Funded Grants

Eyes are the windows to the mind

...... in cases where we continue for some time engaged in a particular form of perception, for then, when we shift the scene of our perceptive activity, the previous affection remains; for instance, when we have turned our gaze from sunlight into darkness. For the result of this is that one sees nothing, owing to the motion excited by the light still subsisting in our eyes. Also, when we have looked steadily for a long while at one colour, e.g. at white or green, that to which we next transfer our gaze appears to be of the same colour. Again if, after having looked at the sun or some other brilliant object, we close the eyes, then, if we watch carefully, it appears in a right line with the direction of vision (whatever this may be), at first in its own colour; then it changes to crimson, next to purple, until it becomes black and disappears. And also when persons turn away from looking at objects in motion, e.g. rivers, and especially those which flow very rapidly, they find that the visual stimulations still present themselves, for the things really at rest are then seen moving: persons become very deaf after hearing loud noises, and after smelling very strong odours their power of smelling is impaired; and similarly in other cases. These phenomena manifestly take place in the way above described.

--ARISTOTLE, Parva Naturalia, Translated by J.I Beare (1908) in McKeon "Basic Works of Aristotle", Random House, 1941, p. 620-621

As Aristotle noted more than 2,300 years ago, our senses are not static. Most, if not all, of us have experienced and been fascinated by the "waterfall illusion" at one point or another. After watching a waterfall, "things (e.g., trees) really at rest are then seen moving". What was perceived a moment ago could have a profound effect on subsequent perceptual experience. These phenomena are now grouped under the name of "sensory aftereffects", or more specifically "visual aftereffects" if they are visual phenomena. These phenomena are indeed fun to experience, but understanding their neural basis can give us some clue to the age-old mystery of human consciousness. Visual aftereffects provide a dissociation between the physical reality and conscious experience. White appears as green after adapting to red, static objects appear to move after watching a waterfall. Somewhere in our brain, those little neurons are tricking us. If we understand how these perceptual experiences are generated (in the absence of corresponding physical stimuli), then we will be a significant step closer to understanding the neural basis of consciousness. Part of the problem is the lack of a concrete definition of consciousness, or even an understanding of exactly what consciousness is. But if we wait for philosophers to give us a clear definition of consciousness before starting our study, we may have to wait another 2000 years. The last decade has seen a tremendous growth of knowledge about the human brain. Many "serious scientists" have turned their attention to the question of "consciousness". Certainly, we do not expect to see the problem solved over night, but we are making small steps in the right direction. It is extremely difficult to understand how a process/object works, if we do not know what it is used for. Imagine someone trying to understand how a computer disk works without knowing that it is used for storing data. For this reason, in order to understand the mechanisms of human consciousness, we need to know what is it used for. In other words, what are the functions of consciousness? If we did not have consciousness, what would it be like? This question is the classical "zombie" question that philosophers have argued over and over. The problem is that we do not know where the "consciousness switch" is in a human, so we can not simply switch off consciousness and leave all the other cognitive functions intact.

What we can do, however, is to create a controlled environment in which one can manipulate a specific aspect of a subject's conscious state, and observe the consequence of that manipulation. Visual aftereffects can be used as a test vehicle, because they are dynamic phenomena that afford the opportunity to study sequential events. Going back to Aristotle's observation of motion aftereffect, what if he were completely engulfed in a deep thought while looking at the river, so much so that he did not even know which way the river flowed-would he still experience the motion aftereffect later, that "the things really at rest are then seen moving"? We have a partial answer to this question. The motion aftereffect can indeed survive the absence of visual awareness', but the magnitude of the aftereffect is reduced. However, there are many other similar questions that remain to be answered. Only when we have a full picture of the effect of visual awareness on various cognitive functions will we be in a solid position to discuss the neural basis of visual awareness.

A related approach to study the neural basis of awareness is to test the correlation between neural activity and awareness. Granted, correlation does not mean causation, but knowing the correlation will give us pointers to potential casual factors. Besides, neural activities uncorrelated with an observer's conscious experience could be ruled out as direct basis of consciousness. Under this premise, studies have been carried out to identify associations and dissociations between neural activity and conscious experience. We mentioned that visual aftereffects provided a case where perceptual experience is not directly associated with the stimulus, thus one can study the correlation between neural activity and "perceptual experience" in the pure sense, independent of the stimulus.

Another case of dissociation between stimulus and visual experience is the case of stimuli that lie beyond the limit of resolution. For example, there is a clear boundary between resolvable and unresolvable stimuli: you can see the flicker of a light modulated at 30 Hz, but not at 60 Hz. At 60 Hz, the light is physically changing, but we do not experience the fluctuation. What are the corresponding neural states for these two conscious states? This question was very difficult to answer in human observers just 10 years ago, because there was not an easy way to look inside the brain to see what it is doing. However, functional brain imaging technology now allows us to "see" the activity inside our brain. Now if a subject is presented with a 60 Hz and a stable light, she/he can not tell the difference between them and is oblivious to the alternation between these two conditions, what if one area in the subject's brain shows different activity corresponding to these two conditions? "Ah-ha", you say, "this brain area is holding back, is not telling the observer what 'it' knows". The observer is not aware of the difference even though many neurons in this observer's brain clearly know that these two conditions are different. One simplistic conclusion is that these neurons are not the observer's "conscious neurons"; in other words, activity in these neurons does not directly support the observer's conscious experience. in the context of visual perception, the term "visual awareness" is used instead of consciousness. We plan to study the effects of visual awareness on various types of perceptual and cognitive functions, aiming at a better understanding of the functional role of consciousness or visual awareness. We also seek to delineate the neural bottlenecks in spatial and temporal visual resolution. At the end of this project, we want to be able to identify what visual processes can not go on normally without awareness; and what are the critical stages where spatial and temporal information is still represented but not available to consciousness. To philosophers, results from this project will give a more concrete answer to the "zombie" question. It may very well be that the "zombie" will forever stay a hypothetical entity, because our prediction is that it is impossible to have completely intact perceptual and cognitive functions without awareness.