Recommender systems have been developed to address the abundance of choice we face in taste domains (films, music, restaurants) when shopping or going out. However, consumers currently struggle to evaluate the appropriateness of recommendations offered. With collaborative filtering, recommendations are based on people's ratings of items. In this paper, we propose that the usefulness of recommender systems can be improved by including more information about recommenders. We conducted a laboratory online experiment with 100 participants simulating a movie recommender system to determine how familiarity of the recommender, profile similarity between decision-maker and recommender, and rating overlap with a particular recommender influence the choices of decision-makers in such a context. While familiarity in this experiment did not affect the participants' choices, profile similarity and rating overlap had a significant influence. These results help us understand the decision-making processes in an online context and form the basis for user-centered social recommender system design.

This paper presents two case studies of informal group communication using multimedia conferencing that supports various media including video, audio and chat. The studies provide a comparison of audio and chat as communication medium and present data on usage patterns, user preferences and attitudes. The quantitative and qualitative data collected suggest that chat does have advantages in some situations when used for informal communication along with video. The results provide evidence against the hypothesis that chat is a low bandwidth alternative only used when audio communication is unavailable. This suggests that video mediated chat deserves further attention from designers and the research community, since it is often ignored as a "useful" scenario.

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.

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.

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.

Studies of video conferencing systems generally focus on scenarios where users communicate using an audio channel. However, text chat serves users in a wide variety of contexts, and is commonly included in multimedia conferencing systems as a complement to the audio channel. This paper introduces a prototype application which integrates video and text communication, and describes a formative evaluation of the prototype with 53 users in a social setting. We focus the evaluation on bandwidth and view navigation requirements in order to determine how to better serve users with video chat, and discuss how the findings from this evaluation can inform the design of future video chat applications. Bandwidth requirements are evaluated through user perceptions of video delivered using three different bandwidth schemes. For view navigation, we examine a system that automatically switches the video focus to the current "chatter", instead of requiring users to navigate manually to find the video steam they are interested in viewing.

We introduce a new methodology to evaluate the perceived quality of video with variable physical quality. The methodology is used to evaluate existing guidelines - that frame is more important than quantization when watching motion video, such as sports coverage. We test this claim in two studies that examine the relationship between these physical quality metrics and perceived quality. In Study 1, 41 soccer fans viewed CIF-sized images on a desktop computer. Study 2 repeated the experiment with 37 soccer fans, viewing the same content, in QCIF size, on a palmtop device. Contrary to existing guidelines, we found that users prefer high-resolution images to frame rate. We conclude that the rule high motion = frame rate does not apply to small screens. With small screen devices, reducing quantization removes important information about the players and the ball. These findings have important implications for service providers and designers of streamed video applications.

Designing for trust in technology-mediated interaction is an increasing concern in CHI. In advertising, images of people have long been used to create positive attitudes to products or trust in brands. However, the evidence as to whether placing photographs of people on e-commerce web sites has the intended effect has been mixed. This paper reports a study that examined the effect of adding such photographs to 12 existing e-commerce sites, whose reputation had been established through customer ratings. In an experiment with 115 participants, trust was measured using methods that induced financial risk, adapted from experimental economics. Averaging across sites, neither the presence of a photo, nor trustworthiness of the person depicted, had a significant effect. However, the presence of photos reduced participants' ability to identify vendors with good and bad reputations -- the perceived trustworthiness of poorly performing vendors was increased, whereas that of vendors with good reputation was decreased. This result advocates caution when using photos on e-commerce sites to boost trustworthiness, and demonstrates the need for further research into interpersonal cues and on-line trust.