The WAIS subtests are grouped into four index scores, each measuring a specific cognitive skill. The Verbal Comprehension Index reflects the ability to express abstract ideas in words. The Perceptual Reasoning Index reflects the ability to process visual and spatial information; the Working Memory Index suggests the ability to hold and manipulate information in memory; and the Processing Speed Index indicates the ability to process information rapidly. These indices show that intelligence, as measured by the WAIS, has several very different components.