The question that interests me most is: how does our visually perceived world differ from the physical world? Obviously our perceptual representation of the world is not a replica, but reflects our unique evolutionary and ecological needs. We selectively amplify certain details in the world and ignore others and, via practice, increase our sensitivity to those details that are deemed important (perceptual learning). We organize these important perceptual details into categories (e.g., objects) and encode them into memory in specific ways so that we can recognize objects effortlessly (object recognition, including face recognition). These organized categories, in turn, impose on our senses so that we perceive the world in a regular, coherent, and stable manner (perceptual organization). Indeed, the nature of our perceptual representations is one of the most important questions in psychology, and it is this question that has been my main research interest.
I am interested in nearly all aspects of visual perception. These include three-dimensional (3D) motion perception, 3D shape perception, perceptual learning, and computational modeling. Recently, our lab has expanded to study action perception and visual motor behavior. The overarching question we ask in the lab is how the perceptual brain integrates sensory information to arrive at a coherent, stable description of the world. Most of the time, this description is consistent with reality. However, there are also times when it is not, and that is when illusions occur. These illusions provide a unique window into the inner workings of the brain, as follows. An illusion occurs when objective sensory information is highly ambiguous. The brain, rather than being indecisive, uses Bayesian priors to disambiguate the sensory information to arrive at a unique and vivid percept. In this context, modeling the brain’s Bayesian inference becomes both natural and necessary.
Experimentally, our techniques include psychophysics, fMRI, TMS (transcranial magnetic stimulation), eye tracking, virtual reality, and motion tracking (using a state of the art multi-camera system).
Alumni of the lab:
- Hongjing Lu, Associate Professor, UCLA (PhD 2006).
- Bas Rokers, Assist Prof, Univ Wisconsin Madison (PhD 2006).
- Ben Thompson, Senior Lecturer, Univ Auckland, NZ (Postdoc, 04 – 06).
- Xiaoyang Yang, Researcher, Blizzard Entertainment, (PhD 2012).
PhD in Cognitive and Linguistic Sciences, Brown University
MSc in Applied Mathematics, Brown University
BSc in Physics, Beijing University, China
- Xiaoxiao Wang, Yifeng Zhou, Zili Liu. Transfer in motion perceptual learning depends on the difficulty of the training task. Journal of Vision. 2013; 13((7):5): 1 -- 9.
- Benjamin Thompson, Bosco S. Tjan, Zili Liu. Perceptual Learning of Motion Direction Discrimination with Suppressed and Unsuppressed MT in Humans: An fMRI Study.PLoS ONE. 2013; 8(1): 1--14.
- Tandra Ghose, Zili Liu. Generalization between canonical and non-canonical views in object recognition. Journal of Vision. 2013; 13(1): 1--15.
- Xuan Huang, Hongjing Lu, Yifeng Zhou, Zili Liu. General and specific perceptual learning in radial speed discrimination. Journal of Vision. 2011; 11(4, article 7): 1 -- 11.
- Hongjing Lu, Zili Liu. When a never-seen but less-occluded image is better recognized: Evidence from same-different matching experiments and a model. Journal of Vision. 2009; 9(4): 1-12.
- Zhou J, Gotch C, Zhou Y, Liu Z Perceiving an object in its context -- is the context cultural or perceptual?. Journal of Vision. 2008; 8(12(2)): 1-5.
- Lu H, Liu Z When a never-seen but less-occluded image is better recognized: Evidence from old?new memory experiments. Journal of Vision. 2008; 8(7(31)): 1-9.
- Zhou J, Tjan B S, Zhou Y, Liu Z Better discrimination for illusory than for occluded perceptual completions. Journal of Vision. 2008; 8(7(26)): 1-17.
- Huang X, Lu H, Tjan BS, Zhou Y, Liu Z Motion perceptual learning: When only task-relevant information is learned. Journal of Vision. 2007; 7(10:14): 1-10.
- Hou F, Lu H, Zhou Y, Liu Z. "Amodal completion impairs stereo acuity discrimination". Vision Research 2006; 46: 2061-2068.
- Lu H, Zavagno D, Liu Z. "The glare effect does not give rise to a longer lasting afterimage". Perception 2006; 35: 701 -- 707.
- Thompson B, Liu Z. Learning motion discrimination with suppressed and unsuppressed MT. Vision Research 2006; 46: 2110-2121.
- Rokers B, Yuille A, Liu Z. The perception of a stereokinetic stimulus. Vision Research 2006; 46: 2375 -- 2387.
- Lu H, Liu Z Computing dynamic classification images from correlation maps. Journal of Vision [electronic resource]. 2006; 6: 475 -- 483.
- Lu H, Tjan B S, Liu Z. "Shape recognition alters sensitivity in stereoscopic depth discrimination". Journal of Vision [electronic resource]. 2006; 6: 75--86.
- Tjan, B S Liu, Z. Symmetry impedes symmetry discrimination. Journal of vision [electronic resource]. 2005; 5(10): 888-900.
- Rokers B, Liu Z. "On the minimal relative motion principle -- lateral displacement of a contracting bar". Journal of Mathematical Psychology 2004; 48(4): 292-295.
- Liu Z. "On the principle of minimal relative motion -- the oscillating tilted bar". Journal of Mathematical Psychology. 2004; 48: 196-198.
- Lu, H Qian, N Liu, Z Learning motion discrimination with suppressed MT. Vision research. 2004; 44(15): 1817-25.
- Liu, Z Kersten, D Three-dimensional symmetric shapes are discriminated more efficiently than asymmetric ones. Journal of the Optical Society of America. A, Optics, image science, and vision. 2003; 20(7): 1331-40.
- Liu Z. "On the principle of minimal relative motion -- the bar, the circle with a dot, and the ellipse". Journal of Vision [electronic resource]. 2003; 3: 625--629.
- Matthews N, Liu Z, Qian N. "The effect of orientation learning on contrast sensitivity". Vision Research. 2001; 41: 463-471.
- Liu, Z Weinshall, D Mechanisms of generalization in perceptual learning. Vision research. 2000; 40(1): 97-109.
- Liu Z. "Learning a visual skill that generalizes across". Proceedings of the National Academy of Sciences USA. 1999; 96: 14085-14087.
- Matthews N, Liu Z, Geesaman B J, Qian N. "Perceptual learning on orientation and direction discrimination". Vision Research. 1999; 39: 3692-3701.
- Liu, Z Jacobs, DW Basri, R The role of convexity in perceptual completion: beyond good continuation. Vision research. 1999; 39(25): 4244-57.
- Liu, Z Kersten, D Knill, DC Dissociating stimulus information from internal representation--a case study in object recognition. Vision research. 1999; 39(3): 603-12.
- Liu, Z Kersten, D 2D observers for human 3D object recognition?. Vision research. 1998; 38(15-16): 2507-19.
- Liu, Z Vaina, LM Simultaneous learning of motion discrimination in two directions.Brain research. Cognitive brain research. 1998; 6(4): 347-9.
- Liu, Z Viewpoint dependency in object representation and recognition. Spatial vision. 1996; 9(4): 491-521.
- Liu, Z Knill, DC Kersten, D Object classification for human and ideal observers. Vision research. 1995; 35(4): 549-68.
- Zhang, S. W. Wang, X. Liu, Z. Srinivasan, M V. Visual tracking of moving targets by freely flying honeybees. Visual neuroscience. 1990; 4(4): 379-86.