The reaction time (RT) task consisted of 31 trials in which a flashing asterisk, 1 cm in height, appeared at the center of a computer screen for 150 ms and alerted the participant of an upcoming computer-generated tone (1200 Hz, 72 dB), with latency of 1500 ms. Participants were instructed to focus their eyes on the screen (50 cm distance) during the trial, and to end the tone as quickly as possible by pressing a button with the right index finger. The RT task was part of a contingent negative variation paradigm [19] , whose electrophysiological results will be presented elsewhere. All reaction times were log-transformed to normalize the data.

2.4.2 Alternate Uses task.

The Alternate Uses (AU) task assesses creativity [36]. In this task, the participant is required to name as many different ways in which a given item might be used. For example, a shoe can be used to walk with or can serve as a drum. In a previous pilot study with the aim of examining changes in creativity following short term and long term training, we clustered a 908-word database developed by Levy-Drori and Henik [57], using hierarchical cluster analysis, and grouped those words having similar ratings of concreteness, availability of context and familiarity assigned by Levy-Drori and Henik. Concreteness was rated by them on a scale from one to seven, where “1” indicated very low concreteness (very abstract word) to “7” which indicated a very concrete word [58]. Availability of context was defined by Schwanenflugel and Shoben [59] as ranging from 1–7, with “1” indicating that it is very difficult to think of a context and “7” indicating that it is very easy. Familiarity was defined by Gilhooly and Logie [60] as ranging from “1” indicating that it is not very familiar and “7” indicating that it is very familiar. In the pilot study, we chose 18 words from the three largest clusters for which the level of concreteness was highest, and similarity on familiarity and availability features was highest (see Table 1). These 18 words were divided into two groups (9 words in each group). A total of 60 participants received one of the two lists, and were asked to produce as many alternate uses as possible, one minute being allocated for each item. Each word was shown on a single page on which the participant had to write down the various uses. The scores for each word were analyzed by counting the number of alternate uses produced. The words were then divided into 6 groups of 3 words so that each group had a similar number of alternate uses. In the main study, three items were successively shown on a computer screen before the training and three others were shown after the training. Presentation order of these items between groups was counterbalanced across subjects.

Two main measures were computed from the AU task: Ideational fluency and ideational flexibility. The ideational fluency score was defined as the mean number of uses given by the participant for the three items [61]. On the basis of all the uses made by the participants, 10 independent categories were defined across all the items. These included broad categories of usage such as “a weapon” or “a costume.” The ideational flexibility score was defined as the mean number of different categories employed by the participant across all three words presented [62]. Hence, in order to calculate the flexibility score, all responses for a given item were first divided into the different independent categories. For example, using an item as a musical instrument and using it as a weapon were regarded as two independent categories; while using it as a drum and as a trumpet would be regarded as the same category. Since flexibility is a subjective measure it is important to examine its reliability [63]. Therefore, two independent judges who were naïve to the identity of the participants and their training groups scored the test independently for flexibility, and consistency between judges was tested. We examined the correlation between the scores of the two judges using a 2-tailed Pearson correlation coefficient test. A high correlation was found between scores given by the two judges both in the scores before the training and after the training: r = 0.89 and 0.87, n = 27, respectively.

Two other scores, thought to represent a failure to monitor responses [37] were also computed: the AU perseveration within object – measuring a repetition of the same use for one object (e.g., using a newspaper to wrap a book and using a newspaper to wrap a box of chocolates), and AU perseveration between objects – repeating the same use for different objects (e.g., throwing a shoe at somebody and throwing a pot at somebody).