Visual pop-out is a phenomenon by which the latency to detect a target in a scene is independent of the number of other elements, the distractors. Pop-out is an effective visual-search guidance that occurs typically when the target is distinct in one feature from the distractors, thus facilitating fast detection of predators or prey. However, apart from studies on primates, pop-out has been examined in few species and demonstrated thus far in rats, archer fish, and pigeons only. To fill this gap, here we study pop-out in barn owls. These birds are a unique model system for such exploration because their lack of eye movements dictates visual behavior dominated by head movements. Head saccades and interspersed fixation periods can therefore be tracked and analyzed with a head-mounted wireless microcamera-the OwlCam. Using this methodology we confronted two owls with scenes containing search arrays of one target among varying numbers (15-63) of similar looking distractors. We tested targets distinct either by orientation (Experiment 1) or luminance contrast (Experiment 2). Search time and the number of saccades until the target was fixated remained largely independent of the number of distractors in both experiments. This suggests that barn owls can exhibit pop-out during visual search, thus expanding the group of species and brain structures that can cope with this fundamental visual behavior. The utility of our automatic analysis method is further discussed for other species and scientific questions.

horseradish peroxidase; HSC, hepatic stellate cells; IL6, interleukin-6; IMDM, Iscove's Modified Dulbecco's Medium; ITGA5, integrin α 5 ; ITGB1, integrin β 1 ; ITS, insulin-selenitetransferrin; LAMA2, laminin α2; LAMA4, laminin α4; LAMA5, laminin α5; LAMB1, laminin β1; LAMB2, laminin β2; LAMC1, laminin γ1; LN-211, laminin-211; LN-521, laminin-521; LRAT, lecithin-retinol acyltransferase; MMP13, metalloproteinase 13; NGF, nerve growth factor; NID, nidogen; PBS, phosphate buffered saline; PCA, principal component analysis; PEG, polyethylene glycol; PPARγ, peroxisome proliferator-activated receptor γ; qPCR, quantitative polymerase chain reaction; SASP, senescence-associated secretory phenotype; SEC, sinusoidal endothelial cells; SEM, standard error of the mean; SPARCL1, secreted protein acidic and rich in cysteines-like 1; TGFb, transforming growth factor β; TLN, talin; TNFR, tumor necrosis factor receptor; VCL, vinculin; α-SMA, α-smooth muscle actin. AbstractHepatic blood flow and sinusoidal endothelial fenestration decrease during aging.Consequently, fluid mechanical forces are reduced in the space of Disse where hepatic stellate cells (HSC) have their niche. We provide evidence that integrin α 5 /β 1 is an important mechanosensor in HSC involved in shear stress-induced release of hepatocyte growth factor (HGF), an essential inductor of liver regeneration which is impaired during aging. The expression of the integrin subunits α 5 and β 1 decreases in liver and HSC from aged rats. CRISPR/Cas9-mediated integrin α 5 and β 1 knockouts in isolated HSC lead to lowered HGF release and impaired cellular adhesion. Fluid mechanical forces increase integrin α 5 and laminin gene expression whereas integrin β 1 remains unaffected. In the aged liver, laminin β2 and γ1 protein chains as components of laminin-521 are lowered. The integrin α 5 knockout in HSC reduces laminin expression via mechanosensory mechanisms. Culture of HSC on nanostructured surfaces functionalized with laminin-521 enhances Hgf expression in HSC, demonstrating that these ECM proteins are critically involved in HSC function. During aging, HSC acquire a senescence-associated secretory phenotype and lower their growth factor expression essential for tissue repair. Our findings suggest that impaired mechanosensing via integrin α 5 /β 1 in HSC contributes to age-related reduction of ECM and HGF release that could affect liver regeneration. K E Y W O R D S aging, hepatic stellate cells, integrins, laminins, mechanobiology S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section.

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