title: A neural-based code for computing image velocity from small sets of middle temporal (MT/V5) neuron inputs

authors: Perrone, John A.

subjects: 2D motion

abstract: It is still not known how the primate visual system is able to measure the velocity of moving stimuli such as edges and dots. Neurons have been found in the Medial Superior Temporal (MST) area of the primate brain that respond at a rate proportional to the speed of the stimulus but it is not clear how this property is derived from the speed-tuned Middle Temporal (MT) neurons that precede area MST along the visual motion pathway. I show that a population code based on the outputs from a number of MT neurons is susceptible to errors if the MT neurons are tuned to a broad range of spatial frequencies and have receptive fields that span a wide range of sizes. I present a solution that uses the activity of just three MT units within a velocity channel to estimate the velocity using a weighted vector average (centroid) technique. I use a range of velocity channels (1, 2, 4, and 88/s) with inhibition between them so that only a single channel passes the velocity estimate onto the next stage of processing (MST). I also include a contrast-dependent redundancy-removal stage which provides tighter spatial resolution for the velocity estimates under conditions of high contrast but which trades off spatial compactness for greater sensitivity at low contrast. The new model produces an output signal proportional to the stimulus input velocity (consistent with MST neurons) and its input stages have properties closely tied to those of neurons in areas V1 and MT.

text: A neural-based code for computing image velocity from small sets of middle temporal (MT/V5) neuron inputs It is still not known how the primate visual system is able to measure the velocity of moving stimuli such as edges and dots. Neurons have been found in the Medial Superior Temporal (MST) area of the primate brain that respond at a rate proportional to the speed of the stimulus but it is not clear how this property is derived from the speed-tuned Middle Temporal (MT) neurons that precede area MST along the visual motion pathway. I show that a population code based on the outputs from a number of MT neurons is susceptible to errors if the MT neurons are tuned to a broad range of spatial frequencies and have receptive fields that span a wide range of sizes. I present a solution that uses the activity of just three MT units within a velocity channel to estimate the velocity using a weighted vector average (centroid) technique. I use a range of velocity channels (1, 2, 4, and 88/s) with inhibition between them so that only a single channel passes the velocity estimate onto the next stage of processing (MST). I also include a contrast-dependent redundancy-removal stage which provides tighter spatial resolution for the velocity estimates under conditions of high contrast but which trades off spatial compactness for greater sensitivity at low contrast. The new model produces an output signal proportional to the stimulus input velocity (consistent with MST neurons) and its input stages have properties closely tied to those of neurons in areas V1 and MT.

year: 2012

title: Extent of seagrass in Tauranga Harbour: a comparison of satellite automated classification versus manual delineation of aerial imagery

authors: Shao, Zhanchao

abstract: This report outlines a comprehensive analysis of seagrass extent in Tauranga Harbour, New Zealand, using advanced remote sensing techniques. It compares two key methods: satellite-based supervised classification using Random Forest, and manual delineation via aerial photography. The research focuses on mapping the spatial and temporal changes in seagrass habitats, particularly the native species Zostera muelleri, from 1959 to 2024. Complementary to the satellite-based classification method, an easy-to-use graphical user interface (GUI) was developed, enabling users to efficiently access satellite imagery and generate detailed habitat maps.
The supervised classification using Random Forest proved effective for detecting seagrass habitats, achieving high accuracy (0.92 for Sentinel-2 and 0.88 for Landsat imagery). Despite occasional misclassifications, particularly in areas with high chlorophyll concentrations (i.e., the Tauranga Harbour sub-estuaries), the method provided a more time-efficient and scalable alternative to manual delineation. Aerial photography and manual mapping served as an important comparison but are less efficient in capturing less visible seagrass areas in deeper water or fragmented meadows.

text: Extent of seagrass in Tauranga Harbour: a comparison of satellite automated classification versus manual delineation of aerial imagery This report outlines a comprehensive analysis of seagrass extent in Tauranga Harbour, New Zealand, using advanced remote sensing techniques. It compares two key methods: satellite-based supervised classification using Random Forest, and manual delineation via aerial photography. The research focuses on mapping the spatial and temporal changes in seagrass habitats, particularly the native species Zostera muelleri, from 1959 to 2024. Complementary to the satellite-based classification method, an easy-to-use graphical user interface (GUI) was developed, enabling users to efficiently access satellite imagery and generate detailed habitat maps.
The supervised classification using Random Forest proved effective for detecting seagrass habitats, achieving high accuracy (0.92 for Sentinel-2 and 0.88 for Landsat imagery). Despite occasional misclassifications, particularly in areas with high chlorophyll concentrations (i.e., the Tauranga Harbour sub-estuaries), the method provided a more time-efficient and scalable alternative to manual delineation. Aerial photography and manual mapping served as an important comparison but are less efficient in capturing less visible seagrass areas in deeper water or fragmented meadows.

year: 2024-11-28

title: Māori Waiata: Discourse structuring, sub-genres and aesthetics

authors: Roa, Raukura

subjects: Te reo Māori

abstract: With particular reference to a discourse-based analysis of five waiata tangi from Ngāti Hauā, it is argued here that different types of Māori waiata (songs and chants) may be characterised by different types of overall discourse structuring. It is also suggested that discourse structuring may be a significant aspect of the aesthetics of Māori waiata.

text: Māori Waiata: Discourse structuring, sub-genres and aesthetics With particular reference to a discourse-based analysis of five waiata tangi from Ngāti Hauā, it is argued here that different types of Māori waiata (songs and chants) may be characterised by different types of overall discourse structuring. It is also suggested that discourse structuring may be a significant aspect of the aesthetics of Māori waiata.

year: 2004-02