The bivalency effect represents an interference-triggered adjustment of cognitive control: an ERP study

When bivalent stimuli (i.e., stimuli with relevant features for two different tasks) occur occasionally among univalent stimuli, performance is slowed on subsequent univalent stimuli even if they have no overlapping stimulus features. This finding has been labeled the bivalency effect. It indexes an adjustment of cognitive control, but the underlying mechanism is not well understood yet. The purpose of the present study was to shed light on this question, using event-related potentials. We used a paradigm requiring predictable alternations between three tasks, with bivalent stimuli occasionally occurring on one task. The results revealed that the bivalency effect elicited a sustained parietal positivity and a frontal negativity, a neural signature that is typical for control processes implemented to resolve interference. We suggest that the bivalency effect reflects interference, which may be caused by episodic context binding.

Age affects the adjustment of cognitive control after a conflict: evidence from the bivalency effect

Age affects cognitive control. When facing a conflict, older adults are less able to activate goal-relevant information and inhibit irrelevant information. However, cognitive control also affects the events after a conflict. The purpose of this study was to determine whether age affects the adjustment of cognitive control following a conflict. To this end, we investigated the bivalency effect, that is, the performance slowing occurring after the conflict induced by bivalent stimuli (i.e., stimuli with features for two tasks). In two experiments, we tested young adults (aged 20-30) and older adults (aged 65-85) in a paradigm requiring alternations between three tasks, with bivalent stimuli occasionally occurring on one task. The young adults showed a slowing for all trials following bivalent stimuli. This indicates a widespread and long-lasting bivalency effect, replicating previous findings. In contrast, the older adults showed a more specific and shorter-lived slowing. Thus, age affects the adjustment of cognitive control following a conflict.

Episodic context binding in task switching: Evidence from amnesia

The purpose of the present study was to investigate whether amnesic patients show a bivalency effect. The bivalency effect refers to the performance slowing that occurs when switching tasks and bivalent stimuli appear occasionally among univalent stimuli. According to the episodic context binding account, bivalent stimuli create a conflict-loaded context that is re-activated on subsequent trials and thus it is assumed that it depends on memory binding processes. Given the profound memory deficit in amnesia, we hypothesized that the bivalency effect would be largely reduced in amnesic patients. We tested sixteen severely amnesic patients and a control group with a paradigm requiring predictable alternations between three simple cognitive tasks, with bivalent stimuli occasionally occurring on one of these tasks. The results showed the typical bivalency effect for the control group, that is, a generalized slowing for each task. In contrast, for amnesic patients, only a short-lived slowing was present on the task that followed immediately after a bivalent stimulus, indicating that the binding between tasks and context was impaired in amnesic patients.

The effect of inner speech on arterial CO2 and cerebral hemodynamics and oxygenation: a functional NIRS study

The aim of the present study was (i) to investigate the effect of inner speech on cerebral hemodynamics and oxygenation, and (ii) to analyze if these changes could be the result of alternations of the arterial carbon dioxide pressure (PaCO2). To this end, in seven adult volunteers, we measured changes of cerebral absolute [O2Hb], [HHb], [tHb] concentrations and tissue oxygen saturation (StO2) (over the left and right anterior prefrontal cortex (PFC)), as well as changes in end-tidal CO2 (PETCO2), a reliable and accurate estimate of PaCO2. Each subject performed three different tasks (inner recitation of hexameter (IRH) or prose (IRP) verses) and a control task (mental arithmetic (MA)) on different days according to a randomized crossover design. Statistical analysis was applied to the differences between pre-baseline, two tasks, and four post-baseline periods. The two brain hemispheres and three tasks were tested separately. During the tasks, we found (i) PETCO2 decreased significantly (p < 0.05) during the IRH ( ~ 3 mmHg) and MA ( ~ 0.5 mmHg) task. (ii) [O2Hb] and StO2 decreased significantly during IRH ( ~ 1.5 μM; ~ 2 %), IRP ( ~ 1 μM; ~ 1.5 %), and MA ( ~ 1 μM; ~ 1.5 %) tasks. During the post-baseline period, [O2Hb] and [tHb] of the left PFC decreased significantly after the IRP and MA task ( ~ 1 μM and ~ 2 μM, respectively). In conclusion, the study showed that inner speech affects PaCO2, probably due to changes in respiration. Although a decrease in PaCO2 is causing cerebral vasoconstriction and could potentially explain the decreases of [O2Hb] and StO2 during inner speech, the changes in PaCO2 were significantly different between the three tasks (no change in PaCO2 for MA) but led to very similar changes in [O2Hb] and StO2. Thus, the cerebral changes cannot solely be explained by PaCO2.