Attention is what helps us to maintain perception, thought, and behavior despite distraction. There are many varieties of attention, each with a different purpose and dependent on different brain mechanisms in order to function. Attention can be separated into three main categories: selection, vigilance, and control. There are many theories regarding the mechanisms of different types of attention.
We are exposed to more sensory stimulation at one time than we can process fully. Without attention, we would be unable to sift through it all to process what we must and disregard what is irrelevant. Different sensory impressions compete with each other for our attention. Selection is the mechanism by which the brain’s resources are directed toward the processing of relevant information and away from irrelevant distracting information, and in this way, the competition between different sensory stimuli is resolved. There are two main types of selective attention: exogenous and endogenous attention.
Exogenous attention refers to attention that is reflexively drawn by the sensory events themselves. For instance, if you hear an unexpected noise or see a flash of light in the corner of your eye, that draws your attention to investigate what just happened. This form of attention is not conscious, that is, you do not plan to move your attention to the location of the unexpected flash or noise—it happens automatically. Endogenous attention is initiated by your conscious desire to gain more information about something in your environment. For example, looking for a friend in a crowded airport involves moving your attention between faces until your friend is seen. Another example is listening to a conversation in the midst of a crowded party. In this case, you attend to the voice of a single person while filtering out other voices and irrelevant noises. Divided attention is another example of selective attention, but one that requires you to maintain your focus on more than one thing at a time. For instance, while driving, you must balance your attention between monitoring your own steering and speed, while also watching for other vehicles, traffic signals, and hazards such as pedestrians. Adding other tasks to these puts further demands on your attentional system, such as talking to a passenger or on a cell phone, and the chances of having an accident are increased.
Vigilance, or sustained attention, is the act of maintaining attention on one thing for a length of time without losing focus. As you read this passage, if you are unable to disregard noises and other distractions, then you may not be able to finish the task. A loss of vigilance can also have more severe consequences. Air-traffic controllers must watch their screens for long hours and quickly detect and respond to signs of danger even when fatigued. Driving a car also involves vigilance. Vigilance involves a number of brain regions, including right frontal and parietal cortex and the dorsal anterior cingulate cortex. Dorsal anterior cingulate is involved in resolving response conflict, such as happens when you are trying to pay attention to something and resist distraction.
Attentional control, or executive function, is the process by which the higher levels of your brain direct the activity of lower levels. There are many forms of attentional control. Planning involves organizing a sequence of behaviors to achieve a goal. Prospective memory involves remembering to do tasks at a specific time, such as paying bills.
There are many theories of attention. Norman’s theory of selective attention states that all stimuli, whether relevant or irrelevant, are simultaneously comprehended to some degree. However, only those events that hold the greatest amount of meaningful information are given close attention, with competition between stimuli based on both “bottom-up,” or sensory-driven, and “top-down,” or conscious, processes. Broadbent’s filter theory is based on the assumption that human information processing has a finite capacity. This filter permits only a limited amount of sensory information to be processed at any one time. This means that if too much information arrives simultaneously, some of the information is placed on hold or rejected. Posner postulates that attention can be divided into three functions: disengagement, shifting, and engagement of attention. These functions are mediated in turn by three core structures: the posterior parietal lobe, superior colliculus, and pulvinar, respectively.
Babies begin their lives primarily with reflexive exogenous attention and develop other forms of attention as they mature. This parallels the development of brain areas involved in these different forms of attention. Babies have many subcortical networks nearly intact at birth or soon after (such as the colliculi and thalamus), which are involved in exogenous attention, but with immature cortical regions, especially the higher-order regions involved in vigilance and attentional control. These brain regions continue to develop well into adulthood. Thus, our attentional control may improve as we grow into adulthood because our brains are maturing. Conversely, because young children lack these brain networks, it may be impossible for them to use these forms of attention until they develop.
Many psychiatric and neurological disorders involve deficits of attention. People with attention deficit hyperactivity disorder (ADHD) demonstrate many inattentive behaviors. They may not pay attention to details, do not seem to listen, do not follow through on instructions, and do not engage in tasks that require attention, and they may make careless mistakes, have difficulty sustaining attention, have difficulty organizing, often lose things, and be easily distracted and forgetful. If these symptoms cause significant impairments for an extended period of time, then the patient is diagnosed as having ADHD. Inattention may also be combined with hyperactivity and impulsivity, although these are considered separate from symptoms of inattention. Many people grow out of these symptoms or learn to cope eventually, but most will carry them through their school years and into adulthood if not treated. The most popular treatment historically has been methylphenidate (Ritalin), which is a mild stimulant, although a number of other behavioral and pharmacological treatments have been developed recently with fewer side effects. At present, there is some controversy regarding whether or not these inattentive behaviors occur during normal development and should be allowed to persist, or whether they are evidence of a true disorder that needs to be treated aggressively at a young age. A number of other psychiatric disorders also include deficits of attention. Two primary features of schizophrenia include the inability to filter out unwanted stimuli, and the inability to control thoughts and behavior. In fact, schizophrenia may arise in part as a reaction by the patient being overstimulated, owing to a lack of attentional filtering and control. Autism and Asperger’s syndromes may also involve a deficit of attention, in which affected people are unable to reduce excessive stimulation and become uncomfortable with situations that others normally find pleasurable, such as close human contact. Obsessive-compulsive disorder (OCD) is another disorder that may involve deficits in attention. Individuals with OCD can have recurrent intrusive and inappropriate thoughts that they cannot suppress and that cause distress. This can be thought of in part as a disorder of attentional control because it involves the inability to control one’s own thoughts. Other brain disorders, such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease, all involve some deficits of attention.
A number of attentional disorders can occur with damage to specific brain regions. Left hemi field neglect occurs after right parietal lobe injury. Patients with severe left hemifield neglect are completely unable to attend to stimuli in the left visual field. For instance, when asked to draw a picture of a house, they may only draw the right side of the house, leaving the left side empty. Vigilance and attentional control can also be disrupted by damage to the frontal and parietal lobes. Patients with damage to the frontal cortex often appear normal for the most part, but have severe difficulty organizing their behavior and planning for the future.
Attention is something we are born with and that develops naturally over our lifetime. Impairments of attention associated with conditions resulting from brain damage, developmental disorders, or other means can lead to severe deficits in behavior. Some forms of attentional deficits may be improved with drug treatment, such as in ADHD, whereas other forms of attention may be improved with training, such as meditation. Further research may lead to a better understanding of the brain mechanisms of attention in healthy individuals and of the causes of attentional disorders, which may ultimately lead to better treatments for attentional disorders.
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