Transient neuronal suppression for exploitation of new sensory evidence

In noisy but stationary environments, decisions should be based on the temporal integration of sequentially sampled evidence. This strategy has been supported by many behavioral studies and is qualitatively consistent with neural activity in multiple brain areas. By contrast, decision-making in the face of non-stationary sensory evidence remains poorly understood. Here, we trained monkeys to identify and respond via saccade to the dominant color of a dynamically refreshed bicolor patch that becomes informative after a variable delay. Animals’ behavioral responses were briefly suppressed after evidence changes, and many neurons in the frontal eye field displayed a corresponding dip in activity at this time, similar to that frequently observed after stimulus onset but sensitive to stimulus strength. Generalized drift-diffusion models revealed consistency of behavior and neural activity with brief suppression of motor output, but not with pausing or resetting of evidence accumulation. These results suggest that momentary arrest of motor preparation is important for dynamic perceptual decision making.

Decision prioritization and causal reasoning in decision hierarchies

From cooking a meal to finding a route to a destination, many real life decisions can be decomposed into a hierarchy of sub-decisions. In a hierarchy, choosing which decision to think about requires planning over a potentially vast space of possible decision sequences. To gain insight into how people decide what to decide on, we studied a novel task that combines perceptual decision making, active sensing and hierarchical and counterfactual reasoning. Human participants had to find a target hidden at the lowest level of a decision tree. They could solicit information from the different nodes of the decision tree to gather noisy evidence about the target’s location. Feedback was given only after errors at the leaf nodes and provided ambiguous evidence about the cause of the error. Despite the complexity of task (with 107 latent states) participants were able to plan efficiently in the task. A computational model of this process identified a small number of heuristics of low computational complexity that accounted for human behavior. These heuristics include making categorical decisions at the branching points of the decision tree rather than carrying forward entire probability distributions, discarding sensory evidence deemed unreliable to make a choice, and using choice confidence to infer the cause of the error after an initial plan failed. Plans based on probabilistic inference or myopic sampling norms could not capture participants’ behavior. Our results show that it is possible to identify hallmarks of heuristic planning with sensing in human behavior and that the use of tasks of intermediate complexity helps identify the rules underlying human ability to reason over decision hierarchies.

A rational account of the repulsion effect

The attraction effect occurs when the presence of an inferior option (the decoy) increases the attractiveness of the option that dominates it (the target). Despite its prominence in behavioral science, recent evidence points to the puzzling existence of the opposite phenomenon—a repulsion effect. In this paper, we formally develop and experimentally test a normative account of the repulsion effect. Our theory is based on the idea that the true values of options are uncertain and must be inferred from available information, which includes the properties of other options. A low-value decoy can signal that the target also has low value when both are believed to be generated by a similar process. We formalize this logic using a hierarchical Bayesian cognitive model that makes predictions about how the strength of the repulsion effect should vary with statistical properties of the decision problem. This theory may help account for several documented phenomena linked to the repulsion effect across both economic and perceptual decision making, as well as new experimental data. Our results shed light on the key drivers of context-dependent judgment across multiple domains and sharpen our understanding of when decoys can be detrimental.

Sampling motion trajectories during hippocampal theta sequences

Efficient planning in complex environments requires that uncertainty associated with current inferences and possible consequences of forthcoming actions is represented. Representation of uncertainty has been established in sensory systems during simple perceptual decision making tasks but it remains unclear if complex cognitive computations such as planning and navigation are also supported by probabilistic neural representations. Here we capitalized on gradually changing uncertainty along planned motion trajectories during hippocampal theta sequences to capture signatures of uncertainty representation in population responses. In contrast with prominent theories, we found no evidence of encoding parameters of probability distributions in the momentary population activity recorded in an open-field navigation task in rats. Instead, uncertainty was encoded sequentially by sampling motion trajectories randomly in subsequent theta cycles from the distribution of potential trajectories. Our analysis is the first to demonstrate that the hippocampus is well equipped to contribute to optimal planning by representing uncertainty.

Divided attention impairs detection of simple visual features

Covert spatial attention allows us to prioritize processing at relevant locations. There is substantial evidence that perception is poorer when attention is distributed across multiple locations than when attention is focused on a single location. However, recent work suggests that may not always be the case: divided attention does not appear to impair detection of simple visual features that are represented in primary visual cortex. Here, we re-examined this possibility. In two experiments, observers detected a simple target (a vertical Gabor), and we manipulated whether attention was focused at one location (focal-cue condition) or distributed across two locations (distributed-cue condition). In Experiment 1, targets could appear independently at each location. Thus, observers needed to judge target presence for each location separately in the distributed-cue condition. Under these conditions, we found a robust cost of dividing attention. In this experiment, the cost of dividing attention could reflect either a limit in perceptual processing or a limit in decision making. Therefore, in Experiment 2, we simplified the task to more directly test whether dividing attention impairs perceptual processing of the target. Specifically, only one target could appear on each trial, such that observers made the exact same decision in both conditions (“was a target present?”). Here, we found a marginal cost of dividing attention on performance, that was weaker than the cost in Experiment 1. Together, our results suggest that divided attention does impair detection of simple visual features, but that this cost is primarily due to limits in post-perceptual decision making.

Speed Is Associated With, But Does Not Cause, Polarization in the Moral Evaluation of Real-World Images

In human perceptual decision-making, the speed-accuracy tradeoff establishes a causal link between urgency and reduced accuracy. Less is known about how urgency affects the moral evaluation of visual images. Here, we asked participants to give ratings for a diverse set of real-world images on a continuous scale from -10 (“very immoral”) to +10 (“very moral”). We used a cueing procedure to inform the participants on a trial-by-trial basis whether they could make a Self-Paced (SP) evaluation or whether they had to perform a Time-Limited (TL) evaluation within 2 seconds. In the SP condition, fast responses were associated with more extreme evaluations. Compared to the SP condition, the responses in the TL condition were much faster, indicating that our urgency manipulation was successful. However, comparing the SP versus TL conditions, we found no significant differences in the moral evaluation of the real-world images. The data indicated that, while speed is associated with polarization, urgency does not cause participants to make more extreme evaluations. Instead, the correlation between speed and polarization likely reflects the ease of processing. Images that are obviously moral or immoral are categorized faster and given more extreme evaluations than images for which the moral interpretation is uncertain.

Early neural activity changes associated with visual conscious perception

The neural mechanisms of visual conscious perception have been investigated for decades. However, the spatiotemporal dynamics associated with the earliest neural responses following consciously perceived stimuli are still poorly understood. Using a dataset of intracranial EEG recordings, the current study aims to investigate the neural activity changes associated with the earliest stages of visual conscious perception. Subjects (N=10, 1,693 grey matter electrode contacts) completed a continuous performance task in which individual letters were presented in series and subjects were asked to press a button when they saw a target letter. Broadband gamma power (40-115Hz) dynamics were analyzed in comparison to baseline prior to stimulus and contrasted for target trials with button presses and non-target trials without button presses. Regardless of event type, we observed early gamma power changes within 30-150 ms from stimulus onset in a network including increases in bilateral occipital, fusiform, frontal (including frontal eye fields), and medial temporal cortex, increases in left lateral parietal-temporal cortex, and decreases in the right anterior medial occipital cortex. No significant differences were observed between target and non-target stimuli until >150 ms post-stimulus, when we saw greater gamma power increases in left motor and premotor areas, suggesting a possible role of these later signals in perceptual decision making and/or motor responses with the right hand. The early gamma power findings suggest a broadly distributed cortical visual detection network that is engaged at early times tens of milliseconds after signal transduction from the retina.

Trial-by-trial fluctuations in amygdala activity track motivational enhancement of desirable sensory evidence during perceptual decision-making

People are biased towards seeing outcomes that they are motivated to see. For example, sports fans of opposing teams often perceive the same ambiguous foul in favor of the team they support. Here, we test the hypothesis that amygdala-dependent allocation of visual attention facilitates motivational biases in perceptual decision-making. Human participants were rewarded for correctly categorizing an ambiguous image into one of two categories while undergoing fMRI. On each trial, we used a financial bonus to motivate participants to see one category over another. The reward maximizing strategy was to perform the categorization task accurately, but participants were biased towards categorizing the images as the category we motivated them to see. Heightened amygdala activity preceded motivation consistent categorizations, and participants with higher amygdala activation exhibited stronger motivational biases in their perceptual reports. Trial-by-trial amygdala activity was associated with stronger enhancement of neural activity encoding desirable percepts in sensory cortices, suggesting that amygdala-dependent effects on perceptual decisions arose from biased sensory processing. Analyses using a drift diffusion model provide converging evidence that trial-by-trial amygdala activity was associated with stronger motivational biases in the accumulation of sensory evidence. Prior work examining biases in perceptual decision-making have focused on the role of frontoparietal regions. Our work highlights an important contribution of the amygdala. When people are motivated to see one outcome over another, the amygdala biases perceptual decisions towards those outcomes.Significance StatementForming accurate perceptions of the environment is essential for adaptive behavior. People however are biased towards seeing what they want to see, giving rise to inaccurate perceptions and erroneous decisions. Here, we combined behavior, modeling, and fMRI to show that the bias towards seeing desirable percepts is related to trial-by-trial fluctuations in amygdala activity. In particular, during moments with higher amygdala activity, sensory processing is biased in favor of desirable percepts, such that participants are more likely to see what they want to see. These findings highlight the role of the amygdala in biasing visual perception, and shed light on the neural mechanisms underlying the influence of motivation and reward on how people decide what they see.

Proactive and reactive accumulation-to-bound processes compete during perceptual decisions

Standard models of perceptual decision-making postulate that a response is triggered in reaction to stimulus presentation when the accumulated stimulus evidence reaches a decision threshold. This framework excludes however the possibility that informed responses are generated proactively at a time independent of stimulus. Here, we find that, in a free reaction time auditory task in rats, reactive and proactive responses coexist, suggesting that choice selection and motor initiation, commonly viewed as serial processes, are decoupled in general. We capture this behavior by a novel model in which proactive and reactive responses are triggered whenever either of two competing processes, respectively Action Initiation or Evidence Accumulation, reaches a bound. In both types of response, the choice is ultimately informed by the Evidence Accumulation process. The Action Initiation process readily explains premature responses, contributes to urgency effects at long reaction times and mediates the slowing of the responses as animals get satiated and tired during sessions. Moreover, it successfully predicts reaction time distributions when the stimulus was either delayed, advanced or omitted. Overall, these results fundamentally extend standard models of evidence accumulation in decision making by showing that proactive and reactive processes compete for the generation of responses.

Response-locked classification image analysis of perceptual decision making in contrast detection

In many situations, humans make decisions based on serially sampled information through the observation of visual stimuli. To quantify the critical information used by the observer in such dynamic decision making, we here applied a classification image (CI) analysis locked to the observer's reaction time (RT) in a simple detection task for a luminance target that gradually appeared in dynamic noise. We found that the response-locked CI shows a spatiotemporally biphasic weighting profile that peaked about 300 ms before the response, but this profile substantially varied depending on RT; positive weights dominated at short RTs and negative weights at long RTs. We show that these diverse results are explained by a simple perceptual decision mechanism that accumulates the output of the perceptual process as modelled by a spatiotemporal contrast detector. We discuss possible applications and the limitations of the response-locked CI analysis.