Perceptual comprehension is the ability and skill needed to understand what is being perceived. It is being able to look at a sign, a set of instructions, or any written or printed material and understand the meanings of the material. The meaning of this term shifts depending on the type of material or scenery being observed. With written material (such as books) it means being able to look at written words and create meaning. With math, it means looking at numbers and symbols and being able to derive abstract meanings. With pictures, or scenery, it means being able to interpret the items present within the field of view and act or react appropriately. This term is used in aptitude, achievement, and IQ tests to describe how well the material is being comprehended.