That there is a propensity to recognise patterns, and relationships between components. Figure and ground. Behavior takes place in an environmental, or psychophysical field in which interacting forces compete until a stable state is reached. Pragnanz, a figure becomes regular, symmetical, simple, stable. Attention can be seen as directing of energy into the grouping processes.
Sensation refers to immediate and basic experiences generated by isolated, simple stimuli.
Perception involves the interpretation of those sensations, giving them meaning and organisation. Cognition involves the acquisition, storage, retrieval, and use of knowledge. Measuring a threshhold, or limen, an average value of the stimulus. Subliminal and supraliminal. JND, just noticeable difference.