Abstract: Recently, Rende explored the role of set shifting in verbal fluency, which is a subfunction of the central executive system. However, the central executive system contains more than one subfunction, including inhibition. During the verbal fluency tasks, participants were required to produce words in a certain time period (one minute); further, they were not permitted to repeat the words that they had just produced. Thus, it is reasonable that verbal fluency might employ the inhibition function. One of the aims of the present study is to explore the impact of short-term storage resource and attentional resource on verbal fluency. This was based on Engle’s model, which proposed that working memory was equal to short-term storage plus attention controlling.
Exp. 1 used set calculation and mouse operation (pasting a sentence in Microsoft Word) as the secondary tasks to explore the impact of the central executive system (shifting and inhibition) on verbal fluency. Forty undergraduates (20 women and 20 men) participated in this experiment. Of the total participants, half of them (10 women and 10 men) participated in set calculation task, while the other half joined in the mouse operation task. The oral speed of all participants was estimated. Subsequently, the participants were given a familiar topic, such as “my college life,” and were required to talk on the subject for one minute. Moreover, they were required to assess their Chinese language level based on a 5-point scale. The scores of all participants were equal to or higher than 3. Those who had participated in the mouse operation secondary task were required to estimate their computer operation level. All of them had spent more than 2 hours per day on a computer and were familiar with mouse operation. We employed a two-factor within-subject design, 2 (phonemic and semantic fluency) × 2 (single- and dual- task conditions), for this experiment.
Exp. 2 employed (1) equation judgment (demanding both storage and attentional resources), (2) odd/even judgment (demanding attentional resource but not storage resource), and (3) pressing keys randomly (demanding neither storage nor attentional resources) as secondary tasks to investigate the role of two different kinds of resources in verbal fluency. Another sixty subjects (30 women and 30 men) participated in Exp 2. The subject selection procedure was the same as that used in Exp.1, with the exception of computer assessment. Similar to Exp. 1, we employed a two-factor mixed design, 2 (phonemic and semantic fluency) × 3 (three different kinds of secondary tasks) in this experiment. The fluency tasks were a within-subject design, while the secondary tasks were a between-subject design.
The results of Exp. 1 indicated that the central executive system had a substantial impact on verbal fluency. When the secondary task was set calculation, the participants produced more words during the semantic fluency task than during the phonemic fluency task; however, they produced fewer words in the dual-task condition than in the single-task condition. Further, the reduction of words in the semantic fluency task was only marginally more than that in the phonemic fluency task under the dual-task condition. The cluster size in the semantic fluency task was significantly larger than that in the phonemic fluency task. Further, the decreasing pattern of the cluster size was the same as words’. The participants generated more switches during the semantic fluency task than during the phonemic fluency task; however, they generated fewer switches in the dual-task condition than in the single-task condition. In addition, the decreasing pattern of switches was also the same as words’. When the secondary task was mouse operation, the patterns of the results for the three different indexes (total words, cluster size, and switches) were exactly the same as that when the secondary task was set calculation.
The results of Exp. 2 indicated that short-term storage and attentional resource had a substantial impact on verbal fluency. In the semantic fluency task, the number of words in the pressings key randomly condition was almost the same as that in the odd/even judgment condition; further, the number of words in the abovementioned two conditions was significantly more than that in the equation judgment condition. With regard to the phonemic fluency task, the number of words in the odd/even judgment condition was almost the same as that in the equation judgment condition; moreover, the number of words in both conditions was significantly less than that in the pressing keys randomly condition. The cluster size in the semantic fluency task was larger than that in the phonemic fluency task. For the semantic fluency task, the number of switches in the pressing keys randomly condition was almost the same as that in the odd/even judgment condition; the switches in the abovementioned two conditions were significantly more than those in the equation judgment condition. For the phonemic fluency task, the difference between the number of switches in the odd/even judgment condition and that in equation judgment condition was not significant; further, the switches in the abovementioned two conditions were both significantly less than that in the pressing keys randomly condition.
These results suggest that: (1) The role of the subfunctions of set shifting and inhibition in both the verbal fluency tasks was quite similar. (2) Semantic fluency relied more on storage resource than phonemic fluency did; conversely, phonemic fluency depended more on attentional resource than semantic fluency did.

Key words: verbal fluency, phonemic fluency, semantic fluency, working memory