Language & Cognitive Control

20mg methylphenidate or placebo capsule - one per session (counterbalanced) approximately 1 week apart

20mg methylphenidate or placebo capsule - one per session (counterbalanced) approximately 1 week apart

The core part of the experiment is the language task, in which the aim is to investigate two critical aspects of language processing: semantic and syntactic processing. In this task, participants will be asked to read a list of sentences.

Brain activity in the EEG is recorded at rest with eyes open and eyes closed to obtain baseline measures of alpha power as a proxy for attention and control under conditions of drug and placebo.

A Go/No-Go task will be implemented in the study design to investigate the functional properties of spatial selective attention and response inhibition. An adapted cued Go/No-Go paradigm from Randall \& Smith (2011) will be employed.

A speeded button response task will be included to measure participants' general processing speed. In this task, participants will be instructed to respond to a simple shape presented in the centre of the screen as fast and accurately as possible through pressing a corresponding button.

In the operation span task, participants are instructed to solve math operations (e.g., (1\*2) +1=?) as soon as possible and then remember a single letter. This to-be-remembered letter is followed by either another math-word combination or a recall screen, which will show up at the end of each set. When the recall screen is presented, participants have to recall all the letters in the correct order they were presented. The experimental trials contain three sets at each set size (i.e., the number of math-word pairs), with set sizes ranging from 3 to 7 items. This results in a total of 75 sets with 75 letters and 75 math problems. The order of set sizes is random for each participant. Participants' operation span will be evaluated by the total number of letters recalled in the correct serial position regardless of whether the entire trial was recalled correctly.

Participants are instructed to judge whether a presented sentence makes sense or not. After each sentence, a to-be-remembered letter will be shown on the screen, which is followed by either another sentence-word combination or the final recall screen. The set size ranges from 3 to 7 items. At the end of each set of sentences, participants will be required to recall all the letters in the current set in order. There will be a total of 75 letters and 75 sentence judgements. The order of the set sizes will be at random for each participant. Participants' performance will be evaluated by calculating the total number of correctly recalled letter sets.

The Barratt impulsiveness scale (BIS-11) will be used in the experiment to measure participants' trait impulsivity. Participants will be required to rate themselves on 30 items that are related to attention, motor, self-control, cognitive complexity, perseverance, and cognitive instability impulsiveness.