There is general agreement that human beings and other animals selectively attend to some of the information available to them through their senses at the expense of the remainder. Some information seems to be processed and acted upon to a much greater extent than other information. One reason advanced for this is the limited capacity of the brain, which cannot process all available information simultaneously.

What are the factors that determine which information will be processed and which will not?
At what stage in the processing sequence does the limitation (bottleneck) occur?

First, following Marr's (1980) injunction, we need to know what the facts are! They are varied, complicated and still being uncovered. Many facts which seem to be associated with attention, however, are quite interesting. I can only highlight some of them. I cannot put them into a coherent network so that we can proceed in a systematic way toward understanding.

1. There are everyday facts. Some of these are what led James to his statement. When we start a new task we seem to need to give it all of our attention. As we develop expertise, the task becomes routine, and we do not need to attend to it any more. Some argue (James did) that it even drops out of consciousness e.g. walking, driving a car. When the conditions are not routine, e.g. walking  ice, driving on an unpaved road with rocks and holes, the task reclaims our attention.

2. Cocktail party phenomena. These are the studies that began to bring attention under experimental control (Cherry (1953). Monitoring the information in one ear while given a secondary task of responding to something in the other ear. Two views were those of Broadbent (early filter) and Deutsch & Deutsch (late filter). Treisman and Geffen had a shadowing task, and secondary task of tapping to a particular stimulus whatever ear it appeared in. People usually miss the information in the nonshadowed ear. If it's a physical filter changes in meaning or context should not have an effect on performance. One can, however, sometimes follow meaningful content as it crosses ears. T and G concluded that it was a perceptual filter that attenuated the nonattended to stimuli.

3. Galambos's 1960's study with the recording of a metronome from the auditory nerve of a cat when it was and was not monitoring a goldfish. Differential ERP recordings from the auditory areas of the cortex in dichotic presentations as a function of instructions to respond to the stimuli entering one ear and not the other.

4. When reading or looking at a scene, our attention is directed to the things in the world and not the activities required to do it. We do not keep our eyes still Our eyes while reading or viewing a picture.  Rather, they move rapidly from one position to another , and differently depeding on the nature of the things they are looking at. We see a whole picture which is generated from a sequence of sudden eye movements from one location to another. We normally are aware of and attend to the object of our vision, not the process.

5. Studies by Posner, LaBerge, and others demonstrating attention without eye movements.
BUT normally eye movements are strong evidence of what is being visually attended to. A recent example varied the content of the task. It takes time to switch attention. There are at least three components of attention switching identified by Posner and Reichle (1994), each with its own neural region of activity. a) disengage attention--posterior parietal cortex. b) refocus on new spatial location-- superior colliculus. c) enhance processing of attended region--Pulvinar region in thalamus.

6. We can sometimes attend to some aspect of a stimulus and not really notice others. Neisser and Becklen (1975)  showed that with overlapping pictures, a sort of a double exposure movie. They hypothesized that attention is an integration of information in a sort of a schema.

7. Sometimes we seem not to be able to ignore particular aspects of a stimulus. Sometimes our experience with certain aspects makes them hard if not impossible to ignore, thus they attract attention. Our experience with text makes reading essentally automatic. This was discovered by Stroop in 1935, and is known as Stroop interference.  See examples

8. Treisman and Gelade found out that certain stimuli pop out, by which they mean that they seem to respond to pre-attentive processes and do not require much, if any, mental resources. Others need more effort and require the "spotlight" of attention to be identified. Treisman and Gelade argued that conjunctions of features and location of objects often required attentional effort. These claims were justified by different patterns of reaction times to different tasks.

7. There are different sources of the selectivity. Some are physical. If a sudden sound occurs, you are likely to switch your attention to the source of the sound. If a bright light suddenly occurs, you will likely switch your attention and your gaze to the direction of that light. and some are due to internal decisions. These may be based on instructions, needs, or ...?

8. Learning and attention. Spence (1966) and the influence of awareness on eyelid conditioning.
Continuity and noncontinuity in learning and memory. R. C. Johnson (UB dissertation 1973). You accept as the same, pictures that are the same in what you attended to, but differ in what you did not attend to.

9. Click studies: Listen to a sentence and determine where a click occurred. The click seems to move to a "break" in the sentence. "John went into the // dining room for dinner."
Is it a perceptual error or a response error?
    Historical event: An issue of attention? Prior entry: Maskelyne fired Kinnebrook in 1796. Tell time by listening to a metronome as a star passed by a cross-hair in a telescope: One seemed to let the metronome into consciousness before the star, and the other seemed to let the star into consciousness before the metronome.

10. Vigilance--One has difficulty keeping a high vigil under conditions where very little is happening. Looking at radar screens. Monitoring a set of dials. Driving on the open road.  Infrequent, though critically important events can, and often are, missed.

12. Attention Deficit Hyperactivity Disorder (ADHD). Panksepp (1998) Attention Deficit Hyperactivity Disorders, Psychostimulants, and Intolerance of Childhood Playfulness: A Tragedy in the Making? Children who have trouble sitting in a classroom and paying attention. They pay attention better when they are on psychostimulants, but is this a widespread disease of the central nervous system or of society?