Rule-based and stimulus-based cues bias auditory decisions via different computational and physiological mechanisms.

Expectations, such as those arising from either learned rules or recent stimulus regularities, can bias subsequent auditory perception in diverse ways. However, it is not well understood if and how these diverse effects depend on the source of the expectations. Further, it is unknown whether different sources of bias use the same or different computational and physiological mechanisms. We examined how rule-based and stimulus-based expectations influenced behavior and pupil-linked arousal, a marker of certain forms of expectation-based processing, of human subjects performing an auditory frequency-discrimination task. Rule-based cues consistently biased choices and response times (RTs) toward the more-probable stimulus. In contrast, stimulus-based cues had a complex combination of effects, including choice and RT biases toward and away from the frequency of recently presented stimuli. These different behavioral patterns also had: 1) distinct computational signatures, including different modulations of key components of a novel form of a drift-diffusion decision model and 2) distinct physiological signatures, including substantial bias-dependent modulations of pupil size in response to rule-based but not stimulus-based cues. These results imply that different sources of expectations can modulate auditory processing via distinct mechanisms: one that uses arousal-linked, rule-based information and another that uses arousal-independent, stimulus-based information to bias the speed and accuracy of auditory perceptual decisions.

The modulation of brain network integration and arousal during exploration.

There is growing interest in how neuromodulators shape brain networks. Recent neuroimaging studies provide evidence that brainstem arousal systems, such as the locus coeruleus-norepinephrine system (LC-NE), influence functional connectivity and brain network topology, suggesting they have a role in flexibly reconfiguring brain networks in order to adapt behavior and cognition to environmental demands. To date, however, the relationship between brainstem arousal systems and functional connectivity has not been assessed within the context of a task with an established relationship between arousal and behavior, with most prior studies relying on incidental variations in arousal or pharmacological manipulation and static brain networks constructed over long periods of time. These factors have likely contributed to a heterogeneity of effects across studies. To address these issues, we took advantage of the association between LC-NE-linked arousal and exploration to probe the relationships between exploratory choice, arousal-as measured indirectly via pupil diameter-and brain network dynamics. Exploration in a bandit task was associated with a shift toward fewer, more weakly connected modules that were more segregated in terms of connectivity and topology but more integrated with respect to the diversity of cognitive systems represented in each module. Functional connectivity strength decreased, and changes in connectivity were correlated with changes in pupil diameter, in line with the hypothesis that brainstem arousal systems influence the dynamic reorganization of brain networks. More broadly, we argue that carefully aligning dynamic network analyses with task designs can increase the temporal resolution at which behaviorally- and cognitively-relevant modulations can be identified, and offer these results as a proof of concept of this approach.

Specifying the domain-general resources that contribute to conceptual construction: Evidence from the child's acquisition of vitalist biology.

There are two dissociable processes that underlie knowledge acquisition: knowledge enrichment, which involves learning information that can be represented with one's current conceptual repertoire; and conceptual construction, which involves acquiring knowledge that can only be represented in terms of concepts one does not yet possess. Theory changes involving conceptual change require conceptual construction. The cognitive mechanisms underlying conceptual change are still poorly understood, though executive function capacities have been implicated. The present study concerns the domain-general resources drawn upon in one well-studied case of the construction of a new framework theory in early childhood: the framework theory of vitalist biology, the ontogenetically earliest theory in which the concepts life and death come to have biological content shared with adults. Eighty-three five- and six-year-old children were tested on a battery of tasks that probe central concepts of the vitalist theory, as well as on a battery of tests of domain-general capacities that may be implicated in development in this domain, including measures of knowledge enrichment, executive function, and fluid IQ. With variance in accumulated knowledge and in knowledge enrichment capacity controlled, two specific executive functions, shifting and inhibition, predicted children's progress in constructing the vitalist theory. In contrast, working memory and fluid IQ were not associated with the acquisition of vitalist biology. These results provide further evidence for the distinction between knowledge enrichment and conceptual construction and impose new constraints on accounts of the mechanisms underlying conceptual construction in this domain.

The role of domain-general cognitive resources in children's construction of a vitalist theory of biology.

Some episodes of learning are easier than others. Preschoolers can learn certain facts, such as "my grandmother gave me this purse," only after one or two exposures (easy to learn; fast mapping), but they require several years to learn that plants are alive or that the sun is not alive (hard to learn). One difference between the two kinds of knowledge acquisition is that hard cases often require conceptual construction, such as the construction of the biological concept alive, whereas easy cases merely involve forming new beliefs formulated over concepts the child already has (belief revision, a form of knowledge enrichment). We asked whether different domain-general cognitive resources support these two types of knowledge acquisition (conceptual construction and knowledge enrichment that supports fast mapping) by testing 82 6-year-olds in a pre-training/training/post-training study. We measured children's improvement in an episode involving theory construction (the beginning steps of acquisition of the framework theory of vitalist biology, which requires conceptual change) and in an episode involving knowledge enrichment alone (acquisition of little known facts about animals, such as the location of crickets' ears and the color of octopus blood). In addition, we measured children's executive functions and receptive vocabulary to directly compare the resources drawn upon in the two episodes of learning. We replicated and extended previous findings highlighting the differences between conceptual construction and knowledge enrichment, and we found that Executive Functions predict improvement on the Vitalism battery but not on the Fun Facts battery and that Receptive Vocabulary predicts improvement the Fun Facts battery but not on the Vitalism battery. This double dissociation provides new evidence for the distinction between the two types of knowledge acquisition, and bears on the nature of the learning mechanisms involved in each.

The Role of Frontostriatal Systems in Instructed Reinforcement Learning: Evidence From Genetic and Experimentally-Induced Variation.

Instructions have a powerful effect on learning and decision-making, biasing choice even in the face of disconfirming feedback. Detrimental biasing effects have been reported in a number of studies in which instruction was given prior to trial-and-error learning. Previous work has attributed individual differences in instructional bias to variations in prefrontal and striatal dopaminergic genes, suggesting a role for prefrontally-mediated cognitive control processes in biasing learning. The current study replicates and extends these findings. Human subjects performed a probabilistic reinforcement learning task after receiving inaccurate instructions about the quality of one of the options. In order to establish a causal relationship between prefrontal cortical mechanisms and instructional bias, we applied transcranial direct current stimulation over dorsolateral prefrontal cortex (anodal, cathodal, or sham) while subjects performed the task. We additionally genotyped subjects for the COMT Val158Met genetic polymorphism, which influences the breakdown of prefrontal dopamine, and for the DAT1/SLC6A3 variable number tandem repeat, which affects expression of striatal dopamine transporter. We replicated the finding that the COMT Met allele is associated with increased instructional bias and further demonstrated that variation in DAT1 has similar effects to variation in COMT, with 9-repeat carriers demonstrating increased bias relative to 10-repeat homozygotes. Consistent with increased top-down regulation of reinforcement learning, anodal subjects demonstrated greater bias relative to sham, though this effect was present only early in training. In contrast, there was no effect of cathodal stimulation. Finally, we fit computational models to subjects' data to better characterize the mechanisms underlying instruction bias. A novel choice bias model, in which instructions influence decision-making rather than learning, was found to best account for subjects' behavior. Overall, these data provide further evidence for the role of frontostriatal interactions in biasing instructed reinforcement learning, which adds to the growing literature documenting both costs and benefits of cognitive control.

Some consequences of normal aging for generating conceptual explanations: A case study of vitalist biology.

Accumulating evidence suggests that not only diseases of old age, but also normal aging, affect elderly adults' ability to draw on the framework theories that structure our abstract causal-explanatory knowledge, knowledge that we use to make sense of the world. One such framework theory, the cross-culturally universal vitalist biology, gives meaning to the abstract concepts life and death. Previous work shows that many elderly adults are animists, claiming that active, moving entities such as the sun and the wind are alive (Zaitchik & Solomon, 2008). Such responses are characteristic of young children, who, lacking an intuitive theory of biology, distinguish animals from non-animals on the basis of a theory of causal and intentional agency. What explains such childlike responses? Do the elderly undergo semantic degradation of their intuitive biological theory? Or do they merely have difficulty deploying their theory of biology in the face of interference from the developmentally prior agency theory? Here we develop an analytic strategy to answer this question. Using a battery of vitalist biology tasks, this study demonstrates-for the first time-that animism in the elderly is due to difficulty in deployment of the vitalist theory, not its degradation. We additionally establish some powerful downstream consequences of theory deployment difficulties, demonstrating that the elderly's use of the agency theory is not restricted to animist judgments-rather, it pervades their explicit reasoning about animates and inanimates. Extending the investigation, we identify specific cognitive mechanisms implicated in adult animism, finding that differences between young and elderly adults are mediated and moderated by differences in inhibition and shifting mechanisms. The analytic strategy developed here could help adjudicate between degradation and deployment in other conceptual domains and other populations.

Mapping the Parameter Space of tDCS and Cognitive Control via Manipulation of Current Polarity and Intensity.

In the cognitive domain, enormous variation in methodological approach prompts questions about the generalizability of behavioral findings obtained from studies of transcranial direct current stimulation (tDCS). To determine the impact of common variations in approach, we systematically manipulated two key stimulation parameters-current polarity and intensity-and assessed their impact on a task of inhibitory control (the Eriksen Flanker). Ninety participants were randomly assigned to one of nine experimental groups: three stimulation conditions (anode, sham, cathode) crossed with three intensity levels (1.0, 1.5, 2.0 mA). As participants performed the Flanker task, stimulation was applied over left dorsolateral prefrontal cortex (DLPFC; electrode montage: F3-RSO). The behavioral impact of these manipulations was examined using mixed effects linear regression. Results indicate a significant effect of stimulation condition (current polarity) on the magnitude of the interference effect during the Flanker; however, this effect was specific to the comparison between anodal and sham stimulation. Inhibitory control was therefore improved by anodal stimulation over the DLPFC. In the present experimental context, no reliable effect of stimulation intensity was observed, and we found no evidence that inhibitory control was impeded by cathodal stimulation. Continued exploration of the stimulation parameter space, particularly with more robustly powered sample sizes, is essential to facilitating cross-study comparison and ultimately working toward a reliable model of tDCS effects.