Biology subjects

Xu, Z.-X.

Publications and source records attributed to Xu, Z.-X..

4 recordsLinked to original sources

bioRxiv2025

Allocentric and egocentric cues constitute an internal reference frame for real-world visual search

Visual search in natural environments involves numerous objects, each composed of countless features. Despite this complexity, our brain efficiently locates targets. Here, we propose that the brain combines multiple reference cues to form an internal reference frame that facilitates real-world visual search. Objects in natural scenes often appear in orientations perceived as upright, enabling quicker recognition. However, how object orientation influences real-world visual search remains unknown. Moreover, the contributions of different reference cues--egocentric, visual context, and gravitational-- are not well understood. To answer these questions, we designed a visual search task in virtual reality. Our results revealed an orientation effect independent of set size, suggesting reference frame transformation rather than object rotation. By rotating virtual scenes and participants in a flight simulator, we found that allocentric cues drastically altered search performance. These findings provide novel insights into the efficiency of real-world visual search and its connection to multimodal cognition. SignificanceA central question in the behavioral sciences concerns how people efficiently perceive natural environments. Visual search exemplifies this challenge. While research has elucidated the basic mechanisms, traditional theories struggle to explain the remarkable efficiency in real-world scenes. Here, we examine a fundamental property of natural scenes: reference frames. Real-world objects typically appear in consistent orientations, suggesting that orientation may guide search. Yet, the influence of object orientation on real-world search--and which reference cues (egocentric, visual context, or gravitational) determine that orientation--remains unknown. We developed a novel virtual-reality paradigm to address these questions. We demonstrated that humans combine multiple reference cues to form an internal reference frame that guides visual search, providing a novel account of the efficiency of real-world search.

animal behavior and cognition↗

bioRxiv2024

Viewing geometry drives flexible perception of object motion and depth

1Vision is an active process. We move our eyes and head to acquire useful information and to track objects of interest. While these movements are essential for many behaviors, they greatly complicate the analysis of retinal image motion--the image motion of an object reflects both how that object moves in the world and how the eye moves relative to the scene. Our brain must account for the visual consequences of self-motion to accurately perceive the 3D layout and motion of objects in the scene. Traditionally, compensation for eye movements (e.g., smooth pursuit) has been modeled as a simple vector subtraction process. While these models are effective for pure eye rotations and 2D scenes, we show that they fail to apply to more natural viewing geometries involving combinations of eye rotation and translation. We develop theoretical predictions for how perception of object motion and depth should depend on the observers inferred viewing geometry. Through psychophysical experiments, we demonstrate novel perceptual biases that manifest when different viewing geometries are simulated by optic flow, in the absence of physical eye movements. Remarkably, these biases occur automatically, without training or feedback, and are well predicted by our theoretical framework. A neural network model trained to perform the same tasks exhibits neural response patterns similar to those observed in macaque area MT, suggesting a possible neural basis for these adaptive computations. Our findings demonstrate that the visual system automatically infers viewing geometry from optic flow and flexibly attributes components of image motion to either self-motion or depth structure according to the inferred geometry. Our findings unify previously separate bodies of work by showing that the visual consequences of self-motion play a crucial role in computing object motion and depth, thus enabling the visual system to adaptively perceive a dynamic 3D environment.

neuroscience↗

bioRxiv2021

Speed tuning in head coordinates as an alternative explanation of depth selectivity from motion parallax in area MT

There are two distinct sources of retinal image motion: motion of objects in the world and movement of the observer. In cases where an object moves in a scene and the eyes also move, a coordinate transformation that involves smooth eye movements and retinal motion will be needed in order to estimate object motion in world coordinates. More recently, interactions between retinal and eye velocity signals have also been suggested to generate depth selectivity from motion parallax (MP) in the macaque middle temporal (MT) area. We explored whether the nature of the interaction between eye and retinal velocities in MT neurons favors one of these two possibilities or a mixture of both. We analyzed responses of MT neurons to retinal and eye velocities in a viewing context in which the observer translates laterally while maintaining visual fixation on a world-fixed target. In this scenario, the depth of an object can be inferred from the ratio between retinal velocity and eye velocity, according to the motion-pursuit law. Previous studies have shown that MT responses to retinal motion are gain-modulated by the direction of eye movement, suggesting a potential mechanism for depth tuning from MP. However, our analysis of the joint tuning profile for retinal and eye velocities reveals that some MT neurons show a partial coordinate transformation toward head coordinates. We formalized a series of computational models to predict neural spike trains as well as selectivity for depth, and we used factorial model comparisons to quantify the relative importance of each model component. Our findings for many MT neurons reveal that the data are equally well explained by gain modulation or a partial coordinate transformation toward head coordinates, although some responses can only be well fit by the coordinate transform model. Our results highlight the potential role of MT neurons in representing multiple higher-level sensory variables, including depth from MP and object motion in the world.

neuroscience↗

bioRxiv2018

Anxiety induced by extra-hypothalamic BDNF deficiency instigates resistance to diet-induced obesity

Anxiety disorders are associated with body weight changes in humans. However, mechanisms underlying anxiety-related weight changes remain poorly understood. Using Emx1Cre/+ mice, we deleted the gene for brain-derived neurotrophic factor (BDNF) in the cortex, hippocampus, and some parts of the amygdala. The resulting mutant mice displayed elevated anxiety levels and were markedly lean when fed either chow diet or high-fat diet (HFD). The mice showed higher levels of sympathetic activity, thermogenesis and lipolysis in both brown and white adipose tissues, and higher oxygen consumption and body temperature, compared with control mice. They were still lean at thermoneurality when fed HFD, indicating elevated basal metabolism in addition to activated thermogenesis. Anxiety induced by site-specific Bdnf deletion similarly increased energy expenditure and minimized HFD-induced weight gain. These results reveal that anxiety can stimulate adaptive thermogenesis and basal metabolism by activating sympathetic nervous system, which enhances lipolysis and limits weight gain.

physiology↗