Sensation refers to the process that the sense organs perform when they encode physical energy from the environment. The physical stimulus energy is broken down into action potentials in the brain through the process of transduction. Perception, the interpretation of this transformed physical energy/stimuli into meaningful information, occurs in the brain. While sensation is a purely physical phenomenon occurring within the confines of a particular sensual modality and its associated neural registers, the process of perception is an interactive one where previous experiences, knowledge, expectations, etc. that are multi-modal interact with the physical sensations from the environment in order to produce current our experience. The mechanisms of these perceptions can either be unconscious (occur below the level of conscious awareness) or conscious (occur at the level of conscious awareness). These processes can also be automatic, occurring without conscious effort and conscious control and therefore use very little cognitive resources or in specific instances they can take the form of controlled processes. Controlled cognitive processes occur with conscious effort and control and use quite a bit of cognitive resources placing a demand on the system (compared to automatic processes).
Attention refers to the complex process of sensation and perception whereby we allocate our cognitive resources to particular aspects of the environment. An issue at hand is that we are bombarded every instant by countless physical stimuli from the environment. It would literally be impossible to process all of the information/stimulation occurring in any environmental context. There must be some mechanism by which stimulation is filtered out so that only the relevant information is processed and perceived. Moreover, cognitive resources are finite and subject to the demand limitations of the brain. People certainly are able to exert conscious control over where they focus their attention (selective attention); however, the process of attention is largely an automatic one and even when one is selectively attending to something the underlying processes...
The process of filtering out much of this incoming information is a bottom-up process occurring in the brain over which we have little control. The process of filtering out incoming information and choosing what information is relevant and what information is not relevant probably includes interactions within the brain with stored representations, schemas, scripts, etc. such that in a given context information/stimulation deemed the irrelevant to that context is automatically disregarded. As an example, think of how inefficient it would be if a person had to consciously try to observe multiple aspects of their environment and make a conscious decision as to which stimuli/aspects of the environment are relevant to the giving context in which are not. For instance, take a simple task like eating one's lunch in the cafeteria. It would be quite inefficient if one had to observe every aspect of the environment including the food on the plate, the table, chairs, people, other people's food, windows, lights, floor, silverware, etc. And decide which of these are relevant to the task at hand and which are not. Then in order to actually eat one would need to decide which hand to use, where to target it in order to pick up one's fork, the right amount of pressure needed to hold fork, aim the exact carrot one wishes to eat ignoring all other stimuli, stab, etc. The process of eating, which is primarily an automatic one, goes smoothly because we are automatically able to filter out irrelevant "noise" focus on the relevant environmental stimuli and simply eat.
Likewise, if one subscribes to bottlenecks theories of attention where a good deal of the environmental energy that we are exposed to must be pared down due to the limited cognitive capacity of the central nervous system, one must assume that this process is an automatic one…
