Neural models of learning and visual grouping in the presence of finite conduction velocities

The hypothesis of object binding-by-synchronization in the visual cortex has been supported by recent experiments in awake monkeys. They demonstrated coherence among gamma-activities (30–90 Hz) of local neural groups and its perceptual modulation according to the rules of figure-ground segregation. Interactions within and between these neural groups are based on axonal spike conduction with finite velocities. Physiological studies confirmed that the majority of transmission delays is comparable to the temporal scale defined by gamma-activity (11–33 ms). How do these finite velocities influence the development of synaptic connections within and between visual areas? What is the relationship between the range of gamma-coherence and the velocity of signal transmission? Are these large temporal delays compatible with recently discovered phenomenon of gamma-waves traveling across larger parts of the primary visual cortex? The refinement of connections in the immature visual cortex depends on temporal Hebbian learning to adjust synaptic efficacies between spiking neurons. The impact of constant, finite, axonal spike conduction velocities on this process was investigated using a set of topographic network models. Random spike trains with a confined temporal correlation width mimicked cortical activity before visual experience. After learning, the lateral connectivity within one network layer became spatially restricted, the width of the connection profile being directly proportional to the lateral conduction velocity. Furthermore, restricted feedforward divergence developed between neurons of two successive layers. The size of this connection profile matched the lateral connection profile of the lower layer neuron. The mechanism in this network model is suitable to explain the emergence of larger receptive fields at higher visual areas while preserving a retinotopic mapping. The influence of finite conduction velocities on the local generation of gamma-activities and their spatial synchronization was investigated in a model of a mature visual area. Sustained input and local inhibitory feedback was sufficient for the emergence of coherent gamma-activity that extended across few millimeters. Conduction velocities had a direct impact on the frequency of gamma-oscillations, but did neither affect gamma-power nor the spatial extent of gamma-coherence. Adding long-range horizontal connections between excitatory neurons, as found in layer 2/3 of the primary visual cortex, increased the spatial range of gamma-coherence. The range was maximal for zero transmission delays, and for all distances attenuated with finite, decreasing lateral conduction velocities. Below a velocity of 0.5 m/s, gamma-power and gamma-coherence were even smaller than without these connections at all, i.e., slow horizontal connections actively desynchronized neural populations. In conclusion, the enhancement of gamma-coherence by horizontal excitatory connections critically depends on fast conduction velocities. Coherent gamma-activity in the primary visual cortex and the accompanying models was found to only cover small regions of the visual field. This challenges the role of gamma-synchronization to solve the binding problem for larger object representations. Further analysis of the previous model revealed that the patches of coherent gamma-activity (1.8 mm half-height decline) were part of more globally occurring gamma-waves, which coupled over much larger distances (6.3 mm half-height decline). The model gamma-waves observed here are very similar to those found in the primary visual cortex of awake monkeys, indicating that local recurrent inhibition and restricted horizontal connections with finite axonal velocities are sufficient requirements for their emergence. In conclusion, since the model is in accordance with the connectivity and gamma-processes in the primary visual cortex, the results support the hypothesis that gamma-waves provide a generalized concept for object binding in the visual cortex

Kognitive Interpretationen mehrdeutiger visueller Reize

Unser Gehirn muss zu jeder Zeit relevante Signale von irrelevanten Informationen trennen. Dazu müssen diese als spezifische Einheiten erkannt und klassifiziert werden. Mehrdeutigkeit ist ein wesentlicher Aspekt dieses Verarbeitungsprozesses und kann durch verrauschte Eingangssignale und durch den Aufbau unserer sensorischer Systeme entstehen. Beispielsweise können Reize mehrdeutig sein, wenn sie verrauscht oder unvollständig sind oder nur kurzzeitig wahrgenommen werden. Unter solchen Bedingungen werden Wahrnehmung und Klassifikation eines Reizes deutlich erschwert. Bereits vorhandene kognitive Repräsentationen werden somit möglicherweise nicht aktiviert. Folglich müssen Rückschlüsse über die Reize aufgrund von Kontext und Erfahrung gezogen werden. Ein und derselbe Reiz kann jedoch unterschiedlich repräsentiert und im sensorischen System kodiert werden. Da nur eine Repräsentation die Basis zukünftigen Handelns bilden kann, entsteht eine Art Konkurrenz innerhalb der Wahrnehmung. Derartige Wahrnehmungsphänomene, die mit der Mehrdeutigkeit von Reizen in Verbindung stehen, bilden den Mittelpunkt der vorliegenden Dissertation. Wenn einem physikalisch konstanten Reiz mehrere Interpretationen zugeordnet werden, entsteht ein Wechsel zwischen diesen Einordnungen, den man wahrnimmt und Rivalität ("rivalry") nennt. In dieser Dissertation werden diverse neue Erkenntnisse zu diesem grundlegenden Phänomen der sensorischen Verarbeitung beschrieben. So wird gezeigt, dass Übergänge zwischen drei wahrgenommenen Interpretationen – ein vergleichsweise selten untersuchtes Phänomen, da Rivalität meist mit zweideutigen Reizen untersucht wird – vorhersehbaren Mustern folgen (Kapitel 2). Darüber hinaus zeigt sich, dass derartige Übergänge spezifische Eigenschaften aufweisen, welche die Geschwindigkeit und die Richtung ihrer räumlichen Ausbreitung im visuellen Feld bestimmen (Kapitel 3). Diese Eigenschaften der Mehrdeutigkeit werden weiterhin stark von Aufmerksamkeit und anderen, introspektiven Prozessen beeinflusst. Um die der Rivalität in der Wahrnehmung tatsächlich zugrundeliegenden Prozesse und die damit verbundenen Änderungen des Bewusstseins von derartigen subjektiven Prozessen abzugrenzen, müssen letztere kontrolliert oder sogar vollständig umgangen werden. Ein objektives Maß der Rivalität in der Wahrnehmung wird zur Lösung dieser Aufgabe vorgeschlagen und bietet eine wertvolle Alternative zu introspektivem Berichten über den Wahrnehmungszustand (Kapitel 4). Übergänge in der Wahrnehmung entstehen entlang einer bestimmten Merkmalsdimension des Reizes, wie beispielsweise der Orientierung des berühmten Neckerwürfels. Zudem kann auch eine Änderung in der Merkmalsdimension der Luminanz eine unterschiedliche Interpretation des Reizes hervorrufen. Es wird gezeigt, dass die Pupille kleiner wird, wenn eine Interpretation mit hoher Luminanz die Wahrnehmung übernimmt, und umgekehrt, dass die Pupille größer wird, wenn eine Interpretation mit niedriger Luminanz die Wahrnehmung übernimmt. Folglich kann die Pupille als ein zuverlässiges und objektives Maß für Änderungen in der Wahrnehmung verwendet werden. Durch die Verwendung solcher objektiven Maße konnten neue Eigenschaften der Übergänge in der Wahrnehmung aufgezeigt werden, welche die Theorie unterstützen, dass Introspektion die der Verarbeitung mehrdeutiger Situationen zugrundeliegenden Prozesse merklich beeinflussen kann. Als Nächstes wurden mehrdeutiger Reize im Zusammenhang mit der Wahrnehmung von Objekten eingesetzt (Kapitel 5). Am Beispiel der Kippfigur des "bewegten Diamanten" wird dabei die Bedeutung von mehrdeutigen Reizen veranschaulicht. Beim bewegten Diamanten werden zwei Interpretationen wahrgenommen, die sich entlang der Dimension der Objektkohärenz abwechseln. Das bedeutet, dass die Wahrnehmung zwischen einem einzelnen zusammenhängenden Objekt (Diamant) und mehreren unzusammenhängenden Komponenten kippt. Es wird gezeigt, dass die Interpretation des Reizes als ein einziges kohärentes Objekt, verglichen mit der Interpretation als mehrere Komponenten, zu einer Erhöhung der visuellen Empfindlichkeit innerhalb des Objektes führt. Diese Ergebnisse sind ein Beleg dafür, wie die Aktivierung einer Interpretation eines Reizes als Einzelobjekt (im Vergleich zur Komponentenwahrnehmung) dazu führt, dass die Aufmerksamkeit top-down zu den relevanten Bereichen des Gesichtsfeldes gelenkt wird. Es wird weiter untersucht, welche Eigenschaften des Reizes zu einer bottom-up Aktivierung der Interpretation solcher Objekte beitragen (Kapitel 6). Die Mehrdeutigkeit von Objekten kann erfolgreich aufgehoben werden, indem man einen starken Kontrast in Luminanz oder Farbe zwischen dem Objekt und dem Hintergrund erzeugt. Auch die Größe und die Form haben einen großen Einfluss auf die Detektion und Identifikation von Objekten. Des Weiteren sind die Eigenschaften eines Objektes nicht nur bestimmend für die Erfolgsquote bei der Objekterkennung, sondern ebenso bedeutend für die Speicherung der Repräsentation im Gedächtnis, beispielsweise von neu wahrgenommenen Objekten. Das Klassifizieren von Objekten durch die Versuchsperson wird ebenfalls durch Mehrdeutigkeit beeinflusst. So kann ein Objekt der Versuchsperson einerseits als neu erscheinen, obwohl es bereits bekannt war, weil es beispielsweise der Versuchsperson schon einmal gezeigt worden ist. Andererseits kann auch ein eigentlich unbekanntes Objekt der Versuchsperson dennoch vertraut vorkommen. In dieser Arbeit wird gezeigt, dass solche subjektiven Effekte einen Einfluss auf die Pupillengröße haben (Kapitel 7). Außerdem verkleinert sich die Pupille der Versuchspersonen beim Betrachten neuer Bilder stärker als bei bekannten. Ein ähnlicher Effekt wird gefunden, wenn das Bild vorher erfolgreich im Gedächtnis gespeichert wurde. Daher ist es wahrscheinlich, dass die Pupille die Verfestigung von neuen Objekten im Gedächtnis widerspiegelt. Abschließend wird untersucht, ob sich kognitive Prozesse, wie Entscheidungsfindung – ein wichtiger Prozess, falls mehreren Optionen zur Verfügung stehen und Mehrdeutigkeit aufgehoben werden soll – auch in der Pupille widerspiegeln (Kapitel 8). Es wird zunächst bestätigt, dass die Pupillen sich erweitern, nachdem man eine Entscheidung getroffen hat. Neu wird gezeigt, dass diese Pupillenausdehnungen erfolgreich von anderen Personen erkannt und verwendet werden können, um ein interaktives Spiel gegen die erste Person (den "Gegner") zu gewinnen. Insgesamt wird in dieser Dissertation untersucht, wie mehrdeutige Reize die Wahrnehmung beeinflussen und wie Mehrdeutigkeit verwendet werden kann, um Prozesse des Gehirns zu studieren. Es hat sich gezeigt, dass Mehrdeutigkeit vorhersehbaren Mustern folgt, sie objektiv mit Reflexen gemessen werden kann, und Einblicke in neuronale Prozesse wie Aufmerksamkeit, Objektwahrnehmung und Entscheidungsmechanismen liefern kann. Diese Ergebnisse zeigen, dass Mehrdeutigkeit eine zentrale Eigenschaft sensorischer Systeme ist, und Lebewesen in die Lage versetzt, mit ihrer Umwelt flexibel zu interagieren. Mehrdeutigkeit macht das Verhalten vielfältiger, ermöglicht es dem Gehirn, mit der Welt auf verschiedenen Wegen zu interagieren, und ist die Basis der Dynamik von Wahrnehmung, Interpretation und Entscheidung.Brains can sense and distinguish signals from background noise in physical environments, and recognize and classify them as distinct entities. Ambiguity is an inherent part of this process. It is a cognitive property that is generated by the noisy character of the signals, and by the design of the sensory systems that process them. Stimuli can be ambiguous if they are noisy, incomplete, or only briefly sensed. Such conditions may make stimuli indistinguishable from others and thereby difficult to classify as single entities by our sensory systems. In these cases, stimuli fail to activate a representation that may have been previously stored in the system. Deduction, through context and experience, is consequently needed to reach a decision on what is exactly sensed. Deduction can, however, also be subject to ambiguity as stimuli and their properties may receive multiple representations in the sensory system. In such cases, these multiple representations compete for perceptual dominance, that is, for becoming the single entity taken by the system as a reference point for subsequent behavior. These types of ambiguity and several phenomena that relate to them are at the center of this dissertation. Perceptual rivalry, the phenomenal experience of alternating percepts over time, is an example of how the brain may give multiple interpretations to a stimulus that is physically constant. Rivalry is a very typical and general sensory process and this thesis demonstrates some newly discovered properties of its dynamics. It was found that alternations between three perceptual interpretations – a relatively rare condition as rivalry generally occurs between two percepts – follow predictable courses (Chapter 2). Furthermore, such alternations had several properties that determine their speed and direction of spatial spread (suppression waves) in the visual field (Chapter 3). These properties of ambiguity were further strongly affected by attention and other introspective processes. To demarcate the true underlying process of perceptual rivalry and the accompanied changes in awareness, these subjective processes need to be either circumvented or controlled for. An objective measure of perceptual rivalry was proposed that resolved this issue and provided a good alternative for introspective report of ambiguous states (Chapter 4). Changes in percepts occur along a specific feature domain such as depth orientation for the famous Necker cube. Alternatively, luminance may also be a rivalry feature and one percept may appear brighter as the other rivaling percept. It was demonstrated that the pupil gets smaller when a percept with high luminance becomes dominant, and vice versa, gets bigger when a percept with low luminance gets dominant during perceptual rivalry. As such, the pupil can serve as a reliable objective indicator of changes in visual awareness. By using such reflexes during rivalry, several new properties of alternations were discovered and it was again confirmed that introspection can confound the true processes involved in ambiguity. Next, the usefulness of ambiguous stimuli was explored in the context of objects as entities (Chapter 5). Some ambiguous stimuli can induce two percepts that alternate along the feature domain of object coherency, that is, whether a single coherent object or multiple incoherent objects are seen. In other words, an ambiguous stimulus can induce two cognitive interpretations of either seeing an entity or not. It was reported that being aware of a single coherent object results in the increase in visual sensitivity for the areas that constitute the object. These results are evidence of how the activation of a representation of a single and unique object can guide and allocate attentional resources to relevant areas in the visual field in a top-down way. It was further explored which features help to bottom-up access such object representations (Chapter 6). Ambiguity of objects can be successfully resolved by adding strong contrasts between the object and its background in luminance and color. The size and variability of the object's shape was also found to be an important factor for its successful detection and identification. Furthermore, the characteristics of objects do not only determine the rate of success in a recognition task, but are equally important for the storage of their representations in memory if, for instance, the object is novel to the observer. The subjective experience of a novel object is also subject to ambiguity and objects may appear novel to the observer although they are familiar (i.e., previously shown to the observer), or vice versa, they appear familiar to the observer although they are actually novel. It was here shown that such subjective effects are reflected in the pupil (Chapter 7). In addition, if novel images were presented to observers, their pupils constricted stronger as compared to if familiar images were presented. Similarly, if novel stimuli were shown to observers, pupillary constrictions were stronger if these stimuli were successfully stored in memory as compared to those later forgotten. As such, the pupil reflected the cognitive process of novelty encoding. Finally, it was tested whether other cognitive processes, such as decision-making – an important process when multiple options are available and ambiguity has to be resolved with a conscious decision – were also reflected in changes of pupil size (Chapter 8). It was confirmed that the pupil tends to dilate after an observer has made a decision. These dilations can successfully be detected between individuals and further used to gain the upper hand during an interactive game. In sum, this thesis has explored how ambiguous signals affect perception and how ambiguity inside perceptual systems can be used to study processes of the brain. It is found that ambiguity follows predictable courses, can be objectively assessed with reflexes, and can provide insights into other neuronal mechanisms such as attention, object representations, and decision-making. These findings demonstrate that ambiguity is a core property of the sensory systems that enable living beings to interact with their surroundings. Ambiguity adds variation to behavior, allows the brain to flexibly interact with the world, and lies at the bottom of the dynamics of sense, interpretations, and behavioral decisions

Bio-Inspired Computer Vision: Towards a Synergistic Approach of Artificial and Biological Vision

To appear in CVIUStudies in biological vision have always been a great source of inspiration for design of computer vision algorithms. In the past, several successful methods were designed with varying degrees of correspondence with biological vision studies, ranging from purely functional inspiration to methods that utilise models that were primarily developed for explaining biological observations. Even though it seems well recognised that computational models of biological vision can help in design of computer vision algorithms, it is a non-trivial exercise for a computer vision researcher to mine relevant information from biological vision literature as very few studies in biology are organised at a task level. In this paper we aim to bridge this gap by providing a computer vision task centric presentation of models primarily originating in biological vision studies. Not only do we revisit some of the main features of biological vision and discuss the foundations of existing computational studies modelling biological vision, but also we consider three classical computer vision tasks from a biological perspective: image sensing, segmentation and optical flow. Using this task-centric approach, we discuss well-known biological functional principles and compare them with approaches taken by computer vision. Based on this comparative analysis of computer and biological vision, we present some recent models in biological vision and highlight a few models that we think are promising for future investigations in computer vision. To this extent, this paper provides new insights and a starting point for investigators interested in the design of biology-based computer vision algorithms and pave a way for much needed interaction between the two communities leading to the development of synergistic models of artificial and biological vision

Seeing the invisible: The scope and limits of unconscious processing in binocular rivalry

When an image is presented to one eye and a very different image is presented to the corresponding location of the other eye, they compete for conscious representation, such that only one image is visible at a time while the other is suppressed. Called binocular rivalry, this phenomenon and its deviants have been extensively exploited to study the mechanism and neural correlates of consciousness. In this paper, we propose a framework, the unconscious binding hypothesis, to distinguish unconscious processing from conscious processing. According to this framework, the unconscious mind not only encodes individual features but also temporally binds distributed features to give rise to cortical representation, but unlike conscious binding, such unconscious binding is fragile. Under this framework, we review evidence from psychophysical and neuroimaging studies, which suggests that: (1) for invisible low level features, prolonged exposure to visual pattern and simple translational motion can alter the appearance of subsequent visible features (i.e. adaptation); for invisible high level features, although complex spiral motion cannot produce adaptation, nor can objects/words enhance subsequent processing of related stimuli (i.e. priming), images of tools can nevertheless activate the dorsal pathway; and (2) although invisible central cues cannot orient attention, invisible erotic pictures in the periphery can nevertheless guide attention, likely through emotional arousal; reciprocally, the processing of invisible information can be modulated by attention at perceptual and neural levels

Cloverleaf Clusters: A Common Macrostructural Organization across Human Visual and Auditory Cortex

One of the fundamental properties of mammalian brains is that sensory regions of cortex are organized into multiple, functionally specialized cortical field maps (CFMs). An individual CFM is composed of two orthogonal topographical representations, reflecting two essential aspects of a sensory feature space. Each CFM is thought to subserve a specific computation or set of computations that underlie particular perceptual behaviors by enabling the comparison and combination of the information carried by the various specialized neuronal populations within this cortical region. Multiple adjacent CFMs, in turn, have now been shown by multiple laboratories to be organized in visual and auditory cortex into a macrostructural pattern called the cloverleaf cluster. CFMs within cloverleaf clusters tend to share properties such as receptive field distribution, cortical magnification, and processing specialization. This chapter will review the evidence for CFM and cloverleaf cluster organization across human visual and auditory cortex and will discuss the utility of these measurements for determining cortical structure and function and for investigating what changes occur in sensory cortex following various types of trauma or disease

The dynamic neural field approach to cognitive robotics

This tutorial presents an architecture for autonomous robots to generate behavior in joint action tasks. To efficiently interact with another agent in solving a mutual task, a robot should be endowed with cognitive skills such as memory, decision making, action understanding and prediction. The proposed architecture is strongly inspired by our current understanding of the processing principles and the neuronal circuitr underlying these functionalities in the primate brain. As a mathematical framework, we use a coupled system of dynamic neural fields, each representing the basic functionality of neuronal populations in different brain areas. It implements goal-directed behavior in joint action as a continuous process that builds on the interpretation of observed movements in terms of the partner’s action goal. We validate the architecture in two experimental paradigms: (1) a joint search task; (2) a reproduction of an observed or inferred end state of a grasping–placing sequence. We also review some of the mathematical results about dynamic neural fields that are important for the implementation work.European Commission fp6-IST2, project no. 00374

Action in Mind: Neural Models for Action and Intention Perception

To notice, recognize, and ultimately perceive the others’ actions and to discern the intention behind those observed actions is an essential skill for social communications and improves markedly the chances of survival. Encountering dangerous behavior, for instance, from a person or an animal requires an immediate and suitable reaction. In addition, as social creatures, we need to perceive, interpret, and judge correctly the other individual’s actions as a fundamental skill for our social life. In other words, our survival and success in adaptive social behavior and nonverbal communication depends heavily on our ability to thrive in complex social situations. However, it has been shown that humans spontaneously can decode animacy and social interactions even from strongly impoverished stimuli and this is a fundamental part of human experience that develops early in infancy and is shared with other primates. In addition, it is well established that perceptual and motor representations of actions are tightly coupled and both share common mechanisms. This coupling between action perception and action execution plays a critical role in action understanding as postulated in various studies and they are potentially important for our social cognition. This interaction likely is mediated by action-selective neurons in the superior temporal sulcus (STS), premotor and parietal cortex. STS and TPJ have been identified also as coarse neural substrate for the processing of social interactions stimuli. Despite this localization, the underlying exact neural circuits of this processing remain unclear. The aim of this thesis is to understand the neural mechanisms behind the action perception coupling and to investigate further how human brain perceive different classes of social interactions. To achieve this goal, first we introduce a neural model that provides a unifying account for multiple experiments on the interaction between action execution and action perception. The model reproduces correctly the interactions between action observation and execution in several experiments and provides a link towards electrophysiological detailed models of relevant circuits. This model might thus provide a starting point for the detailed quantitative investigation how motor plans interact with perceptual action representations at the level of single-cell mechanisms. Second we present a simple neural model that reproduces some of the key observations in psychophysical experiments about the perception of animacy and social interactions from stimuli. Even in its simple form the model proves that animacy and social interaction judgments partly might be derived by very elementary operations in hierarchical neural vision systems, without a need of sophisticated or accurate probabilistic inference

Seuratun kappaleen poikkeuttaminen silmänräpäysten aikana: käyttäytymis- ja neuromagneettisia havaintoja

The visual world is perceived as continuous despite frequent interruptions of sensory data due to eyeblinks and rapid eye movements. To create the perception of constancy, the brain makes use of fill-in mechanisms. This study presents an experiment in which the location of an object during smooth pursuit tracking is altered during eyeblinks. The experiment investigates the effects of blink suppression and fill-in mechanisms to cloud the discrimination of these changes. We employed a motion-tracking task, which promotes the accurate evaluation of the object’s trajectory and thus can counteract the fill-in mechanisms. Six subjects took part in the experiment, during which they were asked to report any perceived anomalies in the trajectory. Eye movements were monitored with a video-based tracking and brain responses with simultaneous MEG recordings. Discrimination success was found to depend on the direction of the displacement, and was significantly modulated by prior knowledge of the triggered effect. Eye-movement data were congruent with previous findings and revealed a smooth transition from blink recovery to object locating. MEG recordings were analysed for condition-dependent evoked and induced responses; however, intersubject variability was too large for drawing clear conclusions regarding the brain basis of the fill-in mechanisms.Visuaalinen maailma koetaan jatkuvana, vaikka silmänräpäykset ja nopeat silmänliikkeet aiheuttavat keskeytyksiä sensoriseen tiedonkeruuseen. Luodakseen käsityksen pysyvyydestä, aivot käyttävät täyttömekanismeja. Tämä tutkimus esittelee kokeen, jossa kappaleen seurantaa hitailla seurantaliikkeillä häiritään muuttamalla sen sijaintia silmänräpäysten aikana. Tämä koe tutkii, kuinka silmänräpäysten aiheuttama suppressio ja täyttömekanismit sumentavat kykyä erotella näitä muutoksia. Käytimme liikeseurantatehtävää, joka vastaavasti edistää kappaleen liikeradan tarkkaa arviointia. Kuusi koehenkilöä osallistui kokeeseen, jonka aikana heitä pyydettiin ilmoittamaan kaikki havaitut poikkeamat kappaleen liikeradassa. Silmänliikkeitä tallennettiin videopohjaisella seurannalla, ja aivovasteita yhtäaikaisella MEG:llä. Erottelykyvyn todettiin riippuvan poikkeutuksen suunnasta, sekä merkittävästi a priori tiedosta poikkeutusten esiintymistavasta. Silmänliikedata oli yhtenevää aiempien tutkimusten kanssa, ja paljasti sujuvan siirtymisen silmänräpäyksistä palautumisesta kappaleen paikallistamiseen. MEG-tallenteet analysoitiin ehdollisten heräte- ja indusoitujen vasteiden löytämiseksi, mutta yksilölliset vaste-erot koehenkilöiden välillä olivat liian suuria selkeiden johtopäätösten tekemiseksi täyttömekanismien aivoperustasta

Mental and sensorimotor extrapolation fare better than motion extrapolation in the offset condition

Evidence for motion extrapolation at motion offset is scarce. In contrast, there is abundant evidence that subjects mentally extrapolate the future trajectory of weak motion signals at motion offset. Further, pointing movements overshoot at motion offset. We believe that mental and sensorimotor extrapolation is sufficient to solve the problem of perceptual latencies. Both present the advantage of being much more flexible than motion extrapolatio