Can inhibition deficit hypothesis account for age-related differences in semantic fluency? Converging evidence from Stroop color and word test and an ERP flanker task.

The inhibition deficit hypothesis (IDH) proposed that individual differences in inhibitory control is an underlying reason for age-related language decline. This study examined whether the hypothesis holds within the domain of lexico-semantic retrieval. Sixty-six older adults aged 60-79 were tested in a semantic fluency task comprising 16 categories; each response was classified as automatic or controlled. Also, Stroop color and word test and an ERP flanker task were employed to yield both behavioral and neural measures of inhibitory control. Mixed-effects modelling revealed that the number of controlled (but not automatic) responses was negatively associated with age. This interaction could be partially accounted for by the behavioral Stroop inhibition score and two neural measures from the ERP flanker task (P2 and Pc amplitudes). These results not only provide converging evidence supporting the IDH, but also demonstrate the involvement of specific inhibitory control components, including attentional control and performance monitoring.