Göte Nyman

Frequency change detection in human auditory cortex.

We offer a model of how human cortex detects changes in the auditory environment. Auditory change detection has recently been the object of intense investigation via the mismatch negativity (MMN). MMN is a preattentive response to sudden changes in stimulation, measured noninvasively in the electroencephalogram (EEG) and the magnetoencephalogram (MEG). It is elicited in the oddball paradigm, where infrequent deviant tones intersperse a series of repetitive standard tones. However, little apart from the participation of tonotopically organized auditory cortex is known about the neural mechanisms underlying change detection and the MMN. In the present study, we investigate how poststimulus inhibition might account for MMN and compare the effects of adaptation with those of lateral inhibition in a model describing tonotopically organized cortex. To test the predictions of our model, we performed MEG and EEG measurements on human subjects and used both small- (<1/3 octave) and large- (>5 octaves) frequency differences between the standard and deviant tones. The experimental results bear out the prediction that MMN is due to both adaptation and lateral inhibition. Finally, we suggest that MMN might serve as a probe of what stimulus features are mapped by human auditory cortex.

Measuring Stereoscopic Image Quality Experience with Interpretation Based Quality Methodology

Stereoscopic technologies have developed significantly in recent years. These advances require also more understanding of the experiental dimensions of stereoscopic contents. In this article we describe experiments in which we explore the experiences that viewers have when they view stereoscopic contents. We used eight different contents that were shown to the participants in a paired comparison experiment where the task of the participants was to compare the same content in stereoscopic and non-stereoscopic form. The participants indicated their preference but were also interviewed about the arguments they used when making the decision. By conducting a qualitative analysis of the interview texts we categorized the significant experiental factors related to viewing stereoscopic material. Our results indicate that reality-likeness as well as artificiality were often used as arguments in comparing the stereoscopic materials. Also, there were more emotional terms in the descriptions of the stereoscopic films, which might indicate that the stereoscopic projection technique enhances the emotions conveyed by the film material. Finally, the participants indicated that the three-dimensional material required longer presentation time, as there were more interesting details to see.

Presence, involvement, and flow in digital games

Digital games elicit rich and meaningful experiences for the gamers. This makes games hard to study solely with usability methods that are used in the field of human–computer interaction. Here is presented a candidate framework to analyze multidimensional user experience (UX) in games. Theoretically, the framework is grounded both on previous game studies and on relevant psychological theories. Methodologically, it relies on multivariate data analysis of approximately 320 games (n = 2182), with the aim of revealing the subcomponents of UX in games. The framework captures the essential psychological determinants of UX, namely, its quality, intensity, meaning, value, and extensity. Mapping these determinants to the game mechanics, the narrative and the interface offers a rich view to UX in games and provides added value to those who want to understand why games are experienced in certain ways.

Content and quality: Interpretation-based estimation of image quality

Test image contents affect subjective image-quality evaluations. Psychometric methods might show that contents have an influence on image quality, but they do not tell what this influence is like, i.e., how the contents influence image quality. To obtain a holistic description of subjective image quality, we have used an interpretation-based quality (IBQ) estimation approach, which combines qualitative and quantitative methodology. The method enables simultaneous examination of psychometric results and the subjective meanings related to the perceived image-quality changes. In this way, the relationship between subjective feature detection, subjective preferences, and interpretations are revealed. We report a study that shows that different impressions are conveyed in five test image contents after similar sharpness variations. Thirty naïve observers classified and freely described the images after which magnitude estimation was used to verify that they distinguished the changes in the images. The data suggest that in the case of high image quality, the test image selection is crucial. If subjective evaluation is limited only to technical defects in test images, important subjective information of image-quality experience is lost. The approach described here can be used to examine image quality and it will help image scientists to evaluate their test images.

What do people look at when they watch stereoscopic movies

We measured the eye movements of participants who watched a 6-minute movie in stereoscopic and non-stereoscopic form. We analyzed four shots of the movie. The results indicate that in a 2D movie viewers tended to look at the actors, as most of the eye movements were clustered there. The significance of the actors started at the beginning of a shot, as the eyes of the viewer focused almost immediately to them. In S3D movie the eye movement patterns were more widely distributed to other targets. For example, complex stereoscopic structures and objects nearer than the actor captured the interest and eye movements of the participants. Also, the tendency to first look at the actors was diminished in the S3D shots. The results suggests that in a S3D movie there are more eye movements which are directed to wider array of objects than in a 2D movie.

Experienced quality factors: qualitative evaluation approach to audiovisual quality

Subjective evaluation is used to identify impairment factors of multimedia quality. The final quality is often formulated via quantitative experiments, but this approach has its constraints, as subjects quality interpretations, experiences and quality evaluation criteria are disregarded. To identify these quality evaluation factors, this study examined qualitatively the criteria participants used to evaluate audiovisual video quality. A semi-structured interview was conducted with 60 participants after a subjective audiovisual quality evaluation experiment. The assessment compared several, relatively low audio-video bitrate ratios with five different television contents on mobile device. In the analysis, methodological triangulation (grounded theory, Bayesian networks and correspondence analysis) was applied to approach the qualitative quality. The results showed that the most important evaluation criteria were the factors of visual quality, contents, factors of audio quality, usefulness - followability and audiovisual interaction. Several relations between the quality factors and the similarities between the contents were identified. As a research methodological recommendation, the focus on content and usage related factors need to be further examined to improve the quality evaluation experiments.

Involvement and presence in digital gaming

This study introduces a psychological measurement model for analyzing involvement and presence in digital game context. These two constructs are both theoretically and methodologically well developed in their own fields. The components forming these two constructs are psychologically relevant to our understanding of the evolvement of a user experience in digital gaming. The measurement model is tested with a large data (n=2182) collected from a web-based questionnaire and laboratory experiments among PC and console players. The results show that these two psychological constructs can be extracted from interactive game environments. It is also shown that involvement and presence are different dimensions of a larger psychological entity that describes the way the players adapt themselves psychologically into a game- world.

Phantom surface captures stereopsis

A phantom surface is a stereoscopic illusory area that can be seen in depth although there is no conventional stereoscopic cues [Liu, L., Stevenson, S.B., & Schor, C.M. (1994). Quantitative stereoscopic depth without binocular correspondence. Nature, 367, 66-69; Gillam, B. & Nakayama, K. (1999). Quantitative depth for a phantom surface can be based on cyclopean occlusion cues alone. Vision Research, 39, 109-112]. The phenomenon has been explained as an example of half-occlusion processing in which the visual system uses information about cyclopean occlusion structure of the visual world. We created stereo capture stereograms in which phantom surfaces changed the perceived depth of conventionally defined binocular textures. Because conventional stereoscopic matching is strongly affected by half-occlusion processing, we suggest that half-occlusion processing is an integral part of the early stereoscopic processing and solving of the correspondence problem.

Depth Asymmetry in da Vinci Stereopsis

We investigated processes that determine the depth localization of monocular points which have no unambiguous depth. It is known that horizontally adjacent binocular objects are used in depth localization and for a distance of 25-40 min arc monocular points localize to the leading edge of a depth constraint zone, which is an area defined by the visibility lines between which the points in the real world must be. We demonstrate that this rule is not valid in complex depth scenes. Adding other disparate objects to the scene changes the localization of the monocular point in a way that cannot be explained by the da Vinci explanation of monocular-binocular integration. The effect of additional disparate objects is asymmetric in depth: a crossed object does not affect the da Vinci effect but an uncrossed object biases the depth localization of monocular objects to uncrossed direction. We conclude that a horizontally adjacent binocular plane does not completely determine the depth localization of a monocular point and that depth spreading from other binocular elements biases the localization process.

User Experience in Digital Games: Differences between Laboratory and Home.

Playing entertainment computer, video, and portable games, namely, digital games, is receiving more and more attention in academic research. Games are studied in different situations with numerous methods, but little is known about if and how the playing situation affects the user experience (UX) in games. In addition, it is hard to understand and study the psychology of UX in games. The objective of this study is to show how UX differs when the first-person shooter HALO is played in a laboratory and at home. To disclose this difference, a psychologically valid and multidimensional measurement framework is introduced. UX is profiled according to the level of the sense of presence, involvement, and flow in a between-subjects design. Statistically, the structure of the framework is grounded on a large and heterogeneous gamer data set (N = 2,182). The results showed that the profile of the sense of presence in the laboratory included higher levels of attention and arousal as compared with that of the natural environment. This finding was independent of any of the measured background variables. Other differences between the two situations were more related to the participants’ background. For example, gamers at home were more involved in the game and they felt a higher level of competence. No strong emotional differences between the two situations were found. The authors discuss the complex UX terminology and implications of the framework for implementation of learning games.