Declarative capacity does not trade-off with procedural capacity in children with specific language impairment

Abstract

Background and aims:The procedural deficit hypothesis attributes the language phenotype in children with specificlanguage impairment to an impaired procedural and relatively intact declarative memory system. The declarative com-pensatory hypothesis is an extension of the procedural deficit hypothesis which claims that the declarative system inspecific language impairment compensates for the procedural deficit. The present study’s aim was to examine the claimsof the procedural deficit hypothesis and declarative compensatory hypothesis by examining these memory systems andrelation between them in specific language impairment.Methods:Participants were children aged 8–13 years, 30 with specific language impairment and 30 typically developingcontrols, who spoke Kannada (an agglutinating language of the Dravidian family). Procedural learning was assessed using aserial reaction time task. Declarative memory was assessed using two non-verbal tasks that differed at the level ofencoding and retrieval: a recognition memory task after incidental encoding using real and novel object images and arecall task after intentional encoding using visual paired associates. Retrieval was examined after short (10 min) and long(60 min) delays after encoding on both declarative tasks.Results:Findings confirmed that children with specific language impairment (SLI) have impaired procedural memory on anon-verbal serial reaction time task. On recognition memory task after incidental encoding though children with specificlanguage impairment encoded less well, they recognized items as well as typically developing controls. Both the groupsretrieved more at short compared to long intervals and retrieved real (verbalizable) objects better than novel objects.On visual paired associates (recall task with intentional encoding) children with specific language impairment retrievedless than typically developing children (even after controlling for non-verbal ability and age). Furthermore, acrossretrieval types of declarative tasks, although children with specific language impairment did less well than typicallydeveloping, their pattern of performance was comparable to typically developing children. Finally, the correlationbetween memory systems did not support a trade-off between memory systems in children with SLI as predicted bythe compensatory wing of procedural deficit hypothesis.Conclusions:The findings supported the major claim of the procedural deficit hypothesis – a procedural learning deficitin specific language impairment and an intact declarative system, however, only if measured on task that was designed tobe undemanding. Furthermore, there was no evidence for a trade-off between these systems.Implications and future directions:Some interventions with specific language impairment use explicit teaching ofgrammar, an approach that uses the declarative rather than the procedural system. Our findings cast doubt on whetherthis is likely to be the most effective strategy.