Deep neural network decodes aspects of stimulus-intrinsic memorability inaccessible to humans.

Some stimuli are more memorable than others. Humans have demonstrated partial access to the properties that make a given stimulus more or less memorable. Recently, a deep neural network named ResMem was shown to successfully decode the memorability of visual stimuli as well. However, it remains unknown whether ResMem's predictions of memorability reflect the influence of stimulus-intrinsic properties or other stimulus-extrinsic factors that are known to induce interindividual consistency in memory performance (e.g., interstimulus similarity). Additionally, it is not clear whether ResMem and humans share access to overlapping properties of memorability. Here, in three experiments, we show that ResMem predicts stimulus-intrinsic memorability independent of stimulus-extrinsic factors, and that it captures aspects of memorability that are inaccessible to human observers. Taken together, our results confirm the multifaceted nature of memorability and establish a method for isolating its aspects that are largely inaccessible to humans. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Testing the flexibility of ensemble coding: Limitations in cross-modal ensemble perception.

Ensemble coding (the brain's ability to rapidly extract summary statistics from groups of items) has been demonstrated across a range of low-level (e.g., average color) to high-level (e.g., average facial expression) visual features, and even on information that cannot be gleaned solely from retinal input (e.g., object lifelikeness). There is also evidence that ensemble coding can interact with other cognitive systems such as long-term memory (LTM), as observers are able to derive the average cost of items. We extended this line of research to examine if different sensory modalities can interact during ensemble coding. Participants made judgments about the average sweetness of groups of different visually presented foods. We found that, when viewed simultaneously, observers were limited in the number of items they could incorporate into their cross-modal ensemble percepts. We speculate that this capacity limit is caused by the cross-modal translation of visual percepts into taste representations stored in LTM. This was supported by findings that (a) participants could use similar stimuli to form capacity-unlimited ensemble representations of average screen size and (b) participants could extract the average sweetness of displays when items were viewed in sequence, with no capacity limitation (suggesting that spatial attention constrains the number of necessary visual cues an observer can integrate in a given moment to trigger cross-modal retrieval of taste). Together, the results of our study demonstrate that there are limits to the flexibility of ensemble coding, especially when multiple cognitive systems need to interact to compress sensory information into an ensemble representation. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Judgments during perceptual comparisons predict distinct forms of memory updating.

Comparing a visual memory with new visual stimuli can bias memory content, especially when the new stimuli are perceived as similar. Perceptual comparisons of this kind may play a mechanistic role in memory updating and can explain how memories can become erroneous in daily life. To test this possibility, we investigated whether comparisons can produce other types of memory distortion beyond memory bias that are commonly implicated in erroneous memories (e.g., memory misattribution). We hypothesized that the type of memory distortion induced during a comparison depends on the perceived overlap between the memory and incoming stimulus-when the input is perceived as similar, it biases memory content; when perceived as the same, it replaces memory content. Participants completed a delayed estimation task in which they compared their memories of color (Experiment 1) and shape stimuli (Experiment 2) to probe stimuli before reporting memory content. We found systematic errors in participants' memory reports following perceived similarity and sameness that were toward the probes and larger following perceived sameness. Simulations confirmed that these errors were not explained by noisy encoding processes that occurred before comparisons. Instead, computational modeling suggested that these errors were likely explained by the probabilistic replacement of the memory by the probe following perceived sameness and integration between the memory and the probe following perceived similarity. Together, these findings suggest that perceptual comparisons can prompt distinct forms of memory updating that have been described previously and may explain how memories become erroneous during their use in everyday behavior. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

The development of modal intuitions: A test of two accounts.

Young children, unlike adults, deny that improbable events can happen. We test two accounts explaining this developmental shift. The development = reflection account posits that this shift is driven by an emerging ability to reflect on modal intuitions. In contrast, the development = intuition account posits that this shift is driven by changes in modal intuitions themselves, due to age-related changes in what people know and how they sample their knowledge and memories. These accounts make competing predictions about how long children and adults should take to make possibility judgments. In Experiment 1, we asked 123 children (39 5-year-olds, 42 7-year-olds, 42 9-year-olds; 49.60% White) and 40 adults (50% White) to judge the possibility of 78 ordinary, improbable, and impossible events and recorded their response times. In Experiment 2, we tested an additional 52 adults (42.32% White) who were under speeded conditions and thus less able to reflect before responding. Our results favor the development = intuition account. At all ages, people judged improbable events more slowly than ordinary or impossible events, and slow responding did not consistently predict affirmation over denial. Further, adults' possibility judgments did not change under speeded conditions. We also fit a drift-diffusion model to our data, which suggested that adults and children may sample different kinds of knowledge when generating intuitions. Our findings suggest that possibility judgments are often driven by modal intuitions with little reflection, and that a developmental shift in what children know and how knowledge is retrieved can explain why these intuitions change over time. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

The role of visual working memory in capacity-limited cross-modal ensemble coding.

Ensemble coding refers to the brain's ability to rapidly extract summary statistics, such as average size and average cost, from a large set of visual stimuli. Although ensemble coding is thought to circumvent a capacity limit of visual working memory, we recently observed a VWM-like capacity limit in an ensemble task where observers extracted the average sweetness of groups of food pictures (i.e., they could only integrate information from four out of six available items), thus suggesting the involvement of VWM in this novel form of cross-modal ensemble coding. Therefore, across two experiments we investigated if this cross-modal ensemble capacity limit could be explained by individual differences in VWM processing. To test this, observers performed both an ensemble task and a VWM task, and we determined 1) how much information they integrated into their ensemble percepts, and 2) how much information they remembered from those displays. Interestingly, we found that individual differences in VWM capacity did not explain differences in performance on the ensemble coding task (i.e., high-capacity individuals did not have significantly higher "ensemble abilities" than low-capacity individuals). While our data cannot definitively state whether or not VWM is necessary to perform the ensemble task, we conclude that it is certainly not sufficient to support this cognitive process. We speculate that the capacity limit may be explained by 1) a bottleneck at the perceptual stage (i.e., a failure to process multiple visual features across multiple items, as there are no singular features that convey taste), or 2) the interaction of multiple cognitive systems (e.g., VWM, gustatory working memory, long term memory). Our results highlight the importance of examining ensemble perception across multiple sensory and cognitive domains to provide a clearer picture of the mechanisms underlying everyday behavior.

Ready for action! When the brain learns, yet memory-biased action does not follow.

Does memory prepare us to act? Long-term memory can facilitate signal detection, though the degree of benefit varies and can even be absent. To dissociate between learning and behavioral expression of learning, we used high-density electroencephalography (EEG) to assess memory retrieval and response processing. At learning, participants heard everyday sounds. Half of these sound clips were paired with an above-threshold lateralized tone, such that it was possible to form incidental associations between the sound clip and the location of the tone. Importantly, attention was directed to either the sound clip (Experiment 1) or the tone (Experiment 2). Participants then completed a novel detection task that separated cued retrieval from response processing. At retrieval, we observed a striking brain-behavior dissociation. Learning was observed neurally in both experiments. Behaviorally, however, signal detection was only facilitated in Experiment 2, for which there was an accompanying explicit memory for tone presence. Further, implicit neural memory for tone location correlated with the degree of response preparation, but not response execution. Together, the findings suggest 1) that attention at learning affects memory-biased action and 2) that memory prepared action via both explicit and implicit associative memory, with the latter triggering response preparation.

Effect of extracellular matrix fiber cross-linkage on cancer cell motility and surrounding matrix deformation.

Cancer incidence is increasing annually, and the invasion of cancer into the stroma significantly affects cancer metastasis. The stroma primarily comprises an abundant extracellular matrix (ECM) that interacts closely with cancer cells. Cancer cells use the ECM as a scaffold to migrate from a tumor via mechanical actions such as pushing and pulling the fibers. The purpose of this study is to clarify the effects of elastic modulus differences on cell migration behavior based on the same ECM fiber structure. We observe temporal changes in the morphology of cancer cells and the surrounding ECM to elucidate the relationship between changes in the mechanical properties of the ECM and the invasive behavior of cancer cells. We analyze the shape and migration distance of cancer cells and the displacement field of the ECM by varying the fiber elastic modulus but fixing the ECM density. Increasing the elastic modulus results in a protruding cell shape, which indicates the maximum displacement of the ECM around the cell. Additionally, differences in cell migration speed and dispersion based on the elastic modulus are observed. The behavior of cells with increasing elasticity is classified via cluster analysis. Owing to the chemical cross-linking of the fibers, some cells cannot deform the surrounding tissue. This is attributable to the gel state of the ECM and microscopic fluctuations in the fiber density around the cells. We successfully assessed the effect of changes in the ECM modulus on cell mortality and morphology to reveal the mechanism of cancer invasion.

Tracing the emergence of the memorability benefit.

Some visual stimuli are consistently better remembered than others across individuals, due to variations in memorability (the stimulus-intrinsic property that determines ease of encoding into visual long-term memory (VLTM)). However, it remains unclear what cognitive processes give rise to this mnemonic benefit. One possibility is that this benefit is imbued within the capacity-limited bottleneck of VLTM encoding, namely visual working memory (VWM). More precisely, memorable stimuli may be preferentially encoded into VLTM because fewer cognitive resources are required to store them in VWM (efficiency hypothesis). Alternatively, memorable stimuli may be more competitive in obtaining cognitive resources than forgettable stimuli, leading to more successful storage in VWM (competitiveness hypothesis). Additionally, the memorability benefit might emerge post-VWM, specifically, if memorable stimuli are less prone to be forgotten (i.e., are "stickier") than forgettable stimuli after they pass through the encoding bottleneck (stickiness hypothesis). To test this, we conducted two experiments to examine how memorability benefits emerge by manipulating the stimulus memorability, set size, and degree of competition among stimuli as participants encoded them in the context of a working memory task. Subsequently, their memory for the encoded stimuli was tested in a VLTM task. In the VWM task, performance was better for memorable stimuli compared to forgettable stimuli, supporting the efficiency hypothesis. In addition, we found that when in direct competition, memorable stimuli were also better at attracting limited VWM resources than forgettable stimuli, supporting the competitiveness hypothesis. However, only the efficiency advantage translated to a performance benefit in VLTM. Lastly, we found that memorable stimuli were less likely to be forgotten after they passed through the encoding bottleneck imposed by VWM, supporting the "stickiness" hypothesis. Thus, our results demonstrate that the memorability benefit develops across multiple cognitive processes.

Comparing visual memories to similar visual inputs risks lasting memory distortion.

Maintaining perceptual experiences in visual working memory (VWM) allows us to flexibly accomplish various tasks, but some tasks come at a price. For example, comparing VWM representations to novel perceptual inputs can induce inadvertent memory distortions. If these distortions can persist, they may explain why everyday memories often become unreliable after people perform perceptual comparisons (e.g., eyewitness testimony). Here, we conducted two experiments to assess the consequences of perceptual comparisons using real-world objects that were temporarily maintained in VWM (n = 32) or recalled from visual long-term memory back into VWM (n = 30). In each experiment, young adults reported systematic memory distortions following perceptual comparisons. These distortions increased in magnitude with the delay between encoding and comparisons and were preserved when memories were retrieved again a day later. These findings suggest that perceptual comparisons play a mechanistic role in everyday memory distortions, including situations where memory accuracy is vital. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Dissociating the Impact of Memorability on Electrophysiological Correlates of Memory Encoding Success.

Despite its unlimited capacity, not all visual information we encounter is encoded into visual long-term memory. Traditionally, variability in encoding success has been ascribed to variability in the types and efficacy of an individual's cognitive processes during encoding. Accordingly, past studies have identified several neural correlates of variability in encoding success, namely, frontal positivity, occipital alpha amplitude, and frontal theta amplitude, by contrasting the electrophysiological signals recorded during successful and failed encoding processes (i.e., subsequent memory). However, recent research demonstrated individuals remember and forget consistent sets of stimuli, thereby elucidating stimulus-intrinsic factors (i.e., memorability) that determine the ease of memory encoding independent of individual-specific variability in encoding processes. The existence of memorability raises the possibility that canonical EEG correlates of subsequent memory may reflect variability in stimulus-intrinsic factors rather than individual-specific encoding processes. To test this, we recorded the EEG correlates of subsequent memory while participants encoded 600 images of real-world objects and assessed the unique contribution of individual-specific and stimulus-intrinsic factors on each EEG correlate. Here, we found that frontal theta amplitude and occipital alpha amplitude were only influenced by individual-specific encoding success, whereas frontal positivity was influenced by stimulus-intrinsic and individual-specific encoding success. Overall, our results offer novel interpretations of canonical EEG correlates of subsequent memory by demonstrating a dissociable impact of stimulus-intrinsic and individual-specific factors of memory encoding success.

Judgments of learning reveal conscious access to stimulus memorability.

Despite the massive capacity of visual long-term memory, individuals do not successfully encode all visual information they wish to remember. This variability in encoding success has been traditionally ascribed to fluctuations in individuals' cognitive states (e.g., sustained attention) and differences in memory encoding processes (e.g., depth of encoding). However, recent work has shown that a considerable amount of variability in encoding success stems from intrinsic stimulus properties that determine the ease of encoding across individuals. While researchers have identified several perceptual and semantic properties that contribute to stimulus memorability, much remains unknown, including whether individuals are aware of the memorability of stimuli they encounter. In the present study, we investigated whether individuals have conscious access to the memorability of real-world stimuli while forming self-referential judgments of learning (JOL) during explicit memory encoding (Experiments 1A-B) and when asked about the perceived memorability of a stimulus in the absence of attempted encoding (Experiments 2A-B). We found that JOLs and perceived memorability estimates (PME) were consistent across individuals and predictive of memorability, confirming that individuals can access memorability with or without stimulus encoding. At the same time, access to memorability was not comprehensive. We found that individuals unexpectedly remembered and forgot consistent sets of stimuli as well. When we compared access to memorability between JOLs and PMEs, we found that individuals had more access during JOLs. Thus, our findings demonstrate that individuals have partial access to stimulus memorability and that explicit encoding increases the amount of access that is available.

Perceptual comparisons modulate memory biases induced by new visual inputs.

It is well-established that stimulus-specific information in visual working memory (VWM) can be systematically biased by new perceptual inputs. These memory biases are commonly attributed to interference that arises when perceptual inputs are physically similar to VWM contents. However, recent work has suggested that explicitly comparing the similarity between VWM contents and new perceptual inputs modulates the size of memory biases above and beyond stimulus-driven effects. Here, we sought to directly investigate this modulation hypothesis by comparing the size of memory biases following explicit comparisons to those induced when new perceptual inputs are ignored (Experiment 1) or maintained in VWM alongside target information (Experiment 2). We found that VWM reports showed larger attraction biases following explicit perceptual comparisons than when new perceptual inputs were ignored or maintained in VWM. An analysis of participants' perceptual comparisons revealed that memory biases were amplified after perceptual inputs were endorsed as similar-but not dissimilar-to one's VWM representation. These patterns were found to persist even after accounting for variability in the physical similarity between the target and perceptual stimuli across trials, as well as the baseline memory precision between the distinct task demands. Together, these findings illustrate a causal role of perceptual comparisons in modulating naturally-occurring memory biases.

Cross-frequency coupling of frontal theta and posterior alpha is unrelated to the fidelity of visual long-term memory encoding.

Given that the encoding of information into visual long-term memory relies on multiple spatially distinct areas in the human brain, encoding into visual memory is a cognitive process likely to rely on networks formed via large-scale coupled neuronal oscillations. Previous research suggests that decreases in occipital alpha power and increases in mid-frontal theta power individually contribute to the encoding of retrievable representations in visual long-term memory. The present study asks whether these oscillations form a coupled network that operates during long-term memory encoding. Here we show that neither amplitude-amplitude coupling nor phase-amplitude coupling between frontal theta and posterior alpha are correlated with observers' subsequent memory when storing pictures in visual long-term memory. Correlations between alpha and theta power were stronger during eyes-open, resting-state periods when no task was performed than immediately following the presentation of a to-be-remembered picture. Finally, we also found that the strength of theta-alpha coupling was not modified by temporal lobe anodal transcranial direct current stimulation, despite observers showing enhanced memory for pictures behaviorally. Collectively, these findings indicate that posterior alpha and frontal theta activity are not simply component parts of a larger scale coupled network underlying visual memory.

Epitaxial growth of SiGe films by annealing Al-Ge alloyed pastes on Si substrate.

A simple, low-cost, and non-vacuum epitaxial growth method to realize large-area semiconductors on crystalline silicon will become the game-changer for various applications. For example, we can expect the disruptive effect on the cost of large-scale III-V multi-junction solar cells if we could replace the high-cost germanium substrate with silicon-germanium (SiGe) on Si. For SiGe epitaxial growth, we attempted to develop a process using original Al-Ge pastes for screen printing and subsequent annealing. We compare two pastes including Al-Ge alloyed pastes with compositional uniformity in each particle and Al-Ge mixed pastes. We revealed that Al-Ge alloyed paste could form flatter SiGe film with much less residual pastes, supported by in-situ observations. The uniform and sufficient dissolution of the alloyed paste is responsible for these and led to higher average Ge-composition by annealing at 500 °C. The composition in SiGe was vertically graded up to ~ 90% at the topmost surface. These results show that printing and firing of Al-Ge alloyed paste on Si is the desirable, simple, and high-speed process for epitaxial growth of SiGe, which could be potentially used as the lattice-matched virtual substrate with III-V semiconductors.

Even affective changes induced by the global health crisis are insufficient to perturb the hyper-stability of visual long-term memory.

Past studies of emotion and mood on memory have mostly focused on the learning of emotional material in the laboratory or on the consequences of a punctate catastrophic event. However, the influence of a long-lasting global condition on memory and learning has not been studied. The COVID-19 pandemic unfortunately offered a unique situation to observe the effects of prolonged, negative events on human memory for visual information. One thousand online subjects were asked to remember the details of real-world photographs of objects to enable fine-grained visual discriminations from novel within-category foils. Visual memory performance was invariant across time, regardless of the infection rate in the local or national population, or the subjects' self-reported affective state using the Positive and Negative Affect Schedule (PANAS). Thus, visual memory provides the human brain with storage that is particularly resilient to changes in emotional state, even when those changes are experienced for months longer than any imaginable laboratory procedure.

Working Memory Content Is Distorted by Its Use in Perceptual Comparisons.

Visual information around us is rarely static. To perform a task in such a dynamic environment, we often have to compare current visual input with our working memory (WM) representation of the immediate past. However, little is known about what happens to a WM representation when it is compared with perceptual input. To test this, we asked young adults (N = 170 total in three experiments) to compare a new visual input with a WM representation prior to reporting the WM representation. We found that the perceptual comparison biased the WM report, especially when the input was subjectively similar to the WM representation. Furthermore, using computational modeling and individual-differences analyses, we found that this similarity-induced memory bias was driven by representational integration, rather than incidental confusion, between the WM representation and subjectively similar input. Together, our findings highlight a novel source of WM distortion and suggest a general mechanism that determines how WM interacts with new visual input.

Independent features form integrated objects: Using a novel shape-color "conjunction task" to reconstruct memory resolution for multiple object features simultaneously.

Though much progress has been made to understand feature integration, debate remains regarding how objects are represented in mind based on their constituent features. Here, we advance this debate by introducing a novel shape-color "conjunction task" to reconstruct memory resolution for multiple object features simultaneously. In a first experiment, we replicate and extend a classic paradigm originally tested using a change detection task. Replicating previous work, memory resolution for individual features was reduced when the number of objects increased, regardless of the number of to-be-remembered features. Extending previous work, we found that high resolution memory near perfect in resemblance to the target was selectively impacted by the number of to-be-remembered features. Applying a data-driven statistical model of stochastic dependence, we found robust evidence of integration for lower-resolution feature memories, but less evidence for integration of high-resolution feature memories. These results suggest that memory resolution for individual features can be higher than memory resolution for their integration. In a second experiment which manipulated the nature of distracting information, we examined whether object features were directly bound to each other or by virtue of shared spatial location. Feature integration was disrupted by distractors sharing visual features of target objects but not when distractors shared spatial location - suggesting that feature integration can be driven by direct binding between shape and color features in memory. Our results constrain theoretical models of object representation, providing empirical support for hierarchical representations of both integrated and independent features.

Alpha suppression indexes a spotlight of visual-spatial attention that can shine on both perceptual and memory representations.

Although researchers have been recording the human electroencephalogram (EEG) for almost a century, we still do not completely understand what cognitive processes are measured by the activity of different frequency bands. The 8- to 12-Hz activity in the alpha band has long been a focus of this research, but our understanding of its links to cognitive mechanisms has been rapidly evolving recently. Here, we review and discuss the existing evidence for two competing perspectives about alpha activity. One view proposes that the suppression of alpha-band power following the onset of a stimulus array measures attentional selection. The competing view is that this same activity measures the buffering of the task-relevant representations in working memory. We conclude that alpha-band activity following the presentation of stimuli appears to be due to the operation of an attentional selection mechanism, with characteristics that mirror the classic views of attention as selecting both perceptual inputs and representations already stored in memory.

Induced forgetting of pictures across shifts in context.

Previous research from our lab has shown that recognizing an object stored in visual long-term memory leads to the forgetting of related objects. Here we ask whether context, an integral aspect to modern models of memory, plays a role in induced forgetting. We manipulated the activated context at test, both externally (e.g., changes in testing room) and internally (e.g., 1 hr and 24 hr later). We found that only interfering with the ability to internally reinstate context after 24 hr eliminated induced forgetting. Thus, we demonstrate that mental context reinstatement plays a role in induced forgetting and specify that models of memory should incorporate internal context reinstatement as an underlying factor of forgetting. We also propose a process model of induced forgetting, discuss limitations of laboratory-based memory tasks, and offer a new term, induced suppression, to collectively describe this robust phenomenon. (PsycInfo Database Record (c) 2021 APA, all rights reserved).