Browsing by Subject "PATCHES"

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  • Hosoya, Haruo; Hyvärinen, Aapo (2017)
    Experimental studies have revealed evidence of both parts-based and holistic representations of objects and faces in the primate visual system. However, it is still a mystery how such seemingly contradictory types of processing can coexist within a single system. Here, we propose a novel theory called mixture of sparse coding models, inspired by the formation of category-specific subregions in the inferotemporal (IT) cortex. We developed a hierarchical network that constructed a mixture of two sparse coding submodels on top of a simple Gabor analysis. The submodels were each trained with face or non-face object images, which resulted in separate representations of facial parts and object parts. Importantly, evoked neural activities were modeled by Bayesian inference, which had a top-down explaining-away effect that enabled recognition of an individual part to depend strongly on the category of the whole input. We show that this explaining-away effect was indeed crucial for the units in the face submodel to exhibit significant selectivity to face images over object images in a similar way to actual face-selective neurons in the macaque IT cortex. Furthermore, the model explained, qualitatively and quantitatively, several tuning properties to facial features found in the middle patch of face processing in IT as documented by Freiwald, Tsao, and Livingstone (2009). These included, in particular, tuning to only a small number of facial features that were often related to geometrically large parts like face outline and hair, preference and anti-preference of extreme facial features (e.g., very large/small inter-eye distance), and reduction of the gain of feature tuning for partial face stimuli compared to whole face stimuli. Thus, we hypothesize that the coding principle of facial features in the middle patch of face processing in the macaque IT cortex may be closely related to mixture of sparse coding models.
  • Magioli, Marcelo; Micchi de Barros Ferraz, Katia Maria Paschoaletto; Chiarello, Adriano Garcia; Galetti, Mauro; Freire Setz, Eleonore Zulnara; Paglia, Adriano Pereira; Abrego, Nerea; Ribeiro, Milton Cezar; Ovaskainen, Otso (2021)
    Land-use changes are a main driver of modifications in tropical ecosystems, leading to the loss of species and ecological traits and affecting key ecological functions. Although much attention has been given to predict the effects of species loss on ecological processes, information on the large-scale effects of land-use changes over ecological functions is scarce. Here, we detected erosion in the prevalence of ecological functions performed by mammals in response to land-use changes in the Atlantic Forest of Brazil. By analyzing the loss of different ecological functions (vertebrate and invertebrate predation, seed dispersal, seed depredation, herbivory) performed by mammal assemblages in a deforestation gradient, we observed that vulnerable functions (performed by sensitive species, such as browsing, seed depredation, medium and large vertebrate predation) were positively related to patch size and forest cover and negatively related to anthropogenic cover. These relationships were reversed for persistent functions (performed by resilient species, such as grazing, small seed dispersal, small vertebrate and invertebrate predation). Vulnerable functions were virtually restricted to large forest remnants, while persistent functions were prevalent in human-modified landscapes. Disturbed forests are not necessarily empty of mammal species, but there is a substantial loss of ecological functions across most of the Atlantic Forest. Five out of ten ecological functions lose prevalence in small forest remnants. Nonetheless, these small remnants serve as refuges for the remaining biodiversity and are on the verge of the functional extinction of important processes. The erosion of ecological functions provided by mammals compromise the persistence of Atlantic Forest's biodiversity. (C) 2021 Associacao Brasileira de Ciencia Ecologica e Conservacao. Published by Elsevier B.V.
  • McKay, D.; Paavilainen, T.; Gustavsson, B.; Kvammen, A.; Partamies, N. (2019)
    The development of a magnetospheric substorm may be classified into three phases: growth, expansion, and recovery. The growth phase is important as it includes processes that lead to the expansion. In a recent growth-phase study, a type of fast discrete auroral transient phenomena-referred to as Lumikot-were observed. The Lumikot are several kilometers across and move in the high-energy precipitation region, parallel to the main growth-phase arc, with both east-west and west-east directions of travel during the same event. Their apparent transverse movement and quasi-stable intensity make them distinct from cooccurring optical pulsating aurorae. Comparison to other studies show that they occur in the cosmic noise absorption region and it is likely that the Lumikot are colocated with high-energy particle populations on the boundary between the outer radiation belt and the plasmasheet.