“There was a hint of a smile on his face. He also seemed to have decided that the examination was over, and began to look around for his hat. He reached out and grabbed his wife's head, tried to lift it and put it on his own head. It seemed he had confused his wife with a hat! She looked as if she were used to things like that.” This excerpt, taken from the book The Man Who Mistook His Wife for a Hat, by Oliver Sacks, shows the dramatic behavior of one of his patients, who had a neurological perception disorder, and illustrates the importance of this faculty in human behavior.
When we are looking for an object, like the key to the front door or the television remote, it is not necessary for us to see them completely; seeing a small part, even if the rest is covered, is enough for us to recognize what we are looking for and guide our movement to the location. This refined ability to associate sensory information with memory and cognition, in order to form concepts about the world and about ourselves, and to guide our behavior, is what we call perception. It is also through this that we are able, for example, to recognize a familiar voice, even if it is hoarse, being whispered or shouted; as well as to distinguish it among a crowd of other voices.
The sensory systems capture the characteristics of each object, such as color, size, movement – this is the first stage of perception; then, this information passes through parallel pathways of the central nervous system, which gradually reconstructs the object. At the end of the process, we do not become aware of this sum of parts and properties, but rather of the objects as global perceptions; that is, the sensory systems, combined with synthetic nature mechanisms (capable of gathering parts and properties into a unique set that makes sense), lead to perception. However, at every moment we are “bombarded” by sensory information of all kinds, whether visual, auditory, tactile, or others; do we perceive all of them?
Imagine that you needed to study for an exam and, when sitting down in front of the study material, you clearly noticed that the dogs started barking, the cars began honking, and the people around you started moving. The truth, however, is that these noises probably existed before, but you were ignoring them; and only when you had to silence to perform your activity did you realize their presence, that is, you began to pay attention to them. It is precisely through attention, or selective perception, that we control which perceptions will reach our consciousness; thus, if we concentrate again on the initial task (studying), we will return to ignoring the distracting sensory stimuli.
Although it is not always so simple to ignore these stimuli, the truth is that the sensory information to which we have conscious access is always a tiny fraction of the whole (like the part of the iceberg that is above water), as we constantly filter this unconsciously; and that is why we do not realize that we are breathing, or wearing glasses or shoes (unless they are tight). This ability to select relevant stimuli is essential for our balance, and events that could evolutionarily be related to the preservation of life have gained the power to capture our attention. For example, pain, like that caused by tight shoes, is a means of making perception conscious, and as we saw in the post - The Battle for Our Attention, emotions are also decisive in this process!
References
Lent R. At the Gates of Perception. In: One Hundred Billion Neurons – Fundamental Concepts of Neuroscience (Lent, R). 2010; p. 612-41, Atheneu Publishing;
Sacks OW. The Man Who Mistook His Wife for a Hat. In: The Man Who Mistook His Wife for a Hat (Sacks, OW). 1997; p. 22-37, Companhia das Letras.
Figure: http://commons.wikimedia.org/wiki/File:Iceberg_at_Baffin_Bay.jpg
