Recognizing a partially occluded object is effortless and automatic: visual cortex fills in the missing parts to infer a recognizable whole. We tested whether part-to-whole visual pattern completion constitutes not just a retrieval operation, but also a learning mechanism. Participants studied whole objects, after which each object was assigned either to retrieval practice, cued by a circular aperture offering a “peephole” view, or to restudy. At final test, retrieval-practiced (peephole-cued) objects were better remembered than restudied objects – a visual testing effect. The task eliminated the utility of conceptual information, suggesting that this testing effect occurs without semantic mediation, contrary to prominent theories. Critically, when retrieval no longer required pattern completion—retrieval without a peephole cue—the testing effect disappeared. Thus, we report a non-semantically mediated visual testing effect driven by occlusion-induced pattern completion. We suggest that visual pattern completion supports not only occluded object recognition, but also robust visual learning.

The hippocampus is one of the first brain regions to deteriorate with age, and these changes have been linked to the decline in declarative memory frequently observed in older adults. There exist several process-based accounts of the effects of hippocampal damage on memory, such as impairments in context-specific memory with spared gist-based memory, or deficits in recollection alongside intact familiarity-based retrieval. In contrast, representational accounts claim that hippocampal involvement depends on the content of the memory—high-dimensional, containing arbitrary associations (e.g., scenes) versus lower-dimensional, single-items (e.g., objects). Thus, representational theories uniquely predict that aging should differentially impair retrieval depending on the memory content (high- versus lower-dimensional) when the retrieval process is held constant. However, testing this prediction is difficult because most recall or recognition tasks draw upon arbitrary associations, which are high-dimensional, even if the memoranda are single items (e.g., Did this item appear in the study context? Which item was paired with this cue?). We tested memory in younger and older adults in a visual recall task that circumvents this problem by cueing memory with a partial “patch view” of a studied item, analogous to word-stem completion. Thus, the newly learned associations needed for good retrieval were not arbitrary but rather linked parts of a coherent image. For scenes, such cued retrieval required item-to-item associations, but for objects it involved intra-item associations. Older adults were impaired relative to younger, for patch-cued recall of scenes but not objects. Given hippocampal deterioration with age, this supports representational accounts of memory.

Recognizing a partially occluded object is effortless and automatic: visual cortex fills in the missing parts to infer a recognizable whole. We tested whether part-to-whole visual pattern completion constitutes not just a retrieval operation, but also a learning mechanism. Participants studied whole objects, after which each object was assigned either to retrieval practice, cued by a circular aperture offering a “peephole” view, or to restudy. At final test, retrieval-practiced (peephole-cued) objects were better remembered than restudied objects – a visual testing effect. The task eliminated the utility of conceptual information, suggesting that this testing effect occurs without semantic mediation, contrary to prominent theories. Critically, when retrieval no longer required pattern completion—retrieval without a peephole cue—the testing effect disappeared. Thus, we report a non-semantically mediated visual testing effect driven by occlusion-induced pattern completion. We suggest that visual pattern completion supports not only occluded object recognition, but also robust visual learning.

The testing effect is a well-established phenomenon in which memory is better for information that has been enhanced through practice tests rather than through restudying. However, this phenomenon has been studied almost exclusively with verbal or semantically meaningful material. We explored whether the testing effect holds for abstract visual material that lacks both meaning and verbal labels. In a series of six experiments, no evidence for a testing effect was found. We discuss the theoretical implications of these results, which suggest either that the testing effect relies on properties that our stimuli did not possess – e.g., semantic content, high-dimensional content, or pre-existing representations in neocortex – or that eliciting a testing effect for visual material requires radically different task parameters than for verbal material.

Three-dimensional (3D) localization and single-particle tracking (SPT) are powerful techniques for characterizing shape, motion, and deformation of materials. However, these methods often require complex optical setups that demand expert use, limiting their accessibility to the wider scientific community. This paper presents a new technique called individualized defocusing particle tracking (IDPT), which uses intrinsic aberrations in ordinary lab microscopes to perform 3D surface measurements at camera frame rates. The IDPT technique comprises a simple in-situ calibration procedure and 3D localization algorithm that leverages particles' unique defocusing patterns to enhance measurement sensitivity while compensating for optics-induced bias errors. Our empirical approach implicitly transforms systematic optical effects-including those caused by misalignment or defects of optical elements-into valuable sources of positional information, allowing our method to work with common lab microscopes. We validate the IDPT technique through synthetic and benchtop experiments involving rigid body motion of a planar substrate and the dynamic deformation of elastic discs, demonstrating that our algorithm surpasses comparable SPT algorithms in accuracy and resolution. The IDPT technique is simple yet robust, offering broad applicability for dynamic surface profilometry and deformation analysis.

A theory and neurocomputational model are presented that explain grid cell responses as the byproduct of equally dissimilar hippocampal memories. On this account, place and grid cells are best understood as the natural consequence of memory encoding and retrieval; a precise hexagonal grid is the exception rather than the rule, emerging when the animal explores a large surface that is devoid of landmarks and objects. In the proposed memory model, place cells represent memories that are conjunctions of both spatial and non-spatial attributes, and grid cells primarily represent the non-spatial attributes (e.g. sounds, surface texture, etc.) found throughout the two-dimensional recording enclosure. Place cells support memories of the locations where non-spatial attributes can be found (e.g. positions with a particular sound), which are arranged in a hexagonal lattice owing to memory encoding and consolidation processes (pattern separation) as applied to situations in which the non-spatial attributes are found at all locations of a two-dimensional surface. Grid cells exhibit their spatial firing pattern owing to feedback from hippocampal place cells (i.e. a hexagonal pattern of remembered locations for the non-spatial attribute represented by a grid cell). Model simulations explain a wide variety of results in the rodent spatial navigation literature.

The hippocampus is one of the first brain regions to deteriorate with age, accounting for some forms of memory loss in older adults, akin to a mild form of hippocampal amnesia. Hippocampal impairment entails the loss of explicit memory (e.g., source recognition) despite preservation of implicit memory (e.g., priming, as observed in word-stem completion paradigms). Many have argued that the crucial factor differentiating between implicit/explicit memory tasks is whether retrieval is automatic or whether it intentionally references a specific episode. We tested an alternative explanation of the implicit/explicit dissociation based on the content of memory rather than different retrieval processes. Under this view, memory for complex, associative items (e.g., scenes) should be impaired by aging, regardless of retrieval mode (i.e., for both implicit and explicit tasks), whereas memory for simpler items (e.g., individual objects) should not. We tested implicit retrieval of objects and scenes in younger and older adults, cueing memory with a partial “patch view” of the images, analogous to word-stem completion; our findings supported the content-based explanation.

When learning a novel visuomotor mapping (e.g., mirror writing), accuracy can improve quickly through explicit, knowledge-based learning (e.g., aim left to go right), but after practice, implicit or procedural learning takes over, producing fast, natural movements. This procedural learning occurs automatically, whereas it has recently been found that knowledge-based learning can be suppressed by the gradual introduction of the novel mapping when participants must make fast movements and visuomotor perturbations are small (e.g., 30° rotations). We explored the range of task instructions, perturbation parameters, and feedback that preclude or encourage this suppression. Using a reaching task with a rotation between screen position and movement direction, we found that knowledge-based learning could be suppressed even for an extreme 90° rotation, but only if it was introduced gradually and only under instructions to move quickly. If the rotation was introduced abruptly or if instructions emphasized accuracy over speed, knowledge-based learning occurred. A second experiment indicated that knowledge-based learning always occurred in the absence of continuous motion feedback, evidenced by the time course of learning, the aftereffects of learning when the rotation was abruptly removed, and the outcome of formal model comparison between a dual-state (procedural and knowledge-based) versus a single-state (procedural only) learning model of the data. A third experiment replicated the findings and verified that the knowledge-based component of the dual-state model corresponded to explicit aiming, whereas the procedural component was slow to unlearn. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Cationic surfactant coatings (e.g., CTAB) are commonly used in CE to control EOF and thereby improve separation efficiencies. However, our understanding of surfactant adsorption and desorption dynamics under EOF conditions is limited. Here, we apply automated zeta potential analysis to study the adsorption and desorption kinetics of CTAB in a capillary under different transport conditions: diameter, length, voltage alternation pattern and frequency, and applied pressure. In contrast to other studies, we observe slower kinetics at distinct capillary wall zeta potential ranges. Within these ranges, which we call "stagnant regimes," the EOF mobility significantly counteracts the electrophoretic (EP) mobility of CTA+ and hinders the net transport. By constructing a numerical model to compare with our experiments and recasting our experimental data in terms of the net CTA+ transport volume normalized by surface area, we reveal that the EP mobility of CTA+ and the capillary surface-area-to-volume ratio dictate the zeta potential range and the duration of the stagnant regime and thereby govern the overall reaction kinetics. Our results indicate that further transport-oriented studies can significantly aid in the understanding and design of electrokinetic systems utilizing CTAB and other charged surfactants.

Continuous flash suppression leverages binocular rivalry to render observers unaware of a static image for several seconds. To achieve this effect, rapidly flashing noise masks are presented to the dominant eye while a static stimulus is presented to the non-dominant eye. Eventually "breakthrough" occurs, wherein awareness shifts to the static image shown to the non-dominant eye. We tested the hypothesis that Gestalt formation can promote breakthrough. In two experiments, we presented pacman-shaped objects that might or might not align to form illusory Kanizsa objects. To measure the inception of breakthrough, observers were instructed to press a key at the moment of partial breakthrough. After pressing the key, which stopped the trial, observers reported how many pacmen were seen and where they were located. Supporting the Gestalt hypothesis, breakthrough was faster when the pacmen were aligned and observers more often reported pairs of pacmen if they were aligned. To address whether these effects reflected illusory shape perception, a computational model was applied to the pacman report distributions and breakthrough times for an experiment with four pacmen. A full account of the data required an increased joint probability of reporting all four pacmen, suggesting an influence of a perceived illusory cross.

The hippocampus is one of the first brain regions to deteriorate with age, accounting for some forms of memory loss in older adults, akin to a mild form of hippocampal amnesia. Hippocampal impairment entails the loss of explicit memory (e.g., source recognition) despite preservation of implicit memory (e.g., priming, as observed in word-stem completion paradigms). Many have argued that the crucial factor differentiating between implicit/explicit memory tasks is whether retrieval is automatic or whether it intentionally references a specific episode. We tested an alternative explanation of the implicit/explicit dissociation based on the content of memory rather than different retrieval processes. Under this view, memory for complex, associative items (e.g., scenes) should be impaired by aging, regardless of retrieval mode (i.e., for both implicit and explicit tasks), whereas memory for simpler items (e.g., individual objects) should not. We tested implicit retrieval of objects and scenes in younger and older adults, cueing memory with a partial “patch view” of the images, analogous to word-stem completion; our findings supported the content-based explanation.

In this study, we present nanofluidic diodes fabricated from straight glass nanochannels and functionalized using bio-inspired polydopamine (PDA) and poly-L-lysine (PLL) coatings. The resulting PDA coatings are shown to be asymmetric due to a combination of transport considerations which can be leveraged to provide a measure of control over the effective channel geometry. By subsequently introducing a layer of amine-bearing PLL chains covalently bound to the PDA, we enhance heterogeneities in the charge and ion distributions within the channel and enable significant current rectification between forward-bias and reverse-bias modes; our PDA-PLL-coated channels yielded a rectification ratio greater than 1000 in a 100 nm channel filled with 0.01× phosphate-buffered saline solution (PBS). We further demonstrated that at higher ionic strength conditions, reducing the solution pH increased the number of protonated amines within the PLL layer, amplifying the charge disparities along the channel and leading to greater rectification. As nanofluidic diodes with bipolar surface charge distributions tend to provide superior performance compared to those with a single wall charge polarity, we imposed a more bipolar charge distribution in our devices by partially coating our PDA-PLL-coated channels with negatively charged polyacrylic acid (PAA). These enhanced bipolar channels exhibited greater current rectification than the PDA-PLL-coated channels, reaching rectification ratios in excess of 100 even in more physiologically-relevant 1× PBS solutions. Our fabrication approach and the results herein provide a promising platform from which the scientific community can build upon in the relentless endeavor for improved sensitivity in biosensors and other analytical devices.

In the "serial dependence" effect, responses to visual stimuli appear biased toward the last trial's stimulus. However, several kinds of serial dependence exist, with some reflecting prior stimuli and others reflecting prior responses. One-factor analyses consider the prior stimulus alone or the prior response alone and can consider both variables only via separate analyses. We demonstrate that one-factor analyses are potentially misleading and can reach conclusions that are opposite from the truth if both dependencies exist. To address this limitation, we developed two-factor analyses (model comparison with hierarchical Bayesian modeling and an empirical "quadrant analysis"), which consider trial-by-trial combinations of prior response and prior stimulus. Two-factor analyses can tease apart the two dependencies if applied to a sufficiently large dataset. We applied these analyses to a new study and to four previously published studies. When applying a model that included the possibility of both dependencies, there was no evidence of attraction to the prior stimulus in any dataset, but there was evidence of attraction to the prior response in all datasets. Two of the datasets contained sufficient constraint to determine that both dependencies were needed to explain the results. For these datasets, the dependency on the prior stimulus was repulsive rather than attractive. Our results are consistent with the claim that both dependencies exist in most serial dependence studies (the two-dependence model was not ruled out for any dataset) and, furthermore, that the two dependencies work against each other.

We introduce the statistical concept of 'compensatory selection', which arises when selecting a subset of applicants based on multiple predictors, such as when standardized test scores are used in combination with other predictors required in a school application (e.g., previous grades, references letters, and personal statements). Post-hoc analyses often fail to find a positive correlation between test scores and subsequent success, and this failure is sometimes taken as evidence against the predictive validity of the standardized test. The present analysis reveals that the failure to find a negative correlation indicates that the standardized test is in fact a valid predictor of success. This is due to compensation between predictors during selection: Some students are admitted despite a low test score because their application is exceptional in other respects, while other students are admitted primarily based on a high test score despite weakness in the rest of their application. This compensatory selection process introduces a negative correlation between test scores and other predictors among those admitted (a 'collider bias' or 'Berkson's paradox' effect). If test scores are valid predictors of success, this negative correlation between the predictors counteracts the positive correlation between test scores and success that would have been observed if all applicants were admitted. If test scores are not predictive of success, but were nevertheless used in a compensatory selection process, there would be a spurious negative correlation between test scores and success (i.e., an admitted student with a weak application except for a high test score would be unlikely to succeed). The selection effect that is described here is fundamentally different from the well-known 'restricted range' problem and can powerfully alter results even in situations that accept most applicants.

Many species of animals exhibit an intuitive sense of number, suggesting a fundamental neural mechanism for representing numerosity in a visual scene. Recent empirical studies demonstrate that early feedforward visual responses are sensitive to numerosity of a dot array but substantially less so to continuous dimensions orthogonal to numerosity, such as size and spacing of the dots. However, the mechanisms that extract numerosity are unknown. Here, we identified the core neurocomputational principles underlying these effects: (1) center-surround contrast filters; (2) at different spatial scales; with (3) divisive normalization across network units. In an untrained computational model, these principles eliminated sensitivity to size and spacing, making numerosity the main determinant of the neuronal response magnitude. Moreover, a model implementation of these principles explained both well-known and relatively novel illusions of numerosity perception across space and time. This supports the conclusion that the neural structures and feedforward processes that encode numerosity naturally produce visual illusions of numerosity. Taken together, these results identify a set of neurocomputational properties that gives rise to the ubiquity of the number sense in the animal kingdom.

Background: Many type 1 diabetes patients using continuous subcutaneous insulin infusion (CSII) suffer from the phenomenon of unexplained hypoglycemia or “site loss.” Site loss is hypothesized to be caused by toxic excipients, for example, phenolic compounds within insulin formulations that are used as preservatives and stabilizers. Here, we develop a bioinspired polyelectrolyte-modified carbon electrode for effective electrooxidative removal of phenol from insulin and eventual incorporations into an infusion set of a CSII device. Methods: We modified a carbon screen printed electrode (SPE) with poly-L-lysine (PLL) to avoid passivation due to polyphenol deposition while still removing phenolic compounds from insulin injections. We characterized these electrodes using scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) and compared their data with data from bare SPEs. Furthermore, we performed electrochemical measurements to determine the extent of passivation, and high-performance liquid chromatography (HPLC) measurements to confirm both the removal of phenol and the integrity of insulin after phenol removal. Results: Voltammetry measurements show that electrode passivation due to polyphenol deposition is reduced by a factor of 2X. HPLC measurements confirm a 10x greater removal of phenol by our modified electrodes relative to bare electrodes. Conclusion: Using bioinspired polyelectrolytes to modify a carbon electrode surface aids in the electrooxidation of phenolic compounds from insulin and is a step toward integration within an infusion set for mitigating site loss.

Many neuroscience theories assume that tuning modulation of individual neurons underlies changes in human cognition. However, non-invasive fMRI lacks sufficient resolution to visualize this modulation. To address this limitation, we developed an analysis framework called Inferring Neural Tuning Modulation (INTM) for "peering inside" voxels. Precise specification of neural tuning from the BOLD signal is not possible. Instead, INTM compares theoretical alternatives for the form of neural tuning modulation that might underlie changes in BOLD across experimental conditions. The most likely form is identified via formal model comparison, with assumed parametric Normal tuning functions, followed by a non-parametric check of conclusions. We validated the framework by successfully identifying a well-established form of modulation: visual contrast-induced multiplicative gain for orientation tuned neurons. INTM can be applied to any experimental paradigm testing several points along a continuous feature dimension (e.g., direction of motion, isoluminant hue) across two conditions (e.g., with/without attention, before/after learning).

When learning a novel visuomotor mapping (e.g., mirror writing), accuracy can improve quickly through explicit learning (e.g., move left to go right) but after considerable practice, implicit learning takes over, producing fast, natural movements. This implicit learning occurs automatically, but it has been unknown whether explicit learning is similarly obligatory. Using a reaching task with a 90-degree rotation between screen position and movement direction, we found that explicit learning could be “turned off” by introducing the rotation gradually (increments of 10-degrees) and instructing participants to move quickly. These specific conditions were crucial, because both explicit and implicit learning occurred if the rotation occurred suddenly, if participants were told to emphasize accuracy, or if visual feedback during movement was removed. We reached these conclusions by examining the time course of learning (e.g., whether there was fast improvement followed by a long tail of additional improvement), by examining the aftereffects of learning when the rotation was abruptly removed, and by using formal model comparison between a dual-state (explicit and implicit) versus a single-state learning model as applied to the data. Author summary In some situations, the relationship between motion direction and what we see is different than normal. For instance, try using a computer mouse that is held sideways (a 90-degree rotation). When first encountering this situation, people move carefully, using explicit strategies (e.g., move right to go up). However, after many learning trials, motion becomes automatic (implicit) and natural. Prior results found that implicit visuomotor learning always occurs with enough experience. In our study, we found that this is not true of explicit visuomotor learning; in some situations, explicit learning can be turned off. More specifically, we found that this occurs when the novel visuomotor situation is: 1) introduced gradually (e.g., a gradual introduction of 90-degree rotation in steps of 10 degrees); 2) when there is pressure to move quickly; and 3) with real-time onscreen views of the motion path. If any of these three components are missing, then people use explicit learning. These conclusions were reached by examining the time course of learning (e.g., whether there was both fast and slow learning as assessed with mathematical models) and by examining the tendency to automatically move in the opposite direction from the rotation when the rotation is abruptly removed after learning.

In the “serial dependence” effect, responses to visual stimuli appear biased toward the last trial’s stimulus. Fischer and Whitney (2014) proposed that this reflects a “continuity field” that promotes visual stability by biasing perception toward the recent past. However, different kinds of serial dependence exist, with some reflecting prior stimuli and others reflecting prior responses. To untangle the two kinds of dependencies, we used a statistical approach that relies on participants’ naturally occurring, trial-by-trial errors, simultaneously considering the combined effects of the prior response and the prior stimulus. To validate the approach, we collected data in an experiment designed to produce relatively large errors, such that the prior response and prior stimulus were dissociated across trials. We applied the approach to our own data, and to data from previous serial dependence studies, including Fischer and Whitney’s. Whenever these two effects could be disentangled, we found that serial dependencies reflected an attraction to the prior response and repulsion from the prior stimulus. In no case did we find evidence of an attraction to the prior stimulus.