Attention is a complex cognitive process that involves selectively focusing on certain stimuli while ignoring others. It allows individuals to concentrate on specific tasks or objects. There are several factors that influence attention, including characteristics of the stimulus like intensity, size, contrast and novelty, as well as internal factors such as interest, motives, mood, and past experiences. The span of attention refers to how many items can be attended to at once, which experiments have shown is typically around 4-5 items. Attention can fluctuate and be divided or distracted over time.