Reaction time and mild mental retardation: high speed scanning reexamined.

When observers judge whether a probe is contained within a small positive set, reaction time (RT) increases linearly with set size (Sternberg, 1969b). Slope and intercept of the function relating RT to positive set size are believed to reflect durations of different processing stages. As results of several investigations suggested inverse slope/intercept relationships, however, studies using "high-speed scanning" tasks to compare retarded with nonretarded individuals were reexamined. When slope was correlated with points along the RT function (intercept, Positive Set Sizes 1, 2, and 4), results showed no interdependencies for nonretarded adults. Slope and intercept were negatively correlated for retarded and nonretarded adolescents, whereas slope and Positive Set Size 1 values apparently were unrelated. These results seem to contradict theoretical expectations, and specification of processing stages where efficiency varies across populations may not be possible based on results from high speed scanning tasks.