CNP TS

Description

The Color/Shape cued switching task (C/S task) is a putative measure of task-switching. The task was presented on a Dell PC running Windows XP and using E-prime (PST) for stimulus presentation. Stimuli were four colored shapes (red or green, circle or triangle). On each trial participants were cued (alternating with either a letter or word) as to which dimension is the correct task set. The cue duration was 150ms and the cue-stimulus interval (CSI) was randomized as either 200ms or 1200ms. Upon presentation of the stimulus (X ms), the participant must make a forced-choice response with the middle or index finger of their dominant hand to the left or right arrow keys (inverted-t) on an extended keyboard. The response set was bivalent (e.g. respond left for green or triangle). This was counter-balanced across subject. Thus, two of the four stimuli presented a congruent response condition (the cue was not necessary to direct the response) and an incongruent response (where the cue is necessary to determine the correct response). On one third of the trials, the cue switched from one dimension to the other. Participants performed 192 trials. The task was self-paced. Participants received three separate practice sessions to ensure encoding of the response mapping. They practiced each dimension separately for 8 trials (8 color only response trials, 8 shape trials). They then practiced both dimensions together with X switch trials. If participants performed below 60% on any block they repeated practice. If they performed below 60% on the second practice block, the task terminated.

Indicators

There are four conditional variables in this C/S task: 1) Cue-stimulus interval, long or short task preparation interval of 1200 or 200 ms; 2) Congruency, whether the two dimensions of the stimulus created conflict in response; 3) Switch condition, whether the previous trial was of the same dimension as the current trial (color or shape); 4) Response choice, whether the response choice was the left or right button. We used these variables to identify several task indicators of behavioral performance. As commonly seen in the literature, we defined switch cost as the difference in reaction time (RT) between repeat trials and switch trials at the short CSI. Residual switch cost was the same RT difference at the long CSI. We defined interference as the difference in reaction time between congruent and incongruent response sets. We also defined response switch as the difference in RT between repeated button presses and switching from one button to the other.

Cleaning Strategy=

We then trimmed the data to include correct only trials with a 3SD trim on the mean and removing switch trials where there was an error at n-1.