Vision provides the primary means by which many animals distinguish foreground objects from their background and coordinate locomotion through complex environments. The present thesis focuses on mechanisms within the visual system that afford figure-ground segregation and self-motion perception. These processes are modeled as emergent outcomes of dynamical interactions among neural populations in several brain areas. This dissertation specifies and simulates how border-ownership signals emerge in cortex, and how the medial superior temporal area (MSTd) represents path of travel and heading, in the presence of independently moving objects (IMOs). Neurons in visual cortex that signal border-ownership, the perception that a border belongs to a figure and not its background, have been identified but the underlying mechanisms have been unclear. A model is presented that demonstrates that inter-areal interactions across model visual areas V1-V2-V4 afford border-ownership signals similar to those reported in electrophysiology for visual displays containing figures defined by luminance contrast. Competition between model neurons with different receptive field sizes is crucial for reconciling the occlusion of one object by another. The model is extended to determine border-ownership when object borders are kinetically-defined, and to detect the location and size of shapes, despite the curvature of their boundary contours. Navigation in the real world requires humans to travel along curved paths. Many perceptual models have been proposed that focus on heading, which specifies the direction of travel along straight paths, but not on path curvature. In primates, MSTd has been implicated in heading perception. A model of V1, medial temporal area (MT), and MSTd is developed herein that demonstrates how MSTd neurons can simultaneously encode path curvature and heading. Human judgments of heading are accurate in rigid environments, but are biased in the presence of IMOs. The model presented here explains the bias through recurrent connectivity in MSTd and avoids the use of differential motion detectors which, although used in existing models to discount the motion of an IMO relative to its background, is not biologically plausible. Reported modulation of the MSTd population due to attention is explained through competitive dynamics between subpopulations responding to bottom-up and top- down signals.

Little is known about how healthy aging impacts figure-ground (FG) perception, which is critical in organizing complex visual input into coherent figures. Inhibitory-suppression is thought to be critical in resolution between competing FG interpretations. Given the age-related changes to inhibitory cortical mechanisms, my thesis investigated the hypothesis that processes underlying FG organization are impaired in aging. We explored the effects of age on the convexity context effect (CCE): the tendency to perceive convex regions as figural [i.e., P(Convex=Figure)] increases with surrounding convex and concave regions. In Chapter 2, we observed that adding context by increasing region number, increased P(Convex=Figure) in younger and older observers, but this CCE was significantly reduced in older adults. Reducing competition between perceptual interpretations by heterogeneously colouring convex regions, thereby invalidating the alternative {Concave=Figure} stimulus interpretation, greatly increased P(Convex=Figure) in older observers. These results supported the notion that aging impairs FG organization, particularly in relatively high competition contexts. In Chapter 3, we explored the possibility that reduced presumption of depth in our stimuli might explain the reduced the CCE in older observers by adding texture motion to region fills consistent with depth in the stimulus. The results were inconsistent with the hypothesis, but supported the reduced inhibitory-suppression hypothesis of the age effect. In Chapter 4, we explored the neural activation associated with the processing mechanisms underlying the resolution of FG competition. The results indicated that the N250 in younger observers but not older observers is sensitive to high vs. low competition contexts. Furthermore, individual differences in this N250-competition effect were correlated with the behavioural effect of competition. Our findings are consistent with the hypothesis that the processing underlying FG organization is impaired in senescence, which may stem from reduced efficacy of the neural architecture supporting this ability. Various implications of this work are discussed. / Dissertation / Doctor of Philosophy (PhD)

The nature of figure-ground relationships and their potential for use as a tool for architectural composition was investigated through the design of a winery. Included in the winery were facilities accomodating both the production and consumption of wine. These programmatic elements were used as guides for the development of multiple figure-ground relationships at a variety of scales. In addition, the dialogue between different figures as well as the careful development of the backdrop surfaces were topics of study. Several design strategies were employed to create relationships between figure elements and their backdrops, including the insertion of volumes into and through one another, the careful development of material and surface, and light. From this work, as well as previous projects, several key findings can now be articulated concerning the potential use of figure-ground relationships in the development of a work of architecture. These include the need to optimize the proportion of figure(s) relative to a given background and the key role that the disposition of figures relative to one another plays in the development of a meaningful figure-ground relationship. / Master of Architecture

In this study we sought to determine whether infants, like adults, utilize previous experience to guide figure/ground processing. After familiarization to a shape, 5-month-olds preferentially attended to the side of an ambiguous figure/ground test stimulus corresponding to that shape, suggesting that they were viewing that portion as the figure. Infants’ failure to exhibit this preference in a control condition in which both sides of the test stimulus were displayed as figures indicated that the results in the experimental condition were not due to a preference between two figure shapes. These findings demonstrate for the first time that figure/ground processing in infancy is sensitive to top-down influence. Thus, a critical aspect of figure/ground processing is functional early in life.

My Trip to Notan charts my own journey from the rawness and acceptance of multiple life losses into understanding, and finally, renewal. The key result of this project is a prototype book, a 48-page digital Print-On-Demand (POD) publication, which also includes a DVD that inserts into book’s back and features live demonstrations, interviews and other segments related to the book. Additionally, the body of work from which the book was gleaned was presented at the thesis exhibition. Ultimately, My Trip to Notan is a sketch of my understanding of the framework that threads through design, physics and philosophy, inspired by the simplicity of the ancient art of Notan, and upon my own fragmentary observations gathered from the journey. My hope was to reveal some sense of the pulse that drives the inquiry, rather than the suggestion of any sort of destination.

Object perception is necessary to our understanding of the visual world, yet its neural mechanism remains poorly understood. The goal of this dissertation is to shed light on this mechanism. Current computational models of object perception suggest that regions on opposite sides of a shared border compete, with the winner perceived as the shaped object and the loser as its locally shapeless background (or ground). Recent behavioral work indicates that the result of this competition is suppression of the ground at the level of object shape--a finding not predicted by models. Here, I present three studies that extend this previous research on ground suppression as a mechanism by which object perception is accomplished. I first show that the amount of suppression applied to the ground depends on the amount of competition for object status (Salvagio, Cacciamani, & Peterson, 2012). I then provide the first neural evidence of ground suppression from shape-level competition at both high and low levels of the visual hierarchy, with the latter arising from top-down feedback (Cacciamani, Scalf, & Peterson, submitted). Finally, I show that semantic information pertaining to the ground is accessed prior to the assignment of object status, but unlike shape information, is not suppressed (Cacciamani, Mojica, Sanguinetti, & Peterson, 2014). Together, the three studies that comprise this dissertation demonstrate that ground suppression arising from shape-level competition underlies object perception. This research contradicts traditional theories stating that objects are processed unidirectionally through the visual system in a single feedforward pass; instead, it supports theories of object perception entailing dynamical feedforward and feedback processes.

Flies are highly visually guided animals. In this thesis, I have used hoverflies as a model for studying motion vision. Flies process motion vision in three visual ganglia: the lamina, the medulla, and the lobula complex. In the posterior part of lobula complex, there are around 60 lobula plate tangential cells (LPTCs). Most of LPTCs have large receptive fields where the local direction sensitivity suggests that they function as matched filters to specific types of optic flow. LPTCs connect to descending or neck motor neurons that control wing and head movements, respectively. Therefore, in this thesis I have focused on the electrophysiological responses of LPTCs to gain understanding of visual behaviors in flies. The elementary motion detector (EMD) is a model that can explain the formation of local motion sensitivity. However, responses to higher order motion, where the direction of luminance change is uncorrelated with the direction of movement, cannot be predicted by classic EMDs. Nevertheless, behavior shows that flies can see and track bars with higher order motion cues. I showed (Paper I) that several LPTCs also respond to higher order motion. Many insects, including flies, release octopamine during flight. Therefore, adding octopamine receptor agonists can mimic physical activity. Our study (Paper II) investigated the effect of octopamine on three adaptation components. We found that the contrast gain reduction showed a frequency dependent increase after octopamine stimulation. Since the contrast gain is non-directional, it is likely presynaptic to the LPTC. We therefore believe that octopamine acts on the delay filter in the EMD. In the third paper we describe a novel LPTC. The centrifugal stationary inhibited flicker excited (cSIFE) is excited by flicker and inhibited by stationary patterns. Neither of these responses can be predicted by EMD models. Therefore, we provide a new type of motion detector that can explain cSIFE’s responses (Paper III). During bar tracking, self-generated optic flow may counteract the steering effect by inducing a contradictory optomotor response. Behavior shows that during bar fixation, flies ignore background optic flow. Our study (Paper IV) focus on the different receptive fields of two LPTCs, and relate these to the bar fixation behavior. In the neuron with a small and fronto-dorsal receptive field, we find a higher correlation with bar motion than with background motion. In contrast, the neuron with a larger receptive field shows a higher correlation with background motion.

Thesis (M.S.)--Indiana University, 2003. / Includes bibliographical references (leaves 56-64). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Thesis (M.S.)--Indiana University, 2003. / Includes bibliographical references (leaves 56-64).

Employer monitoring of communications is prevalent and on the rise due in part to the Sarbanes-Oxley Act, the Health Insurance Privacy Protection Act, and other legislation in the U.S. and other countries. However, the critical effect of this new activity on what is communicated in companies has not been assessed. This dissertation examines the impacts of computer mediated communication systems monitoring on neutral, incriminating and exculpatory content, as well as the overall volume of communications issued on monitored and non-monitored computer mediated communication systems. Incriminating communication is cataloged in a hazard communications taxonomy for this investigation. A controlled laboratory experiment has subjects participate in an instant messaging discussion on a topic for which they are likely to be aware of information that is incriminating to their organization, or its members, or both. Consistent with self awareness theory, monitored subjects engage in significantly less overall and neutral communication. They volunteer fewer high intensity hazard communications, but are less likely to curtail low intensity hazard communications. They issue denials about more incriminating topics. Contributions to research include theory development, especially in the area of standard selection; application of self-awareness theory to the new domain of computer mediated communications monitoring; a research framework; a taxonomy and coding scheme for the new hazard communications constructs; and a relative standards influence instrument and methodology for use in studying competing standards. Implications for corporate monitoring and communications policies are discussed, and a research agenda is outlined.