Research

Neural Correlates of Consciousness

One of the most widely used paradigms for studying the neural correlates of consciousness is bistable visual perception. Bistable phenomena provide an effective tool for studying the neural basis of visual awareness because they allow for a stimulus to be suppressed from consciousness while remaining physically present. (That is, the input remains constant, but the percept alternates.) Therefore, we can measure the changes in neural activity that correspond to perceptual changes, thus potentially revealing the neural substrates and mechanisms of visual awareness. We have used various bistable visual illusions to determine the neural basis of visual awareness, including motion-induced blindness, binocular rivalry, and ambiguous figures. All of these exploit one simple idea: How does neural activity change during changes in the contents of perceptual awareness, even when perceptual inputs remain constant?

Necker Cube (Bistable illusion): What happens in your brain when your percept alternates?

Binocular Rivalry: When two eyes receive conflicting images, conscious percept rivals. How and where does rivalry occur in the brain?

Vision and Visual Illusions

We have discovered and helped characterized several optical illusions, including illusory rebound motion, illusory color mixing, gradient-offset induced motion, infinite regress illusion, dancing bar illusion, and corner angle illusion. These optical illusions are mistakes made by the visual system that may reveal the normal functioning of human mind.

Gradient-offset Induced Motion: Fixate on the dot, and you will see illusory motion after the offset of the stimulus.

Troxler fading (Perceotual Filling-in): fixate on the ceter dot, and the green disk will disappear from your consciousness.

Motion-induced blindness. Fixation on the center dot, and you will see the yellow dot in the upper-left corner disappears from you consciousness.

Attention and Consciousness

Attention and consciousness are tightly entwined. Are they one and the same? Or can they be dissociated? What is the function of consciousness? We use various psychophysical and neuroimaging techniques to tackle these questions.

Unconscious perception: We examine what information can still be processed without awareness by measuring the behavioral and neural consequences of unconsciously presented stimuli.

Brain and Retinotopic Mapping

Retinotopic Mapping. Example of a subject's right and left hemispheres with delineated retinotopic areas marked.

Retinotopic Mapping. (a) A typical retinotopic map of the flattened left hemisphere occipital pole for a subject is shown with the approximate borders between the retinotopic areas specified in black. Blue here represents the lower vertical meridian, cyan/green the horizontal meridian, and red the vertical meridian. (b) Approximate borders specified in black between the central (<4.6 visual degrees), middle (4.6–7.8 visual degrees), and peripheral (>7.8 visual degrees) areas.

Diffusion tensor imaging (DTI) axonal tracking.

Object Perception and Recognition

How do we recognize things in the world ? What is the functional organization of the brain that enable us to recognize objects, faces, words and scenes?

Do you recognize the object in this image? (Click the image to see the answer.) How does the brain change after you recognize the object?

Cluster analysis over fMRI voxels' functional profile. We present a variety of objects and examine what voxels in the brain have similar functional profiles. We "re-discovered" face, body and scene clusters even without assuming specific response profile, stimulus categories, or spatial contiguity of voxels. (collaborated with Danial Lashkari and Polina Golland)