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BackgroundDopamine in prefrontal cortex (PFC) modulates core cognitive processes, notably working memory and executive control. Dopamine regulating genes and polymorphisms affecting PFC - including Catechol-O-Methyltransferase (COMT) Val158Met - are crucial to understanding the molecular genetics of cognitive function and dysfunction. A mechanistic account of the COMT Val158Met effect associates the Met allele with increased tonic dopamine transmission underlying maintenance of relevant information, and the Val allele with increased phasic dopamine transmission underlying the flexibility of updating new information. Thus, consistent with some earlier work, we predicted that Val carriers would display poorer performance when the maintenance component was taxed, while Met carriers would be less efficient when rapid updating was required.MethodsUsing a Stroop task that manipulated level of required cognitive stability and flexibility, we examined reaction time performance of patients with schizophrenia (n = 67) and healthy controls (n = 186) genotyped for the Val/Met variation.ResultsIn both groups we found a Met advantage for tasks requiring cognitive stability, but no COMT effect when a moderate level of cognitive flexibility was required, or when a conflict cost measure was calculated.ConclusionsOur results do not support a simple stability/flexibility model of dopamine COMT Val/Met effects and suggest a somewhat different conceptualization and experimental operationalization of these cognitive components.

How do speakers accommodate distracted listeners? Specifically, how does prosody change when speakers know that their addressees are multitasking? Speakers might use more acoustically prominent words for distracted addressees, to ensure that important information is communicated. Alternatively, speakers might disengage from the task and use less prominent pronunciations with distracted addressees. A further question is whether prosodic prominence changes globally or if there are effects specific to the most relevant information. We studied these effects in two instruction-giving experiments. Speakers instructed listeners to move objects to locations on a board. In the distraction condition, addressees were also completing a demanding secondary computer task; in the attentive condition they paid full attention. Results demonstrated that speakers modify their speech for distracted listeners, and in an instruction-giving task they specifically use more acoustically prominent (longer) pronunciations for distracted listeners. This effect was localised to the most task-relevant information: the object to be moved.

It is known that acoustic variation is influenced by the predictability of words and the information that they represent. What is unknown is whether acoustic reduction is also influenced by the referential predictability of thematic roles. We tested this question in two production experiments, where speakers heard a sentence with goal/source arguments, e.g., "Lady Mannerly [source] gave a painting to Sir Barnes [goal]," and described a picture of a subsequent action, e.g., "Sir Barnes threw it in the closet." We analyzed the duration of full NP descriptions used to refer to the pictured character. We found that duration was shorter for references to the goal than the source, but only in Experiment 2, where the timing of the stimuli encouraged the participant to plan their response incrementally, and not Experiment 1, where participants could pre-plan their responses. The strongest finding across both experiments was that response latency predicted duration, and latency was influenced by the predictability of thematic roles: Goal continuations had significantly shorter latencies. Together, these findings suggest that thematic role predictability does affect acoustic duration, and may be related to the time needed for utterance planning.