title: Investigation into factors affecting perceptual stability of the world during smooth pursuit eye movements

authors: Boer, Alexandra (Sasha)

subjects: perceptual stability

abstract: During pursuit eye movement, a stationary background projected on the retina shifts in the direction opposite to that of the eye movement. This complicates the perception of objects because during an eye movement the retinal and head-centric motions differ. Nevertheless, our visual system is somehow able to compensate for the added eye motion so that the world is perceived as stable. The eye movement compensation is traditionally assumed to consist of a combination of a retinal motion signal and an extra-retinal estimate of eye velocity (Von Holst & Mittelstaedt, 1950; Sperry, 1950).  This view has been expanded upon by a number of researchers in the last few decades with the introduction of vector addition-like models. However, it is not well known how closely the eye movement compensation mechanism follows the rules of vector algebra. Evidence for the presence of a signal coming from the moving eye has come from a variety of neurophysiological and perceptual research on the cortical Medial Superior Temporal (MST) area in primates. 

Previous studies have shown that the spatio-temporal structure of the background plays an important role in the perceptual accuracy of the velocity of a moving object in the visual field. Background characteristics have been shown to influence not only the retinal signal, but also the extra-retinal signal to some degree. The current thesis provides new information on factors that affect the degree of compensation for retinal motion during smooth pursuit eye movement. The findings are based on several experiments that were designed to use a range of pursuit target and stimulus dot velocities across different backgrounds and stimulus exposure times, in order to reveal details about how the retinal and extra-retinal signals are combined. Participants were asked to determine the direction of a moving stimulus by rotating an arrow on the screen. In a separate experiment, participants were also asked to assess the speed of a stimulus using a magnitude estimation task. A linear vector model was developed to separate the retinal and extra-retinal signal contribution to the overall compensation. This model was used to assess the degree of perceptual stability across different visual conditions. Generally, the data indicate that the perceived stimulus motion is well predicted by a vector subtraction mechanism postulated to be occurring in the human brain. However, in situations where there is weak visual stimulation, participants’ estimates of motion are less accurate and tend to follow the retinal image motion. In the current thesis I identify how the type of background, directions of eye movements, and stimulus velocities relative to the eye movements affected participants’ perceptual performance. Based on the data and the model fitting, it was concluded that the visual system appears to utilize the eye-movement related signal differentially depending on the retinal motion content.

text: Investigation into factors affecting perceptual stability of the world during smooth pursuit eye movements During pursuit eye movement, a stationary background projected on the retina shifts in the direction opposite to that of the eye movement. This complicates the perception of objects because during an eye movement the retinal and head-centric motions differ. Nevertheless, our visual system is somehow able to compensate for the added eye motion so that the world is perceived as stable. The eye movement compensation is traditionally assumed to consist of a combination of a retinal motion signal and an extra-retinal estimate of eye velocity (Von Holst & Mittelstaedt, 1950; Sperry, 1950).  This view has been expanded upon by a number of researchers in the last few decades with the introduction of vector addition-like models. However, it is not well known how closely the eye movement compensation mechanism follows the rules of vector algebra. Evidence for the presence of a signal coming from the moving eye has come from a variety of neurophysiological and perceptual research on the cortical Medial Superior Temporal (MST) area in primates. 

Previous studies have shown that the spatio-temporal structure of the background plays an important role in the perceptual accuracy of the velocity of a moving object in the visual field. Background characteristics have been shown to influence not only the retinal signal, but also the extra-retinal signal to some degree. The current thesis provides new information on factors that affect the degree of compensation for retinal motion during smooth pursuit eye movement. The findings are based on several experiments that were designed to use a range of pursuit target and stimulus dot velocities across different backgrounds and stimulus exposure times, in order to reveal details about how the retinal and extra-retinal signals are combined. Participants were asked to determine the direction of a moving stimulus by rotating an arrow on the screen. In a separate experiment, participants were also asked to assess the speed of a stimulus using a magnitude estimation task. A linear vector model was developed to separate the retinal and extra-retinal signal contribution to the overall compensation. This model was used to assess the degree of perceptual stability across different visual conditions. Generally, the data indicate that the perceived stimulus motion is well predicted by a vector subtraction mechanism postulated to be occurring in the human brain. However, in situations where there is weak visual stimulation, participants’ estimates of motion are less accurate and tend to follow the retinal image motion. In the current thesis I identify how the type of background, directions of eye movements, and stimulus velocities relative to the eye movements affected participants’ perceptual performance. Based on the data and the model fitting, it was concluded that the visual system appears to utilize the eye-movement related signal differentially depending on the retinal motion content.

year: 2011

title: Calcium carbonate alters the functional response of coastal sediments to eutrophication-induced acidification

authors: Drylie, Tarn P.

subjects: Science & Technology

abstract: Coastal ocean acidification research is dominated by laboratory-based studies that cannot necessarily predict real-world ecosystem response given its complexity. We enriched coastal sediments with increasing quantities of organic matter in the field to identify the effects of eutrophication-induced acidification on benthic structure and function, and assess whether biogenic calcium carbonate (CaCO₃) would alter the response. Along the eutrophication gradient we observed declines in macrofauna biodiversity and impaired benthic net primary productivity and sediment nutrient cycling. CaCO₃ addition did not alter the macrofauna community response, but significantly dampened negative effects on function (e.g. net autotrophy occurred at higher levels of organic matter enrichment in +CaCO₃ treatments than −CaCO₃ (1400 vs 950 g dw m⁻²)). By identifying the links between eutrophication, sediment biogeochemistry and benthic ecosystem structure and function in situ, our study represents a crucial step forward in understanding the ecological effects of coastal acidification and the role of biogenic CaCO₃ in moderating responses.

text: Calcium carbonate alters the functional response of coastal sediments to eutrophication-induced acidification Coastal ocean acidification research is dominated by laboratory-based studies that cannot necessarily predict real-world ecosystem response given its complexity. We enriched coastal sediments with increasing quantities of organic matter in the field to identify the effects of eutrophication-induced acidification on benthic structure and function, and assess whether biogenic calcium carbonate (CaCO₃) would alter the response. Along the eutrophication gradient we observed declines in macrofauna biodiversity and impaired benthic net primary productivity and sediment nutrient cycling. CaCO₃ addition did not alter the macrofauna community response, but significantly dampened negative effects on function (e.g. net autotrophy occurred at higher levels of organic matter enrichment in +CaCO₃ treatments than −CaCO₃ (1400 vs 950 g dw m⁻²)). By identifying the links between eutrophication, sediment biogeochemistry and benthic ecosystem structure and function in situ, our study represents a crucial step forward in understanding the ecological effects of coastal acidification and the role of biogenic CaCO₃ in moderating responses.

year: 2019

title: The Struggle For Success: A Socio-Cultural Perspective on the French Marist Priests and their Māori Mission 1838-1867

authors: Harman, Sandy Angela

subjects: missionaries

abstract: The nineteenth-century Roman Catholic missionary endeavour in New Zealand had its origins in a society of priests from Lyon, known as the Marists. The Marists’ mission has been deemed a failure due to its ongoing financial problems, its reputation for having abandoned Māori adherents, and its less visible impact compared to the Anglican Mission. This thesis examines the challenges facing the pioneer Marist priests in New Zealand and asks the question: was the Mission indeed a failure? The answer lies in the correspondence of the French Marists themselves, a largely untapped historical source which contains a different view of early New Zealand contact and religious history from that of the Church Missionary Society (CMS) evangelists. ‘The Struggle for Success’ consists of three parts examining the Mission before, during and after the pioneer phase. The first describes the Marists’ early influences and religious formation in France, which serve to elucidate the missionaries’ raison d’être and provide an historical context for the Mission. It is also an important attempt at a prosopography of men whose early lives were barely documented, and whose connection with contemporaneous and historical France, and the Lyon area in particular, would greatly affect the missions in Oceania. The subsequent comparative mission history in Part Two highlights the difficulties and conflicts that affected the progress of the Marist Māori Mission in New Zealand compared with other Christian missions in Oceania, notably the CMS in New Zealand and the early Marists in Wallis, Futuna, Tonga and New Caledonia. It describes the factors leading to the alleged failure of the Marist Māori Mission and demonstrates that hardships and struggle were the common lot of pioneer missionaries in Oceania. But the Marists on the Māori Mission had the added obstacles of being Frenchmen in a British colony, ascetics surrounded by and dependent on commerce, and dutiful religious under the authority of overburdened bishops. Irish immigration into New Zealand distorted the original aims of the French Marist missionaries, and Māori politico-religious initiatives to combat the devastating impacts of British colonialism essentially quashed Marist hopes that Māori would become a decidedly Catholic people. Having considered the obstacles to success, the thesis discusses in Part Three how the pioneer Marists understood success and conversion. In retrospect, it is clear that the missionaries underestimated the tenacity of early Māori catechists, but the CMS in New Zealand and Marists throughout Oceania were equally insensible in this respect. Finally the thesis offers an assessment of the mission’s overall success taking into account the revival of the Marist Māori Mission in the late 1870s and its continuation into the twentieth century. The social, cultural and political complexities of missionary endeavour demand a less rigid evaluation of missions than has been previously offered; and success and failure are problematic terms for the pioneer Marist Māori Mission because evangelisation was and is a work in progress.

text: The Struggle For Success: A Socio-Cultural Perspective on the French Marist Priests and their Māori Mission 1838-1867 The nineteenth-century Roman Catholic missionary endeavour in New Zealand had its origins in a society of priests from Lyon, known as the Marists. The Marists’ mission has been deemed a failure due to its ongoing financial problems, its reputation for having abandoned Māori adherents, and its less visible impact compared to the Anglican Mission. This thesis examines the challenges facing the pioneer Marist priests in New Zealand and asks the question: was the Mission indeed a failure? The answer lies in the correspondence of the French Marists themselves, a largely untapped historical source which contains a different view of early New Zealand contact and religious history from that of the Church Missionary Society (CMS) evangelists. ‘The Struggle for Success’ consists of three parts examining the Mission before, during and after the pioneer phase. The first describes the Marists’ early influences and religious formation in France, which serve to elucidate the missionaries’ raison d’être and provide an historical context for the Mission. It is also an important attempt at a prosopography of men whose early lives were barely documented, and whose connection with contemporaneous and historical France, and the Lyon area in particular, would greatly affect the missions in Oceania. The subsequent comparative mission history in Part Two highlights the difficulties and conflicts that affected the progress of the Marist Māori Mission in New Zealand compared with other Christian missions in Oceania, notably the CMS in New Zealand and the early Marists in Wallis, Futuna, Tonga and New Caledonia. It describes the factors leading to the alleged failure of the Marist Māori Mission and demonstrates that hardships and struggle were the common lot of pioneer missionaries in Oceania. But the Marists on the Māori Mission had the added obstacles of being Frenchmen in a British colony, ascetics surrounded by and dependent on commerce, and dutiful religious under the authority of overburdened bishops. Irish immigration into New Zealand distorted the original aims of the French Marist missionaries, and Māori politico-religious initiatives to combat the devastating impacts of British colonialism essentially quashed Marist hopes that Māori would become a decidedly Catholic people. Having considered the obstacles to success, the thesis discusses in Part Three how the pioneer Marists understood success and conversion. In retrospect, it is clear that the missionaries underestimated the tenacity of early Māori catechists, but the CMS in New Zealand and Marists throughout Oceania were equally insensible in this respect. Finally the thesis offers an assessment of the mission’s overall success taking into account the revival of the Marist Māori Mission in the late 1870s and its continuation into the twentieth century. The social, cultural and political complexities of missionary endeavour demand a less rigid evaluation of missions than has been previously offered; and success and failure are problematic terms for the pioneer Marist Māori Mission because evangelisation was and is a work in progress.

year: 2010