Proactive response preparation contributes to contingency learning: novel evidence from force-sensitive keyboards.

Contingency learning can involve learning that the identity of one stimulus in a sequence predicts the identity of the next stimulus. It remains unclear, however, whether such learning speeds responses to the next stimulus only by reducing the threshold for triggering the expected response after stimulus onset or also by preparing the expected response before stimulus onset. To distinguish between these competing accounts, we manipulated the probabilities with which each of two prime arrows (Left and Right) were followed by each of two probe arrows (Up and Down) in a prime-probe task while using force-sensitive keyboards to monitor sub-threshold finger force. Consistent with the response preparation account, two experiments revealed greater force just before probe onset on the response key corresponding to the direction in which the probe was more (versus less) likely to point (e.g., Up vs. Down). Furthermore, mirroring sequential contingency effects in behavior, this pre-probe force effect vanished after a single low-probability trial. These findings favor the response preparation account over the threshold only account. They also suggest the possibility that contingency learning in our tasks indexes trial-by-trial expectations regarding the utility of the prime for predicting the upcoming probe.

Network segregation varies with neural distinctiveness in sensorimotor cortex.

Normal aging is associated with declines in sensorimotor function. Previous studies have linked age-related behavioral declines to decreases in neural differentiation (i.e., dedifferentiation), including decreases in the distinctiveness of neural activation patterns and in the segregation of large-scale neural networks at rest. However, no studies to date have explored the relationship between these two neural measures and whether they explain the same aspects of behavior. To investigate these issues, we collected a battery of sensorimotor behavioral measures in older and younger adults and estimated (a) the distinctiveness of neural representations in sensorimotor cortex and (b) sensorimotor network segregation in the same participants. Consistent with prior findings, sensorimotor representations were less distinct and sensorimotor resting state networks were less segregated in older compared to younger adults. We also found that participants with the most distinct sensorimotor representations exhibited the most segregated sensorimotor networks. However, only sensorimotor network segregation was associated with individual differences in sensorimotor performance, particularly in older adults. These novel findings link network segregation to neural distinctiveness, but also suggest that network segregation may play a larger role in maintaining sensorimotor performance with age.

Sensorimotor network segregation declines with age and is linked to GABA and to sensorimotor performance.

Aging is typically associated with declines in sensorimotor performance. Previous studies have linked some age-related behavioral declines to reductions in network segregation. For example, compared to young adults, older adults typically exhibit weaker functional connectivity within the same functional network but stronger functional connectivity between different networks. Based on previous animal studies, we hypothesized that such reductions of network segregation are linked to age-related reductions in the brain's major inhibitory transmitter, gamma aminobutyric acid (GABA). To investigate this hypothesis, we conducted graph theoretical analyses of resting state functional MRI data to measure sensorimotor network segregation in both young and old adults. We also used magnetic resonance spectroscopy to measure GABA levels in the sensorimotor cortex and collected a battery of sensorimotor behavioral measures. We report four main findings. First, relative to young adults, old adults exhibit both less segregated sensorimotor brain networks and reduced sensorimotor GABA levels. Second, less segregated networks are associated with lower GABA levels. Third, less segregated networks and lower GABA levels are associated with worse sensorimotor performance. Fourth, network segregation mediates the relationship between GABA and performance. These findings link age-related differences in network segregation to age-related differences in GABA levels and sensorimotor performance. More broadly, they suggest a neurochemical substrate of age-related dedifferentiation at the level of large-scale brain networks.

Neural distinctiveness declines with age in auditory cortex and is associated with auditory GABA levels.

Neural activation patterns in the ventral visual cortex in response to different categories of visual stimuli (e.g., faces vs. houses) are less selective, or distinctive, in older adults than in younger adults, a phenomenon known as age-related neural dedifferentiation. In this study, we investigated whether neural dedifferentiation extends to the auditory cortex. Inspired by previous animal work, we also investigated whether individual differences in GABA are associated with individual differences in neural distinctiveness in humans. 20 healthy young adults (ages 18-29) and 23 healthy older adults (over 65) completed a functional magnetic resonance imaging (fMRI) scan, during which neural activity was estimated while they listened to music and foreign speech. GABA levels in the auditory, ventrovisual and sensorimotor cortex were estimated in the same individuals in a separate magnetic resonance spectroscopy (MRS) scan. Relative to the younger adults, the older adults exhibited both (1) less distinct activation patterns for music vs. speech stimuli and (2) lower GABA levels in the auditory cortex. Also, individual differences in auditory GABA levels (but not ventrovisual or sensorimotor GABA levels) were associated with individual differences in neural distinctiveness in the auditory cortex in the older adults. These results demonstrate that age-related neural dedifferentiation extends to the auditory cortex and suggest that declining GABA levels may play a role in neural dedifferentiation in older adults.

Michigan Neural Distinctiveness (MiND) study protocol: investigating the scope, causes, and consequences of age-related neural dedifferentiation.

BACKGROUND: Aging is often associated with behavioral impairments, but some people age more gracefully than others. Why? One factor that may play a role is individual differences in the distinctiveness of neural representations. Previous research has found that neural activation patterns in visual cortex in response to different visual stimuli are often more similar (i.e., less distinctive) in older vs. young participants, a phenomenon referred to as age-related neural dedifferentiation. Furthermore, older people whose neural representations are less distinctive tend to perform worse on a wide range of behavioral tasks. The Michigan Neural Distinctiveness (MiND) project aims to investigate the scope of neural dedifferentiation (e.g., does it also occur in auditory, motor, and somatosensory cortex?), one potential cause (age-related reductions in the inhibitory neurotransmitter gamma-aminobutyric acid (GABA)), and the behavioral consequences of neural dedifferentiation. This protocol paper describes the study rationale and methods being used in complete detail, but not the results (data collection is currently underway). METHODS: The MiND project consists of two studies: the main study and a drug study. In the main study, we are recruiting 60 young and 100 older adults to perform behavioral tasks that measure sensory and cognitive function. They also participate in functional MRI (fMRI), MR spectroscopy, and diffusion weighted imaging sessions, providing data on neural distinctiveness and GABA concentrations. In the drug study, we are recruiting 25 young and 25 older adults to compare neural distinctiveness, measured with fMRI, after participants take a placebo or a benzodiazepine (lorazepam) that should increase GABA activity. DISCUSSION: By collecting multimodal imaging measures along with extensive behavioral measures from the same subjects, we are linking individual differences in neurochemistry, neural representation, and behavioral performance, rather than focusing solely on group differences between young and old participants. Our findings have the potential to inform new interventions for age-related declines. TRIAL REGISTRATION: This study was retrospectively registered with the ISRCTN registry on March 4, 2019. The registration number is ISRCTN17266136 .

Behavioral and neural correlates of disrupted orienting attention in posttraumatic stress disorder.

Prior work has revealed that posttraumatic stress disorder (PTSD) is associated with altered (a) attentional performance and (b) resting-state functional connectivity (rsFC) in brain networks linked to attention. Here, we sought to characterize and link these behavioral and brain-based alterations in the context of Posner and Peterson's tripartite model of attention. Male military veterans with PTSD (N = 49; all deployed to Iraq or Afghanistan) and healthy age-and-gender-matched community controls (N = 26) completed the Attention Network Task. A subset of these individuals (36 PTSD and 21 controls) also underwent functional magnetic resonance imaging (fMRI) to assess rsFC. The behavioral measures revealed that the PTSD group was impaired at disengaging spatial attention, relative to the control group. FMRI measures further revealed that, relative to the control group, the PTSD group exhibited greater rsFC between the salience network and (a) the default mode network, (b) the dorsal attention network, and (c) the ventral attention network. Moreover, problems with disengaging spatial attention increased the rsFC between the networks above in the control group, but not in the PTSD group. The present findings link PTSD to both altered orienting of spatial attention and altered relationships between spatial orienting and functional connectivity involving the salience network. Interventions that target orienting and disengaging spatial attention may be a new avenue for PTSD research.

Congruency sequence effects and previous response times: conflict adaptation or temporal learning?

In the present study, we followed up on a recent report of two experiments in which the congruency sequence effect-the reduction of the congruency effect after incongruent relative to congruent trials in Stroop-like tasks-was observed without feature repetition or contingency learning confounds. Specifically, we further scrutinized these data to determine the plausibility of a temporal learning account as an alternative to the popular conflict adaptation account. To this end, we employed a linear mixed effects model to investigate the role of previous response time in producing the congruency sequence effect, because previous response time is thought to influence temporal learning. Interestingly, slower previous response times were associated with a reduced current-trial congruency effect, but only when the previous trial was congruent. An adapted version of the parallel episodic processing (PEP) model was able to fit these data if it was additionally assumed that attention "wanders" during different parts of the experiment (e.g., due to fatigue or other factors). Consistent with this assumption, the magnitude of the congruency effect was correlated across small blocks of trials. These findings demonstrate that a temporal learning mechanism provides a plausible account of the congruency sequence effect.

Both congruent and incongruent trials drive the congruency sequence effect: Novel support for an episodic retrieval view of adaptive control in the prime-probe task.

The congruency effect in Stroop-like tasks-a popular measure of distraction-is smaller after incongruent relative to congruent trials. However, it is unclear whether this congruency sequence effect (CSE)-a popular index of coping with distraction-reflects adjustments of control after congruent trials, incongruent trials, or both. The episodic retrieval account of the CSE posits adjustments of control after both congruent and incongruent trials. In this account, retrieving a memory of the previous trial's congruency (i.e., congruent or incongruent) biases control processes to prepare for an upcoming trial with the same congruency (i.e., congruent or incongruent). In contrast, the default setting account posits adjustments of control after a single trial type. For example, control processes might increase inhibition of the response cued by the distractor after incongruent trials but make no adjustments after congruent trials. To distinguish between these accounts for the first time while (a) using long distractor-target intervals and (b) excluding prevalent feature integration and contingency learning confounds, we employed a confound-minimized prime-probe task with neutral trials. We usually observed adjustments of control after both trial types. Furthermore, whether the reduction of the congruency effect after incongruent trials indexed (a) inhibition of the distractor-congruent response or (b) activation of the distractor-incongruent response depended on whether the distractor and target were same-sized or different-sized, respectively. These findings favor the episodic retrieval account of the CSE over the default setting account. They also indicate that "low-level" stimulus properties may influence the nature of "high-level" control adjustments. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Modulations of response activation contribute to block-wide control: Evidence from proportion congruency effects in the prime-probe task.

Distractor-related congruency effects are smaller in blocks of mostly incongruent (vs. mostly congruent) trials. It remains unclear, though, how control processes produce this proportion congruency effect (PCE). The attentional shift account posits that experiencing conflict more frequently in mostly incongruent (vs. mostly congruent) blocks biases control processes to shift attention away from the distractor. The response modulation account posits that, if participants identify the distractor before the target, control processes use the distractor's identity to prepare a congruent response in mostly congruent blocks and/or an incongruent response in mostly incongruent blocks. We conducted four experiments (N = 192) to investigate whether a modulation of response activation contributes to the PCE in the prime-probe task. We observed a larger PCE when the prime/distractor appeared 166 ms before (vs. simultaneously with) the probe/target (Experiment 1) and a PCE without an overall congruency effect at a longer, 933-ms stimulus onset asynchrony (SOA; Experiment 2). Critically, the latter PCE was associated with a negative congruency effect in mostly incongruent blocks, consistent with a modulation of response activation but not a shift of attention. Finally, in a modified prime-probe task, wherein participants respond to each stimulus before the next one appears (1,133 ms SOA), we observed analogous PCEs and negative congruency effects (Experiment 3) and a PCE-like effect in response force just before the probe appeared (Experiment 4). These findings indicate an independent contribution of control processes that modulate response activation to the PCE at long prime-probe SOAs, which extends beyond minimizing distraction from irrelevant stimuli. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

The binary structure of event files generalizes to abstract features: A nonhierarchical explanation of task set boundaries for the congruency sequence effect.

Current views posit that forming and retrieving memories of ongoing events influences action control. However, the organizational structure of these memories, or event files, remains unclear. The hierarchical coding view posits a hierarchical structure, wherein task sets occupy a high level of the hierarchy. Here, the contents of an event file can be retrieved only if the task set repeats. In contrast, the binary coding view posits a nonhierarchical structure, which consists of a collection of independent, binary bindings between different feature pairs. In this view, repeating an abstract feature from a previous event (e.g., the previous trial's S-R mapping) triggers the retrieval of the associated feature from the same binding (e.g., the previous trial's congruency) even if the task set changes. To distinguish between these views, we investigated the nature of task set boundaries for the congruency sequence effect (CSE), an index of adaptive control that reflects event file formation and retrieval. Specifically, we investigated whether or not a CSE appears when the task set changes but the previous trial's S-R mapping repeats. Three experiments involving a cross-modal prime-probe task yielded a CSE under these conditions and ruled out alternative explanations. These findings show that the typical binary structure of event files generalizes from concrete features (e.g., colors and locations) to abstract features (e.g., S-R mappings and task sets). Therefore, contrary to the hierarchical coding view, they provide a nonhierarchical explanation of task set boundaries for the CSE. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Effect-less? Event-files are not terminated by distal action effects.

Event-files that bind features of stimuli, responses, and action effects figure prominently in contemporary views of action control. When a previous feature repeats, a previous event-file is retrieved and can influence current performance. It is unclear, however, what terminates an event-file. A tacit assumption is that registering the distal (e.g., visual or auditory) sensory consequences of an action (i.e., the "action effect") terminates the event-file, thereby making it available for retrieval. We tested three different action-effect conditions (no distal action effect, visual action effect, or auditory action effect) in the same stimulus-response (S-R) binding task and observed no modulation of S-R binding effects. Instead, there were comparably large binding effects in all conditions. This suggests that proximal (e.g., somatosensory, proprioceptive) action effects terminate event-files independent of distal (e.g., visual, auditory) action effects or that the role event-file termination plays for S-R binding effects needs to be corrected. We conclude that current views of action control require further specification.

Comparing partial repetition costs in two- and four-choice tasks: Evidence for abstract relational codes.

Responses are slower in two-choice tasks when either a previous stimulus feature or the previous response repeats than when all features repeat or all features change. Current views of action control posit that such partial repetition costs (PRCs) index the time to update a prior "binding" between a stimulus feature and the response or to resolve processing conflicts between retrieved and current features. However, violating a heuristic that stimulus feature repetitions and changes "signal" repetitions or changes of the previous response, respectively, may also contribute to such costs. To determine whether such relational codes affect performance, we compared PRCs in two- and four-choice tasks. While a stimulus feature repetition signals a response repetition in both tasks, a stimulus feature change signals a specific alternative response only in a two-choice task. Consistent with the signaling hypothesis, we observed similar complete repetition benefits in the two- and four-choice tasks but smaller complete change benefits in the four-choice task. We also investigated whether the smaller complete change benefit in the four-choice task-that is, the signaling effect-varies with the validity of the signal in the previous trial. In all four experiments, we observed a larger signaling effect after trials in which stimulus changes or repetitions corresponded to response changes or repetitions, respectively, than after trials in which stimulus changes did not correspond with response changes. We conclude that signaling contributes to PRCs, which indicates that bindings include relational codes. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Response-repetition costs in task switching do not index a simple response-switch bias: Evidence from manipulating the number of response alternatives.

Response repetitions aid performance when a task repeats but impair performance when a task switches. Although this interaction is robust, theoretical accounts remain controversial. Here, we used an un-cued, predictable task-switching paradigm with univalent targets to explore whether a simple bias to switch the response when the task switches can explain the interaction. In Experiment 1A (n = 40), we replicated the basic interaction in a two-choice task. In Experiment 1B (n = 60), we observed the same interaction in a three-choice task, wherein a bias to switch the response when the task switches cannot prime a specific alternative response because both remaining response alternatives are equally likely. Exploratory comparisons revealed a larger interaction between task repetition and response repetition in the three-choice task than in the two-choice task for mean response time (RT) and the opposite pattern for mean error rate (ER). Critically, in the three-choice task, response-repetition costs in task switches were significant in both RT and ER. Since a bias to switch the response cannot prime a specific response alternative in a three-choice task, we conclude that such a bias cannot account for response-repetition costs in task-switch trials.

Partial repetition costs index a mixture of binding and signaling.

People respond more slowly in two-choice tasks when either a previous stimulus feature or the previous response repeats in partial repetition trials than when (a) both repeat in complete repetition trials or (b) both alternate in complete alternation trials. The binding account posits that such partial repetition costs index a memory-retrieval conflict, which occurs because partial repetition trials trigger the retrieval of a previous stimulus feature or response that conflicts with a current stimulus feature or response. However, such costs may additionally reflect a simple decision-making heuristic that uses the repetition or alternation of a previous stimulus feature as a "signal" to bias response selection toward a repetition or an alternation of the previous response. To determine whether signaling contributes to partial repetition costs, we employed a four-choice task. Here, a stimulus feature repetition still signals a response repetition, but a stimulus feature alternation does not signal which of the three remaining responses to make. Consistent with an influence of signaling, we sometimes observed complete repetition advantages without complete alternation advantages. Exploratory analyses further revealed that partial repetition costs measured more broadly were smaller in the four-choice task than in a matched two-choice task. These findings suggest that partial repetition costs index a mixture of binding and signaling.

Altruistic responses to the most vulnerable involve sensorimotor processes.

Introduction: Why do people help strangers? Prior research suggests that empathy motivates bystanders to respond to victims in distress. However, this work has revealed relatively little about the role of the motor system in human altruism, even though altruism is thought to have originated as an active, physical response to close others in immediate need. We therefore investigated whether a motor preparatory response contributes to costly helping. Methods: To accomplish this objective, we contrasted three charity conditions that were more versus less likely to elicit an active motor response, based on the Altruistic Response Model. These conditions described charities that (1) aided neonates versus adults, (2) aided victims requiring immediate versus preparatory support, and (3) provided heroic versus nurturant aid. We hypothesized that observing neonates in immediate need would elicit stronger brain activation in motor-preparatory regions. Results: Consistent with an evolutionary, caregiving-based theory of altruism, participants donated the most to charities that provided neonates with immediate, nurturant aid. Critically, this three-way donation interaction was associated with increased BOLD signal and gray matter volume in motor-preparatory regions, which we identified in an independent motor retrieval task. Discussion: These findings advance the field of altruism by shifting the spotlight from passive emotional states toward action processes that evolved to protect the most vulnerable members of our group.

Heightened activity in a key region of the ventral attention network is linked to reduced activity in a key region of the dorsal attention network during unexpected shifts of covert visual spatial attention.

To enable unexpected shifts of covert visual spatial attention, a ventral attention network is thought to dampen activity in a dorsal attention network that maintains the current focus of attention. However, direct evidence to support this view is scarce. In the present study, we investigated this hypothesis by asking healthy young adults to perform a covert visual spatial attention task while their brain activity was recorded with functional magnetic resonance imaging (fMRI). In each trial, participants discriminated the orientation of a target-colored letter in the cued visual field (valid trials) or, occasionally, in the uncued visual field (invalid trials). Consistent with prior work, the ventral attention network was more active in invalid trials than in valid trials. Most importantly, functional connectivity analyses revealed that an increase of activity in the right inferior frontal gyrus (a key region of the ventral attention network) was linked to smaller increases of activity in (a) the right inferior parietal lobe (a key region of the dorsal attention network) and (b) the left dorsolateral prefrontal cortex and dorsal anterior cingulate cortex (other regions enabling the control of attention) in invalid trials, relative to valid trials. These findings provide novel support for the view that key regions of the ventral attention network help to enable unexpected shifts of covert visual spatial attention by dampening activity in brain regions that participate in maintaining the current focus of attention.

Removing the effect of response time on brain activity reveals developmental differences in conflict processing in the posterior medial prefrontal cortex.

In functional magnetic resonance imaging (fMRI) studies, researchers often attempt to ensure that group differences in brain activity are not confounded with group differences in mean reaction time (RT). However, even when groups are matched for performance, they may differ in terms of the RT-BOLD relationship: the degree to which brain activity varies with RT on a trial-by-trial basis. Group activation differences might therefore be influenced by group differences in the relationship between brain activity and time on task. Here, we investigated whether correcting for this potential confound alters group differences in brain activity. Specifically, we reanalyzed data from a functional MRI study of response conflict in children and adults, in which conventional analyses indicated that conflict-related activity did not differ between groups. We found that the RT-BOLD relationship was weaker in children than in adults. Consequently, after removing the effect of RT on brain activity, children exhibited greater conflict-related activity than adults in both the posterior medial prefrontal cortex and the right dorsolateral prefrontal cortex. These results identify the RT-BOLD relationship as an important potential confound in fMRI studies of group differences. They also suggest that the magnitude of the RT-BOLD relationship may be a useful biomarker of brain maturity.

The influence of response conflict on voluntary task switching: a novel test of the conflict monitoring model.

The conflict monitoring model of cognitive control posits that response conflict triggers a top-down enhancement of a task's representation in working memory. In the present study, we conducted a novel test of the conflict monitoring model using a voluntary task switching paradigm. We predicted that a task's representation would be enhanced following events associated with high response conflict (i.e., incongruent trials and incorrect responses), leading participants to voluntarily choose to repeat that task more often after these events than after events associated with low response conflict (i.e., congruent trials and correct responses). In two experiments, performance following incongruent trials was consistent with the conflict monitoring model. However, performance following incorrect trials did not fit with the model's predictions. These findings provide novel support for the conflict monitoring model while revealing new effects of incorrect trials that the model cannot explain.

Rethinking attentional reset: Task sets determine the boundaries of adaptive control.

Adaptive control processes that minimise distraction often operate in a context-specific manner. For example, they may minimise distraction from irrelevant conversations during a lecture but not in the hallway afterwards. It remains unclear, however, whether (a) salient perceptual features or (b) task sets based on such features serve as contextual boundaries for adaptive control in standard distractor-interference tasks. To distinguish between these possibilities, we manipulated whether the structure of a standard, visual distractor-interference task allowed (Experiment 1) or did not allow (Experiment 2) participants to associate salient visual features (i.e., colour patches and colour words) with different task sets. We found that changing salient visual features across consecutive trials reduced a popular measure of adaptive control in distractor-interference tasks-the congruency sequence effect (CSE)-only when the task structure allowed participants to associate these visual features with different task sets. These findings extend prior support for the task set hypothesis from somewhat atypical cross-modal tasks to a standard unimodal task. In contrast, they pose a challenge to an alternative "attentional reset" hypothesis, and related views, wherein changing salient perceptual features always results in a contextual boundary for the CSE.

Spatial attention influences trial-by-trial relationships between response time and functional connectivity in the visual cortex.

Variations of response time (RT) in selective attention tasks are often associated with variations of activity and functional connectivity in sensory cortices that process relevant stimuli. Here, we investigated whether such relationships are influenced by spatial attention. To investigate this hypothesis, we asked fourteen healthy adults to perform a covert spatial attention task, which made use of bilateral stimulus displays, while we recorded their brain activity using functional magnetic resonance imaging (fMRI). As expected, activity in the middle occipital gyrus increased when spatial attention was directed to the contralateral (versus the ipsilateral) visual field. Surprisingly, variations of RT were not associated with variations in the magnitude of this attentional enhancement. As predicted, however, they were linked to opposing variations of functional connectivity between middle occipital regions contralateral (but not ispilateral) to the attended visual field and the left fusiform gyrus, which is thought to figure prominently in the perceptual processing of visually presented letters. These findings suggest that trial-by-trial variations of RT reflect, at least partially, trial-by-trial variations in the extent to which spatial attention enhances functional connectivity between sensory regions that process relevant stimuli.