Anne E. Urai

Conscious Vision Proceeds from Global to Local Content in Goal-Directed Tasks and Spontaneous Vision

The reverse hierarchy theory (Hochstein and Ahissar, 2002) makes strong, but so far untested, predictions on conscious vision. In this theory, local details encoded in lower-order visual areas are unconsciously processed before being automatically and rapidly combined into global information in higher-order visual areas, where conscious percepts emerge. Contingent on current goals, local details can afterward be consciously retrieved. This model therefore predicts that (1) global information is perceived faster than local details, (2) global information is computed regardless of task demands during early visual processing, and (3) spontaneous vision is dominated by global percepts. We designed novel textured stimuli that are, as opposed to the classic Navons letters, truly hierarchical (i.e., where global information is solely defined by local information but where local and global orientations can still be manipulated separately). In line with the predictions, observers were systematically faster reporting global than local properties of those stimuli. Second, global information could be decoded from magneto-encephalographic data during early visual processing regardless of task demands. Last, spontaneous subjective reports were dominated by global information and the frequency and speed of spontaneous global perception correlated with the accuracy and speed in the global task. No such correlation was observed for local information. We therefore show that information at different levels of the visual hierarchy is not equally likely to become conscious; rather, conscious percepts emerge preferentially at a global level. We further show that spontaneous reports can be reliable and are tightly linked to objective performance at the global level. SIGNIFICANCE STATEMENT Is information encoded at different levels of the visual system (local details in low-level areas vs global shapes in high-level areas) equally likely to become conscious? We designed new hierarchical stimuli and provide the first empirical evidence based on behavioral and MEG data that global information encoded at high levels of the visual hierarchy dominates perception. This result held both in the presence and in the absence of task demands. The preferential emergence of percepts at high levels can account for two properties of conscious vision, namely, the dominance of global percepts and the feeling of visual richness reported independently of the perception of local details.

An Action-Independent Signature of Perceptual Choice in the Human Brain

Imagine walking on a busy street with a large number of people approaching you. To successfully navigate through such a moving crowd and avoid bumping into other pedestrians, you must continuously collect sensory information to decide whether to swerve left or right. But how exactly does your brain

Choice history biases subsequent evidence accumulation

Perceptual choices depend not only on the current sensory input, but also on the behavioral context. An important contextual factor is the history of one’s own choices. Choice history often strongly biases perceptual decisions, and leaves traces in the activity of brain regions involved in decision processing. Yet, it remains unknown how such history signals shape the dynamics of later decision formation. Models of perceptual choice construe decision formation as the accumulation of sensory evidence towards decision bounds. In this framework, it is commonly assumed that choice history signals shift the starting point of accumulation towards the bound reflecting the previous choice. We here present results that challenge this idea. We fit bounded-accumulation decision models to behavioral data from perceptual choice tasks, and estimated bias parameters that depended on observers’ previous choices. Across multiple task protocols and sensory modalities, individual history biases in overt behavior were consistently explained by a history-dependent change in the evidence accumulation, rather than in its starting point. Choice history signals thus seem to bias the interpretation of current sensory input, akin to shifting endogenous attention towards (or away from) the previously selected interpretation.

Task-evoked pupil responses reflect internal belief states

Perceptual decisions about the state of the environment are often made in the face of uncertain evidence. Internal uncertainty signals are considered important regulators of learning and decision-making. A growing body of work has implicated the brain’s arousal systems in uncertainty signaling. Here, we found that two specific computational variables, postulated by recent theoretical work, evoke boosts of arousal at different times during a perceptual decision: decision confidence (the observer’s internally estimated probability that a choice was correct given the evidence) before feedback, and prediction errors (deviations from expected reward) after feedback. We monitored pupil diameter, a peripheral marker of central arousal state, while subjects performed a challenging perceptual choice task with a delayed monetary reward. We quantified evoked pupil responses during decision formation and after reward-linked feedback. During both intervals, decision difficulty and accuracy had interacting effects on pupil responses. Pupil responses negatively scaled with decision confidence prior to feedback and scaled with uncertainty-dependent prediction errors after feedback. This pattern of pupil responses during both intervals was in line with a model using the observer’s graded belief about choice accuracy to anticipate rewards and compute prediction errors. We conclude that pupil-linked arousal systems are modulated by internal belief states.

Author Correction: Task-evoked pupil responses reflect internal belief states

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

The Churchland birthday data cake

My lab is the best!! They got me this incredible science cake highlighting our latest observations. However, I fear it makes us vulnerable to being scooped! If you want to refer to the figures, may I request that you cite the cake? #labmeeting #birthdaycake Cake by Barbara Cascone

Reading memory formation from the eyes

At any time, we are processing thousands of stimuli, but only few of them will be remembered hours or days later. Is there any way to predict which ones? Here, we tested whether the pupil response to ongoing stimuli, an indicator of physiological arousal known to be relevant for memory formation, is a reliable predictor of long‐term memory for these stimuli, over at least 1 day. Pupil dilation was tracked while participants performed visual and auditory encoding tasks. Memory was tested immediately after encoding and 24 hr later. Irrespective of the encoding modality, trial‐by‐trial variations in pupil dilation predicted reliably which stimuli were recalled in the immediate and 24 hr‐delayed tests, in particular for emotionally arousing stimuli. These results show that our eyes may provide a window into the formation of long‐term memories. Furthermore, our findings underline the important role of central arousal systems in the rapid formation of memories in the brain, possibly by gating synaptic plasticity mechanisms in the neocortex.

Confidence-dependent accumulation of past decision variables biases perceptual choice

Perceptual decision-making is biased by previous events, including the history of preceding choices: Observers tend to repeat (or alternate) their judgments of the sensory environment more often than expected by chance. Computational models postulate that these so-called choice history biases result from the accumulation of internal decision signals across trials. Here, we provide psychophysical evidence for such a mechanism and its adaptive utility. Male and female human observers performed different variants of a challenging visual motion discrimination task near psychophysical threshold. In a first experiment, we decoupled categorical perceptual choices and motor responses on a trial-by-trial basis. Choice history bias was explained by previous perceptual choices, not motor responses, highlighting the importance of internal decision signals in action-independent formats. In a second experiment, observers performed the task in stimulus environments containing different levels of auto-correlation and providing no external feedback about choice correctness. Despite performing under overall high levels of uncertainty, observers adjusted both the strength and the sign of their choice history biases to these environments. When stimulus sequences were dominated by either repetitions or alternations, the individual degree of this adjustment of history bias was about as good a predictor of individual performance as individual perceptual sensitivity. The history bias adjustment scaled with two proxies for observers9 confidence about their previous choices (accuracy and reaction time). Taken together, our results are consistent with the idea that action-independent, confidence-modulated decision variables are accumulated across choices in a flexible manner that depends on decision-makers9 model of their environment.Perceptual decision-making is biased by previous events, including the history of preceding choices: Observers tend to repeat (or alternate) their choices more often than expected by chance. Here, we find that such sequential choice biases result from the accumulation of action-independent, internal decision variables. Human observers performed different variants of a visual motion discrimination task around psychophysical threshold. First, we decoupled perceptual choices and motor responses on a trial-by-trial basis, to disentangle their relative contributions to sequential biases. The impact of previous choices outweighed the impact of previous motor responses and previous stimuli. Second, observers performed the task in both random and biased environments (containing systematic tendencies towards either repetition or alternation of motion directions) and in the absence of external feedback about the correctness of their choices. Observers adapted their sequential choice biases to the biased environmental statistics, in a way that indicated memory for previous choices and predicted their overall performance. We further found that this adaptation was enhanced by the confidence about the correctness of previous choices, consistent with the idea that decision variables driving choice encode both the categorical choice, as well as the graded confidence associated with it. Thus, our results are consistent with the idea that high-level decision variables, dissociable from both, sensory input and motor output, are accumulated across choices towards biases for upcoming choices. These insights constrain the candidate neural sources of sequential choice biases. Significance statement: Studies of perceptual decision-making show that participants’ choices are often influenced by the history of their preceding choices. This manifests as a bias to repeat (or alternate) choices more often than expected by chance. We found that such history biases in perceptual choice arise from the accumulation of internal signals referred to as decision variables. These decision variables encode the observers’ categorical perceptual choice, they are dissociable from both, sensory input and motor output, and they are modulated by decision confidence. This accumulation of decision variables helps adapt choice behavior to the temporal structure of sensory environments, thus boosting overall performance.

The brain as target image detector: the role of image category and presentation time

The brain can be very proficient in classifying images that are hard for computer algorithms to deal with. Previous studies show that EEG can contribute to sorting shortly presented images in targets and non-targets. We examine how EEG and classification performance are affected by image presentation time and the kind of target: humans (a familiar category) or kangaroos (unfamiliar). Humans are much easier detected as indicated by behavioral data, EEG and classifier performance. Presentation of humans is reflected in the EEG even if observers were attending to kangaroos. In general, 50ms presentation time decreased markers of detection compared to 100ms.