Much of the information received by the brain is processed at an unconscious level. We need only think for a moment about the regulation of the internal processes such as heart rate, saliva flow or sweat production, or the many muscular adjustments involved in activities such as riding a bicycle or raising a cup of tea to our lips, to realise that they are all carried out without conscious awareness.
More surprisingly, there is also evidence of unconscious processing in areas usually considered to fall within our field of awareness as the following examples show.
Blindsight
In the condition known as blindsight, damage to part of the primary visual cortex results in the patient having no conscious awareness of seeing objects in the corresponding part of the visual field. The images are, however, still being registered and processed in the brain. This can be demonstrated as follows:
- Observation of the patient's eye movements shows that he is giving attention to objects he claims not to see;
- When asked to grasp an item in the blindfield, the patient is generally able to do so although he feels he is reaching out at random; and
- When asked to make a choice between differing descriptions of an object in the blindfield (e.g., vertical or horizontal stripes) the patient chooses correctly at a rate far greater than chance although he feels that he is guessing.
Backward masking experiments
In these experiments, participants are exposed to an image of brief duration, the target stimulus, followed by a second image, the masking stimulus. They generally have no conscious awareness of having seen the first because of a 'backward masking' effect. However, as the following examples show, there is evidence that the target stimulus is both perceived and processed.
In an experiment devised by Whalen et al, participants were shown either a happy or a fearful face as the target stimulus, followed by a neutral face as the masking stimulus. Brain scans indicated greater activation of the amygdala ( a structure involved in attaching emotional significance to sensory information) in those who had seen the fearful face although most reported seeing only the neutral face.
In a similar experiment, participants were asked to assess a drink after being shown backwardly masked images of happy, neutral and angry faces. Their reaction to the drink in terms of amount poured and drunk and the price estimated showed a correlation between the emotion portrayed and the reactions, suggesting that behaviour can be influenced by factors of which we are not consciously aware (in this case exposure to different moods).
Prosopagnosia
Patients affected by prosopagnosia, a condition arising from damage to the inferior posterior temporal lobe, are unable to recognise a familiar face. Although they are well aware that they are seeing a face, they cannot put a name to it. Unconscious recognition of faces by such patients has been demonstrated in an experiment devised by Tranel and Damasio.
In the experiment, patients were shown slides of a number of faces, some familiar and some unfamiliar, while connected to a skin conductance response (SCR) machine. When asked to rate the faces in terms of familiarity, no difference was found between the two groups. However, the SCR results showed an emotional response to the familiar faces, indicating unconscious processing at the level of the autonomic nervous system (ANS).
Benefits of unconscious processing
The ANS, which does its work beyond the sphere of consciousness, prepares the body to respond to danger by, for example, increasing the heart rate and releasing adrenalin into the bloodstream, in the 'flight or fight' response. The speed with which it is able to respond is increased, it has been suggested, by the presence of two pathways for the input of sensory information: a slower, cortical one conveying more detail at the conscious level, and a faster, unconscious, subcortical one via the amygdala which triggers the emotionally appropriate response by the ANS.
Another benefit is seen in the way in which many learned activities can become automatic, and therefore unconscious, thereby freeing parts of the brain for other tasks. PET scans carried out in the course of experiments by Raichle et al have demonstrated that the prefrontal cortex and the anterior cingulate cortex, both of which are involved in attention, are active during the learning of a task. Once the participant becomes practised in the task, however, activity in these areas ceases and can be directed elsewhere.
Clearly. therefore, not only does unconscious information processing exist, it also works to our advantage.
Sources
- Datta, S. et al. From Cells to Consciousness (Open University, 2004).
Hilda Reilly - Hilda Reilly has an MSc in Consciousness Studies. She is the author of travel books about Palestine and Sudan.
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