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"Global illumination (GI) rendering simulates the propagation of light through a 3D volume and its interaction with surfaces, dramatically increasing the fidelity of computer generated images. While off-line GI algorithms such as ray tracing and radiosity can generate physically accurate images, their rendering speeds are too slow for real-time applications. The many-light method is one of many novel emerging real-time global illumination algorithms. However, it requires many shadow maps to be generated for Virtual Point Light (VPL) visibility tests, which reduces its efficiency. Prior solutions restrict either the number or accuracy of shadow map updates, which may lower the accuracy of indirect illumination or prevent the rendering of fully dynamic scenes. In this thesis, we propose a hybrid real-time GI algorithm that utilizes an efficient Sparse Voxel Octree (SVO) ray marching algorithm for visibility tests instead of the shadow map generation step of the many-light algorithm. Our technique achieves high rendering fidelity at about 50 FPS, is highly scalable and can support thousands of VPLs generated on the fly. A survey of current real-time GI techniques as well as details of our implementation using OpenGL and Shader Model 5 are also presented."

Faces communicate a wealth of information, including cues to others’ internal emotional states. Face processing is often studied using static stimuli; however, in real life, faces are dynamic. The current project examines face detection and emotion recognition from isolated motion cues. Across two studies, facial motion is presented in point-light displays (PLDs), in which moving white dots against a black screen correspond to dynamic regions of the face. In Study 1, adults were asked to identify the upright facial motion of five basic emotional expressions (e.g., surprise) and five neutral non-rigid movements (e.g., yawning) versus inverted and scrambled distractors. Prior work with static stimuli finds that certain cues, including the addition of motion information, the spatial arrangement of elements, and the emotional significance of stimuli affect face detection. This study found significant effects involving each of these factors using facial PLDs. Notably, face detection was most accurate in response to face-like arrangements, and motion information was useful in response to unusual point configurations. These results suggest that similar processes underlie the processing of static face images and isolated facial motion cues. In Study 2, children and adults were asked to match PLDs of emotional expressions to their corresponding labels (e.g., match a smiling PLD with the word “happy”). Prior work with face images finds that emotion recognition improves with age, but the developmental trajectory depends critically on the emotion to be recognized. Emotion recognition in response to PLDs improved with age, and there were different trajectories across the five emotions tested. Overall, this dissertation contributes to the understanding of the influence of motion information in face processing and emotion recognition, by demonstrating that there are similarities in how people process full-featured static faces and isolated facial motion cues in PLDs (which lack features). The finding that even young children can detect emotions from isolated facial motion indicates that features are not needed for making these types of social judgments. PLD stimuli hold promise for future interventions with atypically developing populations.

<p>Research on biological motion, using point-light displays to present the motions, have been unravelling what information factors are still embedded in those impoverished stimuli and which of these factors are essential in visual processing of biological motion. Earlier studies suggest that orientation is a crucial factor in biological motion processing. The short-term priming experiment presented in this paper will further investigate the legitimacy of the primacy of orientation and suggest different solutions based on contradicting findings in previously published studies.</p><p>In a serial two-choice reaction-time task, participants were presented with a patch-light display of a human engaged in one of three possible actions: climbing up a rope, jumping jacks, and walking. Participants had to identify the in-plane orientation of the human figure emerging from the moving patch-lights. Reliable facilitation effect was established for transitions containing same-oriented upright trails and same-oriented inverted trials. Interestingly, transitions of same-oriented upright trials produced significantly greater facilitation effect than transitions of same-oriented inverted trials.</p>

The ability to recognise the movements made by humans and other animals, referred to as biological motion, is a specialised human ability that develops at an early age. This perceptual ability is strong even for the minimal amount of information contained in a point-light display, which has been used to study specific features of biological motion to find out what properties contribute to this ability. The perception of biological motion depends on visual perception, visual attention and motor cognition, and perception depends both on the global form, configural information and local information of a body in motion. Depending on the situation, either global or local motions will be more salient and processed to a greater extent by the perceptual system. Previous research has shown that the local and configural information contained in the feet play an important role for identification, direction discrimination and the inversion effect. The salience of the feet for perception has previously been studied when they are subjected to focused attention, but not reflexive attention. The goal of this study was to investigate if the local and configural information of the feet can trigger reflexive attention and be incidentally processed by the visual system in a direction discrimination task. To test this experimentally, a masking paradigm was used where the feet were placed in a mask consisting of scrambled walkers. The results show that the feet affect recognition of target direction when the target is upright, but not when inverted. An interesting and unexpected finding was that for upright targets, the feet aid recognition when they move in the opposite direction of the target. Due to the experimental setup, it is difficult to say with certainty what the results imply, and suggestions for a follow-up study are presented. / Kognitionsvetenskap handlar om hur människor tänker, uppfattar världen och interagerar med omgivningen och med andra människor. Inom kognitiv psykologi har människors förmåga att uppfatta andra människors och djurs rörelser studerats länge. Vi kan känna igen vänner och familj på det unika sätt som de rör sig och forskningen har visat att vi har förmågan att identifiera många olika typer av rörelser och handlingar även när den tillgängliga informationen är minimal. Studier som använt s.k. punktljusdisplayer, där endast vita punkter som representerar kroppens stora leder visas mot en svart bakgrund, har visat att förmågan att känna igen biologiska rörelser är mycket känslig och robust för störningar. Forskare har undersökt vilken information hos rörelser som vi använder för att lyckas med detta, och hur visuell perception och uppmärksamhet fungerar då vi tittar på punktljusdisplayer. Det har visat sig att fötterna har en stor inverkan på igenkänning av rörelseriktning och att det framförallt är på grund av fötterna som det är svårt att känna igen rörelser som presenteras uppochner. Något som inte har testats tidigare är om fötterna är så starka signaler att de kan påverka vår perception även om vi inte riktar fokuserad uppmärksamhet mot dem, utan endast reflexiv uppmärksamhet. Den här studien har testat om fötter kan trigga just reflexiv uppmärksamhet och påverka hur vi känner igen rörelseriktningen hos en gående punktljus-figur. Resultaten visar att fötternas specifika rörelsemönster kan trigga reflexiv uppmärksamhet i situationer då rörelserna är upprätta och då fötterna rör sig i motsatt riktning från den figur som deltagare fokuserar på. Experimentdesignen har dock inneburit att resultaten är svåra att tolka. För att säkrare kunna säga huruvida resultaten beror på fötterna föreslås en ny studie, och detaljer kring vilka justeringar som borde göras i en sådan studie presenteras.

Earlier research has repeatedly shown that individuals with autism spectrum disorders are significantly impaired in emotional recognition of biological motion. This study adopted an approach where the typically developed and the autistic participants rated emotional valence and recognition of isolated gestures in Point-light display. Results revealed that participant groups did not differ in their emotional valence of the gestures but differed in recognition of the gestures. The method of using isolated gestures in Point-light display has not been used in autism emotional research earlier and this paper functions as a pilot of this technique. The results are discussed from a perspective that individuals with autism perceive the world differently and hence understand and interact differently with the world.

Research on biological motion, using point-light displays to present the motions, have been unravelling what information factors are still embedded in those impoverished stimuli and which of these factors are essential in visual processing of biological motion. Earlier studies suggest that orientation is a crucial factor in biological motion processing. The short-term priming experiment presented in this paper will further investigate the legitimacy of the primacy of orientation and suggest different solutions based on contradicting findings in previously published studies. In a serial two-choice reaction-time task, participants were presented with a patch-light display of a human engaged in one of three possible actions: climbing up a rope, jumping jacks, and walking. Participants had to identify the in-plane orientation of the human figure emerging from the moving patch-lights. Reliable facilitation effect was established for transitions containing same-oriented upright trails and same-oriented inverted trials. Interestingly, transitions of same-oriented upright trials produced significantly greater facilitation effect than transitions of same-oriented inverted trials.

Being able to generate predictions about what is going to happen next while observing other people’s actions plays a crucial role in our daily lives. Different theoretical explanations for the underlying processes of humans’ action prediction abilities have been suggested. Whereas an embodied account posits that predictive gaze relies on embodied simulations in the observer’s motor system, other accounts do not assume a causal role of the motor system for action prediction. The general aim of this thesis was to augment current knowledge about the functional mechanisms behind humans’ action prediction abilities. In particular, the present thesis outlines and tests an embodied account of action prediction. The second aim of this thesis was to extend prior action prediction studies by exploring infants’ online gaze during observation of social interactions. The thesis reports 3 eye-tracking studies that were designed to measure adults’ and infants’ predictive eye movements during observation of different manual and social actions. The first two studies used point-light displays of manual reaching actions as stimuli to isolate human motion information. Additionally, Study II used transcranial magnetic stimulation (TMS) to directly modify motor cortex activity. Study I showed that kinematic information from biological motion can be used to anticipate the goal of other people’s point-light actions and that the presence of biological motion is sufficient for anticipation to occur. Study II demonstrated that TMS-induced temporary lesions in the primary motor cortex selectively affected observers’ gaze latencies. Study III examined 12-month-olds’ online gaze during observation of a give-and-take interaction between two individuals. The third study showed that already at one year of age infants shift their gaze from a passing hand to a receiving hand faster when the receiving hand forms a give-me gesture compared to an inverted hand shape. The reported results from this thesis make two major contributions. First, Studies I and II provide evidence for an embodied account of action prediction by demonstrating a direct connection between anticipatory eye movements and motor cortex activity. These findings support the interpretation that predictive eye movements are driven by a recruitment of the observer’s own motor system. Second, Study III implicates that properties of social action goals influence infants’ online gaze during action observation. It further suggests that at one year of age infants begin to show sensitivity to social goals within the context of give-and-take interactions while observing from a third-party perspective.

The simplicity principle posits that we interpret sense data as the simplest consistent distal cause, or that our high level perceptual representations of stimuli are optimized for simplicity. The traditional paradigm used to test this principle is coding theory, where alternate representations of stimuli are constructed, simplicity is measured as shortness of representation length, and behavioural experiments attempt to show that the shortest representations correspond best to perception. In this study we apply coding theory to marker-based human walking motion. We compare two representation schemes. The first is based on marker coordinates in a body-centred Cartesian coordinate system. The second is based on a model of 15 rigid body segments with Euler angles and a Cartesian translation for each. Both of our schemes are principal component (PC)-based implementations of a norm-based multidimensional object space – a type of model for high level perceptual schemes that has received attention in the literature over the past two decades. Representation length is quantified as number of retained PC’s, with error increasing with discarded PC’s. We generalize simplicity to efficiency measured as error across all possible lengths, where more efficient schemes admit less error across lengths. We find that the Cartesian coordinates-based scheme is more efficient than the Euler angles and translations-based scheme across a database of 100 walkers. In order to link this finding to perception we turn to the caricature effect that subjects can identify caricatures of familiar stimuli more accurately than veridicals. Our design was to compare walker caricatures generated in our two schemes in the hope of finding that one gives caricatures that benefit identification more than the other, from which we would conclude the former to be a better model of the true perceptual scheme. However, we find that analogous caricatures between the two schemes are only distinguishable at caricature levels so extreme that identification performance breaks down, so our design became infeasible and no conclusion for a simplicity principle in walker perception is reached. We also measure a curve of increasing then decreasing identification performance with caricature level and an optimal level at approximately double the distinctiveness of a typical walker. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2010-10-29 19:16:39.943