Response sequence organization and reproduction by stutterers.

Male stutterers and fluent speakers were compared on their performance of a task requiring tapping keys as rapidly and as accurately as possible to reproduce different finger movement sequences demonstrated on a visual display panel. Although overall finger tapping rate was the same in the two groups, indicating no difficulty by stutterers in performing simple motor movements, stutterers achieved fewer correct sequences and made more errors than fluent speakers. In addition, their response initiation times were slower. Once a correct response was initiated, however, the time to execute the sequence was similar to that of fluent speakers. Replicating earlier work, the two groups were not found to differ on a repetitive sequential finger tapping task with respect to correct sequences or total presses, although the probability of error was greater for the stutterers. The data were interpreted as indicating that in stutterers sequential response mechanisms are lateralized normally as they are in fluent speakers; these left-hemisphere sequential response mechanisms in stutterers appear unusually susceptible to interference, possibly from on-going right-hemisphere activity; stutterers have special difficulty in organizing and/or initiating new response sequences, but once the sequence is initiated, they can perform the sequence as rapidly (but with greater probability of error) as do fluent speakers; and stuttering reflects not a simple motor problem per se, but a higher level organizational problem of a cognitive nature.