A third eye for the surgeon
(2006)
How the eyes move the body
(2005)
Eye movements and balance
(2003)
Anterior canal failure: ocular torsion without perceptual tilt due to preserved otolith function
(2003)
I spy with my little eye: a simple behavioral assay to test color sensitivity on digital displays
(2018)
Short-term synaptic depression can increase the rate of information transfer at a release site
(2019)
The release of neurotransmitters from synapses obeys complex and stochastic dynamics. Depending on the recent history of synaptic activation, many synapses depress the probability of releasing more neurotransmitter, which is known as synaptic depression. Our understanding of how synaptic depression affects the information efficacy, however, is limited. Here we propose a mathematically tractable model of both synchronous spike-evoked release and asynchronous release that permits us to quantify the information conveyed by a synapse. The model transits between discrete states of a communication channel, with the present state depending on many past time steps, emulating the gradual depression and exponential recovery of the synapse. Asynchronous and spontaneous releases play a critical role in shaping the information efficacy of the synapse. We prove that depression can enhance both the information rate and the information rate per unit energy expended, provided that synchronous spike-evoked release depresses less (or recovers faster) than asynchronous release. Furthermore, we explore the theoretical implications of short-term synaptic depression adapting on longer time scales, as part of the phenomenon of metaplasticity. In particular, we show that a synapse can adjust its energy expenditure by changing the dynamics of short-term synaptic depression without affecting the net information conveyed by each successful release. Moreover, the optimal input spike rate is independent of the amplitude or time constant of synaptic depression. We analyze the information efficacy of three types of synapses for which the short-term dynamics of both synchronous and asynchronous release have been experimentally measured. In hippocampal autaptic synapses, the persistence of asynchronous release during depression cannot compensate for the reduction of synchronous release, so that the rate of information transmission declines with synaptic depression. In the calyx of Held, the information rate per release remains constant despite large variations in the measured asynchronous release rate. Lastly, we show that dopamine, by controlling asynchronous release in corticostriatal synapses, increases the synaptic information efficacy in nucleus accumbens.
Head stabilization is fundamental for balance during locomotion but can be impaired in elderly or diseased populations. Previous studies have identified several parameters of head stability with possible diagnostic value in a laboratory setting. Recently, the ecological validity of measures obtained in such controlled contexts has been called into question. The aim of this study was to investigate the ecological validity of previously described parameters of head stabilization in a real-world setting. Ten healthy subjects participated in the study. Head and trunk movements of each subject were recorded with inertial measurement units (IMUs) for a period of at least 10 h. Periods of locomotion were extracted from the measurements and predominant frequencies, root mean squares (RMSs) and bout lengths were estimated. As parameters of head stabilization, attenuation coefficients (ACs), harmonic ratios (HRs), coherences, and phase differences were computed. Predominant frequencies were distributed tightly around 2 Hz and ACs, HRs, and coherences exhibited the highest values in this frequency range. All head stability parameters exhibited characteristics consistent with previous reports, although higher variances were observed. These results suggest that head stabilization is tuned to the 2 Hz fundamental frequency of locomotion and that previously described measures of head stability could generalize to a real-world setting. This is the first study to address the ecological validity of these measures, highlighting the potential use of head stability parameters as diagnostic tools or outcome measures for clinical trials. The low cost and ease of use of the IMU technology used in this study could additionally be of benefit for a clinical application.
Perceptual biases found experimentally are often taken to indicate that we should be cautious about the veridicality of our perception in everyday life. Here we show, to the contrary, that such biases may be a consequence of the experimental protocol that cannot be generalized to other situations. We show that the central tendency, an overestimation of small magnitudes and underestimation of large ones, strongly depends on stimulus order. If the same set of stimuli is, rather than being presented in the usual randomized order, is applied in an order that displays only small changes from one trial to the next, the central tendency decreases significantly. This decrease is predicted by a probabilistic model that assumes iterative trial-wise updating of a prior of the stimulus distribution. We conclude that the commonly used randomization of stimuli introduces systematic perceptual biases that may not relevant in everyday life.
Sequential Bayesian updating has been proposed as model for explaining various systematic biases in human perception, such as the central tendency, range effects, and serial dependence. The present chapter introduces to the principal ideas behind Bayesian updating for the random-change model introduced previously and shows how to implement sequential updating using the exact method via probability distributions, the Kalman filter for Gaussian distributions, and a particle filter for approximate sequential updating. Finally, it is demonstrated how to couple perception to action by selecting an appropriate action based on the posterior distribution that results from sequential updating.
Action potentials (spikes) can trigger the release of a neurotransmitter at chemical synapses between neurons. Such release is uncertain, as it occurs only with a certain probability. Moreover, synaptic release can occur independently of an action potential (asynchronous release) and depends on the history of synaptic activity. We focus here on short-term synaptic facilitation, in which a sequence of action potentials can temporarily increase the release probability of the synapse. In contrast to the phenomenon of short-term depression, quantifying the information transmission in facilitating synapses remains to be done. We find rigorous lower and upper bounds for the rate of information transmission in a model of synaptic facilitation. We treat the synapse as a two-state binary asymmetric channel, in which the arrival of an action potential shifts the synapse to a facilitated state, while in the absence of a spike, the synapse returns to its baseline state. The information bounds are functions of both the asynchronous and synchronous release parameters. If synchronous release facilitates more than asynchronous release, the mutual information rate increases. In contrast, short-term facilitation degrades information transmission when the synchronous release probability is intrinsically high. As synaptic release is energetically expensive, we exploit the information bounds to determine the energy–information trade-off in facilitating synapses. We show that unlike information rate, the energy-normalized information rate is robust with respect to variations in the strength of facilitation.
Unilateral peripheral vestibular lesions not only lead to vertigo, nystagmus and imbalance, but also to a bias in the perception of verticality, which can be measured as tilt of the subjective visual vertical (SVV). Previously, this tilt has been assumed to be caused by a residual otolith bias, for example, because unequal numbers of active haircells on both sides of the utricular striola might result in an imbalance of the firing rates of central otolith neurons. Here we propose that a tilt of the subjective visual vertical might as well be caused by a vertical semicircular canal bias in the roll axis after unilateral peripheral lesions. The canal bias, acting similar to angular velocity stimuli, influences the SVV via the central gravity estimator, which under normal circumstances resolves a perceptual tilt-translation ambiguity. To illustrate our hypothesis, we compare model predictions to data on SVV measurements in patients with unilateral vestibular lesions while being tilted or being rotated eccentrically. We further embed the model of peripheral processing in a neural network that implements the idiotropic bias and represents the direction of gravity as population code in a three dimensional spherical topography.
Understanding the mechanisms of symptoms that are insufficiently explained by organic dysfunction remains challenging. Recently, it has been proposed that such “functional symptoms” are based on erroneous sensory processing in the central nervous system (CNS), with internal expectations dominating sensory inputs.
In a pilot study, we used a head motor control set-up to assess the interplay between sensory input and expectation on the example of patients with functional dizziness. Eight patients and 11 age-matched healthy controls performed large active eye-head gaze shifts towards visual targets in the natural situation and with the head moment of inertia 3.3-fold increased. The latter induces head oscillations and the expected sensory outcome of the movement, estimated in the CNS, does not match the actual sensory input. Head oscillations were assessed in patients and in healthy subjects and compared to prior results from patients with organic disease (vestibular loss and cerebellar ataxia). Head oscillations in patients with functional dizziness were different from those of healthy subjects (F(1,17) = 27.26, P < 0.001, partial η2 = 0.62), and similar to those of patients with cerebellar ataxia, and with vestibular loss (F(2,19) = 0.56, P = 0.58). Even in the natural, unweighted, condition, head oscillations were higher in functional dizziness patients than in healthy subjects (P = 0.001). Since an extensive work-up failed to demonstrate any explanatory peripheral vestibular, motor, or cerebellar organic dysfunction, these motor control deficits are a first indication of erroneous interplay between expectations and sensory input in the CNS that could account for persistent physical symptoms.
Head motion predictability explains activity-dependent suppression of vestibular balance control
(2020)
Vestibular balance control is dynamically weighted during locomotion. this might result from a selective suppression of vestibular inputs in favor of a feed-forward balance regulation based on locomotor efference copies. The feasibility of such a feed-forward mechanism should however critically depend on the predictability of head movements (HMP) during locomotion. To test this, we studied in 10 healthy subjects the differential impact of a stochastic vestibular stimulation (SVS) on body sway (center-of-pressure, COP) during standing and walking at different speeds and compared it to activity-dependent changes in HMp. SVS-cop coupling was determined by correlation analysis in frequency and time domains. HMP was quantified as the proportion of head motion variance that can be explained by the average head trajectory across the locomotor cycle. SVS-COP coupling decreased from standing to walking and further dropped with faster locomotion. Correspondingly, HMP increased with faster locomotion. Furthermore, SVS-COP coupling depended on the gait-cycle-phase with peaks corresponding to periods of least HMP. These findings support the assumption that during stereotyped human self-motion, locomotor efference copies selectively replace vestibular cues, similar to what was previously observed in animal models.
Magnitude Estimation
(2020)
Data from the publication
Petzschner FH, Glasauer S (2011) Iterative Bayesian Estimation as an Explanation for Range and Regression Effects: A Study on Human Path Integration. J Neurosci 31(47):17220 –17229. DOI:10.1523/JNEUROSCI.2028-11.2011
Data is stored in two Matlab files. AE_all.mat contains the raw angular estimation data, DE_all.mat the raw distance estimation data for all participants. Each structure in the cell array Data is for one participant and contains pdata (produced distance or angle, that’s the stimulus) and rdata (re-produced distance or angle, the response). There are 3x180 values, first dimension are the three ranges used, so Data{1}.pdata(1,:) contains the stimuli for participant 1 and the short range in the angular estimation experiment (given you loaded AE_all.mat).
The vestibulo-ocular reflex (VOR) consists of two components, the rotational VOR (rVOR) elicited by semicircular canal signals and the translational VOR (tVOR) elicited by otolith signals. Given the relevant role of the vertical tVOR in human walking, this study aimed at measuring the time delay of eye movements in relation to whole-body vertical translations in natural standing position. Twenty (13 females and 7 males) healthy, young subjects (mean 25 years) stood upright on a motor-driven platform and were exposed to sinusoidal movements while fixating a LED, positioned at a distance of 50 cm in front of the eyes. The platform motion induced a vertical translation of 2.6 cm that provoked counteracting eye movements similar to self-paced walking. The time differences between platform and eye movements indicated that the subject's timing of the extraocular motor reaction depended on stimulus frequency and number of repetitions. At low stimulus frequencies (<0.8 Hz) and small numbers of repetitions (<3), eye movements were phase advanced or in synchrony with platform movements. At higher stimulus frequencies or continuous stimulation, eye movements were phase lagged by ~40 ms. Interestingly, the timing of eye movements depended on the initial platform inclination. Starting with both feet in dorsiflexion, eye movements preceded platform movements by 137 ms, whereas starting with both feet in plantar flexion eye movement precession was only 19 ms. This suggests a remarkable influence of foot proprioceptive signals on the timing of eye movements, indicating that the dynamics of the vertical tVOR is controlled by somatosensory signals.
Complementing conceptual models of persistent somatic symptoms with mathematical formalization
(2020)
While learning from an instructor by watching a ‘how-to’ video has become common practice, we know sur- prisingly little about the relation between brain activities in instructor and observers. In this fMRI study we investigated the temporal synchronization between instructor and observers using intersubject correlation in the naturalistic setting of learning to fold origami. Brain activity of the blindfolded instructor during action pro- duction was compared to the observers while they viewed the instructor’s video-taped actions. We demonstrate for the first time that the BOLD activity in the instructor’s and observer’s brain are synchronized while observing and learning a manual complex task with the goal of reproducing it. We can rule out that this synchrony originates from visual feedback. Observers exhibiting higher synchrony with the instructor in the ventral premotor cortex, while viewing the video for the first time, were more successful in reproducing the origami afterwards. Furthermore, changes in instructor-observer synchrony across observational learning sessions occur in cerebellar areas, as well as differences in instructor-observer synchrony between learning and the counting folds, our non- learning control. Not only known cerebellar motor production areas show synchrony, shedding new light on the involvement of the cerebellum in action observation and learning.
Introduction: Artificial intelligence (AI) is one of the most considered topics of the current time. AI has the power to bring revolutionary improvements to the world of technology not only in the field of computer science but also in other fields like medical sciences. Objectives: This paper assumes the adoption of appropriate AI engineering principals in previous studies, and focusses on providing a structured review of the impact of AI on human society and the individual human being as a technology user. Additionally, it opens a window on how the future will look like in terms of AI and personalised medicine. Methods: The paper employed a qualitative research approach and data were collected through a structured literature review. Twenty-three peer reviewed papers were identified and analysed in relation to their relevance to the study. Results: Previous studies show a positive impact on users' behaviour is expected in supporting their healthcare needs especially in decision-making, personalised treatment and future diseases prediction, and that integrating users in studying AI impact is essential to test possible implications of the technology. Conclusion: Results indicate that without a clear understanding of why patients need AI, or how AI can support individuals with their healthcare needs, it is difficult to visualise the kinds of AI applications that have a meaningful and sustainable impact the daily lives of individuals. Therefore, there is an emerging need to understand the impact of AI technology on users' behaviour to maximise the potential benefits of AI technology.
The synergy between neurotransmitter spillover and asynchronous release in information transmission
(2018)
Interaction with the visual world critically depends on when and how we move our eyes. Eye movements, in turn, alter our experience of the world by selecting objects to foveate and tracking objects over time. The interaction between vision and eye movements continues indefinitely, one process modulating the strength and timing of the other. Despite this tight linkage, vision is often studied outside the context of eye movements, during stable fixation. Likewise, eye movements are often studied with sparse visual stimuli and under ideal viewing conditions. A more accurate understanding of vision requires studying perception in the context of eye movements.
Different types of eye movements reveal different aspects of how the brain works. The continuous nature of tracking smooth pursuit eye movements, combined with its ubiquitous presence in natural vision, makes it an excellent system in which to analyze perception at fine spatial and temporal resolutions. For example, how does vision change during the transition from fixation to pursuit, and when does the brain allocate resources to account for these changes? In contrast, the ballistic nature of saccades requires analysis divided into discrete epochs, including well before the saccade during the planning stage, during saccade execution, and after the movement. At the neuronal level, how do heterogeneous populations of visual- and saccade-related cells come to represent a single saccade vector during these different epochs? What are the effects on visual perception when saccades and pursuit interact? This symposium will reveal how research incorporating both types of eye movements and visual perception can provide a more ecologically valid account of visual-motor integration and the intervening cognitive processes.
This symposium will review innovative approaches and recent advances in understanding the interplay of eye movements and vision. We will take a multifaceted approach to understanding the effects of both exploratory (saccades) and tracking (smooth pursuit) eye movements on vision by using a range of methodologies and animal models (data-driven modeling, clinical populations, and simultaneous recordings of neuronal populations; humans, macaques, and marmosets). This symposium will appeal to vision scientists interested in selective attention, motion processing, neuronal modeling, motor control, neural circuits, and related topics. Our collective goal is to uncover the dynamics of visual perception and the candidate neuronal mechanisms that support eye movements.
In 1868, Karl Vierordt discovered one type of errors in time perception—an overestimation of short duration and underestimation of long durations, known as Vierordt's law. Here we reviewed the original study in its historical context and asked whether Vierordt's law is a result of an unnatural experimental randomization protocol. Using iterative Bayesian updating, we simulated the original results with high accuracy. Importantly, the model also predicted that a slowly changing random-walk sequence produces less central tendency than a random sequence with the same durations. This was validated by a duration reproduction experiment from two sequences (random and random walk) with the same sampled distribution. The results showed that trial-wise variation influenced the magnitude of Vierordt's law. We concluded that Vierordt's law is caused by an unnatural yet widely used experimental protocol.
Watching an instructional video has become a common way to learn a new task. However, we have but a sparse understanding of the neural processes involved during observational learning in naturalistic settings. Recently developed data driven methods for analyzing brain activity provide an opportunity for further investigation. Here, we evaluate intersubject synchrony during fMRI to understand common brain processes during naturalistic observational learning. Participants solitarily watched an instructional video and learned how to fold a paper figure. Three learning runs were sufficient to successfully solve the task. To assess interbrain synchrony, we extended previous principal component (PCA)-based methods to an intersubject principal component analysis (PCA), which offers multiple measures for additional insights into the nature of the synchrony. Using the different metrics of this method, we show a robust synchronous involvement of the action observation execution network (AOEN) in observational learning, between subjects as well as within subjects, regardless of the task or video content. Importantly, additional areas such as the cerebellum, primary motor cortex, control, and sensory integration areas also showed robust synchrony in observational learning. Complimentary to this robust general synchrony, individual regions of the AOEN exhibited task-related differences. Synchrony decreased during the learning process, likely reflecting task state and individual learning strategies. To test the stimulus as a possible source of synchrony, we quantified the temporal structure as the optic flow of the instructional video. Optic flow was strongly related to common activation of the somatomotor areas of the AOEN well beyond visual areas, but could not completely explain synchrony. Thus, although visual motion provides a proxy for meaningful hand actions, our results suggest that intersubject synchrony reflects common cognitive processing during observa- tional learning beyond sensory input.
Perception of magnitudes such as duration or distance is often found to be systematically biased.
The biases, which result from incorporating prior knowledge in the perceptual process, can vary considerably between individuals. The variations are commonly attributed to differences in sensory precision and reliance on priors. However, another factor not considered so far is the implicit belief about how successive sensory stimuli are generated: independently from each other or with certain temporal continuity. The main types of explanatory models proposed so far—static or iterative—mirror this distinction but cannot adequately explain individual biases. Here we propose a new unifying model that explains individual variation as combination of sensory precision and beliefs about temporal continuity and predicts the experimentally found changes in biases when altering temporal continuity. Thus, according to the model, individual differences in perception depend on beliefs about how stimuli are generated in the world.
The angular vestibulo-ocular reflex (aVOR) stabilizes retinal images by counter-rotating the eyes during head rotations. Perfect compensatory movements would thus rotate the eyes exactly opposite to the head, that is, eyes vs. head would exhibit a unity gain. However, in many species, but also in elderly humans or patients with a history of vestibular damage, the aVOR is far from compensatory with gains that are in part considerably lower than unity. The reason for this apparent suboptimality is unknown. Here, we propose that low VOR gain values reflect an optimal adaptation to sensory and motor signal variability. According to this hypothesis, gaze stabilization mechanisms that aim at minimizing the overall retinal image slip must consider the effects of (1) sensory and motor noise and (2) dynamic constraints of peripheral and central nervous processing. We demonstrate that a computational model for optimizing retinal image slip in the presence of such constraints of signal processing in fact predicts gain values smaller than unity. We further show specifically for tadpoles of the clawed toad, Xenopus laevis with particularly low gain values that previously reported VOR gains quantitatively correspond to the observed variability of eye movements and thus constitute an optimal adaptation mechanism. We thus hypothesize that lower VOR gain values in elderly human subjects or recovered patients with a history of vestibular damage may be the sign of an optimization given higher noise levels rather than a direct consequence of the damage, such as an inability of executing fast compensatory eye movements.
Our perception and decision-making are susceptible to prior context. Such sequential dependence has been extensively studied in the visual domain, but less is known about its impact on time perception. Moreover, there are ongoing debates about whether these sequential biases occur at the perceptual stage or during subsequent post-perceptual processing. Using functional magnetic resonance imaging, we investigated neural mechanisms underlying temporal sequential dependence and the role of action in time judgments across trials. Participants performed a timing task where they had to remember the duration of green coherent motion and were cued to either actively reproduce its duration or simply view it passively. We found that sequential biases in time perception were only evident when the preceding task involved active duration reproduction. Merely encoding a prior duration without reproduction failed to induce such biases. Neurally, we observed activation in networks associated with timing, such as striato-thalamo-cortical circuits, and performance monitoring networks, particularly when a “Response” trial was anticipated. Importantly, the hippocampus showed sensitivity to these sequential biases, and its activation negatively correlated with the individual’s sequential bias following active
reproduction trials. These findings highlight the significant role of memory networks in shaping time-related sequential biases at the post-perceptual stages.
Introduction: Functional disorders are prevalent in all medical fields and pose a tremendous public health problem, with pain being one of the most common functional symptoms. Understanding the underlying, potentially unifying mechanism in functional (pain) disorders is instrumental in facilitating timely diagnosis, stigma reduction, and adequate treatment options. Neuroscientific models of perception suggest that functional symptoms arise due to dysregulated sensorimotor processing in the central nervous system, with brain-based predictions dominating the eventual percept. Experimental evidence for this transdiagnostic mechanism has been established in various functional symptoms. The goal of the current study was to investigate whether erroneous sensorimotor processing is an underlying transdiagnostic mechanism in chronic (functional) pain.
Method: A total of 13 patients with chronic (functional) pain [three patients with chronic (functional) pain disorder, F45.40, ICD-10; 10 patients with chronic pain disorder with somatic and psychological factors, F45.41, ICD-10]; and 15 healthy controls performed large combined eye-head gaze shifts toward visual targets, naturally and with increased head moment of inertia. We simultaneously measured participants’ eye and head movements to assess head oscillations at the end of the gaze shift, which are an established indicator of (transdiagnostic) sensorimotor processing deficits of head control.
Results: Using a Bayesian analysis protocol, we found that patients with chronic (functional) pain and control participants stabilized their heads equally well (Bayes Factor 01 = 3.7, Bayes Factor exclusion = 5.23; corresponding to substantial evidence) during all sessions of the experiment.
Conclusion: Our results suggest that patients with chronic (functional) pain do not show measurable symptom-unspecific sensorimotor processing deficits.