Implicit manual and oculomotor sequence learning in developmental language disorder

Procedural memory functioning in developmental language disorder (DLD) has largely been investigated by examining implicit sequence learning by the manual motor system. This study examined whether poor sequence learning in DLD is present in the oculomotor domain. Twenty children with DLD and 20 age-matched typically developing (TD) children were presented with a serial reaction time (SRT) task. On the task, a visual stimulus repeatedly appears in different positions on a computer display which prompts a manual response. The children were unaware that on the first three blocks and final block of trials, the visual stimulus followed a sequence. On the fourth block, the stimulus appeared in random positions. Manual reaction times (RT) and saccadic amplitudes were recorded, which assessed sequence learning in the manual and oculomotor domains, respectively. Manual RT were sensitive to sequence learning for the TD group, but not the DLD group. For the TD group, manual RT increased when the random block was presented. This was not the case for the DLD group. In the oculomotor domain, sequence learning was present in both groups. Specifically, sequence learning was found to modulate saccadic amplitudes resulting in both DLD and TD children being able to anticipate the location of the visual stimulus. Overall, the study indicates that not all aspects of the procedural memory system are equally impaired in DLD.