A matter of availability: sharper tuning for memorized than for perceived stimulus features.

Our visual environment is relatively stable over time. An optimized visual system could capitalize on this by devoting less representational resources to objects that are physically present. The vividness of subjective experience, however, suggests that externally available (perceived) information is more strongly represented in neural signals than memorized information. To distinguish between these opposing predictions, we use EEG multivariate pattern analysis to quantify the representational strength of task-relevant features in anticipation of a change-detection task. Perceptual availability was manipulated between experimental blocks by either keeping the stimulus available on the screen during a 2-s delay period (perception) or removing it shortly after its initial presentation (memory). We find that task-relevant (attended) memorized features are more strongly represented than irrelevant (unattended) features. More importantly, we find that task-relevant features evoke significantly weaker representations when they are perceptually available compared with when they are unavailable. These findings demonstrate that, contrary to what subjective experience suggests, vividly perceived stimuli elicit weaker neural representations (in terms of detectable multivariate information) than the same stimuli maintained in visual working memory. We hypothesize that an efficient visual system spends little of its limited resources on the internal representation of information that is externally available anyway.

How retaining objects containing multiple features in visual working memory regulates the priority for access to visual awareness.

The content of visual working memory influences the access to visual awareness. Thus far, research has focused on retention of a single feature, whereas memoranda in real life typically contain multiple features. Here, we intermixed a delayed match-to-sample task to manipulate VWM content, and a breaking Continuous Flash Suppression (b-CFS) task to measure prioritization for visual awareness. Observers memorized either the color (Exp. 1), the shape (Exp. 2) or both the features (Exp. 3) of an item and indicated the location of a suppressed target. We observed that color-matching targets broke suppression faster than color-mismatching targets both when color was memory relevant or irrelevant. Shape only impacted priority for visual awareness through an interaction with color. We conclude that: (1) VWM can regulate the priority of visual information to access visual awareness along a single feature dimension; (2) different features of a memorandum vary in their potency to impact access to visual awareness, and the more dominant feature may even suppress the effect of the less dominant feature; (3) even stimuli that match an irrelevant feature dimension of the memorandum can be prioritized for visual awareness.

The development of retro-cue benefits with extensive practice: Implications for capacity estimation and attentional states in visual working memory.

Accessing the contents of visual short-term memory (VSTM) is compromised by information bottlenecks and visual interference between memorization and recall. Retro-cues, displayed after the offset of a memory stimulus and prior to the onset of a probe stimulus, indicate the test item and improve performance in VSTM tasks. It has been proposed that retro-cues aid recall by transferring information from a high-capacity memory store into visual working memory (multiple-store hypothesis). Alternatively, retro-cues could aid recall by redistributing memory resources within the same (low-capacity) working memory store (single-store hypothesis). If retro-cues provide access to a memory store with a capacity exceeding the set size, then, given sufficient training in the use of the retro-cue, near-ceiling performance should be observed. To test this prediction, 10 observers each performed 12 hours across 8 sessions in a retro-cue change-detection task (40,000+ trials total). The results provided clear support for the single-store hypothesis: retro-cue benefits (difference between a condition with and without retro-cues) emerged after a few hundred trials and then remained constant throughout the testing sessions, consistently improving performance by two items, rather than reaching ceiling performance. Surprisingly, we also observed a general increase in performance throughout the experiment in conditions with and without retro-cues, calling into question the generalizability of change-detection tasks in assessing working memory capacity as a stable trait of an observer (data and materials are available at osf.io/9xr82 and github.com/paulzerr/retrocues). In summary, the present findings suggest that retro-cues increase capacity estimates by redistributing memory resources across memoranda within a low-capacity working memory store.

No evidence for mnemonic modulation of interocularly suppressed visual input.

Visual working memory (VWM) allows for keeping visual information available for upcoming goal-directed behavior, while new visual input is processed concurrently. Interactions between the mnemonic and perceptual systems cause VWM to affect the processing of visual input in a content-specific manner: visual input that is initially suppressed from consciousness is detected faster when it matches rather than mismatches the content of VWM. It is currently under debate whether such mnemonic influences on perception occur prior to or after conscious access. To address this issue, we investigated whether VWM content modulates the neural response to visual input that remains suppressed from consciousness. We measured fMRI responses to interocularly suppressed stimuli in 20 human participants performing a delayed match-to-sample task: Participants were retro-cued to memorize one of two geometrical shapes for subsequent recognition. During retention, an interocularly suppressed peripheral stimulus (the probe) was briefly presented, which was either of the cued (memorized) or uncued (not memorized) shape category. We found no evidence that VWM content modulated the neural response to the probe. Substantial evidence for the absence of this modulation was found despite leveraging a highly liberal analysis approach: (1) selecting regions of interest that were particularly prone to detecting said modulation, and (2) using directional Bayesian tests favoring the presence of the hypothesized modulation. We did observe faster detection of memory-matching compared to memory-mismatching probes in a behavioral control experiment, thus validating the stimulus set. We conclude that VWM impacts the processing of visual input only once suppression is mostly alleviated.

Scenes Modulate Object Processing Before Interacting With Memory Templates.

When searching for relevant objects in our environment (say, an apple), we create a memory template (a red sphere), which causes our visual system to favor template-matching visual input (applelike objects) at the expense of template-mismatching visual input (e.g., leaves). Although this principle seems straightforward in a lab setting, it poses a problem in naturalistic viewing: Two objects that have the same size on the retina will differ in real-world size if one is nearby and the other is far away. Using the Ponzo illusion to manipulate perceived size while keeping retinal size constant, we demonstrated across 71 participants that visual objects attract attention when their perceived size matches a memory template, compared with mismatching objects that have the same size on the retina. This shows that memory templates affect visual selection after object representations are modulated by scene context, thus providing a working mechanism for template-based search in naturalistic vision.

Visual Working Memory Enhances the Neural Response to Matching Visual Input.

Visual working memory (VWM) is used to maintain visual information available for subsequent goal-directed behavior. The content of VWM has been shown to affect the behavioral response to concurrent visual input, suggesting that visual representations originating from VWM and from sensory input draw upon a shared neural substrate (i.e., a sensory recruitment stance on VWM storage). Here, we hypothesized that visual information maintained in VWM would enhance the neural response to concurrent visual input that matches the content of VWM. To test this hypothesis, we measured fMRI BOLD responses to task-irrelevant stimuli acquired from 15 human participants (three males) performing a concurrent delayed match-to-sample task. In this task, observers were sequentially presented with two shape stimuli and a retro-cue indicating which of the two shapes should be memorized for subsequent recognition. During the retention interval, a task-irrelevant shape (the probe) was briefly presented in the peripheral visual field, which could either match or mismatch the shape category of the memorized stimulus. We show that this probe stimulus elicited a stronger BOLD response, and allowed for increased shape-classification performance, when it matched rather than mismatched the concurrently memorized content, despite identical visual stimulation. Our results demonstrate that VWM enhances the neural response to concurrent visual input in a content-specific way. This finding is consistent with the view that neural populations involved in sensory processing are recruited for VWM storage, and it provides a common explanation for a plethora of behavioral studies in which VWM-matching visual input elicits a stronger behavioral and perceptual response.SIGNIFICANCE STATEMENT Humans heavily rely on visual information to interact with their environment and frequently must memorize such information for later use. Visual working memory allows for maintaining such visual information in the mind's eye after termination of its retinal input. It is hypothesized that information maintained in visual working memory relies on the same neural populations that process visual input. Accordingly, the content of visual working memory is known to affect our conscious perception of concurrent visual input. Here, we demonstrate for the first time that visual input elicits an enhanced neural response when it matches the content of visual working memory, both in terms of signal strength and information content.

Assessing the generalizability of eye dominance across binocular rivalry, onset rivalry, and continuous flash suppression.

It is commonly assumed that one eye is dominant over the other eye. Eye dominance is most frequently determined by using the hole-in-the-card test. However, it is currently unclear whether eye dominance as determined by the hole-in-the-card test (so-called sighting eye dominance) generalizes to tasks involving interocular conflict (engaging sensory eye dominance). We therefore investigated whether sighting eye dominance is linked to sensory eye dominance in several frequently used paradigms that involve interocular conflict. Eye dominance was measured by the hole-in-the-card test, binocular rivalry, and breaking continuous flash suppression (b-CFS). Relationships between differences in eye dominance were assessed using Bayesian statistics. Strikingly, none of the three interocular conflict tasks yielded a difference in perceptual report between eyes when comparing the dominant eye with the nondominant eye as determined by the hole-in-the-card test. From this, we conclude that sighting eye dominance is different from sensory eye dominance. Interestingly, eye dominance of onset rivalry correlated with that of ongoing rivalry but not with that of b-CFS. Hence, we conclude that b-CFS reflects a different form of eye dominance than onset and ongoing rivalry. In sum, eye dominance seems to be a multifaceted phenomenon, which is differently expressed across interocular conflict paradigms. Finally, we highly discourage using tests measuring sighting eye dominance to determine the dominant eye in a subsequent experiment involving interocular conflict. Rather, we recommend that whenever experimental manipulations require a priori knowledge of eye dominance, eye dominance should be determined using pretrials of the same task that will be used in the main experiment.

Attention-based perceptual learning does not affect access to awareness.

Visual information that is relevant for an observer gains prioritized access to awareness (Gayet, Van der Stigchel, & Paffen, 2014). Here we investigate whether information that was relevant for an extended duration is prioritized for access to awareness when it is no longer relevant. We applied a perceptual-learning paradigm, in which observers were trained for 3 days on a speed-discrimination task. This task used a stimulus consisting of two motion directions, of which one was relevant to the task and one irrelevant. Before and after training, we applied a motion-coherence task to validate whether perceptual learning took place, and a breaking continuous flash-suppression (b-CFS) paradigm to assess how training affected access to awareness. The results reveal that motion-coherence thresholds for the task-relevant motion direction selectively decreased after compared to before training, revealing that task-relevant perceptual learning took place. The results of the b-CFS task, however, reveal that access to awareness was not affected by task-relevant learning: Instead, detection times for motion undergoing CFS decreased, irrespective of its direction, after compared to before training. A follow-up experiment showed that the time to detect visual motion also decreased after 3 days without training, revealing that perceptual learning did not cause the general decrease in detection times. The latter is in line with results by Mastropasqua, Tse, and Turatto (2015) and has important consequences for studies applying b-CFS to assess access to awareness: Studies that intend to apply measurements involving b-CFS on different testing days should consider that breakthrough times will dramatically decrease from pre- to postmeasurement.

Visual input that matches the content of visual working memory requires less (not faster) evidence sampling to reach conscious access.

The content of visual working memory (VWM) affects the processing of concurrent visual input. Recently, it has been demonstrated that stimuli are released from interocular suppression faster when they match rather than mismatch a color that is memorized for subsequent recall. In order to investigate the nature of the interaction between visual representations elicited by VWM and visual representations elicited by retinal input, we modeled the perceptual processes leading up to this difference in suppression durations. We replicated the VWM modulation of suppression durations, and fitted sequential sampling models (linear ballistic accumulators) to the response time data. Model comparisons revealed that the data was best explained by a decrease in threshold for visual input that matches the content of VWM. Converging evidence was obtained by fitting similar sequential sampling models (shifted Wald model) to published datasets. Finally, to confirm that the previously observed threshold difference reflected processes occurring before rather than after the stimuli were released from suppression, we applied the same procedure to the data of an experiment in which stimuli were not interocularly suppressed. Here, we found no decrease in threshold for stimuli that match the content of VWM. We discuss our findings in light of a preactivation hypothesis, proposing that matching visual input taps into the same neural substrate that is already activated by a representation concurrently maintained in VWM, thereby reducing its threshold for reaching visual awareness.

Cogito ergo video: Task-relevant information is involuntarily boosted into awareness.

Only part of the visual information that impinges on our retinae reaches visual awareness. In a series of three experiments, we investigated how the task relevance of incoming visual information affects its access to visual awareness. On each trial, participants were instructed to memorize one of two presented hues, drawn from different color categories (e.g., red and green), for later recall. During the retention interval, participants were presented with a differently colored grating in each eye such as to elicit binocular rivalry. A grating matched either the task-relevant (memorized) color category or the task-irrelevant (nonmemorized) color category. We found that the rivalrous stimulus that matched the task-relevant color category tended to dominate awareness over the rivalrous stimulus that matched the task-irrelevant color category. This effect of task relevance persisted when participants reported the orientation of the rivalrous stimuli, even though in this case color information was completely irrelevant for the task of reporting perceptual dominance during rivalry. When participants memorized the shape of a colored stimulus, however, its color category did not affect predominance of rivalrous stimuli during retention. Taken together, these results indicate that the selection of task-relevant information is under volitional control but that visual input that matches this information is boosted into awareness irrespective of whether this is useful for the observer.

Physiological arousal underlies preferential access to visual awareness of fear-conditioned (and possibly disgust-conditioned) stimuli.

Fear and disgust have been associated with opposite influences on visual processing, even though both constitute negative emotions that motivate avoidance behavior and entail increased arousal. In the current study, we hypothesized that (a) homeostatic relevance modulates early stages of visual processing, (b) through widespread physiological responses, and that (c) the direction of these modulations depends on whether an emotion calls for immediate regulatory behavior or not. Specifically, we expected that increased arousal should facilitate the detection of fear-related stimuli, and inhibit the detection of disgust-related stimuli. These hypotheses were tested in two preregistered experiments (data collected in 2022, total N = 120, ethnically homogeneous Polish sample). Using a novel, response bias-free version of the breaking continuous flash suppression paradigm, we examined localization and discrimination of fear- and disgust-conditioned stimuli at individually determined perceptual thresholds. Our first hypothesis was confirmed: fear-conditioned stimuli were detected and discriminated better than neutral stimuli, and the magnitude of conditioning-related perceptual preference was related to arousal during conditioning acquisition. In contrast with our second hypothesis, perceptual access to disgust-conditioned stimuli was not diminished. Exploratory analyses suggest that discrimination of disgust-conditioned stimuli was also enhanced, although these effects appeared weaker than those evoked by fear conditioning. The current study strengthens previous evidence for facilitated perception of threatening objects and shows for the first time that stimuli evoking disgust might also gain preferential access to awareness. The results imply that homeostatically relevant stimuli are prioritized by the visual system and that this preference is grounded in the underlying arousal levels. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Memory reports are biased by all relevant contents of working memory.

Sensory input is inherently noisy while the world is inherently predictable. When multiple observations of the same object are available, integration of the available information necessarily increases the reliability of a world estimate. Optimal integration of multiple instances of sensory evidence has already been demonstrated during multisensory perception but could benefit unimodal perception as well. In the present study 330 participants observed a sequence of four orientations and were cued to report one of them. Reports were biased by all simultaneously memorized items that were similar and relevant to the target item, weighted by their reliability (signal-to-noise ratio). Orientations presented before and presented after the target biased report, demonstrating that the bias emerges in memory and not (exclusively) during perception or encoding. Only attended, task-relevant items biased report. We suggest that these results reflect how the visual system integrates information that is sampled from the same object at consecutive timepoints to promote perceptual stability and behavioural effectiveness in a dynamic world. We suggest that similar response biases, such as serial dependence, might be instances of a more general mechanism of working memory averaging. Data is available at https://osf.io/embcf/ .

Searching near and far: The attentional template incorporates viewing distance.

According to theories of visual search, observers generate a visual representation of the search target (the "attentional template") that guides spatial attention toward target-like visual input. In real-world vision, however, objects produce vastly different visual input depending on their location: your car produces a retinal image that is 10 times smaller when it is parked 50 compared to 5 m away. Across four experiments, we investigated whether the attentional template incorporates viewing distance when observers search for familiar object categories. On each trial, participants were precued to search for a car or person in the near or far plane of an outdoor scene. In "search trials," the scene reappeared and participants had to indicate whether the search target was present or absent. In intermixed "catch-trials," two silhouettes were briefly presented on either side of fixation (matching the shape and/or predicted size of the search target), one of which was followed by a probe-stimulus. We found that participants were more accurate at reporting the location (Experiments 1 and 2) and orientation (Experiment 3) of probe stimuli when they were presented at the location of size-matching silhouettes. Thus, attentional templates incorporate the predicted size of an object based on the current viewing distance. This was only the case, however, when silhouettes also matched the shape of the search target (Experiment 2). We conclude that attentional templates for finding objects in scenes are shaped by a combination of category-specific attributes (shape) and context-dependent expectations about the likely appearance (size) of these objects at the current viewing location. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Action consequences guide the use of visual working memory.

Visual working memory (VWM) is a store for temporary maintenance of visual information. It is often disregarded, though, that information is typically stored to enable actions. Therefore, the context of these actions is of great importance for how VWM is used. Here, we questioned whether the severity of the consequence of an action might affect how well information is memorized, and how cautiously it is utilized. We employed an (online) copying task, in which participants reproduced an example display comprised of six items in a grid, using a pool of items. Crucially, we manipulated the severity of penalties: participants had to wait 5 (high) or 0.5 (low error cost) s after an error. Additionally, we manipulated the accessibility of task-relevant information (a well-studied manipulation in this paradigm): participants had to wait 5 (high) or 0.5 (low sampling cost) s to inspect the example. Our results show that with higher error cost the number of inspections remained comparable, but the number of errors decreased. Furthermore, they show that with higher sampling cost the number of inspections halved, and the number of errors increased. Thus, more severe action consequences increase the reluctance to act on uncertain information in VWM, but do not lead to more attempts to store information in VWM. We conclude that, in contrast to the effect of the accessibility of information, action consequences do not affect how well information is memorized, but affect how cautiously this stored information is utilized. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Information matching the content of visual working memory is prioritized for conscious access.

Visual working memory (VWM) is used to retain relevant information for imminent goal-directed behavior. In the experiments reported here, we found that VWM helps to prioritize relevant information that is not yet available for conscious experience. In five experiments, we demonstrated that information matching VWM content reaches visual awareness faster than does information not matching VWM content. Our findings suggest a functional link between VWM and visual awareness: The content of VWM is recruited to funnel down the vast amount of sensory input to that which is relevant for subsequent behavior and therefore requires conscious access.

Scene context automatically drives predictions of object transformations.

As our viewpoint changes, the whole scene around us rotates coherently. This allows us to predict how one part of a scene (e.g., an object) will change by observing other parts (e.g., the scene background). While human object perception is known to be strongly context-dependent, previous research has largely focused on how scene context can disambiguate fixed object properties, such as identity (e.g., a car is easier to recognize on a road than on a beach). It remains an open question whether object representations are updated dynamically based on the surrounding scene context, for example across changes in viewpoint. Here, we tested whether human observers dynamically and automatically predict the appearance of objects based on the orientation of the background scene. In three behavioral experiments (N = 152), we temporarily occluded objects within scenes that rotated. Upon the objects' reappearance, participants had to perform a perceptual discrimination task, which did not require taking the scene rotation into account. Performance on this orthogonal task strongly depended on whether objects reappeared rotated coherently with the surrounding scene or not. This effect persisted even when a majority of trials violated this real-world contingency between scene and object, showcasing the automaticity of these scene-based predictions. These findings indicate that contextual information plays an important role in predicting object transformations in structured real-world environments.

Mountains of memory in a sea of uncertainty: Sampling the external world despite useful information in visual working memory.

A large part of research on visual working memory (VWM) has traditionally focused on estimating its maximum capacity. Yet, humans rarely need to load up their VWM maximally during natural behavior, since visual information often remains accessible in the external world. Recent work, using paradigms that take into account the accessibility of information in the outside world, has indeed shown that observers utilize only one or two items in VWM before sampling from the external world again. One straightforward interpretation of this finding is that, in daily behavior, much fewer items are memorized than the typically reported capacity limits. Here, we first investigate whether this lower reliance on VWM when information is externally accessible might instead reflect resampling before VWM is actually depleted. To this aim we devised an online task, in which participants copied a model (six items in a 4x4 grid; always accessible) in an adjacent empty 4x4 grid. A key aspect of our paradigm is that we (unpredictably) interrupted participants just before inspection of the model with a 2-alternative-forced-choice (2-AFC) question, probing their VWM content. Critically, we observed above-chance performance on probes appearing just before model inspection. This finding shows that the external world was resampled, despite VWM still containing relevant information. We then asked whether increasing the cost of sampling causes participants to load up more information in VWM or, alternatively, to squeeze out more information from VWM (at the cost of making more errors). To manipulate the cost of resampling, we made it more difficult (specifically, more time-consuming) to access the model. We show that with increased cost of accessing the model (which lead to fewer, but longer model inspections), participants could place more items correctly immediately after sampling, and they kept attempting to place items for longer after their first error. These findings demonstrate that participants both encoded more information in VWM and made attempts to squeeze out more information from VWM when sampling became more costly. We argue that human observers constantly evaluate how certain they are of their VWM contents, and only use that VWM content of which their certainty exceeds a context-dependent "action threshold". This threshold, in turn, depends on the trade-off between the cost of resampling and the benefits of making an action. We argue that considering the interplay between the available VWM contents and a context-dependent action threshold, is key for reconciling the traditional VWM literature with VWM use in our day-to-day behavior.

Preparatory attention incorporates contextual expectations.

Humans are remarkably proficient at finding objects within complex visual scenes. According to current theories of attention,1-3 visual processing of an object of interest is favored through the preparatory activation of object-specific representations in visual cortex.4-15 One key problem that is inherent to real-world visual search but is not accounted for by current theories is that a given object will produce a dramatically different retinal image depending on its location, which is unknown in advance. For instance, the color of the retinal image depends on the illumination on the object, its shape depends on the viewpoint, and (most critically) its size can vary by several orders of magnitude, depending on the distance to the observer. In order to benefit search, preparatory activity thus needs to incorporate contextual expectations. In the current study, we measured fMRI blood-oxygen-level-dependent (BOLD) activity in human observers while they prepared to search for objects at different distances in indoor-scene photographs. First, we established that observers instantiated preparatory object representations: activity patterns in object-selective cortex evoked during search preparation (while no objects were presented) resembled activity patterns evoked by viewing those objects in isolation. Second, we demonstrated that these preparatory object representations were systematically modulated by expectations derived from scene context: activity patterns reflected the predicted retinal image of the object at each distance (i.e., distant search evoking smaller object representations and nearby search evoking larger object representations). These findings reconcile current theories of attentional selection with the challenges of real-world vision.

Correction: Protocol of the Healthy Brain Study: An accessible resource for understanding the human brain and how it dynamically and individually operates in its bio-social context.

[This corrects the article DOI: 10.1371/journal.pone.0260952.].