Expectation creates something out of nothing: The role of attention in iconic memory reconsidered

The role of brain oscillations in feature integration

Our sensory system is able to build a unified perception of the world, which although rich, is limited and inaccurate. Sometimes, features from different objects are erroneously combined. At the neural level, the role of the parietal cortex in feature integration is well-known. However, the brain dynamics underlying correct and incorrect feature integration are less clear. To explore the temporal dynamics of feature integration, we studied the modulation of different frequency bands in trials in which feature integration was correct or incorrect. Participants responded to the color of a shape target, surrounded by distractors. A calibration procedure ensured that accuracy was around 70% in each participant. To explore the role of expectancy in feature integration, we introduced an unexpected feature to the target in the last blocks of trials. Results demonstrated the contribution of several frequency bands to feature integration. Alpha and beta power was reduced for hits compared to illusions. Moreover, gamma power was overall larger during the experiment for participants who were aware of the unexpected target presented during the last blocks of trials (as compared to unaware participants). These results demonstrate that feature integration is a complex process that can go wrong at different stages of information processing and is influenced by top-down expectancies.

Brain Mechanisms of Conscious Awareness: Detect, Pulse, Switch, and Wave

Consciousness is a fascinating field of neuroscience research where questions often outnumber the answers. We advocate an open and optimistic approach where converging mechanisms in neuroscience may eventually provide a satisfactory understanding of consciousness. We first review several characteristics of conscious neural activity, including the involvement of dedicated systems for content and levels of consciousness, the distinction and overlap of mechanisms contributing to conscious states and conscious awareness of transient events, nonlinear transitions and involvement of large-scale networks, and finally the temporal nexus where conscious awareness of discrete events occurs when mechanisms of attention and memory meet. These considerations and recent new experimental findings lead us to propose an inclusive hypothesis involving four phases initiated shortly after an external sensory stimulus: (1) Detect-primary and higher cortical and subcortical circuits detect the stimulus and select it for conscious perception. (2) Pulse-a transient and massive neuromodulatory surge in subcortical-cortical arousal and salience networks amplifies signals enabling conscious perception to proceed. (3) Switch-networks that may interfere with conscious processing are switched off. (4) Wave-sequential processing through hierarchical lower to higher cortical regions produces a fully formed percept, encoded in frontoparietal working memory and medial temporal episodic memory systems for subsequent report of experience. The framework hypothesized here is intended to be nonexclusive and encourages the addition of other mechanisms with further progress. Ultimately, just as many mechanisms in biology together distinguish living from nonliving things, many mechanisms in neuroscience synergistically may separate conscious from nonconscious neural activity.

The mechanisms of selective attention in phenomenal consciousness

In three experiments we investigated the effects of selective attention in iconic memory and fragile-visual short-term memory (VSTM), which have been related to phenomenal consciousness. We used a novel retro-cue paradigm with different delays (early vs late) and object priorities (high vs equal vs low), to investigate (a) attentional costs and benefits and the role of (b) bottom-up factors and (c) fragile-VSTM in feature-based attentional selection. Experiment 1 showed that attentional costs modulate visual maintenance at longer delays, while Experiment 2 showed that by reducing the time exposure of the memory array from 250 ms to 100 ms, as a bottom-up factor, participants were not able to select the objects based on their priorities. Finally, Experiment 3 showed that a pattern mask presented before the transfer in visual working memory, attenuates the overall performance while preserving the priority effect. The implications for phenomenal consciousness before conscious access are discussed.

EXPRESS: Attention does not always help: the role of expectancy, divided, and spatial attention on illusory conjunctions

Humans have the subjective impression of a rich perceptual experience, but this perception is riddled with errors that might be produced by top-down expectancies or failures in feature integration. The role of attention in feature integration is still unclear. Some studies support the importance of attention in feature integration (Paul & Schyns, 2003), whereas others suggest that feature integration does not require attention (Humphreys, 2016). Understanding attention as a heterogeneous system, in this study we explored the role of divided (as opposed to focused - Experiment 1) attention, and endogenous-exogenous spatial orienting (Experiments 2 and 3) in feature integration. We also explored the role of feature expectancy, by presenting stimulus features that were completely unexpected to the participants. Results demonstrated that both endogenous and exogenous orienting improved feature integration while divided attention did not. Moreover, a strong and consistent feature expectancy effect was observed, demonstrating perceptual completion when an unexpected perceptual feature was presented in the scene. These results support the feature confirmation account (Humphreys, 2016), which proposes that attention is important for top-down matching of stable representations.

Awareness and Stimulus-Driven Spatial Attention as Independent Processes

To investigate the relation between attention and awareness, we manipulated visibility/awareness and stimulus-driven attention capture among metacontrast-masked visual stimuli. By varying the time interval between target and mask, we manipulated target visibility measured as target discrimination accuracies (ACCs; Experiments 1 and 2) and as subjective awareness ratings (Experiment 3). To modulate stimulus-driven attention capture, we presented the masked target either as a color-singleton (the target stands out by its unique color among homogeneously colored non-singletons), as a non-singleton together with a distractor singleton elsewhere (an irrelevant distractor has a unique color, whereas the target is colored like the other stimuli) or without a singleton (no stimulus stands out; only in Experiment 1). As color singletons capture attention in a stimulus-driven way, we expected target visibility/discrimination performance to be best for target singletons and worst with distractor singletons. In Experiments 1 and 2, we confirmed that the masking interval and the singleton manipulation influenced ACCs in an independent way and that attention capture by the singletons, with facilitated performance in target-singleton compared to distractor-singleton conditions, was found regardless of the interval-induced (in-)visibility of the targets. In Experiment 1, we also confirmed that attention capture was the same among participants with worse and better visibility/discrimination performance. In Experiment 2, we confirmed attention capture by color singletons with better discrimination performance for probes presented at singleton position, compared to other positions. Finally, in Experiment 3, we found that attention capture by target singletons also increased target awareness and that this capture effect on subjective awareness was independent of the effect of the masking interval, too. Together, results provide new evidence that stimulus-driven attention and awareness operate independently from one another and that stimulus-driven attention capture can precede awareness.

Apical drive-A cellular mechanism of dreaming?

Dreams are internally generated experiences that occur independently of current sensory input. Here we argue, based on cortical anatomy and function, that dream experiences are tightly related to the workings of a specific part of cortical pyramidal neurons, the apical integration zone (AIZ). The AIZ receives and processes contextual information from diverse sources and could constitute a major switch point for transitioning from externally to internally generated experiences such as dreams. We propose that during dreams the output of certain pyramidal neurons is mainly driven by input into the AIZ. We call this mode of functioning "apical drive". Our hypothesis is based on the evidence that the cholinergic and adrenergic arousal systems, which show different dynamics between waking, slow wave sleep, and rapid eye movement sleep, have specific effects on the AIZ. We suggest that apical drive may also contribute to waking experiences, such as mental imagery. Future studies, investigating the different modes of apical function and their regulation during sleep and wakefulness are likely to be richly rewarded.

Among the Two Kinds of Metacognitive Evaluation, Only One Is Predictive of Illusory Object Perception

The relationship between expectation-induced hallucination proneness and self-confidence in performance was studied in a visual perception task. Participants were prompted either to recognize briefly shown faces as male or female or to rate the subjective vividness of a square surrounding the face. Importantly, in a few critical trials, the square was absent. Upon completion, participants rated their performance in the face recognition task; they were also asked whether they were sure that their estimation was correct. Out of 35 participants, 33 "hallucinated" on at least one trial, rating the square as visible when it was actually absent. Negative correlation between hallucination proneness and self-confidence in performance (metacognitive rating) was found: The more hallucinations a participant experienced, the less confident he/she was in his/her performance in the face recognition task. Most subjects underestimated their performance; higher ratings were also more accurate. Thus, higher hallucination proneness was associated with more inaccurate ratings of one's own perception. However, confidence in self-ratings as measured by the second follow-up question was unrelated to both, hallucination proneness and self-confidence in performance, supporting the view that there is no unitary mechanism of metacognitive evaluations and extending this view to the domain of visual hallucinatory perception.

Coupling the State and Contents of Consciousness

One fundamental feature of consciousness is that the contents of consciousness depend on the state of consciousness. Here, we propose an answer to why this is so: both the state and the contents of consciousness depend on the activity of cortical layer 5 pyramidal (L5p) neurons. These neurons affect both cortical and thalamic processing, hence coupling the cortico-cortical and thalamo-cortical loops with each other. Functionally this coupling corresponds to the coupling between the state and the contents of consciousness. Together the cortico-cortical and thalamo-cortical loops form a thalamo-cortical broadcasting system, where the L5p cells are the central elements. This perspective makes one quite specific prediction: cortical processing that does not include L5p neurons will be unconscious. More generally, the present perspective suggests that L5p neurons have a central role in the mechanisms underlying consciousness.

Exploring the role of expectations and stimulus relevance on stimulus-specific neural representations and conscious report

Subjective experience can be influenced by top-down factors, such as expectations and stimulus relevance. Recently, it has been shown that expectations can enhance the likelihood that a stimulus is consciously reported, but the neural mechanisms supporting this enhancement are still unclear. We manipulated stimulus expectations within the attentional blink (AB) paradigm using letters and combined visual psychophysics with magnetoencephalographic (MEG) recordings to investigate whether prior expectations may enhance conscious access by sharpening stimulus-specific neural representations. We further explored how stimulus-specific neural activity patterns are affected by the factors expectation, stimulus relevance and conscious report. First, we show that valid expectations about the identity of an upcoming stimulus increase the likelihood that it is consciously reported. Second, using a series of multivariate decoding analyses, we show that the identity of letters presented in and out of the AB can be reliably decoded from MEG data. Third, we show that early sensory stimulus-specific neural representations are similar for reported and missed target letters in the AB task (active report required) and an oddball task in which the letter was clearly presented but its identity was task-irrelevant. However, later sustained and stable stimulus-specific representations were uniquely observed when target letters were consciously reported (decision-dependent signal). Fourth, we show that global pre-stimulus neural activity biased perceptual decisions for a ‘seen’ response. Fifth and last, no evidence was obtained for the sharpening of sensory representations by top-down expectations. We discuss these findings in light of emerging models of perception and conscious report highlighting the role of expectations and stimulus relevance.

Excess of individual variability of priors prevents successful development of general models

Perceptual judgments are influenced by a multitude of factors in addition to the perceptual input. Particularly, the widely varying individual neurobiological endophenotypes and individual differences in the propensity for expectation-based illusory percepts make it unlikely that optimality is possible to define and defend by the type of abstract modeling approach criticized by Rahnev & Denison (R&D).

The relationship between attention and consciousness: an expanded taxonomy and implications for 'no-report' paradigms

Tensions between global neuronal workspace theory and recurrent processing theory have sparked much debate in the field of consciousness research. Here, we focus on one of the key distinctions between these theories: the proposed relationship between attention and consciousness. By reviewing recent empirical evidence, we argue that both theories contain key insights and that certain aspects of each theory can be reconciled into a novel framework that may help guide future research. Alternative theories are also considered, including attended intermediate-level representations theory, integrated information theory and higher order thought theory. With the aim of offering a fresh and nuanced perspective to current theoretical debates, an updated taxonomy of conscious and non-conscious states is proposed. This framework maps a wider spectrum of conscious states by incorporating contemporary views from cognitive neuroscience regarding the variety of attentional mechanisms that are known to interact with sensory processing. Whether certain types of attention are necessary for phenomenal and access consciousness is considered and incorporated into this extended taxonomy. To navigate this expanded space, we review recent 'no-report' paradigms and address several methodological misunderstandings in order to pave a clear path forward for identifying the neural basis of perceptual awareness.This article is part of the theme issue 'Perceptual consciousness and cognitive access'.

It's all in your head: Expectations create illusory perception in a dual-task setup

Predictions about the world can guide our perception and action, but they can also misguide us. We developed novel dual-task setups where the participants are occupied by a primary task and are from time to time queried about the phenomenal contents of the auxiliary task. We show that "hallucinating" the presence of an actually absent stimulus is not an exception, but a common phenomenon (more than 90% of participants experienced illusory objects at least once). Additionally, in experiment 1 we found a negative correlation between the amount of illusory perceptions and the Autism Spectrum Quotient score. People who scored higher on the questionnaire, were less likely to experience illusory objects. Finally, we observed no effect of spatial attention on expectation-based illusory presence of an object. More generally our results demonstrate that expectations misguide perception when attention is diverted to another task.

Experimental Effects of Acute Exercise on Iconic Memory, Short-Term Episodic, and Long-Term Episodic Memory

The present experiment evaluated the effects of acute exercise on iconic memory and short- and long-term episodic memory. A two-arm, parallel-group randomized experiment was employed (n = 20 per group; Mage = 21 year). The experimental group engaged in an acute bout of moderate-intensity treadmill exercise for 15 min, while the control group engaged in a seated, time-matched computer task. Afterwards, the participants engaged in a paragraph-level episodic memory task (20 min delay and 24 h delay recall) as well as an iconic memory task, which involved 10 trials (at various speeds from 100 ms to 800 ms) of recalling letters from a 3 × 3 array matrix. For iconic memory, there was a significant main effect for time (F = 42.9, p < 0.001, η²p = 0.53) and a trend towards a group × time interaction (F = 2.90, p = 0.09, η²p = 0.07), but no main effect for group (F = 0.82, p = 0.37, η²p = 0.02). The experimental group had higher episodic memory scores at both the baseline (19.22 vs. 17.20) and follow-up (18.15 vs. 15.77), but these results were not statistically significant. These findings provide some suggestive evidence hinting towards an iconic memory and episodic benefit from acute exercise engagement.

Dynamic Interactions between Top-Down Expectations and Conscious Awareness

It is well known that top-down expectations affect perceptual processes. Yet, remarkably little is known about the relationship between expectations and conscious awareness. We address three crucial outstanding questions: (1) how do expectations affect the likelihood of conscious stimulus perception?; (2) does the brain register violations of expectations nonconsciously?; and (3) do expectations need to be conscious to influence perceptual decisions? Using human participants, we performed three experiments in which we manipulated stimulus predictability within the attentional blink paradigm, while combining visual psychophysics with electrophysiological recordings. We found that valid stimulus expectations increase the likelihood of conscious access of stimuli. Furthermore, our findings suggest a clear dissociation in the interaction between expectations and consciousness: conscious awareness seems crucial for the implementation of top-down expectations, but not for the generation of bottom-up stimulus-evoked prediction errors. These results constrain and update influential theories about the role of consciousness in the predictive brain.SIGNIFICANCE STATEMENT While the relationship between expectations and conscious awareness plays a major role in many prediction-based theories of brain functioning, thus far few empirical studies have examined this relationship. Here, we address this gap in knowledge in a set of three experiments. Our results suggest that the effect of expectations on conscious awareness varies between different steps of the hierarchy of predictive processing. While the active use of top-down expectations for perceptual decisions requires conscious awareness, prediction errors can be triggered outside of conscious awareness. These results constrain and update influential theories about the role of consciousness in the predictive brain.