Practice makes imperfect: stronger implicit interference with practice in individuals at high risk of developing Alzheimer's disease.

Early screening to determine patient risk of developing Alzheimer's will allow better interventions and planning but necessitates accessible methods such as behavioral biomarkers. Previously, we showed that cognitively healthy older individuals whose cerebrospinal fluid amyloid/tau ratio indicates high risk of cognitive decline experienced implicit interference during a high-effort task, signaling early changes in attention. To further investigate attention's effect on implicit interference, we analyzed two experiments completed sequentially by the same high- and low-risk individuals. We hypothesized that if attention modulates interference, practice would affect the influence of implicit distractors. Indeed, while both groups experienced a strong practice effect, the association between practice and interference effects diverged between groups: stronger practice effects correlated with more implicit interference in high-risk participants, but less interference in low-risk individuals. Furthermore, low-risk individuals showed a positive correlation between implicit interference and EEG low-range alpha event-related desynchronization when switching from high- to low-load tasks. This suggests that lower attention on the task was correlated with stronger interference, a typical phenomenon in the younger population. These results demonstrate how attention impacts implicit interference and highlight early differences in perception between high- and low-risk individuals.

Practice makes imperfect: stronger implicit interference with practice in individuals at high risk of developing Alzheimer's disease.

Early screening to determine patient risk of developing Alzheimer's will allow better interventions and planning but necessitates accessible methods such as behavioral biomarkers. Previously, we showed that cognitively healthy older individuals whose cerebrospinal fluid amyloid / tau ratio indicates high risk of cognitive decline experienced implicit interference during a high-effort task, signaling early changes in attention. To further investigate attention's effect on implicit interference, we analyzed two experiments completed sequentially by the same high- and low-risk individuals. We hypothesized that if attention modulates interference, practice would affect the influence of implicit distractors. Indeed, while both groups experienced a strong practice effect, the association between practice and interference effects diverged between groups: stronger practice effects correlated with more implicit interference in high-risk participants, but less interference in low-risk individuals. Furthermore, low-risk individuals showed a positive correlation between implicit interference and EEG low-range alpha event-related desynchronization when switching from high- to low-load tasks. These results demonstrate how attention impacts implicit interference and highlight early differences in cognition between high- and low-risk individuals.

The connection between heart rate variability (HRV), neurological health, and cognition: A literature review.

The heart and brain have bi-directional influences on each other, including autonomic regulation and hemodynamic connections. Heart rate variability (HRV) measures variation in beat-to-beat intervals. New findings about disorganized sinus rhythm (erratic rhythm, quantified as heart rate fragmentation, HRF) are discussed and suggest overestimation of autonomic activities in HRV changes, especially during aging or cardiovascular events. When excluding HRF, HRV is regulated via the central autonomic network (CAN). HRV acts as a proxy of autonomic activity and is associated with executive functions, decision-making, and emotional regulation in our health and wellbeing. Abnormal changes of HRV (e.g., decreased vagal functioning) are observed in various neurological conditions including mild cognitive impairments, dementia, mild traumatic brain injury, migraine, COVID-19, stroke, epilepsy, and psychological conditions (e.g., anxiety, stress, and schizophrenia). Efforts are needed to improve the dynamic and intriguing heart-brain interactions.

Extracting probability in the absence of visual awareness.

Extracting statistical regularities from the environment is crucial for survival. It allows us to learn cues for where and when future events will occur. Can we learn these associations even when the cues are not consciously perceived? Can these unconscious processes integrate information over long periods of time? We show that human visual system can track the probability of location contingency between an unconscious prime and a conscious target over a period of time of minutes. In a series of psychophysical experiments, we adopted an exogenous priming paradigm and manipulated the location contingency between a masked prime and a visible target (i.e., how likely the prime location predicted the target location). The prime's invisibility was verified both subjectively and objectively. Although the participants were unaware of both the existence of the prime and the prime-target contingency, our results showed that the probability of location contingency was tracked and manifested in the subsequent priming effect. When participants were first entrained into the fully predictive prime-target probability, they exhibited faster responses to the more predictive location. On the contrary, when no contingency existed between the prime and target initially, participants later showed faster responses to the less predictive location. These results were replicated in two more experiments with increased statistical power and a fine-grained delineation of prime awareness. Together, we report that the human visual system is capable of tracking unconscious probability over a period of time, demonstrating how implicit and uncertain regularity guides behavior.

Stronger implicit interference in cognitively healthy older participants with higher risk of Alzheimer's disease.

Introduction: Abnormal cerebrospinal fluid amyloid beta (Aß)42 and tau levels have been revealed decades before symptoms onset in Alzheimer's disease (AD); however, the examination is usually invasive and inaccessible to most people. We thus aimed to develop a non-invasive behavioral test that targets early potential cognitive changes to gauge cognitive decline. Specifically, we hypothesized that older cognitive healthy participants would exhibit comparable performance when the task was explicit and relied on conscious cognition. However, when the task was implicit, the performance of participants at high and low risks for AD would bifurcate. That is, early changes in unconscious cognition could be linked to cognitive health. Methods: We measured implicit interference elicited by an imperceptible distractor in cognitively healthy elderly participants with normal (low risk) and pathological (high risk) Aß42/total tau ratio. Participants were required to perform a Stroop task (word-naming or color-naming on an ink-semantics inconsistent word) with a visually masked distractor presented prior to the target task. Results: We found that, under a high-effort task (i.e., color-naming in the Stroop task), high-risk participants suffered interference when the imperceptible distractor and the subsequent target were incongruent in the responses they triggered. Their reaction times were slowed down by approximately 4%. This implicit interference was not found in the low-risk participants. Discussion: These findings indicate that weakened inhibition of distracting implicit information can be a potential behavioral biomarker of early identification of AD pathology. Our study thus offers a new experimental paradigm to reveal early pathological aging by assessing how individuals respond to subperceptual threshold visual stimuli.

Crossmodal Postdiction: Conscious Perception as Revisionist History.

Postdiction occurs when later stimuli influence the perception of earlier stimuli. As the multisensory science field has grown in recent decades, the investigation of crossmodal postdictive phenomena has also expanded. Crossmodal postdiction can be considered (in its simplest form) the phenomenon in which later stimuli in one modality influence earlier stimuli in another modality (e.g., Intermodal Apparent Motion). Crossmodal postdiction can also appear in more nuanced forms, such as unimodal postdictive illusions (e.g., Apparent Motion) that are influenced by concurrent crossmodal stimuli (e.g., Crossmodal Influence on Apparent Motion), or crossmodal illusions (e.g., the Double Flash Illusion) that are influenced postdictively by a stimulus in one or the other modality (e.g., a visual stimulus in the Illusory Audiovisual Rabbit Illusion). In this review, these and other varied forms of crossmodal postdiction will be discussed. Three neuropsychological models proposed for unimodal postdiction will be adapted to the unique aspects of processing and integrating multisensory stimuli. Crossmodal postdiction opens a new window into sensory integration, and could potentially be used to identify new mechanisms of crossmodal crosstalk in the brain.

Task switching reveals abnormal brain-heart electrophysiological signatures in cognitively healthy individuals with abnormal CSF amyloid/tau, a pilot study.

Electroencephalographic (EEG) alpha oscillations have been related to heart rate variability (HRV) and both change in Alzheimer's disease (AD). We explored if task switching reveals altered alpha power and HRV in cognitively healthy individuals with AD pathology in cerebrospinal fluid (CSF) and whether HRV improves the AD pathology classification by alpha power alone. We compared low and high alpha event-related desynchronization (ERD) and HRV parameters during task switch testing between two groups of cognitively healthy participants classified by CSF amyloid/tau ratio: normal (CH-NAT, n = 19) or pathological (CH-PAT, n = 27). For the task switching paradigm, participants were required to name the color or word for each colored word stimulus, with two sequential stimuli per trial. Trials include color (cC) or word (wW) repeats with low load repeating, and word (cW) or color switch (wC) for high load switching. HRV was assessed for RR interval, standard deviation of RR-intervals (SDNN) and root mean squared successive differences (RMSSD) in time domain, and low frequency (LF), high frequency (HF), and LF/HF ratio in frequency domain. Results showed that CH-PATs compared to CH-NATs presented: 1) increased (less negative) low alpha ERD during low load repeat trials and lower word switch cost (low alpha: p = 0.008, Cohen's d = -0.83, 95% confidence interval -1.44 to -0.22, and high alpha: p = 0.019, Cohen's d = -0.73, 95% confidence interval -1.34 to -0.13); 2) decreasing HRV from rest to task, suggesting hyper-activated sympatho-vagal responses. 3) CH-PATs classification by alpha ERD was improved by supplementing HRV signatures, supporting a potentially compromised brain-heart interoceptive regulation in CH-PATs. Further experiments are needed to validate these findings for clinical significance.

Team Flow Is a Unique Brain State Associated with Enhanced Information Integration and Interbrain Synchrony.

Team flow occurs when a group functions in a high task engagement to achieve a goal, commonly seen in performance and sports. Team flow can enable enhanced positive experiences, as compared with individual flow or regular socializing. However, the neural basis for this enhanced behavioral state remains unclear. Here, we identified neural correlates (NCs) of team flow in human participants using a music rhythm task with electroencephalogram hyperscanning. Experimental manipulations held the motor task constant while disrupting the corresponding hedonic music to interfere with the flow state or occluding the partner's positive feedback to impede team interaction. We validated these manipulations by using psychometric ratings and an objective measure for the depth of flow experience, which uses the auditory-evoked potential (AEP) of a task-irrelevant stimulus. Spectral power analysis at both the scalp sensors and anatomic source levels revealed higher ß-γ power specific to team flow in the left middle temporal cortex (L-MTC). Causal interaction analysis revealed that the L-MTC is downstream in information processing and receives information from areas encoding the flow or social states. The L-MTC significantly contributes to integrating information. Moreover, we found that team flow enhances global interbrain integrated information (II) and neural synchrony. We conclude that the NCs of team flow induce a distinct brain state. Our results suggest a neurocognitive mechanism to create this unique experience.

Attractiveness in the Eyes: A Possibility of Positive Loop between Transient Pupil Constriction and Facial Attraction.

Contrary to the long-held belief of a close linkage between pupil dilation and attractiveness, we found an early and transient pupil constriction response when participants viewed an attractive face (and the effect of luminance/contrast was controlled). While human participants were making an attractiveness judgment on faces, their pupil constricted more for the more attractive (as-to-be-rated) faces. Further experiments showed that the effect of pupil constriction to attractiveness judgment extended to intrinsically esthetic visual objects such as natural scene images (as well as faces) but not to line-drawing geometric figures. When participants were asked to judge the roundness of faces, pupil constriction still correlated with their attractiveness but not the roundness rating score, indicating the automaticity of the pupil constriction to attractiveness. When pupillary responses were manipulated implicitly by relative background luminance changes (from the prestimulus screen), the facial attractiveness ratings were in accordance with the amount of pupil constriction, which could not be explained solely by simultaneous or sequential luminance contrast. The overall results suggest that pupil constriction not only reflects but, as a part of self-monitoring and attribution mechanisms, also possibly contributes to facial attractiveness implicitly.

Causally linking neural dominance to perceptual dominance in a multisensory conflict.

When different senses are in conflict, one sense may dominate the perception of other sense, but it is not known whether the sensory cortex associated with the dominant modality exerts directional influence, at the functional brain level, over the sensory cortex associated with the dominated modality; in short, the link between sensory dominance and neuronal dominance is not established. In a task involving audio-visual conflict, using magnetoencephalography recordings in humans, we first demonstrated that the neuronal dominance - auditory cortex functionally influencing visual cortex - was associated with the sensory dominance - sound qualitatively altering visual perception. Further, we found that prestimulus auditory-to-visual connectivity could predict the perceptual outcome on a trial-by-trial basis. Subsequently, we performed an effective connectivity-guided neurofeedback electroencephalography experiment and showed that participants who were briefly trained to increase the neuronal dominance from auditory to visual cortex showed higher sensory, that is auditory, dominance during the conflict task immediately after the training. These results shed new light into the interactive neuronal nature of multisensory integration and open up exciting opportunities by enhancing or suppressing targeted mental functions subserved by effective connectivity.

Task-induced attention load guides and gates unconscious semantic interference.

The tight relationship between attention and conscious perception has been extensively researched in the past decades. However, whether attentional modulation extended to unconscious processes remained largely unknown, particularly when it came to abstract and high-level processing. Here we use a double Stroop paradigm to demonstrate that attention load gates unconscious semantic processing. We find that word and color incongruencies between a subliminal prime and a supraliminal target cause slower responses to non-Stroop target words-but only if the task is to name the target word (low-load task), and not if the task is to name the target's color (high-load task). The task load hypothesis is confirmed by showing that the word-induced incongruence effect can be detected in the color-naming task, but only in the late, practiced trials. We further replicate this task-induced attentional modulation phenomenon in separate experiments with colorless words (word-only) and words with semantic relationship but no orthographic similarities (semantics-only).

The Dynamic Double Flash Illusion: Auditory Triggered Replay of Illusory Visual Expansion.

In the original double flash illusion, a visual flash (e.g., a sharp-edged disk, or uniformly filled circle) presented with two short auditory tones (beeps) is often followed by an illusory flash. The illusory flash has been previously shown to be triggered by the second auditory beep. The current study extends the double flash illusion by showing that this paradigm can not only create the illusory repeat of an on-off flash, but also trigger an illusory expansion (and in some cases a subsequent contraction) that is induced by the flash of a circular brightness gradient (gradient disk) to replay as well. The perception of the dynamic double flash illusion further supports the interpretation of the illusory flash (in the double flash illusion) as similar in its spatial and temporal properties to the perception of the real visual flash, likely by replicating the neural processes underlying the illusory expansion of the real flash. We show further that if a gradient disk (generating an illusory expansion) and a sharp-edged disk are presented simultaneously side by side with two sequential beeps, often only one visual stimulus or the other will be perceived to double flash. This indicates selectivity in auditory-visual binding, suggesting the usefulness of this paradigm as a psychophysical tool for investigating crossmodal binding phenomena.

Eye movement analysis with switching hidden Markov models.

Here we propose the eye movement analysis with switching hidden Markov model (EMSHMM) approach to analyzing eye movement data in cognitive tasks involving cognitive state changes. We used a switching hidden Markov model (SHMM) to capture a participant's cognitive state transitions during the task, with eye movement patterns during each cognitive state being summarized using a regular HMM. We applied EMSHMM to a face preference decision-making task with two pre-assumed cognitive states-exploration and preference-biased periods-and we discovered two common eye movement patterns through clustering the cognitive state transitions. One pattern showed both a later transition from the exploration to the preference-biased cognitive state and a stronger tendency to look at the preferred stimulus at the end, and was associated with higher decision inference accuracy at the end; the other pattern entered the preference-biased cognitive state earlier, leading to earlier above-chance inference accuracy in a trial but lower inference accuracy at the end. This finding was not revealed by any other method. As compared with our previous HMM method, which assumes no cognitive state change (i.e., EMHMM), EMSHMM captured eye movement behavior in the task better, resulting in higher decision inference accuracy. Thus, EMSHMM reveals and provides quantitative measures of individual differences in cognitive behavior/style, making a significant impact on the use of eyetracking to study cognitive behavior across disciplines.

Transduction of the Geomagnetic Field as Evidenced from alpha-Band Activity in the Human Brain.

Magnetoreception, the perception of the geomagnetic field, is a sensory modality well-established across all major groups of vertebrates and some invertebrates, but its presence in humans has been tested rarely, yielding inconclusive results. We report here a strong, specific human brain response to ecologically-relevant rotations of Earth-strength magnetic fields. Following geomagnetic stimulation, a drop in amplitude of electroencephalography (EEG) alpha-oscillations (8-13 Hz) occurred in a repeatable manner. Termed alpha-event-related desynchronization (alpha-ERD), such a response has been associated previously with sensory and cognitive processing of external stimuli including vision, auditory and somatosensory cues. Alpha-ERD in response to the geomagnetic field was triggered only by horizontal rotations when the static vertical magnetic field was directed downwards, as it is in the Northern Hemisphere; no brain responses were elicited by the same horizontal rotations when the static vertical component was directed upwards. This implicates a biological response tuned to the ecology of the local human population, rather than a generic physical effect. Biophysical tests showed that the neural response was sensitive to static components of the magnetic field. This rules out all forms of electrical induction (including artifacts from the electrodes) which are determined solely on dynamic components of the field. The neural response was also sensitive to the polarity of the magnetic field. This rules out free-radical "quantum compass" mechanisms like the cryptochrome hypothesis, which can detect only axial alignment. Ferromagnetism remains a viable biophysical mechanism for sensory transduction and provides a basis to start the behavioral exploration of human magnetoreception.

What you saw is what you will hear: Two new illusions with audiovisual postdictive effects.

Neuroscience investigations are most often focused on the prediction of future perception or decisions based on prior brain states or stimulus presentations. However, the brain can also process information retroactively, such that later stimuli impact conscious percepts of the stimuli that have already occurred (called "postdiction"). Postdictive effects have thus far been mostly unimodal (such as apparent motion), and the models for postdiction have accordingly been limited to early sensory regions of one modality. We have discovered two related multimodal illusions in which audition instigates postdictive changes in visual perception. In the first illusion (called the "Illusory Audiovisual Rabbit"), the location of an illusory flash is influenced by an auditory beep-flash pair that follows the perceived illusory flash. In the second illusion (called the "Invisible Audiovisual Rabbit"), a beep-flash pair following a real flash suppresses the perception of the earlier flash. Thus, we showed experimentally that these two effects are influenced significantly by postdiction. The audiovisual rabbit illusions indicate that postdiction can bridge the senses, uncovering a relatively-neglected yet critical type of neural processing underlying perceptual awareness. Furthermore, these two new illusions broaden the Double Flash Illusion, in which a single real flash is doubled by two sounds. Whereas the double flash indicated that audition can create an illusory flash, these rabbit illusions expand audition's influence on vision to the suppression of a real flash and the relocation of an illusory flash. These new additions to auditory-visual interactions indicate a spatio-temporally fine-tuned coupling of the senses to generate perception.

Triple dissociation of duration perception regulating mechanisms: Top-down attention is inherent.

The brain constantly adjusts perceived duration based on the recent event history. One such lab phenomenon is subjective time expansion induced in an oddball paradigm ("oddball chronostasis"), where the duration of a distinct item (oddball) appears subjectively longer when embedded in a series of other repeated items (standards). Three hypotheses have been separately proposed but it remains unresolved which or all of them are true: 1) attention prolongs oddball duration, 2) repetition suppression reduces standards duration, and 3) accumulative temporal preparation (anticipation) expedites the perceived item onset so as to lengthen its duration. We thus conducted critical systematic experiments to dissociate the relative contribution of all hypotheses, by orthogonally manipulating sequences types (repeated, ordered, or random) and target serial positions. Participants' task was to judge whether a target lasts shorter or longer than its reference. The main finding was that a random item sequence still elicited significant chronostasis even though each item was odd. That is, simply being a target draws top-down attention and induces chronostasis. In Experiments 1 (digits) and 2 (orientations), top-down attention explained about half of the effect while saliency/adaptation explained the other half. Additionally, for non-repeated (ordered and random) sequence types, a target with later serial position still elicited stronger chronostasis, favoring a temporal preparation over a repetition suppression account. By contrast, in Experiment 3 (colors), top-down attention was likely the sole factor. Consequently, top-down attention is necessary and sometimes sufficient to explain oddball chronostasis; saliency/adaptation and temporal preparation are contingent factors. These critical boundary conditions revealed in our study serve as quantitative constraints for neural models of duration perception.

Decision ambiguity is mediated by a late positive potential originating from cingulate cortex.

People often make decisions in the face of ambiguous information, but it remains unclear how ambiguity is represented in the brain. We used three types of ambiguous stimuli and combined EEG and fMRI to examine the neural representation of perceptual decisions under ambiguity. We identified a late positive potential, the LPP, which differentiated levels of ambiguity, and which was specifically associated with behavioral judgments about choices that were ambiguous, rather than passive perception of ambiguous stimuli. Mediation analyses together with two further control experiments confirmed that the LPP was generated only when decisions are made (not during mere perception of ambiguous stimuli), and only when those decisions involved choices on a dimension that is ambiguous. A further control experiment showed that a stronger LPP arose in the presence of ambiguous stimuli compared to when only unambiguous stimuli were present. Source modeling suggested that the LPP originated from multiple loci in cingulate cortex, a finding we further confirmed using fMRI and fMRI-guided ERP source prediction. Taken together, our findings argue for a role of an LPP originating from cingulate cortex in encoding decisions based on task-relevant perceptual ambiguity, a process that may in turn influence confidence judgment, response conflict, and error correction.

Auditory Sensory Substitution is Intuitive and Automatic with Texture Stimuli.

Millions of people are blind worldwide. Sensory substitution (SS) devices (e.g., vOICe) can assist the blind by encoding a video stream into a sound pattern, recruiting visual brain areas for auditory analysis via crossmodal interactions and plasticity. SS devices often require extensive training to attain limited functionality. In contrast to conventional attention-intensive SS training that starts with visual primitives (e.g., geometrical shapes), we argue that sensory substitution can be engaged efficiently by using stimuli (such as textures) associated with intrinsic crossmodal mappings. Crossmodal mappings link images with sounds and tactile patterns. We show that intuitive SS sounds can be matched to the correct images by naive sighted participants just as well as by intensively-trained participants. This result indicates that existing crossmodal interactions and amodal sensory cortical processing may be as important in the interpretation of patterns by SS as crossmodal plasticity (e.g., the strengthening of existing connections or the formation of new ones), especially at the earlier stages of SS usage. An SS training procedure based on crossmodal mappings could both considerably improve participant performance and shorten training times, thereby enabling SS devices to significantly expand blind capabilities.

Length and orientation constancy learning in 2-dimensions with auditory sensory substitution: the importance of self-initiated movement.

A subset of sensory substitution (SS) devices translate images into sounds in real time using a portable computer, camera, and headphones. Perceptual constancy is the key to understanding both functional and phenomenological aspects of perception with SS. In particular, constancies enable object externalization, which is critical to the performance of daily tasks such as obstacle avoidance and locating dropped objects. In order to improve daily task performance by the blind, and determine if constancies can be learned with SS, we trained blind (N = 4) and sighted (N = 10) individuals on length and orientation constancy tasks for 8 days at about 1 h per day with an auditory SS device. We found that blind and sighted performance at the constancy tasks significantly improved, and attained constancy performance that was above chance. Furthermore, dynamic interactions with stimuli were critical to constancy learning with the SS device. In particular, improved task learning significantly correlated with the number of spontaneous left-right head-tilting movements while learning length constancy. The improvement from previous head-tilting trials even transferred to a no-head-tilt condition. Therefore, not only can SS learning be improved by encouraging head movement while learning, but head movement may also play an important role in learning constancies in the sighted. In addition, the learning of constancies by the blind and sighted with SS provides evidence that SS may be able to restore vision-like functionality to the blind in daily tasks.