General and specific speed mediation of adult age differences in memory.

The proposal that age-related differences in some measures of speed of performance may not be independent of the age-related differences in other measures of speed of performance has been associated with considerable controversy. Because converging evidence can often resolve this type of controversy, correlation-based procedures are proposed to distinguish general (or common) and specific (or unique) age-related influences on measures of speeded performance. Results from three earlier studies and from a new study suggest that a large proportion of the age-related variance in a wide range of speed measures is shared and is not distinct. Furthermore, the common or general speed factor appears to play an important role in the mediation of age-related differences in memory.