Hi. I'm David Carmel, I'm a Lecturer in Psychology, at the University of Edinburgh. In the first part of this lecture, Mark Sprevak talked about philosophical approaches to consciousness. In this second part, I'll be talking about scientific investigations. So what sorts of questions do scientists ask when we investigate consciousness? And how much progress have we made in turning these questions from philosophical musings, into issues that can be investigated empirically? The most fundamental question, is how is it that the activity of a physical system, the brain, can create consciousness and subjective experience in the first place? As we saw earlier, this is known as the 'hard problem' and science is no closer than it has ever been to being able to answer it. The problem is that we don't know what an answer would look like. We don't have the ways of thinking, or the conceptual framework, to answer such a question, and it may be staring us in the face, and we just don't recognize it. Other major questions, are considered easy questions. It's important to be clear by what we mean by 'easy' in this case. It's not that these questions are easy to solve, but rather that it would be easy for us to recognize an answer, if and when we ever found one. And we have some idea of how to go about this. The two questions that scientists are most interested in these days, both fall under the heading 'neural correlates of consciousness' or NCC for short. Both questions are concerned with, what kinds of neural activity correlate with, happen at the same time as, processes related to consciousness. The first of these, asks what neural activity determines the state or level of consciousness that a person is in; what kind of activity determines whether we are awake or asleep, in a comma or in a vegetative state and so on. The second question asks what processes determine the content of our consciousness; our momentary awareness of ourselves and of the world around us, at any given time. A lot of recent research, has focused on perceptual awareness, discovering what links the information coming in to our brain through our senses, with what we become aware of. How does brain activity give rise to different states of consciousness? Let's start by examining what states exist. It's useful to think of ones state of consciousness, as a combination of two factors: wakefulness, or what one's level of consciousness is; and awareness, having conscious content. Our level of wakefulness, determines whether we're awake or not. Our awareness is our capacity to think, feel and perceive our environment and ourselves. It's what enables us to interact with the world, in a meaningful way. It may seem strange to divide attention in to these two separate factors, but as we'll see, it's useful. Right now you're fully awake, or at least I hope you are. So, you're at the high end of the scale for both wakefulness and awareness. When you fall asleep tonight, you'll first become drowsy and then eventually fall into a deep sleep, where both your wakefulness and awareness will be low. For people under anaesthesia or in a coma, awareness and wakefulness are reduced even further. If these were the only states that existed, we wouldn't need two separate axis to describe them, they'd all fall along a single line. However, there are cases where the two axis are dissociated. One is high, while the other is low. The most obvious example is dreaming where wakefulness is low because the person is asleep, and awareness is high; the person experiences feelings, sensations and thoughts. In the rare condition of lucid dreaming people are even aware that they are in a dream. Unfortunately, there are also clinical conditions known collectively as disorders of consciousness, where brain injury leads to high wakefulness and low awareness at the same time. These conditions include, the vegetative state and the minimally conscious state. Patients in the vegetative state, have normal sleep wake cycles, but when they're awake, with their eyes open, they don't respond to their environment, and don't interact with it in any way that would indicate they're aware of what's going on around them. Sometimes these patients' condition improves, and they are reclassified as being in a minimally conscious state, indicating that they sometimes show, limited responsiveness to their environment. What sort of brain activity determines one's state of consciousness? There's no single brain area whose activity is solely responsible for either awareness or wakefulness. The brain is a vastly integrated system, and a person's state of consciousness is the outcome of many subsystems' combined activity. There are, however, certain brain areas, whose activity contributes to specific aspects of consciousness. Wakefulness is highly dependent on activity in the subcortical structures. So to see what I mean, here's a little model of a brain. The cortex is the outer layer. And if we look at the inside, subcortical structures lie deep below the cortex. The areas involved in wakefulness, include the reticular formation and the thalamus which is right here in the middle. And these are evolutionarily ancient regions. The reticular formation and the thalamus are involved in diverse functions, amongst them the regulation of arousal and sleep wake cycles. Damage to these areas, can cause disorders of consciousness such as a coma or a vegetative state. But those conditions can also arise from damage to a variety of other brain areas. Unlike wakefulness, which as we said is dependent mostly on subcortical functions, awareness is mostly dependent on activity in the cortex. The cortex is a relatively recent evolutionary development and is responsible for higher mental functions in humans. Awareness can be divided into two complimentary elements. The first is external awareness, the awareness we have whenever we navigate through the environment and interact with it. This awareness is largely dependent on activity, in the frontal and parietal lobes of the cortex. Roughly speaking, the areas that are in the upper, outer surface of the brain. The second element of awareness is the kind that occurs when we're not focused on the external environment, but on our internal world; daydreaming, retrieving memories, or planning for the future. This kind of awareness, depends on a network of regions that are on the medial side of the brain, that is the side where the two hemispheres of the brain face each other. When we're awake, we're usually either focusing on something in our external environment or direction our attention inwards. It's rare, and some would say impossible, to be doing both things at the same time. It's therefore unsurprising that the activity of the two networks involved in awareness, is negatively correlated. That is, when either one of them is high the other is low. Changes in wakefulness, which, as we saw, are governed by subcortical structures, affect activity in the cortex too. While we're awake, different areas of the cortex busily communicate with one another. As we fall asleep, these areas' communication with each other is reduced. The most sharp reduction occurs between areas of the frontal and posterior, or back part of the cortex. The physical connections between these areas still exist, but as we fall asleep, they communicate with each other less and less. So far, we've focused on states of consciousness and the brain activity that underlies them. But as we mentioned earlier, researchers are also interested in the processes that determine the content of our consciousness at any given time; our perceptual awareness. One question we can ask, is just how much of the world around us we're actually aware of. Although, normally we think we're aware of many of the different things around us, research shows that at any given time, we're actually aware of a surprisingly small subset of the information entering our brain through our senses. There are many great demonstrations that test the limitations of our awareness. If you want to experience this for yourself, click on the following YouTube videos. These include demonstrations by Daniel Simons, and Christopher Chabris. Make sure you follow the instructions. Did those demonstrations work for you? The phenomenon these videos demonstrate is called inattentional blindness, and its very existence attests to the intimate link between awareness and attention. Hundreds of studies have looked at inattentional blindness, in an effort to figure out, what we will see, and what we will miss, and what factors affect those things. As we just saw, one of the relevant factors seems to be our attentional set, what we happen to be looking for. The chances of missing something that we're not looking for are greater. Another relevant factor seems to be the capacity limits of our visual working memory. That's the store of visual information that's available for our immediate use. Researchers have examined how many elements can appear in a picture before people start missing things. Now it depends on the exact object, and on the type of change that happens. But in most cases the number isn't large at all. It's limited to about four elements. We now turn to the processes that shape our awareness of the things we do perceive. To investigate this, researchers often use something called 'bistable images'. And most well-known example of a bistable image is the Necker Cube, which can be perceived as if one side of it is in front or as if the other side of it is in front. The Necker Cube has all three hallmarks of a bistable image. First of all, it has two possible conscious interpretations. Second, you can't see both interpretations at the same time. Try it. And third, these interpretations tend to alternate every few seconds. Another famous example of a bistable image is the Rubin face vase, where you can see the same image either as two faces facing each other, or as a single vase. Why are bistable images so useful to consciousness researchers? Well, what we have here is a case of dissociation between perception and awareness. The external stimulus, the thing that's out there in the world, does not change. Yet our perception does change. Since the only change is happening in our own brains, if we understood the process that causes this to happen, we would have a window into how the brain selects content for representation and consciousness. Several kinds of bistable image have been used in neuroimaging research, where researchers have looked to see which areas of the brain would be active at the same time as perceptual switches. Repeatedly, researchers have found time-locked activity, where brain areas were active at the same time as a perceptual switch. Not only in visual areas of the brain, which are in the occipital lobe, way back here. But also in frontal and parietal regions of the brain. Areas we have mentioned before, as related to external awareness. So can we conclude that this frontal and parietal activity causes the changes in perception? Not so fast. Just because something happens to the brain at the same time as a perceptual event, such as a switch in the bi-stable image, that doesn't mean that this activity causes that change. We know that it correlates with the change, we know that it happens at the same time as the change, but correlation is not causation. It could be that this brain activity is involved in noticing that the change has occurred at the same time that it's occurring. It could also be that something else, like activity in a completely different brain area, is causing both the change in perception and the activity in frontal and parietal cortex. If a certain brain region has a causal influence, then actively manipulating it's activity will cause changes in perception. That's what we need to do to infer causality. To do this, to manipulate brain activity, researches often use a technique called transcranial magnetic stimulation, or TMS for short. We do it in places like this, the University of Edinburgh's TMS lab. TMS works by applying a brief powerful magnetic pulse to the surface of the head, and this interferes temporarily with the activity of the area of cortex right underneath it. So, to demonstrate that I've got Suilin here, who's going to help me by applying TMS to my Broca's area. That's the area in my, the left side of my brain, that produces speech. So we're going to see if applying TMS to my Broca's area can interfere with my speech production. So I'm going to count up. And when I reach five, please press the button. One, two, three, four, five, six, seven, eight, nine, ten. So yes, TMS interfered with my speech production and this is how we learn about brain activity, by interfering with activity in specific areas and seeing what kind of function gets interfered with. Supplying TMS to Broca's area, the way we did just now, that has immediate functional consequences. We can see what the activation does. But not every bit of the brain that we apply TMS to will have immediate observable consequences. And sometimes we want to apply TMS to an area where we won't see immediately that something jumps or something changes, just to see what kinds of effects this has on things like, perception. So a number of researchers have applied TMS to parietal cortex. That's up here. In order to see what kind of an effect this has on bistable perception. Surprisingly, it turns out, that different parts of parietal cortex play a different role, in bistable perception. Applying TMS to certain part of parietal cortex makes the switching a lot slower. And applying TMS to slightly different parts of parietal cortex has the opposite effect. Making switches, faster. So we now know the parietal cortex is definitely causally involved in bistable perception. But we still need to figure out what role exactly each of these different areas within parietal cortex plays and how the neural system as a whole reaches a consensus, about what we're seeing. To understand consciousness we need to know the difference between processes that require awareness, and those that don't. If we can perceive something without awareness, that tells us awareness is not necessary for that kind of perception. It therefore narrows down the list, of the processes that awareness is necessary for. So how do we investigate unconscious perception? Researchers have developed various ways of showing people things that enter the eyes, but don't reach people's awareness. This is different from showing people things that they don't notice because they're not paying attention, as we saw earlier with inattentional blindness. It's also different from visual illusions, which distort perception. What we're talking about here, is showing people things, but actively suppressing them from awareness. Here, we'll talk about one widely used technique as an example. This technique is backward visual masking, where one image is shown very briefly, and it's followed immediately after by another image at the same location, presented for longer. When this is done right, people can't report the first of the two images, and often deny that it was there at all. One of the first studies to use backward masking to investigate unconscious perception, employed a method called 'masked priming'. People were shown a single word followed immediately by a mask that was a meaningless pattern. After each such presentation, they were shown a string of letters and they had to decide whether it was a real word or not. Interestingly, people were faster to detect real words when they were semantically related to the word that had been masked, than when it was not. For example, if the masked word was 'infant', people would then be faster to recognize the word 'child' than they would to recognize the word 'orange'. This indicated that the masked word had activated a semantic network in the brain. And that the masked word had been processed deeply enough to enable faster recognition of related words. And this priming effect, was just as large without awareness as with it. In recent brain imaging work, researchers have shown that masked words activate visual areas of the brain more than meaningless strings of letters do, even when people remain unaware of the masked words. However, unmasked words activate many more regions of the brain, and these areas communicate with each other much more when the words are unmasked. In this lecture we have examined several of the philosophical and scientific current approaches to consciousness. At this point, there is no theory, that offers a full unified account of consciousness and how it arises from the activity of physical systems. Current theories offer agendas for future research: what themes and what issues we should be following if we want to reach an understanding of consciousness. But only time will tell which ones of these teams and which ones of these directions will turn out to be fruitful. And only time will tell how much progress we will make.
