedural learning when performing music programming tasks with and without a visual display. No procedural instructions were provided. Tasks could be completed successfully with and without a visual display, though programming without a display needed more time to complete. Prior experience with a visual display did not improve performance without a visual display. When working without a display, procedures have to be acquired and remembered explicitly, as more procedures were remembered after working without a visual display. It is demonstrated that multimodality provides new ways to interact with music.