Consciousness - An introduction (ch5)

What do attention and timing have to do with consciousness? - Chapter 5

A few centuries ago, James asked the following question: does consciousness cause attention to be directed or is consciousness the effect of paying attention? We feel that our consciousness causes some parts of the world to light up, while leaving some other parts in darkness. This is also called 'spotlight of attention'. So it feels like we can focus our attention on something consciously.

Numerous theories about attention have been carried out. For example, around 1950, researchers conducted experiments with the dichotic listening task. In such an experiment, someone gets to hear different messages in both ears. It is the intention that someone only pays attention to the messages that come into one ear. The result of this experiment was that what comes into the other ear is perceived unconsciously, even though no attention is paid to it. These kinds of findings led to the ongoing debate about the moment of attention selection: early, close to the sensory level, or only after much processing has taken place.

Other theories saw attention as a bottleneck, where pre-conscious sensory filters were needed to decide what should be passed to deeper stages of processing. This perception fits well with the idea that the brain has a limited capacity for detailed processing. There is then parallel processing.

Attention and consciousness

There are various ideas today about the relationship between attention and consciousness. Mack states on the basis of 'inattentional blindness' (see section 6) that no conscious perception can exist without attention. Crick, on the other hand, states that consciousness is closely linked to attention.

So there are basically two opposing ideas about consciousness and attention. The first idea is that if attention is paid to something, it will end up in consciousness. The other idea is that consciousness leads the attention processes and that this is the greatest function of consciousness. This fits with our own experience of consciousness, namely that we choose what we focus our attention on.

James mentioned the above ideas as the effect theory and cause theory. He stated that it is almost impossible to know which theory is correct and based his decision on ethical grounds, saying that personal will (or spiritual force) is the reason for consciousness (and therefore a cause). Today, researchers are still wondering whether consciousness is a cause or a consequence.

Directing attention

Attention can be involuntary or intentional and these two processes depend largely on different systems in the brain. Often attention is involuntarily focused on something. For example, we react immediately when we hear a loud sound or when someone speaks our name. This involuntary attention is driven by the ventral attention system and mainly takes place in the right hemisphere in the frontal, parietal and temporal areas. Some physical systems constantly try to ensure that the body, the eyes and the head always remain coordinated in relation to the outside world.

Some of these control systems are based on 'retinocentric coordinates'. This means that they try to keep objects stable on the retina. Other systems use 'craniocentric coordinates'. This means that the world is kept stable in relation to the position of the head. Often, both types of control systems go together with fast and unconscious processes.

Directing the eyes to an object is not the same as paying attention to that object. Helmholz proved that it is possible to look at the one object, but to focus attention elsewhere. This is also called 'covert attention scanning'. The superior colliculus and the frontal eye areas (FEFs: 'frontal eye fields') are responsible for looking at an object and neurons in the posterior parietal cortex ensure that attention can be shifted. Activity in these FEF neurons corresponds to the mental 'spotlight of attention'.

Another form of involuntary visual attention occurs in 'pop-out'. If there is a stimulus between different stimuli that is different from the rest, it will 'pop out', and attract attention.

Half a second delay in consciousness

Libet carried out experiments showing that there should be about half a second of neural activity to cause consciousness. This is also called 'half-second delay'. During his experiments, Libet stimulated the sensory cortex of people who were awake and aware. Their somatosensory cortex was stimulated with electrodes. This stimulation always differed in frequency, intensity and duration. The result was that the participants stated that they had conscious sensory perceptions.

Libet discovered the connection between the intensity of the stimulation and how long the sensory experience lasts (train duration). He stated that a certain amount of intensity is needed for sensory perceptions. If this amount is not achieved, no observation would take place, no matter how long a part of the brain was stimulated. He discovered that that the 'train duration' must last at least half a second. Libet also concluded that only the somatosensory cortex itself can provide conscious perception.

The referral hypothesis ('backwards referral hypothesis') predicts that stimulation of the medial lemniscus should be referred back ('subjective referral'). Lemniscus is part of the pathway leading to the somatosensory cortex. Libet investigated this hypothesis by asking participants about the timing of different stimuli. As predicted, he found that when a touch on the skin occurred at the same time as the stimulation of the medial lemniscus, participants felt that they were both occurring at the same time. The stimulation of the medial lemniscus was only felt when the stimulation lasted long enough. In general, critics have not reached agreement on the weaknesses and results of Libet's experiments. The only way to be sure is to repeat the experiments. It is unfortunately no longer possible to replicate his experiments, because nowadays stricter rules are used for stimulating the brain. There are researchers who come to a different conclusion about consciousness on the basis of Libet's experiments.

Interpretation of the work of Libet

Libet therefore states that an experience is only conscious when it lasts for at least half a second. With this he distinguishes between conscious and unconscious processes. Milner and Goodale state that the ventral route leads to consciousness, while that does not apply to the dorsal route. Libet only states that an activity must last a certain length of time for it to be deliberately noticed. Libet also states that the referral hypothesis provides evidence against materialism and the 'theory of psychoneural identity'. This theory states that the consciousness and activity of neurons are the same thing. Eccles, Popper and Penrose believe that Libet's findings provide evidence for dualism.

Flashes

Wundt discovered the 'subjective time displacement' phenomenon. This means that when you ask participants to determine the relative timing of auditory or visual stimuli, people make mistakes in determining which event happened first.

We do not always experience things in the order in which they happen. An idea is that there are two worlds:

1. an outside world in which events happen in one order.

2. An inner experienced world of consciousness in which events happen in another order.

Evidence for this idea is given by the so-called phi phenomenon.

If two flashes (in different positions) are shown very shortly after each other, then the observer has the feeling that there is one light that moves. He or she therefore does not see two separate flashes. With the phi phenomenon, the color of the flash changes from red to green even before the second flash is shown. However, someone who observes this only sees one moving light point that changes from red to green.

Another example is what is called 'cutaneous rabbit'. If you are touched on your wrist a number of times, then on your elbow and finally on your upper arm, those touches do not feel as separate, but as a whole. It feels as if something 'climbs' from the bottom to the top.

Resources: Blackmore; Susan. (2010). Consciousness, Second Edition An Introduction. Abingdon, Oxon: Taylor & Francis.