15 research outputs found
A Neural Model of First-order and Second-order Motion Perception and Magnocellular Dynamics
A neural model of motion perception simulates psychophysical data. concerning first-order and second-order motion stimuli, including the reversal of perceived motion direction with distance from the stimulus (I display), and data about directional judgments as a function of relative spatial phase or spatial and temporal frequency. Many other second-order motion percepts that have been ascribed to a second non-Fourier processing stream can also be explained in the model by interactions between ON and OFF cells within a single, neurobiologically interpreted magnocellular processing stream. Yet other percepts may be traced to interactions between form and motion processing streams, rather than to processing within multiple motion processing strea.ms. The model hereby explains why monkeys with lesions of the parvocellular layers, but not the magnocellular layers, of the lateral geniculate nucleus (LGN) are capable of detecting the correct direction of second-order motion, why most cells in area MT are sensitive to both first-order and second-order motion, and why after APB injection selectively blocks retinal ON bipolar cells, cortical cells are sensitive only to the motion of a moving bright bar's trailing edge. Magnoccllular LGN cells show relatively transient responses while parvoccllular LGN cells show relatively sustained responses. Correspondingly, the model bases its directional estimates on the outputs of model ON and OFF transient cells that are organized in opponent circuits wherein antagonistic rebounds occur in response to stimmulus offset. Center-surround interactions convert these ON and OFF outpr1ts into responses of lightening and darkening cells that are sensitive both to direct inputs and to rebound responses in their receptive field centers and surrounds. The total pattern of activity increments and decrements is used by subsequent processing stages (spatially short-range filters, competitive interactions, spatially long-range filters, and directional grouping cells) to dntermine the perceived direction of motion
Formação dos profissionais das ĂĄreas de ciĂȘncias agrĂĄrias em segurança do trabalho rural
Pegamento da enxertia em diferentes combinaçÔes de variedades e espécies utilizadas como copa e como porta-enxertos de maracujazeiro
ANĂLISE SILVICULTURAL E ECONĂMICA DE PLANTIOS CLONAIS E SEMINAIS DE Tectona grandis L.f. EM SISTEMA TAUNGYA1
CaracterĂsticas estruturais e agronĂŽmicas da Brachiaria brizantha cv. XaraĂ©s submetida a doses de nitrogĂȘnio
Produção de mudas de maracujazeiro-amarelo por enxertia hipocotiledonar sobre sete espécies de passifloras
Fluxo de biomassa em capim-tanzĂąnia pastejado por ovinos sob trĂȘs perĂodos de descanso Biomass flow in tanzaniagrass pasture under three resting periods grazed by sheep
Avaliou-se o fluxo de biomassa em Panicum maximum cv. TanzĂąnia pastejado por ovinos com trĂȘs perĂodos de descanso (PD), definidos pela expansĂŁo de 1,5; 2,5 e 3,5 novas folhas por perfilho, em um delineamento inteiramente casualizado, com duas repetiçÔes (piquetes). Estimaram-se as taxas de alongamento de lĂąmina foliar total (TAlF), de senescĂȘncia de lĂąminas foliares remanescentes do pastejo anterior (TSFA), de senescĂȘncia das novas folhas formadas no PD (TSFP) e de senescĂȘncia total (TSFT=TSFA+TSFP), a taxa de alongamento das hastes (TAlH), a razĂŁo entre as TAlF das folhas 1 e 2 (razĂŁo TAlF1/TAlF2), a densidade populacional de perfilhos (DPP), o filocrono e as taxas de crescimento (TCC) e de acĂșmulo (TAC) da cultura. A razĂŁo TAlF1/2 nĂŁo foi afetada pelos PD, mas reduziu ao longo dos ciclos na pastagem sob PD 3,5. A TAlF nĂŁo foi afetada pelos PD. A TAlH, a TSFA e a TSFT na pastagem sob PD 1,5 foram menores que nas demais. Houve TSFP somente na pastagem sob PD 3,5. O filocrono da pastagem sob PD 1,5 foi superior ao observado nas demais. A densidade populacional de perfilhos (DPP) da pastagem sob o PD 2,5 foi similar Ă verificada na pastagem sob PD 1,5 e superior Ă verificada sob PD 3,5. Houve redução na DPP ao longo dos ciclos na pastagem sob PD 3,5. As taxas de crescimento (TCC) e de acĂșmulo (TAC) foram superiores na pastagem sob PD 2,5. O prolongamento do PD elevou as TAlH e TSFT e reduziu a DPP e a TAC. Portanto, o PD do capim-tanzĂąnia pastejado por ovinos nĂŁo deve exceder o tempo necessĂĄrio Ă expansĂŁo de 2,5 novas folhas por perfilho.<br>The biomass flow in Panicum maximum cv. TanzĂąnia pasture grazed by sheep under three resting periods (PD), defined by the expansion of 1.5; 2.5 and 3.5 new leaves per tiller (1.5F; 2.5F and 3.5F, respectively) was evaluated in a randomized completely design with two replicates (paddocks). It was determined the leaf elongation rate (TAlF), the residual leaf senescence rate (TSFA), the post-grazing leaf senescence rate (TSFP) and the total leaf senescence rate (TSFT), the stem elongation rate (TAlH), the TAlF of leaves 1 and 2 ratio (TALF1/2), the tiller population density (DPP), the phylochron and the crop growth (TCC) and accumulation (TAC) rates. The TAlF1/2 ratio was not affected by the PD, however, it decreased over the cycles at the 3.5F PD pasture. The TAlF was not affected by the PD. The TAlH was inferior at the 1.5F PD pasture, as well as the TSFA and the TSFT. There was TSFP only at the 3.5F PD pasture. The phylochron of the 1.5F PD pasture was superior to the others. The DPP of the 2.5F PD pasture was similar to that of the 1.5F PD pasture, and it was superior to the 3.5F PD pasture. There was reduction of the DPP following the cycles at the 3.5F PD pasture. The TCC and the TAC of the 2.5F PD pasture were superior than the others. The extension of the PD raised the TAlH and the TSFT and reduced the DPP and the TAC. As a conclusion, the resting period should not exceed the time necessary to the expansion of 2.5 leaves on the tiller for tanzaniagrass pastures grazed by sheep