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Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / Visual movement is important to most animals that move quickly, and even some that do not. What neural computations do animals use to see visual motion in their natural environment? The visual stimulus used to perform experiments on such questions is critical, and has historically limited the ability to perform experiments asking critical questions about responses to naturalistic moving scenes. The ability to display, at high frame rates, moving natural panoramas and other stimuli distorted to compensate for projection onto a flat screen was important to the experiments described here. I therefore created a software library called the 'Vision Egg' that allows creation of motion stimuli with recent, inexpensive computer hardware, and was used for the experiments described here. Additionally, I developed a mathematical model to determine the quality of motion simulation possible with computer displays. This model was applied to reach an understanding of the 'ghosting' artifact sometimes perceived on such apparent motion displays. Psychophysical experiments on human observers confirmed model predictions and allowed testing of synthetic motion blur for simulation of smooth motion and elimination of the ghosting artifact. I show this synthetic motion blur is optimal in the sense of creating the closest perception possible to that of smooth motion experienced in natural settings. Experiments on humans and flies show that such synthetic 'motion blur' has no effect on motion detection per se. However, ghosting in sampled displays results in information not present in smooth motion at high velocities, permitting inappropriate discrimination of rapidly moving features. I performed experiments measuring the responses of hoverfly wide-field motion detecting neurons (HS cells) in adapted and unadapted states to the velocity of natural scenes. Responses to natural images of varied intrinsic contrast depend little on the choice of image. Artificially reducing contrast, however, does reduce response magnitudes. Finally, the greatest component of response variation to natural scenes is directly related to local structure in the scenes, and could thus be called 'pattern noise.' The large receptive field of HS cells arises from a (non-linear) spatial summation of numerous elementary motion detectors. I measured spatial and temporal contrast sensitivity of small patches in the large receptive field. As predicted from the presence of a frontal optical acute zone, spatial tuning is highest frontally. A sexually dimorphic 'bright zone' in the frontodorsal eye is correlated with enhanced contrast sensitivity and faster temporal tuning in HS cells with receptive fields in this region of male flies. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1125182 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2004

Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / Visual movement is important to most animals that move quickly, and even some that do not. What neural computations do animals use to see visual motion in their natural environment? The visual stimulus used to perform experiments on such questions is critical, and has historically limited the ability to perform experiments asking critical questions about responses to naturalistic moving scenes. The ability to display, at high frame rates, moving natural panoramas and other stimuli distorted to compensate for projection onto a flat screen was important to the experiments described here. I therefore created a software library called the 'Vision Egg' that allows creation of motion stimuli with recent, inexpensive computer hardware, and was used for the experiments described here. Additionally, I developed a mathematical model to determine the quality of motion simulation possible with computer displays. This model was applied to reach an understanding of the 'ghosting' artifact sometimes perceived on such apparent motion displays. Psychophysical experiments on human observers confirmed model predictions and allowed testing of synthetic motion blur for simulation of smooth motion and elimination of the ghosting artifact. I show this synthetic motion blur is optimal in the sense of creating the closest perception possible to that of smooth motion experienced in natural settings. Experiments on humans and flies show that such synthetic 'motion blur' has no effect on motion detection per se. However, ghosting in sampled displays results in information not present in smooth motion at high velocities, permitting inappropriate discrimination of rapidly moving features. I performed experiments measuring the responses of hoverfly wide-field motion detecting neurons (HS cells) in adapted and unadapted states to the velocity of natural scenes. Responses to natural images of varied intrinsic contrast depend little on the choice of image. Artificially reducing contrast, however, does reduce response magnitudes. Finally, the greatest component of response variation to natural scenes is directly related to local structure in the scenes, and could thus be called 'pattern noise.' The large receptive field of HS cells arises from a (non-linear) spatial summation of numerous elementary motion detectors. I measured spatial and temporal contrast sensitivity of small patches in the large receptive field. As predicted from the presence of a frontal optical acute zone, spatial tuning is highest frontally. A sexually dimorphic 'bright zone' in the frontodorsal eye is correlated with enhanced contrast sensitivity and faster temporal tuning in HS cells with receptive fields in this region of male flies. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1125182 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2004

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This thesis shows how to detect boundaries on the basis of motion information alone. The detection is performed in two stages: (i) the local estimation of motion discontinuities and of the visual flowsfield; (ii) the extraction of complete boundaries belonging to differently moving objects. For the first stage, three new methods are presented: the "Bimodality Tests,'' the "Bi-distribution Test,'' and the "Dynamic Occlusion Method.'' The second stage consists of applying the "Structural Saliency Method,'' by Sha'ashua and Ullman to extract complete and unique boundaries from the output of the first stage. The developed methods can successfully segment complex motion sequences.

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Communication is the exchange of thoughts and ideas from one person to another, often through the form of narratives. People communicate using speech, gesture, and drawing, or some multimodal combination of the three. Although there has been much research on how we understand and produce speech and pantomimes, there is relatively little on drawing, and even less on cross-modal communication. This dissertation presents novel empirical findings that contribute to a better understanding of the brain areas that mediate narrative communication across speech, pantomime, and drawing. Since the neuroscience of drawing was so understudied, I first used functional magnetic resonance imaging (fMRI) to investigate the existence of a basic drawing network in the human brain (Chapter 2). The drawing network was shown to contain three visual-motion areas that process the emanation of the visual image as drawing occurs. Next, to follow up on the poorly-characterized structural connectivity of these areas in the human dorsal visual stream, I used diffusion imaging to explore how these dorsal stream areas are connected (Chapter 3). The tractography results showed structural connectivity for two of the three predicted branches connecting the three visual-motion areas. Finally, I used fMRI to investigate how the basic drawing network is recruited during the more complex task of narrative drawing, and to find common brain areas among narrative speech, pantomime, and drawing (Chapter 4). Results suggest that people approached narratives in an intrinsically mentalistic fashion in terms of the protagonist, rather than as a mere description of action sequences. Together, these studies advance our understanding of the brain areas that comprise a basic drawing network, how these brain areas are interconnected, and how we communicate stories across three modalities of production. I conclude with a general discussion of my findings (Chapter 5). / Thesis / Doctor of Philosophy (PhD)

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A terrestrial robotic electrophysiology platform has been developed that can hold a moth (<italic>Manduca sexta</italic>), record signals from its brain or muscles, and use these signals to control the rotation of the robot. All signal processing (electrophysiology, spike detection, and robotic control) was performed onboard the robot with custom designed electronic circuits. Wireless telemetry allowed remote communication with the robot. In this study, we interfaced directionally-sensitive visual neurons and pleurodorsal steering muscles of the mesothorax with the robot and used the spike rate of these signals to control its rotation, thereby emulating the classical optomotor response known from studies of the fly visual system. The interfacing of insect and machine can contribute to our understanding of the neurobiological processes underlying behavior and also suggest promising advancements in biosensors and human brain-machine interfaces.

A representation of visual motion convenient for recognition shouldsmake prominent the qualitative differences among simple motions. Wesargue that the first stage in such a motion representation is to makesexplicit boundaries that we define as starts, stops, and forcesdiscontinuities. When one of these boundaries occurs in motion, humansobservers have the subjective impression that some fleeting,ssignificant event has occurred. We go farther and hypothesize that onesof the subjective motion boundaries is seen if and only if one of oursdefined boundaries occurs. We enumerate all possible motion boundariessand provide evidence that they are psychologically real.