It is more than Interference: Examining the neurohemodynamic correlates of the flanker task with functional near‐infrared spectroscopy

• Published in: The European journal of neuroscience 2020-08, Vol.52 (3), p.3022-3031
• Main Authors: Geissler (Geißler), Christoph F., Hofmann, Markus J., Frings, Christian
• Format: Article
• Language: English
• Subjects: executive functions; Familiarity; Frontal gyrus; Functional magnetic resonance imaging; Hemoglobin; Information processing; Infrared spectroscopy; Magnetic resonance imaging; perceptual familiarity; prefrontal cortex; Spectrum analysis; strategic readjustment
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/ejn.14708

Previous functional near‐infrared spectroscopy studies using the Eriksen flanker task, in contrast to functional magnetic resonance imaging studies, revealed the quite puzzling finding of an inverted conflict effect, that is, greater middle and superior frontal activation in response compatible than in response incompatible trials. However, since neither prior functional near‐infrared spectroscopy studies nor most previous functional magnetic resonance imaging studies separated between an identical and a compatible condition, it is hard to pinpoint whether this discrepancy occurs on the level of stimulus processing or response generation. By assigning two letters to both left (D, F) and right (J, K) hand reactions, we were able to separate identical (e.g., JJJ) and compatible (e.g., JKJ) conditions that solely differ in their stimulus congruency. Replicating prior functional magnetic resonance imaging findings, we found the standard conflict effect at the transition of superior and middle frontal gyrus, when comparing the activation in compatible trials to that in incompatible trials. Both changes in oxygenated and deoxygenated hemoglobin thus pointed to more effortful processing in incompatible trials. Interestingly, however, identical trials showed the highest activation in this region, according to both changes in oxygenated and deoxygenated blood. A finding that mirrors and extends prior functional near‐infrared spectroscopy findings, which only regarded oxygenated blood. We argue that this pattern of results does not reflect the standard conflict effect. We rather assume that other processes like perceptual familiarity or strategic readjustment might be at play. Prefrontal cortex activity during Eriksen flanker task was analyzed. The right superior frontal gyrus showed the strongest distinction in activation between identical and compatible trials. This points to the involvement of mechanisms other than interference resolution on a perceptual level of flanker processing.