Search for: All records

The tilt illusion—a bias in the perceived orientation of a center stimulus induced by an oriented surround—illustrates how context shapes visual perception. Although extensively studied for decades, we still lack a comprehensive account of the illusion that connects its behavioral and neural characteristics. Here, we demonstrate that the tilt illusion originates from dynamic changes in neural coding precision induced by the surround context. We simultaneously obtained psychophysical and functional MRI responses from human subjects while they viewed gratings in the absence and presence of an oriented surround and independently extracted sensory encoding precision from their behavioral and neural data. Both measures show that in the absence of an oriented surround, encoding reflects the natural scene statistics of orientation. However, with an oriented surround, encoding precision is significantly increased for stimuli similar to the surround orientation. This local change in encoding is sufficient to predict the behavioral characteristics of the tilt illusion using a Bayesian observer model. The effect of surround modulation increases along the ventral stream and is localized to the portion of the visual cortex with receptive fields at the center-surround boundary. The pattern of change in coding accuracy reflects the surround-conditioned orientation statistics in natural scenes, but cannot be explained by local stimulus configuration. Our results suggest that the tilt illusion naturally emerges from an adaptive coding strategy that efficiently reallocates neural coding resources based on the current stimulus context. 

This study concerns the cognitive process of mathematical problem posing, conceptualized in three stages: understanding the task, constructing the problem, and expressing the problem. We used the eye tracker and think-aloud methods to deeply explore students’ behavior in these three stages of problem posing, especially focusing on investigating the influence of task situation format and mathematical maturity on students’ thinking. The study was conducted using a 2×2 mixed design: task situation format (with or without specific numerical information)×subject category (master’s students or sixth graders). Regarding the task situation format, students’ performance on tasks with numbers was found to be significantly better than that on tasks without numbers, which was reflected in the metrics of how well they understood the task and the complexity and clarity of the posed problems. In particular, students spent more fixation duration on understanding and process- ing the information in tasks without numbers; they had a longer fixation duration on parts involving presenting uncertain numerical information; in addition, the task situation format with or without numbers had an effect on students’ selection and processing of information related to the numbers, elements, and relationships rather than information regarding the context presented in the task. Regarding the subject category, we found that mathematical maturity did not predict the quantity of problems posed on either type of task. There was no significant main group difference found in the eye-movement metrics. 

Verified compilation of open modules (i.e., modules whose functionality depends on other modules) provides a foundation for end-to-end verification of modular programs ubiquitous in contemporary software. However, despite intensive investigation in this topic for decades, the proposed approaches are still difficult to use in practice as they rely on assumptions about the internal working of compilers which make it difficult for external users to apply the verification results. We propose an approach to verified compositional compilation without such assumptions in the setting of verifying compilation of heterogeneous modules written in first-order languages supporting global memory and pointers. Our approach is based on the memory model of CompCert and a new discovery that a Kripke relation with a notion of memory protection can serve as a uniform and composable semantic interface for the compiler passes. By absorbing the rely-guarantee conditions on memory evolution for all compiler passes into this Kripke Memory Relation and by piggybacking requirements on compiler optimizations onto it, we get compositional correctness theorems for realistic optimizing compilers as refinements that directly relate native semantics of open modules and that are ignorant of intermediate compilation processes. Such direct refinements support all the compositionality and adequacy properties essential for verified compilation of open modules. We have applied this approach to the full compilation chain of CompCert with its Clight source language and demonstrated that our compiler correctness theorem is open to composition and intuitive to use with reduced verification complexity through end-to-end verification of non-trivial heterogeneous modules that may freely invoke each other (e.g., mutually recursively). 

Transcriptional divergence of duplicated genes after whole genome duplication (WGD) has been described in many plant lineages and is often associated with subgenome dominance, a genome-wide mechanism. However, it is unknown what underlies the transcriptional divergence of duplicated genes in polyploid species that lack subgenome dominance. Soybean is a paleotetraploid with a WGD that occurred 5 to 13 Mya. Approximately 50% of the duplicated genes retained from this WGD exhibit transcriptional divergence. We developed accessible chromatin region (ACR) datasets from leaf, flower, and seed tissues using MNase-hypersensitivity sequencing. We validated enhancer function of several ACRs associated with known genes using CRISPR/Cas9-mediated genome editing. The ACR datasets were used to examine and correlate the transcriptional patterns of 17,111 pairs of duplicated genes in different tissues. We demonstrate that ACR dynamics are correlated with divergence of both expression level and tissue specificity of individual gene pairs. Gain or loss of flanking ACRs and mutation ofcis-regulatory elements (CREs) within the ACRs can change the balance of the expression level and/or tissue specificity of the duplicated genes. Analysis of DNA sequences associated with ACRs revealed that the extensive sequence rearrangement after the WGD reshaped the CRE landscape, which appears to play a key role in the transcriptional divergence of duplicated genes in soybean. This may represent a general mechanism for transcriptional divergence of duplicated genes in polyploids that lack subgenome dominance.