Biology subjects

Samaha, J.

Publications and source records attributed to Samaha, J..

At least 19 recordsLinked to original sources

bioRxiv2026

Opposite Effects of Alpha Oscillations on Mind-Wandering With Eyes Open and Closed

Spontaneous fluctuations in brain activity are thought to underlie mind-wandering, moments when mental experience becomes unrelated to what one is currently doing. A large body of research has investigated ongoing neural oscillations in the alpha band (7-14 Hz), reflecting changes in arousal and attention. However, studies disagree whether the power of alpha oscillations increases or decreases during mind-wandering compared to on-task focus. We hypothesized that these opposite effects arise from differences in eye state across studies, as eye closure increases alpha power and can reverse alphas relationship with sleepiness, which is itself related to mind-wandering. To test this, we recorded EEG while male and female participants with eyes either open or closed were probed to report whether they were focused on the auditory attention task or mind-wandering, as well as how sleepy they were. Consistent with our hypothesis, we found that increased alpha power made both mind-wandering and sleepiness more likely in the eyes-open group but less likely in the eyes-closed group. A systematic review of past literature largely replicated these opposite relationships across eye states in different paradigms. We propose that these results reflect an inverted-U relationship between alpha power and mind-wandering, formed by a positive relationship at low alpha power values typical of eyes-open states and a negative relationship at high alpha power values typical of eyes-closed states. By sampling alpha power across eye states in the same paradigm, this work reconciles contradictions in prior literature and clarifies how ongoing neural oscillations reflect the stream of mental experiences. Significance StatementBrain signals tracked with electroencephalography (EEG) can provide a read-out of a persons current mental experience. Increases in a brain signal called alpha oscillations usually indicate sleepiness when recorded with eyes open. Surprisingly, the read-out can be reversed when eyes are closed: increases in alpha oscillations indicate alertness. Here, we found that this reversal explains the puzzling relationship between alpha oscillations and mind-wandering, when mental experience becomes unrelated to the task-at-hand. In moments of increased alpha, participants with eyes open reported more mind-wandering and sleepiness, whereas participants with eyes closed reported more on-task focus and alertness. One intriguing possibility is that decreases in arousal reflected by changes in alpha oscillations trigger episodes of mind-wandering.

neuroscience↗

bioRxiv2025

A Common Neural Signal of Evidence Accumulation for Perceptual and Mnemonic Decisions

Humans frequently make decisions based on sensory input from the external environment or information retrieved from memory. The centro-parietal positivity (CPP), an event-related EEG potential, has recently been identified as a neural correlate of sensory evidence accumulation during perceptual decision-making tasks. However, it remains unclear whether this component also reflects the accumulation of evidence in service of decisions grounded in semantic and episodic long-term memory. Across two experiments, we investigated whether the CPP serves as a domain-general neural signal of evidence accumulation. In Experiment 1, participants completed 2AFC perceptual and semantic memory tasks with varying levels of evidence strength. Perceptual judgements involved luminance discrimination of alphanumeric strings with three luminance difference levels controlling perceptual evidence strength. Semantic memory judgements involved discriminating population differences between U.S. states with census data used to define three bins of memory evidence strength. A CPP component was observed in both tasks whose build-up rate (i.e., slope) scaled with evidence strength, response time, and confidence in both stimulus-and response-locked analyses. Extending these findings to episodic memory, participants in Experiment 2 completed a two-alternative forced-choice word recognition task with target words varying in exposure frequency during learning to control episodic memory strength. Again, we found that CPP slopes scaled with memory strength, response time, and confidence. Together, these findings support the CPP as a domain-general neural signature of evidence accumulation across perceptual, semantic, and episodic mnemonic decisions.

neuroscience↗

bioRxiv2025

Alpha-Band Phase Modulates Perceptual Sensitivity by Changing Internal Noise and Sensory Tuning

Alpha-band neural oscillations (8-13 Hz) are theorized to phasically inhibit visual processing based, in part, on results showing that pre-stimulus alpha phase predicts detection (i.e., hit rates). However, recent failures to replicate and a lack of a mechanistic understanding regarding how alpha impacts detection have called this theory into question. We recorded EEG while six observers (6,020 trials each) detected near-threshold Gabor targets embedded in noise. Using signal detection theory (SDT) and reverse correlation, we observed an effect of occipital and frontal pre-stimulus alpha phase on sensitivity (d), not criterion. Hit and false alarm rates were counterphased, consistent with a reduction in internal noise during optimal alpha phases. Perceptual reports were also more consistent when two identical stimuli were presented during the optimal phase, suggesting a decrease in internal noise rather than signal amplification. Classification images revealed sharper spatial frequency and orientation tuning during the optimal alpha phase, implying that alpha phase shapes sensitivity by modulating sensory tuning towards relevant stimulus features.

neuroscience↗

bioRxiv2025

Spatial grouping modulates the link between individual alpha frequency and temporal integration windows in crowding

Previous research has linked endogenous alpha oscillations ([~]7-13 Hz) to temporal integration windows in visual perception, with higher individual alpha frequency (IAF) predicting improved temporal segregation. Here, we investigated whether alpha-rhythmic temporal integration is a factor in visual crowding and whether this relationship is mediated by spatial grouping mechanisms. 47 participants performed a Vernier discrimination task, in which we manipulated both the stimulus onset asynchrony (SOA) between flankers and targets, and the spatial configuration of the flankers. Specifically, flankers were arranged to either induce crowding or "uncrowding", through the manipulation of good-Gestalt properties. Our results show that crowding has a temporal integration period of around 170 ms but this varies substantially across individuals. Importantly, resting-state IAF predicted individual variance in temporal integration windows: individuals with faster endogenous alpha rhythms could begin to segregate targets from distractors at shorter SOAs. Crucially, this effect was specific for crowding-inducing flankers and disappeared when flankers led to uncrowding. These results suggest that top-down spatial grouping can overwrite the temporal integration constraint imposed by alpha oscillations, highlighting both the relevance of alpha for understanding limits on peripheral visual processing as well as the flexible and context-dependent role of alpha in temporal integration. SIGNIFICANCE STATEMENTThe frequency of alpha-band activity varies across individuals and has previously been linked to temporal integration windows for low-level stimulus properties (e.g., flashes). However, the relevance of individual alpha frequency (IAF) for everyday perception is less clear. We tested whether IAF predicts temporal integration in spatial crowding, a phenomenon that strongly limits perceptual abilities. We found that individuals with higher IAF were better able to spatially segregate targets from flankers at shorter flanker-target offsets, indicating that they spatially integrated the flankers over a smaller temporal window. Interestingly, this effect disappeared when crowding was alleviated by flanker configurations following good-Gestalt principles. Our results suggest that bottom-up mediated spatio-temporal constraints on perception are linked to alpha oscillations but can be overridden by top-down spatial cues.

neuroscience↗

bioRxiv2025

Temporal windows of perceptual organization: Evidence from crowding and uncrowding

Organizing visual input into coherent percepts requires dynamic grouping and segmentation mechanisms that operate across both spatial and temporal domains. While crowding disrupts target perception when nearby elements fall within the same spatial pooling window, specific flanker configurations can alleviate this effect through Gestalt-based grouping, a phenomenon known as uncrowding. Here, we examined the temporal dynamics underlying these spatial organization processes using a Vernier discrimination task. In Experiment 1, we varied stimulus duration and found that uncrowding emerged only after 160 ms, suggesting a time-consuming process. In Experiment 2, we manipulated the stimulus onset asynchrony (SOA) between the target and flankers. We found that presenting good-Gestalt flankers briefly before the target (as little as 32 ms) significantly boosted uncrowding, even in the absence of temporal overlap between the two stimuli. This effect was specific to conditions in which flankers preceded the target, ruling out pure temporal integration and masking accounts. These findings suggest that spatial segmentation can be dynamically facilitated when the temporal order of presentation allows grouping mechanisms to engage prior to target processing. Moreover, the observed time course indicates that segmentation is not purely feedforward, particularly for stimuli that are likely to recruit higher-level visual areas, pointing instead to the involvement of recurrent or feedback processes.

neuroscience↗

bioRxiv2025

Non-conscious Multisensory Integration in the Ventriloquist Effect

The degree to which information from distinct sensory modalities can interact in the absence of conscious awareness remains controversial. According to the Global Neuronal Workspace Theory (GNWT), unconscious sensory information remains relatively confined to sensory cortex and should not be capable of interacting with other modalities until it is broadcast into the (conscious) global workspace comprising late (>300ms) frontal-parietal activation. The ventriloquist effect is a classical multisensory integration phenomenon that refers to the misperception of sound location towards concurrent visual stimulation, such as perceiving the voice of a ventriloquist actor as coming from the moving dummy. Here we used meta-contrast masking to render a brief flash stimulus non-conscious while 30 participants (male, female, and non-binary) performed a sound localization task. We found that, despite being subjectively invisible and at chance at discriminating the flash location, participants were nevertheless biased to localize sounds towards the unconscious flash locations. The effect was present in virtually all participants, was nearly as large as the effect on conscious trials, and was robust to controls for individual differences in task performance. Decoding and ERP analyses of concurrently recorded EEG signals showed that the non-conscious flash location information was present up until around 220ms but not after; suggesting that the visual influence on sound perception may have occurred before conscious broadcast. In support of this, early decoding accuracy on non-conscious trials predicted individual variation in the size of the unconscious ventriloquist effect. Our findings suggest that subjective perception is not required for the integration of signals originating in distinct sensory modalities prompting new questions about the role of subjective perception in multisensory integration.

neuroscience↗

bioRxiv2025

Enhanced Episodic Memory Following Putative Inhibition of the Amygdala via Transcranial Low-Intensity Focused Ultrasound

The amygdala is considered crucial to the formation of emotional episodic memories, but causal evidence in humans is limited due to challenges in non-invasive neuromodulation of deep brain structures. In a double-blind, sham-controlled, repeated measures study, we examined whether transcranial low-intensity focused ultrasound (tFUS) targeting the left amygdala prior to the encoding of emotional and neutral pictures impacted memory for these pictures 24 hours later. We used a putative inhibitory tFUS protocol shown to attenuate amygdala blood-oxygenation- level-dependent signal, thus testing the hypothesis that pre-encoding amygdala inhibition diminishes emotional memory. Surprisingly, active vs. sham sonication enhanced multiple measures of neutral and emotional memory across two memory tests. A secondary test of amygdala function found that active sonication enhanced fear recognition in faces. Computational modeling further supported these results. These findings motivate a novel conceptualization of the amygdalas role in emotional episodic memory. Rather than enhancing memory via amplification of salient stimuli, the amygdala may instead act as a filter that attenuates the maintenance of non-salient stimuli in long-term memory. Finally, the potential to enhance memory serves as an impetus to test tFUS of the amygdala in disorders such as depression and posttraumatic disorder that exhibit comorbid hyperreactive amygdalae and memory impairments.

neuroscience↗

bioRxiv2024

Individual Alpha Frequency Predicts the Sensitivity of Time Perception

A growing body of research links individual differences in the alpha-band frequency to temporal aspects of perception. However, whether the human alpha rhythm is a correlate of time perception itself has remained controversial. This study combined EEG with multiple duration perception tasks to evaluate whether individual alpha frequency (IAF) is associated with sensitivity or bias in judging visual durations across a range of peri-second durations (spanning 100-1200ms). In a temporal estimation task, participants (n = 55; 38 female, 13 male, 4 non-binary) reported the duration of a single stimulus between 300-1200ms. In a temporal discrimination task, participants reported which of two stimuli was longer: a standard (100, 600, or 1200ms) or comparison (50-150% of the standard). Stimuli also varied in whether their luminance was static or dynamically varying over time. We found that IAF was significantly related to the variance of duration estimates, a precision measure, but not average duration estimates, a bias measure. Further supporting this relationship, psychometric function slopes obtained from the independent duration discrimination tasks were positively correlated with IAF, particularly for the static stimulus conditions. These individual differences effects held when controlling for participant age. We also explored trial-level variability in alpha frequency and found it was predictive of shifts in the point of subjective equality (PSE) during discrimination of very short (100ms). Taken together, these results suggest that IAF plays a role in shaping individual differences in the sensitivity of time perception and that spontaneous variations around ones IAF can lead to a bias in temporal representations. Significance StatementBrain waves in the 8-13 Hz range, known as alpha waves, have long been hypothesized to modulate our perception of time, yet the evidence remains unclear. This study investigates the relationship between an individuals alpha frequency (IAF) and temporal sensitivity using a wide range of time perception tasks and stimulus durations to address gaps in the literature. We demonstrate that IAF is significantly associated with the precision of duration estimates and sensitivity in duration discrimination, particularly for static unchanging stimuli. These findings provide novel evidence that IAF shapes individual differences in time perception, emphasizing its role as a neural marker of temporal sensitivity.

neuroscience↗

bioRxiv2024

Metacognitive Introspection Alters the Dynamics of Pre-Decisional Neural Evidence Accumulation

Metacognitive introspection refers to the capacity to monitor and evaluate ones own performance, such as when expressing confidence in ones choice. In the context of perceptual decision making, current computational models of confidence typically assume that confidence is computed after the evidence collection process underlying the initial choice has unfolded. This account predicts that the act of introspection required in order to provide a confidence judgment about ones decision should have little impact on the dynamics of evidence accumulation leading up to that decision. We tested this by examining whether a neural proxy for perceptual evidence accumulation (the central-parietal positivity; CPP) exhibits different dynamics when participants do or do not rate confidence in their perceptual decisions. Behavioral results showed that confidence introspection increased decision accuracy and response time. Importantly, confidence introspection also resulted in a steeper CPP slope beginning shortly after ([~]250 ms) decision evidence was available. We further observed an effector-specific neural signal of confidence evidence which both built up prior to the perceptual choice and which was predictive of the amount of confidence subsequently expressed by the participants. Our results indicate that introspection can alter the dynamics of perceptual evidence accumulation, possibly by acting on the gain of evidence accumulation, and that motor-related confidence signals emerge in tandem with pre-decisional evidence accumulation signals rather than post-choice.

neuroscience↗

bioRxiv2024

Metacognition in Putative Magno- and Parvocellular Vision

A major distinction in early visual processing is the magnocellular (MC) and parvocellular (PC) pathways. The MC pathway preferentially processes motion, transient events, and low spatial frequencies, while the PC pathway preferentially processes color, sustained events, and high spatial frequencies. Prior work has theorized that the PC pathway more strongly contributes to conscious object recognition via projections to the ventral "what" visual pathway, whereas the MC pathway underlies non-conscious, action-oriented motion and localization processing via the dorsal stream "where/how" pathway. This invites the question: Are we equally aware of activity in both pathways? And if not, do task demands interact with which pathway is more accessible to awareness? We investigated this question in a set of two studies measuring participants metacognition for stimuli biased towards MC or PC processing. The "Steady/Pulsed Paradigm" presents brief stimuli under two conditions thought to favor either pathway. In the "pulsed" condition, the target appears atop a strong luminance pedestal which theoretically saturates the transient MC response and leaves the PC pathway to process the stimulus. In the "steady" condition, the stimulus is identical except the luminance pedestal is constant throughout the trial, rather than flashed alongside the target. This theoretically adapts the PC neurons and leaves MC for processing. Experiment 1 was a spatial localization task thought to rely on information relayed from the MC pathway. Using both a model-based and model-free approach to quantify participants metacognitive sensitivity to their own task performance, we found greater metacognition in the steady (MC-biased) condition. Experiment 2 was a fine-grained orientation-discrimination task more reliant on PC pathway information. Our results show an abolishment of the MC pathway advantage seen in Experiment 1 and suggest that the metacognitive advantage for MC processing may hold for stimulus localization tasks only. More generally, our results highlight the need to consider the possibility of differential access to low-level stimulus properties in studies of visual metacognition

animal behavior and cognition↗

bioRxiv2024

Selective Effects of Ongoing Alpha-Band Activity on Magno- and Parvo-Mediated Detection

Spontaneous fluctuations in cortical excitability, as reflected in variation in occipital alpha-band activity (8-12 Hz), have been shown to explain trial-to-trial variability in perception. Specifically, observers typically report seeing a stimulus more often during states of weak alpha power, likely due to a shift in detection criterion. However, prior work has paid little attention to the specific stimulus properties mediating detection. In early vision, different stimulus properties are preferentially processed along the magnocellular (MC) and parvocellular (PC) pathways, which vary in their preference for spatial and temporal frequency content and chromatic information. The goal of this study was to understand how spontaneous alpha power affects the detection of stimuli which are preferentially processed by either the MC or PC pathway. To achieve this, we used the "Steady/Pulsed Paradigm which presented a brief, near-threshold stimulus in two conditions intended to bias processing to one or the other pathway. Our results showed an interaction effect of pre-stimulus alpha power on detection between the two conditions. While weak alpha power was predictive of seeing the stimulus in the steady condition (MC-biased), no significant effect was found in the pulsed condition (PC-biased). This interaction was driven by a selective alpha-related criterion shift in the steady condition, with no effect of pre-stimulus alpha on sensitivity (d) in either condition. Our results imply that alpha oscillations may differentially regulate excitability in the MC and PC pathways.

neuroscience↗

bioRxiv2023

Double dissociation of spontaneous alpha-band activity and pupil-linked arousal on additive and multiplicative perceptual gain

Perception is a probabilistic process dependent on external stimulus properties and ones internal state. However, which internal states influence perception and via what mechanisms remain debated. We studied how spontaneous alpha-band activity (8-12 Hz) and pupil fluctuations impact visual detection and confidence across stimulus contrast levels (i.e., the contrast response function or CRF). We found that weak pre-stimulus alpha power induced an "additive" shift in the CRF, whereby stimuli were reported present more frequently at all contrast levels, including contrast of zero (i.e., false alarms). Conversely, pre-stimulus pupil size had a "multiplicative" effect on detection such that stimuli occurring during large pupil states (putatively corresponding to higher arousal) were perceived more frequently as contrast increased. Signal detection modeling reveals that alpha power changes detection criteria equally across the CRF but not detection sensitivity (d) whereas pupil-linked arousal modulated sensitivity, particularly for higher contrasts. Interestingly, pupil size and alpha power were positively correlated, meaning that some of the effect of alpha on detection may be mediated by pupil fluctuations. However, pupil-independent alpha still induced an additive shift in the CRF corresponding to a criterion effect. Our data imply that weak alpha boosts detection and confidence by an additive factor, rather than by a multiplicative scaling of contrast responses, a profile which captures the effect of pupil-linked arousal. We suggest that alpha-power and arousal fluctuations have dissociable effects on behavior. Alpha reflects the baseline level of visual excitability, which can vary independent of arousal. Significance statementNearly a century ago, brain waves around 8-13 Hz (the "alpha-band") were discovered and linked to visual processing and cortical arousal. However, the precise way that alpha activity shapes perception and relates to arousal is unsettled. We recorded pupillometry and EEG while subjects detected and reported confidence for visual stimuli with varying intensity. Stimuli occurring during states of strong alpha were seen less often, regardless of intensity level, suggesting alpha exerts subtractive inhibition on perception and confidence. Pupil size (a proxy for arousal) was found to correlate with alpha yet, surprisingly, has a different effect on perception. Small pupil lowered perceptual sensitivity more as stimulus intensity increased. Our findings reveal distinct effects of alpha activity and arousal on visual perception.

neuroscience↗

bioRxiv2023

Alpha-band frequency and temporal windows in perception: A review andmeta-analysis of 25 experiments

Temporal windows in perception refer to windows of time within which distinct stimuli interact to influence perception. A simple example is two temporally proximal stimuli fusing into a single percept. It has long been hypothesized that the human alpha rhythm (an 8-13 Hz neural oscillation maximal over posterior cortex) is linked to temporal windows, with higher frequencies corresponding to shorter windows and finer-grained temporal resolution. This hypothesis has garnered support from studies demonstrating a correlation between individual differences in alpha frequency (IAF) and behavioral measures of temporal processing. However, non-significant effects have also been reported. Here, we review and meta-analyze 27 experiments correlating IAF with measures of visual and audio-visual temporal processing. Our results estimate the true correlation in the population to be between 0.39 to 0.53, a medium-to-large effect. The effect held when considering visual or audio-visual experiments separately, when examining different IAF estimation protocols (i.e., eyes-open and eyes-closed), and when using analysis choices that favor a null result. Our review shows that 1) effects have been internally and independently replicated 2) several positive effects are based on larger sample sizes than the null effects and 3) many reported null effects are actually in the direction predicted by the hypothesis. A free interactive web-app was developed to allow users to replicate our meta-analysis and change or update the study selection at will, making this a "living" meta-analysis (https://randfxmeta.streamlit.app). We discuss possible factors underlying null reports, design recommendations, and open questions for future research

neuroscience↗

bioRxiv2023

Neural Signatures of Evidence Accumulation Encode Subjective Perceptual Confidence

Confidence is an adaptive computation when environmental feedback is absent, yet there is little consensus regarding how perceptual confidence is computed in the brain. Difficulty arises because confidence correlates with other factors such as accuracy, response time (RT), or evidence quality. We investigated whether neural signatures of evidence accumulation during a perceptual choice predict subjective confidence independently of these factors. Using motion stimuli, a central-parietal EEG component (CPP) behaves as an accumulating decision variable that predicts evidence quality, RT, accuracy, and confidence (Experiment 1). Psychophysically varying confidence while holding accuracy constant (Experiment 2), the CPP still predicts confidence. Statistically controlling for RT, accuracy, and evidence quality (Experiment 3), the CPP still explains unique variance in confidence. The results indicate that evidence accumulation, indexed by the CPP, is tightly linked to the subjective perceptual experience of sensory information. Independent of other factors, pre-decision neural signatures of evidence accumulation encode subjective confidence.

neuroscience↗

bioRxiv2023

Brain signatures indexing variation in internal processing during perceptual decision-making

Brain activity is highly variable even while performing the same cognitive task with consequences for performance. Discovering, characterizing, and linking variability in brain activity to internal processes has primarily relied on experimentally inducing changes (e.g., via attention manipulation) to identify neuronal and behavioral consequences or studying spontaneous changes in ongoing brain dynamics. However, changes in internal processing could arise from many factors, such as variation in strategy or arousal, that are independent of experimental conditions. Here we utilize a data-driven clustering method based on modularity-maximation to identify consistent spatial-temporal EEG activity patterns across individual trials and relate this activity to behavioral performance. Subjects (N = 25) performed a motion direction discrimination task with six interleaved levels of motion coherence. Modularity-maximization based clustering identified two discrete spatial-temporal clusters, or subtypes, of trials with different patterns of brain activity. Surprisingly, even though Subtype 1 occurred more frequently with lower motion coherence, it was nonetheless associated with faster response times. Computational modeling suggests that Subtype 1 was characterized by a lower threshold for reaching a decision. These results highlight trial-to-trial variability in decision processes usually masked to experimenters and provide a method for identifying endogenous brain state variability relevant to cognition and behavior. Highlights Brain activity is highly variable. We find multiple and distinct stimulus-driven patterns in EEG. With changes in decision-making and drift-diffusion parameters. These results suggest a new way to identify brain states relevant to behavior. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=178 HEIGHT=200 SRC="FIGDIR/small/523502v3_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@e6e448org.highwire.dtl.DTLVardef@95512eorg.highwire.dtl.DTLVardef@104a976org.highwire.dtl.DTLVardef@11191e2_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2022

Unique Effects of Sedatives, Dissociatives, Psychedelics, Stimulants, and Cannabinoids on Episodic Memory: A Review and Reanalysis of Acute Drug Effects on Recollection, Familiarity, and Metamemory

Despite distinct classes of psychoactive drugs producing putatively unique states of consciousness, there is surprising overlap in terms of their effects on episodic memory and cognition more generally. Episodic memory is supported by multiple subprocesses that have been mostly overlooked in psychopharmacology and could differentiate drug classes. Here, we reanalyzed episodic memory confidence data from 10 previously published datasets (28 drug conditions total) using signal detection models to estimate 2 conscious states involved in episodic memory and 1 consciously-controlled metacognitive process of memory: the retrieval of specific details from ones past (recollection), noetic recognition in the absence of retrieved details (familiarity), and accurate introspection of memory decisions (metamemory). We observed that sedatives, dissociatives, psychedelics, stimulants, and cannabinoids had unique patterns of effects on these mnemonic processes dependent on which phase of memory (encoding, consolidation, or retrieval) was targeted. All drugs at encoding except stimulants impaired recollection, and sedatives, dissociatives, and cannabinoids at encoding impaired familiarity. The effects of sedatives on metamemory were mixed, whereas dissociatives and cannabinoids at encoding tended to enhance metamemory. Surprisingly, psychedelics at encoding tended to enhance familiarity and did not impact metamemory. Stimulants at encoding and retrieval enhanced metamemory, but at consolidation, they impaired metamemory. Together, these findings may have relevance to mechanisms underlying unique subjective phenomena under different drug classes, such as blackouts from sedatives or deja vu from psychedelics. This study provides a framework for interrogating drug effects within a domain of cognition beyond the global impairments on task performance typically reported in psychopharmacology. Public significance statementThis systematic review and reanalysis of several datasets indicate that sedatives (alcohol, zolpidem, triazolam), dissociatives (ketamine, dextromethorphan), psychedelics (psilocybin, MDMA), stimulants (dextroamphetamine, dextromethamphetamine), and cannabinoids (THC) can each have idiosyncratic effects on episodic memory, differentially impairing certain mnemonic processes while sparing or even facilitating others. Such findings inform how different drugs can produce unique subjective phenomena and provide a framework for future work to differentiate the effects of psychoactive drugs within a domain of cognition.

neuroscience↗

bioRxiv2022

Task feedback suggests a post-perceptual locus of serial dependence

Decisions across a range of perceptual tasks are biased toward past stimuli. Such serial dependence is thought to be an adaptive low-level mechanism that promotes perceptual stability across time. However, recent studies suggest post-perceptual mechanisms may also contribute to serially-biased responses, calling into question a single locus of serial dependence and the nature of integration of past and present sensory inputs. We measured serial dependence in the context of a 3D motion perception task where uncertainty in the sensory information varied substantially from trial to trial. We found that serial dependence varied with stimulus properties that impact sensory uncertainty on the current trial. Reduced stimulus contrast was associated with an increased bias toward the previous trials stimulus direction. Critically, performance feedback, which reduced sensory uncertainty, abolished serial dependence. These results provide clear evidence for a post-perceptual locus of serial dependence in 3D motion perception and support the role of serial dependence as a response strategy in the face of substantial sensory uncertainty.

neuroscience↗

bioRxiv2021

Spectral distribution dynamics across different attentional priority states

Anticipatory covert spatial attention improves performance on tests of visual detection and discrimination, and shifts are accompanied by decreases and increases of alpha-band power at EEG electrodes corresponding to the attended and unattended location, respectively. Although the increase at the unattended location is often interpreted as an active mechanism (e.g., inhibiting processing at the unattended location), most experiments cannot rule out the alternative possibility that it is a secondary consequence of selection elsewhere. To adjudicate between these accounts, we designed a Posner-style cuing task in which male and female human participants made orientation judgments of targets appearing at one of four locations: up, down, right, or left. Critically, trials were blocked such that within a block the locations along one meridian alternated in status between attended and unattended, and targets never appeared at the other two, making them irrelevant. Analyses of the concurrently measured EEG signal were carried out on traditional narrowband alpha (8-14 Hz), as well as on two components resulting from the decomposition of this signal: periodic alpha; and the slope of the aperiodic 1/f-like component. Although data from right-left blocks replicated the familiar pattern of lateralized asymmetry in narrowband alpha power, with neither alpha signal could we find evidence for any difference in the time course at unattended versus irrelevant locations, an outcome consistent with the secondary-consequence interpretation of attention-related dynamics in the alpha band. Additionally, 1/f slope was lower at attended and unattended locations, relative to irrelevant, suggesting a tonic adjustment of physiological state.

neuroscience↗