Transient activation of speech areas following language task

My fMRI study of primed dichotic listening from 2009 showed that stimulus conflict increased medial prefrontal activation, and response conflict increased left dorsolateral activation. That went some way in terms of figuring out which mechanisms are involved in the task, and we accounted for it in terms of the Desimone and Duncan's biased competition model and/or Botvinick's model of interaction between cognitive conflict and control.

After publishing this work, I started thinking whether the data could also be used to understand how the mechanisms interacted. Some recent studies have indicated that high cognitive conflict on one trial leads to  increased cognitive control on the following trial. The increased control is typically seen as faster and more accurate performance, and increased activation in cortical areas assumed to hold the task set instructions. Could I do something similar with my task? Given that I had formally left the neurocognitive research group at this time, I was perhaps also motivated to get the most out of my already collected fMRI data.

The 2009 analysis had analysed according to what the current stimuli and the current response was. The new analysis restructured the data file according to whether the previous and the current trial was high (prime repeated in targets) or low conflict (no prime-target repetition). This yielded four different categories (previous trial - current trial):

1. High - high
2. Low - high
3. High - low
4. Low - low

From this we could run two different analyses: In the first contrast, we compared sequence 1+2 with sequence 3+4, i.e. examined what the effect of the current trial was, regardless of what happened on the previous trial. As expected, this yielded much the same result as the 2009 analysis, showing that task conflict activates medial and dorsolateral prefrontal areas. The second contrast compared sequence 1+3 with sequence 2+4, i.e. examined what the effect of the previous trial was, regardless of the current trial. This showed that following a stimulus conflict, activation increased in temporal areas, more on left than on right side. No behavioural after effect of conflict was seen, perhaps since there is no defined correct answer in the prime dichotic listening task (both syllables are correct, and error rates are low), and response times were not measured. 

In line with current models for how cognitive conflict modulates cognitive control, we interpreted the effect as challenging task leading to more resources being dedicated to the type of processing involved in the task, in this case discriminating verbal stimuli. The fact that sequential effects showed temporal rather than e.g. dorsolateral activation, may indicate that conflict did not lead to increased task or instruction focus, as has been seen in e.g. sequential effects of Stroop tasks, perhaps as the task is rather simple. 

  

My by then former college Karsten Specht helped me with the analyses and the manuscript, and we published this in "Brain and Cognition" in 2012. A lab meeting presentation of this study can be found here. 

Cognitive conflict in a syllable identification task causes transient activation of speech perception area of speech perception area - Brain and Cognition