Perception of duration in the parvocellular system

Both theoretical and experimental evidence suggests that duration perception is mediated preferentially by the color-blind but high temporally sensitive luminance pathway. In this experiment we tested whether color modulated stimuli and high spatial frequency luminance modulated stimuli, which are known to be relayed mostly by the slow parvocellular system, are able to elicit reliable sense of duration. We show that ramped color modulated stimuli seem to last less than luminance modulated stimuli matched for visibility. The effect is large, about 200 ms and is constant at all durations tested (range 500–1100 ms). However, high spatial frequency luminance stimuli obtain duration matches similar to those of low spatial frequency luminance modulated stimuli. The results at various levels of contrast and temporal smoothing indicate that equiluminant stimuli have higher contrast thresholds to activate the mechanisms which time visual stimuli. Overall the results imply that both the magnocellular and the parvocellular systems access reliably the timing mechanisms with a difference only in the way these are engaged

Convergence of Wnt signalling on the HNF4a-driven transcription in controlling liver zonation

BACKGROUND & AIMS: In each hepatocyte, the specific repertoire of gene expression is influenced by its exact location along the portocentrovenular axis of the hepatic lobule and provides a reason for the liver functions compartmentalization defined "metabolic zonation." So far, few molecular players controlling genetic programs of periportal (PP) and perivenular (PV) hepatocytes have been identified; the elucidation of zonation mechanisms remains a challenge for experimental hepatology. Recently, a key role in induction and maintenance of the hepatocyte heterogeneity has been ascribed to Wnt/beta-catenin pathway. We sought to clarify how this wide-ranging stimulus integrates with hepatocyte specificity. METHODS: Reverse transcriptase polymerase chain reaction (RT-PCR) allowed the transcriptional profiling of hepatocytes derived from in vitro differentiation of liver stem cells. The GSK3beta inhibitor 6-bromoindirubin-3'-oxime (BIO) was used for beta-catenin stabilization. Co-immunoprecipitations were used to study biochemical protein interactions while ChIP assays allowed the in vivo inspection of PV and PP genes regulatory regions. RESULTS: We found that spontaneous differentiation of liver stem cells gives rise to PP hepatocytes that, after Wnt pathway activation, switch into PV hepatocytes. Next, we showed that the Wnt downstream player LEF1 interacts with the liver-enriched transcriptional factor HNF4alpha. Finally, we unveiled that the BIO induced activation of PV genes correlates with LEF1 binding to both its own and HNF4alpha consensus, and the repression of PP genes correlates with HNF4alpha displacement from its own consensus. CONCLUSION: Our data show a direct and hitherto unknown convergence of the canonical Wnt signaling on the HNF4alpha-driven transcription providing evidences of a mechanism controlling liver zonated gene expression

Ideal observer analysis for continuous tracking experiments

Continuous tracking is a newly developed technique that allows fast and efficient data acquisition by asking participants to “track” a stimulus varying in some property (usually position in space). Tracking is a promising paradigm for the investigation of dynamic features of perception and could be particularly well suited for testing ecologically relevant situations difficult to study with classical psychophysical paradigms. The high rate of data collection may be useful in studies on clinical populations and children, who are unable to undergo long testing sessions. In this study, we designed tracking experiments with two novel stimulus features, numerosity and size, proving the feasibility of the technique outside standard object tracking. We went on to develop an ideal observer model that characterizes the results in terms of efficiency of conversion of stimulus strength into responses, and identification of early and late noise sources. Our ideal observer closely modeled results from human participants, providing a generalized framework for the interpretation of tracking data. The proposed model allows to use the tracking paradigm in various perceptual domains, and to study the divergence of human participants from ideal behavior

Human papillomavirus infection is inhibited by host autophagy in primary human keratinocytes

AbstractHuman papillomavirus (HPV) infection is severely limited in its natural host, primary human keratinocytes. Our data show HPV infectivity in primary keratinocytes is over 100- and 1,000-fold lower than in established keratinocyte cell lines NIKS and HaCaT, respectively. Here, we show that the basal level of autophagy in primary human foreskin keratinocytes (HFKs) is higher than in immortalized keratinocytes, and that HPV16 virions significantly induce autophagy in HFKs. Interestingly, HPV16 infectivity is dramatically enhanced by knockdown of essential autophagy genes as well as biochemical inhibition of autophagy. The increase in HPV16 infectivity by autophagy inhibition is most significant in HFKs, showing an inverse correlation with basal HPV16 infectivity in HFK, NIKS, HaCaT, and 293FT cells. Further, inhibition of autophagy delays degradation of HPV16 capsid proteins during virus trafficking, indicating that host autophagy induced by HPV16 virions inhibits infection of primary keratinocytes through rapid degradation of viral capsid proteins

Perceptual History Acts in World-Centred Coordinates

Serial dependence effects have been observed using a variety of stimuli and tasks, revealing that the recent past can bias current percepts, leading to increased similarity between two. The aim of this study is to determine whether this temporal integration occurs in egocentric or allocentric coordinates. We asked participants to perform an orientation reproduction task using grating stimuli while the head was kept at a fixed position, or after a 40° yaw rotation between trials, from left (−20°) to right (+20°), putting the egocentric and allocentric cues in conflict. Under these conditions, allocentric cues prevailed

spatiotemporal filtering and motion illusions

We are perplexed by Clarke et al.'s (2013) criticisms on our recent contribution to Journal of Vision (Pooresmaeili, Cicchini, Morrone, & Burr, 2012). Our group has long championed the idea that perceptual processing of information can be anchored in a dynamic coordinate system that need not correspond to the instantaneous retinal representation. Our recent evidence shows that temporal duration (Burr, Tozzi, & Morrone, 2007; Morrone, Cicchini, & Burr, 2010), orientation (Zimmermann, Morrone, Fink, & Burr, 2013), motion (Melcher & Morrone, 2003; Turi & Burr, 2012) and saccadic error-correction (Zimmermann, Burr, & Morrone, 2011) are all processed to some extent in spatiotopic coordinates. Imaging studies reinforce these studies (d'Avossa et al., 2007; Crespi et al., 2011). Much earlier, we showed that the processing of smoothly moving objects was not anchored in instantaneous, retinotopic coordinates, but in the reference frame given by the trajectory of motion. There is an effective interpolation along the trajectory, so temporal offsets in spatially collinear stimuli causes them to appear spatially offset, corresponding to the physical reality of stimuli moving over large regions of space, behind occluders (Burr, 1979; Burr & Ross, 1979). Our explanation for this surprising effect was that it could be a direct consequence of the spatiotemporal orientation of the impulsive response of motion detectors, providing the spatiotemporal reference frame needed to account for the interactions between time and space (Burr & Ross, 1986; Burr, Ross, & Morrone, 1986; Burr & Ross, 2004; Nishida, 2004). Recently, we have applied the concept of spatiotemporal oriented receptive fields to account for ''predictive remapping,'' the ''nonretinotopic'' effects that occur on each saccadic eye-movement (Burr & Morrone, 2010; Burr & Morrone, 2012; Cicchini, Binda, Burr, & Morrone, 2012). We were most impressed by the compelling demonstrations of Herzog's group, clearly showing that the reference frame of processing is not the instantaneous retinal position, but is flexible, depending not only on real physical motion, but on an illusory apparent motion where the stimuli do not actually move (Boi, Ogmen, Krummenacher, Otto, & Herzog, 2009). This seemed to us important, worthy of quantitative measurement and modeling, particularly to see whether these new effects may fall within the framework that so successfully explained previous demonstrations, such as spatiotemporal interpolation. It is reassuring that Clarke et al. (2013) confirm our results, albeit with some variability between subjects. But more importantly add a very nice result in showing that our simplified version of the ''litmus test'' can be enhanced by attending to the motion. This is an excellent point that we overlooked. The strength of this type of motion is well known to depend on attention (Cavanagh, 1992), and it is indeed interesting that the strength of motion-induced effects depends not only on the physical conditions, but on internal states such as attention. Perhaps attention may also provide the flexibility in choosing the most appropriate scale for analysis, which in this case would be lower, given that attention is diverted to the periphery. This would add strength to our model, and an idea worth following up

Spatiotopic selectivity of adaptation-based compression of event duration

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Reduced 2D form coherence and 3D structure from motion sensitivity in developmental dyscalculia

Developmental dyscalculia (DD) is a specific learning disability affecting the development of numerical and arithmetical skills. The origin of DD is typically attributed to the suboptimal functioning of key regions within the dorsal visual stream (parietal cortex) which support numerical cognition. While DD individuals are often impaired in visual numerosity perception, the extent to which they also show a wider range of visual dysfunctions is poorly documented. In the current study we measured sensitivity to global motion (translational and flow), 2D static form (Glass patterns) and 3D structure from motion in adults with DD and control subjects. While sensitivity to global motion was comparable across groups, thresholds for static form and structure from motion were higher in the DD compared to the control group, irrespective of associated reading impairments. Glass pattern sensitivity predicted numerical abilities, and this relation could not be explained by recently reported differences in visual crowding. Since global form sensitivity has often been considered an index of ventral stream function, our findings could indicate a cortical dysfunction extending beyond the dorsal visual stream. Alternatively, they would fit with a role of parietal cortex in form perception under challenging conditions requiring multiple element integration

"Non-retinotopic processing" in Ternus motion displays modeled by spatiotemporal filters

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Pupillometry correlates of visual priming, and their dependency on autistic traits

In paradigms of visual search where the search feature (say color) can change from trial to trials, responses are faster for trials where the search color is repeated than when it changes. This is a clear example of "priming" of attention. Here we test whether the priming effects can be revealed by pupillometry, and also whether they are related to autistic-like personality traits, as measured by the Autism-Spectrum Quotient (AQ). We repeated Maljkovic and Nakayama's (1994) classic priming experiment, asking subjects to identify rapidly the shape of a singleton target defined by color. As expected, reaction times were faster when target color repeated, and the effect accumulated over several trials; but the magnitude of the effect did not correlate with AQ. Reaction times were also faster when target position was repeated, again independent of AQ. Presentation of stimuli caused the pupil to dilate, and the magnitude of dilation was greater for switched than repeated trials. This effect did not accumulate over trials, and did not correlate with the reaction times difference, suggesting that the two indexes measure independent aspects of the priming phenomenon. Importantly, the amplitude of pupil modulation correlated negatively with AQ, and was significant only for those participants with low AQ. The results confirm that pupillometry can track perceptual and attentional processes, and furnish useful information unobtainable from standard psychophysics, including interesting dependencies on personality traits