Social perception in the real world : employing visual adaptation paradigms in the investigation of mechanisms underlying emotion and trustworthiness perception

Social context can substantially influence our perception and understanding of emotion and action of observed individuals. However, less is known about how temporal context can affect our judgement of behaviour of other people. The aim of this thesis was to explore how immediate perceptual history influences social perception. Further aims were: (i) to examine whether prior visual experience influences the perception of behaviour of other individuals in a naturalistic virtual environment resembling the real world; (ii) to determine whether our judgement of emotional state or trustworthiness of observed individuals is influenced by perceptual history, and (iii) by cognitive processes such as mental state attribution to the observer; (iv) to investigate whether processing of emotion information from dynamic, whole-body action is dependent on the processing of body identity, and (v) dependent on the body part that conveys it. Here, visual adaptation paradigms were used to examine systematic biases in social perception following prior visual experience, and to infer potential neural mechanisms underlying social perception. The results presented in this thesis suggest that perception and understanding of behaviour of other individuals in the naturalistic virtual environment are influenced by the behaviour of other individuals within the shared social environment. Specifically, in Chapter 3, I presented data suggesting that visual adaptation mechanisms examined thus far in laboratory settings may influence our everyday perception and judgement of behaviour of other people. In Chapters 4 and 5, I showed that these biases in social perception can be attributed to visual adaptation mechanisms, which code emotions and intentions derived from actions with respect to specific action kinematics and the body part that conveyed the given emotion. The results of experiments presented in Chapter 4 demonstrated that emotions conveyed by actions are represented with respect to, and independently of, actors’ identity. These finding suggest that the mechanisms underlying processing of action emotion may operate in parallel with the mechanisms underlying processing emotion from other social signals such as face and voice. In Chapter 6, I showed that cognitive processes underlying Theory of Mind, such as mental state attribution, can also influence perceptual processing of emotional signals. Finally, results presented in Chapter 7 suggest that judgments of complex social traits such as trustworthiness derived from faces are also influenced by perceptual history. These results also yielded strong sex differences in assessing trustworthiness of an observed individual; female observers showed a strong bias in perception resulting from adaptation to (un)trustworthiness, while male observers were less influenced by prior visual context. Together these findings suggest that social perception in the real world may be sensitive not only to the social context in which an observed act is embedded, but also to the prior visual context and the observer’s beliefs regarding the observed individual. Visual adaptation mechanisms may therefore operate during our everyday perception, in order to adjust our visual system to allow for efficient and accurate judgement of socially meaningful stimuli. The findings presented in this thesis highlight the importance of studying social perception using naturalistic stimuli embedded in a meaningful social scene, in order to gain a better understanding of the mechanisms that underlie our judgement of behaviour of other people. They also demonstrate the utility of visual adaptation paradigms in studying social perception and social cognition

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

The Influence of the Dorsal Pathway on Enhanced Visual Processing

Overall our visual experience is such a seamless one that unless specifically told, we might never know that what we see is actually the visual system taking the very simple input provided by cells in the retina and constructing an image based on rules and calculations and algorithms neuroscientists have yet to fully uncover. This is an incredible feat given the plethora of visual stimuli within our environment, that this information is used to inform and plan actions, and if that wasnt enough, the visual system also has the capacity to selectively enhance certain aspects of visual processing if needs be. The research contained within this dissertation seeks to investigate how the dorsal visual pathway enhances both decision-making processes and visual stimuli presented near the hand. Our findings suggest that the formation of object representations in the dorsal pathway can include both ventral (colour, contrast) and dorsal (speed) stream features (chapters two and three), which in turn greatly speed decision-making processes within the dorsal pathway. In addition, contrast and speed are integrated automatically but purely ventral stream features, such as colour, require top-down attention to facilitate enhanced processing speeds (chapter three). In chapter four we find that visual processing near the hand is enhanced in a novel way. When the hand is nearby, orientation tuning is sharpened in a manner not consistent with either oculomotor-driven spatial or feature based attention. In addition, response variability is reduced when the hand is nearby, raising the possibility that enhanced processing near the hand maybe be driven by feedback from frontoparietal reaching and grasping regions. The research within this dissertation includes important new information regarding how the dorsal pathway can speed visual processing, and provides insight as to the next stage in understanding how we use vision for action

Touching is believing: creating illusions and feeling of embodiment with mid-air haptic technology

Over the last two decades, the sense of touch has received new attention from the scientific community.Several haptic devices have been developed to address the complexity of the sense of touch, the latest addition being mid-air (contactless) haptic technology. An interesting series of previous research has suggested an easier way to tackle the complexity of designing convincing tactile sensations by exploiting tactile illusions. Tactile illusions rely on perceptual shortcuts based on the psychophysics of the tactile receptors. Currently, studies exploring the perceptual space of mid-air haptics and its applicability in the tactile illusions field are still limited in number. This thesis aims to contribute to the field of Human-Computer Interaction (HCI) by investigating the perceptual design space of ultrasonic mid-air haptics technology. Specifically, in a first set of three studies, we investigate the absolute thresholds (minimal amount of a property of astimulus that a user can detect) for control points (CP) at different frequencies on the hand and arm (Study 1). Then we investigate the optimal sampling rate needed to drive the device in an optimal fashion and its relationship with shape size (Study 2). Next, we apply a new technique to increase users’ performance in a shape discrimination task (Study 3). In Study 4, we start the exploration of a tactile illusion of movement using contact touch and later, we apply a similar procedure to investigate the feasibility of creating a tactile illusion of movement between the two non-interconnected hands by using mid-air touch (Study 5). Finally, in Study 6, we explore our sense of touch in VR, while providing an illusion of rain drops through mid-air haptics, to recreate a virtual hand illusion (VHI) to explore the boundaries of our sense of embodiment. Therefore, the contribution of this work is threefold: a) we contribute by adding new knowledge on the psychophysical space for mid-air haptics, b) we test the potential to create realistic tactile sensations by exploiting tactile illusions with mid-air haptic technology, and c) we demonstrate how tactile illusions mediated by mid-air haptics can convey a sense of embodiment in VR environments

Male Movements as Honest Cues to Reproductive Quality

Background: Research concerning sexual selection suggests that ornaments and traits convey information that is valuable to observers when making decisions based on adaptive problems. In the animal kingdom males perform dynamic courtship displays and females assess such displays when choosing a mate. In humans however this avenue of research is in its infancy but an emerging field of study has sought to find out if dance movements, which are thought to be courtship displays, provide observers with condition dependent information. Objectives: i) To create a methodology that records dance movements with high accuracy whilst eliminating structural cues known to influence mate choice decisions while maintaining a highly realistic human form. ii) Use this methodology to assess whether traits of interest (health, fitness, strength and age) can be detected by observers. iii) To establish if particular movements are mediating perceptions of dance quality and their condition. Methods: A cutting edge motion capture system and professional animation software was used to record dances. Each male dancer either provided information on his health status, physical fitness, strength or age. Dance animations were shown to observers and their perceptions were correlated against the traits of interest. These were also correlated against basic biomechanical characteristics to establish possible mediators. Results: It was revealed that whilst health measures were not related to dance ratings, strength measures were and these perceptions were mediated by movements of the upper body. A final study found that age was detectable by male participants and related to masculinity ratings of female raters but no biomechanical mediators were found. Conclusion: Men and women are able to derive certain quality cues from observing male dance and in some instances biomechanical characteristics mediated this relationship. This provides evidence that dance may be used in the assessment of males in the context of sexual selection

3D motion : encoding and perception

The visual system supports perception and inferences about events in a dynamic, three-dimensional (3D) world. While remarkable progress has been made in the study of visual information processing, the existing paradigms for examining visual perception and its relation to neural activity often fail to generalize to perception in the real world which has complex dynamics and 3D spatial structure. This thesis focuses on the case of 3D motion, developing dynamic tasks for studying visual perception and constructing a neural coding framework to relate neural activity to perception in a 3D environment. First, I introduce target-tracking as a psychophysical method and develop an analysis framework based on state space models and the Kalman filter. I demonstrate that target-tracking in conjunction with a Kalman filter analysis framework produce estimates of visual sensitivity that are comparable to those obtained with a traditional forced-choice task and a signal detection theory analysis. Next, I use the target-tracking paradigm in a series of experiments examining 3D motion perception, specifically comparing the perception of frontoparallel motion with the perception of motion-through-depth. I find that continuous tracking of motion-through-depth is selectively impaired due to the relatively small retinal projections resulting from motion-through-depth and the slower processing of binocular disparities. The thesis then turns the neural representation of 3D motion and how that underlies perception. First I introduce a theoretical framework that extends the standard neural coding approach, incorporating the environment-to-retina transformation. Neural coding typically treats the visuals stimulus as a direct proxy for the pattern of stimulation that falls on the retina. Incorporating the environment-to-retina transformation results in a neural representation fundamentally shaped by the projective geometry of the world onto the retina. This model explains substantial anomalies in existing neurophysiological recordings in primate visual cortical neurons during presentations of 3D motion and in psychophysical studies of human perception. In a series of psychophysical experiments, I systematically examine the predictions of the model for human perception by observing how perceptual performance changes as a function of viewing distance and eccentricity. Performance in these experiments suggests a reliance on a neural representation similar to the one described by the model. Taken together, the experimental and theoretical findings reported here advance the understanding of the neural representation and perception of the dynamic 3D world, and adds to the behavioral tools available to vision scientists.Neuroscienc

Use your illusion: the flash-lag effect as a tool for psychophysics

The flash-lag effect is an illusion in which a moving object is perceived advanced beyond an aligned flash. The majority of research into the effect has been directed at specifying its source, though a small body of literature simply makes use of flash-lag to answer diverse questions about perception – without necessarily arbitrating between competing accounts of its nature. The current thesis expands on this little-explored potential of the flash-lag effect with the presentation of three papers reporting programmes of research that exploit the phenomenon to address issues unrelated to its cause. In the first paper it is shown that, like in visual flash-lag, a similar motion direction based anisotropy is evident in the motor version of the effect, in which one’s unseen limb is perceived ahead of a flash. Specifically, the effect is greater for motion towards, rather than away from fixation. Furthermore, Paper I also demonstrates for the first time a motor flash-drag effect, in which one’s unseen moving hand ‘drags’ the perceived position of a nearby flash. It is argued that both of these findings are evidence of parallels between vision and action systems. Paper II takes advantage of the explicitly perceptual nature of the flash-lag effect to investigate whether the visuospatial perception of threatening objects is different to that of non-threatening objects. It is ultimately shown that when a moving stimulus is threatening, the flash-lag effect is greater, regardless of its direction of motion. Paper III shows that gamma movement (the apparent contraction of disappearing stimuli) adds to and subtracts from the forward displacement of contracting and expanding stimuli, respectively. Prior to these papers, however, an overview chapter reviews the flash-lag literature, and argues that the effect can be a useful tool for psychophysics, even without a consensus on its origin

Motion Capture Study of Human Movement Recognition

In this thesis, we address questions about recognition of human movement through motion capture. We begin by capturing the martial arts movements of four actors as they each perform three different techniques. We then conduct a survey to determine if participants in the survey are able to distinguish the various martial arts techniques and differentiate the actors that portray said techniques. A secondary consideration of our survey is to determine if the participants can distinguish the sex of the actors as they perform the martial arts techniques. Our hypothesis is that people are able to distinguish actors and sex; however, determining sex may be more difficult with digital actor representations that are anatomically ambiguous. With this thesis we will attempt to provide insight into human perception and motion capture, and help validate the use of motion capture in video games and movies for realistic human animation and interactions and to help improve the immersion of the player/viewer