John D. McCarthy

The Influence of Body Movement on Subjective Presence in Virtual Environments

We describe an experiment to assess the influence of body movements on presence in a virtual environment. In the experiment 20 participants were to walk through a virtual field of trees and count the trees with diseased leaves. A 2 × 2 between-subjects design was used to assess the influence of two factors on presence: tree height variation and task complexity. The field with greater variation in tree height required participants to bend down and look up more than in the lower variation tree height field. In the higher complexity task participants were told to remember the distribution of diseased trees in the field as well as to count them. The results showed a significant positive association between reported presence and the amount of body movement - in particular, head yaw - and the extent to which participants bent down and stood up. There was also a strong interaction effect between task complexity and gender: Women in the morecomplex task reported a much lower sense of presence than in the simpler task. For applications in which presence is an important requirement, the research in this paper suggests that presence will be increased when interaction techniques are employed that permit the user to engage in whole-body movement.

The researcher's dilemma: evaluating trust in computer-mediated communication

The aim of this paper is to establish a methodological foundation for human-computer interaction (HCI) researchers aiming to assess trust between people interacting via computer-mediated communication (CMC) technology. The most popular experimental paradigm currently employed by HCI researchers are social dilemma games based on the Prisoners Dilemma (PD), a technique originating from economics. HCI researchers employing this experimental paradigm currently interpret the rate of cooperation--measured in the form of collective pay-off--as the level of trust the technology allows its users to develop. We argue that this interpretation is problematic, since the games synchronous nature models only very specific trust situations. Furthermore, experiments that are based on PD games cannot model the complexity of how trust is formed in the real world, since they neglect factors such as ability and benevolence. In conclusion, we recommend (a) means of improving social dilemma experiments by using asynchronous Trust Games, (b) collecting a broader range of data (in particular qualitative) and (c) increased use of longitudinal studies.

Can small be beautiful?: assessing image resolution requirements for mobile TV

Mobile TV services are now being offered in several countries, but for cost reasons, most of these services offer material directly recoded for mobile consumption (i.e. without additional editing). The experiment reported in this paper, aims to assess the image resolution and bitrate requirements for displaying this type of material on mobile devices. The study, with 128 participants, examined responses to four different image resolutions, seven video encoding bitrates, two audio bitrates and four content types. The results show that acceptability is significantly lower for images smaller than 168x126, regardless of content type. The effect is more pronounced when bandwidth is abundant, and is due to important detail being lost in the smaller screens. In contrast to previous studies, participants are more likely to rate image quality as unacceptable when the audio quality is high.

Design requirements for mobile TV

In this paper we examine the interaction and delivery requirements for Mobile TV. By comparing the features of traditional TV with current Mobile TV services we outline the design requirements for a future Mobile TV interface. The proposed design is implemented on an iPAQ and evaluated with end-users in a field trial. Preliminary results of the user study suggest that use of the interface is intuitive and successful in giving a TV-like experience. As a secondary study we investigate the bandwidth requirements for different types of TV content on a 3G phone and a PDA. The results reveal marked differences in bandwidth requirements for different content types. The findings are discussed in the context of future Mobile TV services.

Could I have the Menu Please? An Eye Tracking Study of Design Conventions

Existing Web design guidelines give conflicting advice on the best position for the navigation menu. One set of guidelines is based on user expectation of layout, the other on results from user testing with alternative layouts. To resolve this conflict we test whether placing the menu in an unexpected position has a negative impact on search performance. The results show that users rapidly adapt to an unexpected screen layout. We conclude that designers should not be inhibited in applying design recommendations that violate layout conventions as long as consistency is maintained within a site.

How low can you go? The effect of low resolutions on shot types in mobile TV

The advent of mobile TV which is often viewed on small screens with low resolution has made TV content producers think about refraining from using shots that depict subjects from a great distance. Shot types where the object of interest fills the screen are deemed to be more appropriate for mobile devices. This paper reports a study on how shot types used in regular broadcast television are affected when shown on mobile devices at reduced levels of resolution. Seventy-two native speakers judged the acceptability of four different content types at four resolutions (240 × 180, 208 × 156, 168 × 126, 120 × 90). The results show that acceptability of shot types depends on the content and the resolution. Extreme long shots of football content were only less acceptable than other shot types at resolutions smaller than 240 × 180. The medium shot which portrays the upper half of a subject’s body was the most acceptable for news content but for football content was judged worse than shot types that showed less detail. Our results suggest that for a young audience extreme long shots may be used with no detrimental effect for resolutions of 240 × 180 and higher. At lower resolutions and for content with a high degree of dynamism both the medium shot and the extreme long shot might render poorly for the audience. Service providers are well advised to include the results at hand to customize content in terms of shot type use for their audience that will watch the content at very low resolutions. Further research should assess older audiences and the effectiveness of cropping schemes that zoom in on part of the content for low target resolutions.

Shifting visuo-spatial attention in a virtual three-dimensional space

The present investigation, with a virtual reality set-up, aimed to study attentional orienting within a three-dimensional visual world. Near and far stimuli were used. Half of the subjects were provided with a virtual representation of their body, whereas half were not. Results showed a different distribution of attentional resources in the two conditions, suggesting a dissociation between attentional systems controlling the proximal and the distal visual space. In particular, attention was focused close to the subjects body when a virtual representation of it was present, whereas attention was focused away from the body when a virtual representation of the body was not present.

Reading the fine print: the effect of text legibility on perceived video quality in mobile tv

Mobile TV services are available in an increasing number of countries. For cost reasons, most of these services offer material directly recoded for mobile consumption (i.e. without additional editing). This paper reports the findings of a study on the influence of text legibility and quality on the perceived video quality of mobile TV content. The study, with 64 participants, examined responses to news footage presented at four image resolutions and seven video encoding bitrates. The results showed that a simulated separate delivery of a news ticker and other textual information significantly increased the perceived video quality of the entire screen for native speakers. In addition, some automatable changes to the layout of news content resulted in substantial increases in perceived video quality. The results can be used to quantify the perceived quality gains when considering text delivery separately from the video stream and in the development of more accurate multimedia quality models.

Rich Media, Poor Judgement? A Study of Media Effects on Users’ Trust in Expertise

In this paper, we investigate how interpersonal cues of expertise affect trust in different media representations. Based on a review of previous research, richer representations could lead either to a positive media bias (P1) or increased sensitivity for cues of expertise (P2). In a laboratory study, we presented 160 participants with two advisors — one represented by text-only; the other represented by one of four alternate formats: video, audio, avatar, or photo+text. Unknown to the participants, one was an expert (i.e. trained) and the other was a non-expert (i.e. untrained). We observed participants’ advice seeking and advice uptake to infer their sensitivity to correct advice in a situation of financial risk. We found that most participants preferred seeking advice from the expert, but we also found a tendency for seeking audio and in particular video advice. Users’ self-reports indicate that they believed that video in particular would give them the most detailed insight into expertise. Data for advice uptake, however, showed that all media representation, including text-only, resulted in good sensitivity to correct advice.

The effect of video-augmented chat on collaborative learning with cases

Efficient learning with cases requires discussion on the facts of the case as well as on their meaning. We investigated the focus (factual vs. abstract) of a case-based learning discussion when video was added to a chat-based learning system. Students whose first experience includes high-quality video, focus significantly more on abstract knowledge than students first exposed to chat-only or chat + low-quality video. We also found that these students expressed a preference for face-to-face discussion. We conclude that video may improve learning where discussions on abstract and concrete knowledge are important.