fMRI study on primed dichotic listening

In the third and final paper in my PhD, we repeated the primed dichotic listening experiment from the two previous papers in an fMRI setting. We found response choice and RT comparable to the previous studies. One analysis compared the activation on trials that repeated the prime to the activation on the trials that did not, and showed increased activation in medial frontal gyrus and in right inferior frontal gyrus (IFG). This was associated with the cognitive processes of cognitive conflict and inhibition, respectively. A second analysis compared the trials where the repeated syllable was ignored to the trials where the repeated syllable was attended. Ignoring the repeated syllable (the response bias) correlated with right IFG activation, while attending the repeated syllable correlated with cingulum / frontal gyrus and IFG activation. This was accounted for by associating one response pattern with inhibition, and the other to increased conflict and decision making.

Satrevik & Specht (2009) Cognitive conflict and inhibition in primed dichotic listening - Brain and Cognition

Paper on interaction between priming and directed attention in dichotic listening

In the second paper in my PhD, we presented a prime syllable that participants were instructed to ignore, followed by a dichotic syllable pair. In the first part of the experiment, the participant was asked to report the syllable heard best overall, while in the second and final part of the experiment, the participant was asked to report the syllable heard in the left or the right ear. The results showed

1. the same negative priming effect as reported in the previous paper,
2. an effect of directed attention and
   
3. an interaction between priming and directed attention.

It was argued that the study showed that the two types of attention modulations could coexist, while the interaction indicated that the two may have some overlapping cognitive features.

Sætrevik & Hugdahl (2007a) - Endogenous and exogenous control of attention in dichotic listening - Neuropsychology

As a methodological aside, this paper presents the responses analyzed in three different ways:

1. in terms of laterality of the responses (number of left and right ear responses),
   
2. the response laterality calculated into a "laterality index", and
   
3. responses rescored according to whether the repeated syllable was selected or not, and then calculated into a "priming index".

In light of the following research, I find the third of these approaches to be the most effective in communicating the priming effect.

Paper on crossmodal primed dichotic listening

This was the first paper in my PhD. Two experiments presented a single prime syllable (the first experiment presented it as sound, the second as text on screen), followed by a dichotic (one in each ear) syllable pair, and asked participants which syllable they heard from the dichotic pair. The results from both experiments showed that participants tended to report the syllable that had been repeated from the prime. In accounting for the results, we said that the selection between the dichotic syllables is a demanding task, and to facilitate the selection, participants inhibit the prime syllable. The inhibition of the syllable is retained at the time of the selection process, and creates a bias for the response. It's interesting that the priming was effective also when it was crossmodal (prime as text, dichotic syllables as sound), from which we can make assumptions about the cognitive level of the mechanism.

Sætrevik & Hugdahl (2007b) Priming inhibits the right ear advantage in dichotic listening - Implications for auditory laterality - Neuropsychologia

I initially intended this as a simple pilot study that should give a positive priming effect, and was quite surprised by the negative priming effect found. This required me to rethink the theoretical model, and consequently changed the form of my PhD project.

This first paper reported the results in terms of laterality of the response (whether the stimulus from the left or right ear was reported), as was common in our research community. I later abandoned this approach, as the priming effect appears to be symmetrical for both ears (although it acts on the background bias of the "right ear advantage"), and instead reported whether or not the repeated syllable was selected or not.

I have not since followed up on the crossmodality of the priming effect.