The perceptual system organizes stimuli by a variety of strategies based on stimulus characteristics. This is done at a very basic level, before the attentional processes makes a decision about selecting the stimulus to present for higher processing to awareness.

The gross features of the stimulus are analysed: size, shape, colour, etc., and the physical arrangement of the stimulus relative to the surrounding (physical and temporal) environment; the way the stimuli are organized physically and temporally (though the pattern detection elements group stimuli according to physical features - this can be seen in the experience of looking at ambiguous figures, such as the rabbit and duck figure. Similarities, and the extent to which complex patterns can be reduced to more basic ones, also influence what is generated at this pre-attentive level.

Some decision must then be made, perhaps based on salience and other top-down influences, as to whether further processing will occur to this input.