Cause Of Sensation Research Articles

Disentangling sensory precision and prior expectation of change in autism during tactile discrimination

Predictive coding theories suggest that core symptoms in autism spectrum disorders (ASD) may stem from atypical mechanisms of perceptual inference (i.e., inferring the hidden causes of sensations). Specifically, there would be an imbalance in the precision or weight ascribed to sensory inputs relative to prior expectations. Using three tactile behavioral tasks and computational modeling, we specifically targeted the implicit dynamics of sensory adaptation and perceptual learning in ASD. Participants were neurotypical and autistic adults without intellectual disability. In Experiment I, tactile detection thresholds and adaptation effects were measured to assess sensory precision. Experiments II and III relied on two-alternative forced choice tasks designed to elicit a time-order effect, where prior knowledge biases perceptual decisions. Our results suggest a subtler explanation than a simple imbalance in the prior/sensory weights, having to do with the dynamic nature of perception, that is the adjustment of precision weights to context. Compared to neurotypicals, autistic adults showed no difference in average performance and sensory sensitivity. Both groups managed to implicitly learn and adjust a prior that biased their perception. However, depending on the context, autistic participants showed no, normal or slower adaptation, a phenomenon that computational modeling of trial-to-trial responses helped us to associate with a higher expectation for sameness in ASD, and to dissociate from another observed robust difference in terms of response bias. These results point to atypical perceptual learning rather than altered perceptual inference per se, calling for further empirical and computational studies to refine the current predictive coding theories of ASD.

The Active Inference Model of Coherence Therapy.

Coherence Therapy is an empirically derived experiential psychotherapy based on Psychological Constructivism. Symptoms are viewed as necessary output from an implicit model of the world. The therapist curates experiences and directs attention toward discovering the model. Rendered explicit, the model is juxtaposed with contradictory knowledge driving memory re-consolidation with resolution of the symptom. The Bayesian Brain views perception and action as inferential processes. Prior beliefs are combined in a generative model to explain the hidden causes of sensations through a process of Active Inference. Prior beliefs that are poor fits to the real world are suboptimal. Suboptimal priors with optimal inference produce Bayes Optimal Pathology with behavioral symptoms. The Active Inference Model of Coherence Therapy posits that Coherence Therapy is a dyadic act of therapist guided Active Inference that renders the (probable) hidden causes of a client's behavior conscious. The therapist's sustained attention on the goal of inference helps to overcome memory control bias against retrieval of the affectively charged suboptimal prior. Serial experiences cue memory retrieval and re-instantiation of the physiological/affective state that necessitates production of the symptom in a particular context. As this process continues there is a break in modularity with assimilation into broader networks of experience. Typically, the symptom produced by optimal inference with the suboptimal prior is experienced as unnecessary/inappropriate when taken out of the particular context. The implicit construct has been re-represented and rendered consciously accessible, by a more complex but more accurate model in which the symptom is necessary in some contexts but not others. There is an experience of agency and control in symptom creation, accompanied by the spontaneous production of context appropriate behavior. The capacity for inference has been restored. The Active Inference Model of Coherence Therapy provides a framework for Coherence Therapy as a computational process which can serve as the basis for new therapeutic interventions and experimental designs integrating biological, cognitive, behavioral, and environmental factors.

The Active Bayesian Brain and the Rorschach Task

Abstract. The Rorschach offers a unique and interesting paradigm from the perspective of the (Bayesian) brain. This contribution to the cross-disciplinary special issue considers the Rorschach from the perspective of perceptual inference in the brain and how it might inform subject-specific differences in perceptual synthesis. Before doing so, we provide a broad overview of active inference in its various manifestations. In brief, active inference supposes that our perceptions are the best hypothesis to explain sensory impressions. On a Bayesian account, the requisite belief updating rests sensitively upon the precision or confidence ascribed to sensory input, relative to prior beliefs about the causes of sensations. This focus – on the balance between sensory and prior precision – has been a useful construct in both cognitive science (e.g., as a formal explanation for attention) and neuropsychology (e.g., as a formal explanation for aberrant or false inference in hallucinations). In this setting, false inference is generally understood as abnormally high precision afforded to high-level hypotheses or explanations for visual input, which may compensate for a failure to attenuate sensory precision. On this view, the Rorschach offers an interesting paradigm because the amount of precise information about the causes of visual input is deliberately minimized – and rendered ambiguous – thereby placing greater emphasis on prior beliefs entertained by the respondent. We close by exploring this issue and several other areas of intersection between Rorschach responding and active inference.

Neuromodulatory Control and Language Recovery in Bilingual Aphasia: An Active Inference Approach.

Understanding the aetiology of the diverse recovery patterns in bilingual aphasia is a theoretical challenge with implications for treatment. Loss of control over intact language networks provides a parsimonious starting point that can be tested using in-silico lesions. We simulated a complex recovery pattern (alternate antagonism and paradoxical translation) to test the hypothesis—from an established hierarchical control model—that loss of control was mediated by constraints on neuromodulatory resources. We used active (Bayesian) inference to simulate a selective loss of sensory precision; i.e., confidence in the causes of sensations. This in-silico lesion altered the precision of beliefs about task relevant states, including appropriate actions, and reproduced exactly the recovery pattern of interest. As sensory precision has been linked to acetylcholine release, these simulations endorse the conjecture that loss of neuromodulatory control can explain this atypical recovery pattern. We discuss the relevance of this finding for other recovery patterns.

Degeneracy and Redundancy in Active Inference.

The notions of degeneracy and redundancy are important constructs in many areas, ranging from genomics through to network science. Degeneracy finds a powerful role in neuroscience, explaining key aspects of distributed processing and structure–function relationships in the brain. For example, degeneracy accounts for the superadditive effect of lesions on functional deficits in terms of a “many-to-one” structure–function mapping. In this paper, we offer a principled account of degeneracy and redundancy, when function is operationalized in terms of active inference, namely, a formulation of perception and action as belief updating under generative models of the world. In brief, “degeneracy” is quantified by the “entropy” of posterior beliefs about the causes of sensations, while “redundancy” is the “complexity” cost incurred by forming those beliefs. From this perspective, degeneracy and redundancy are complementary: Active inference tries to minimize redundancy while maintaining degeneracy. This formulation is substantiated using statistical and mathematical notions of degenerate mappings and statistical efficiency. We then illustrate changes in degeneracy and redundancy during the learning of a word repetition task. Finally, we characterize the effects of lesions—to intrinsic and extrinsic connections—using in silico disconnections. These numerical analyses highlight the fundamental difference between degeneracy and redundancy—and how they score distinct imperatives for perceptual inference and structure learning that are relevant to synthetic and biological intelligence.

Working With the Predictable Life of Patients: The Importance of "Mentalizing Interoception" to Meaningful Change in Psychotherapy.

To understand our patients and optimize their treatment, psychotherapists of all theoretical orientations may benefit from considering current scientific evidence alongside psychodynamic constructs. There is recent neuroscientific evidence that subjective awareness, feelings and emotions depend upon “interoception,” defined as the neural signaling to the brain from all tissues of the body. Interoception is the obvious basis of homeostasis (in the brainstem) but some interoceptive signals rise above this level and contribute to inferential processes that substantiate intrapersonal and interpersonal experience. The focus of this paper is on the essential role that their “interoception” plays in our patients’ emotional experience and subjective awareness, and how the process referred to as “mentalizing interoception” may be harnessed in therapy. This can best be understood in terms of “predictive processing,” which describes how subjective states, and particularly emotion, are inferred from sensory inputs – both interoceptive and exteroceptive. Predictive processing assumes that the brain infers (probabilistically) the likely cause of sensation experienced through the sense organs, by testing this sensory data against its innate and learned “priors.” This implies that any effort at changing heavily over-learned prior beliefs will require action upon the system that has generated that set of prior beliefs. This involves, quite literally, acting upon the world to alter inferential processes, or in the case of interoceptive priors, acting on the patient’s body to alter habitual autonomic nervous system (ANS) reflexes. Focused attention to bodily sensations/reactions, in the safety of the therapeutic relationship, provides a route to “mentalizing interoception,” by means of the bodily cues that may be the only conscious element of deeply hidden priors and thus the clearest way to access them. This can: update patients’ characteristic, dysfunctional responses to emotion and feelings; increase emotional insight; decrease cognitive distortions; and engender a more acute awareness of the present moment. These important ideas are outlined below from the perspective of psychodynamic psychotherapeutic practice, in order to discuss how relevant information from neuroscientific theory and current research can best be applied in clinical treatment. A clinical case will be presented to illustrate how this argument or treatment relates directly to clinical practice.

Hallucinations both in and out of context: An active inference account.

Hallucinations, including auditory verbal hallucinations (AVH), occur in both the healthy population and in psychotic conditions such as schizophrenia (often developing after a prodromal period). In addition, hallucinations can be in-context (they can be consistent with the environment, such as when one hallucinates the end of a sentence that has been repeated many times), or out-of-context (such as the bizarre hallucinations associated with schizophrenia). In previous work, we introduced a model of hallucinations as false (positive) inferences based on a (Markov decision process) formulation of active inference. In this work, we extend this model to include content–to disclose the computational mechanisms behind in- and out-of-context hallucinations. In active inference, sensory information is used to disambiguate alternative hypotheses about the causes of sensations. Sensory information is balanced against prior beliefs, and when this balance is tipped in the favor of prior beliefs, hallucinations can occur. We show that in-context hallucinations arise when (simulated) subjects cannot use sensory information to correct prior beliefs about hearing a voice, but beliefs about content (i.e. the sequential order of a sentence) remain accurate. When hallucinating subjects also have inaccurate beliefs about state transitions, out-of-context hallucinations occur; i.e. their hallucinated speech content is disordered. Note that out-of-context hallucinations in this setting does not refer to inference about context, but rather to false perceptual inference that emerges when the confidence in–or precision of–sensory evidence is reduced. Furthermore, subjects with inaccurate beliefs about state transitions but an intact ability to use sensory information do not hallucinate and are reminiscent of prodromal patients. This work demonstrates the different computational mechanisms that may underlie the spectrum of hallucinatory experience–from the healthy population to psychotic states.

Dynamic Causal Modelling of Active Vision.

In this paper, we draw from recent theoretical work on active perception, which suggests that the brain makes use of an internal (i.e., generative) model to make inferences about the causes of sensations. This view treats visual sensations as consequent on action (i.e., saccades) and implies that visual percepts must be actively constructed via a sequence of eye movements. Oculomotor control calls on a distributed set of brain sources that includes the dorsal and ventral frontoparietal (attention) networks. We argue that connections from the frontal eye fields to ventral parietal sources represent the mapping from “where”, fixation location to information derived from “what” representations in the ventral visual stream. During scene construction, this mapping must be learned, putatively through changes in the effective connectivity of these synapses. Here, we test the hypothesis that the coupling between the dorsal frontal cortex and the right temporoparietal cortex is modulated during saccadic interrogation of a simple visual scene. Using dynamic causal modeling for magnetoencephalography with (male and female) human participants, we assess the evidence for changes in effective connectivity by comparing models that allow for this modulation with models that do not. We find strong evidence for modulation of connections between the two attention networks; namely, a disinhibition of the ventral network by its dorsal counterpart.SIGNIFICANCE STATEMENT This work draws from recent theoretical accounts of active vision and provides empirical evidence for changes in synaptic efficacy consistent with these computational models. In brief, we used magnetoencephalography in combination with eye-tracking to assess the neural correlates of a form of short-term memory during a dot cancellation task. Using dynamic causal modeling to quantify changes in effective connectivity, we found evidence that the coupling between the dorsal and ventral attention networks changed during the saccadic interrogation of a simple visual scene. Intuitively, this is consistent with the idea that these neuronal connections may encode beliefs about “what I would see if I looked there”, and that this mapping is optimized as new data are obtained with each fixation.

Computational Neuropsychology and Bayesian Inference.

Computational theories of brain function have become very influential in neuroscience. They have facilitated the growth of formal approaches to disease, particularly in psychiatric research. In this paper, we provide a narrative review of the body of computational research addressing neuropsychological syndromes, and focus on those that employ Bayesian frameworks. Bayesian approaches to understanding brain function formulate perception and action as inferential processes. These inferences combine ‘prior’ beliefs with a generative (predictive) model to explain the causes of sensations. Under this view, neuropsychological deficits can be thought of as false inferences that arise due to aberrant prior beliefs (that are poor fits to the real world). This draws upon the notion of a Bayes optimal pathology – optimal inference with suboptimal priors – and provides a means for computational phenotyping. In principle, any given neuropsychological disorder could be characterized by the set of prior beliefs that would make a patient’s behavior appear Bayes optimal. We start with an overview of some key theoretical constructs and use these to motivate a form of computational neuropsychology that relates anatomical structures in the brain to the computations they perform. Throughout, we draw upon computational accounts of neuropsychological syndromes. These are selected to emphasize the key features of a Bayesian approach, and the possible types of pathological prior that may be present. They range from visual neglect through hallucinations to autism. Through these illustrative examples, we review the use of Bayesian approaches to understand the link between biology and computation that is at the heart of neuropsychology.

Working memory, attention, and salience in active inference

The psychological concepts of working memory and attention are widely used in the cognitive and neuroscientific literatures. Perhaps because of the interdisciplinary appeal of these concepts, the same terms are often used to mean very different things. Drawing on recent advances in theoretical neurobiology, this paper tries to highlight the correspondence between these established psychological constructs and the formal processes implicit in mathematical descriptions of brain function. Here, we consider attention and salience from the perspective offered by active inference. Using variational principles and simulations, we use active inference to demonstrate how attention and salience can be disambiguated in terms of message passing between populations of neurons in cortical and subcortical structures. In brief, we suggest that salience is something that is afforded to actions that realise epistemic affordance, while attention per se is afforded to precise sensory evidence – or beliefs about the causes of sensations.

Virtual reality and consciousness inference in dreaming.

This article explores the notion that the brain is genetically endowed with an innate virtual reality generator that – through experience-dependent plasticity – becomes a generative or predictive model of the world. This model, which is most clearly revealed in rapid eye movement (REM) sleep dreaming, may provide the theater for conscious experience. Functional neuroimaging evidence for brain activations that are time-locked to rapid eye movements (REMs) endorses the view that waking consciousness emerges from REM sleep – and dreaming lays the foundations for waking perception. In this view, the brain is equipped with a virtual model of the world that generates predictions of its sensations. This model is continually updated and entrained by sensory prediction errors in wakefulness to ensure veridical perception, but not in dreaming. In contrast, dreaming plays an essential role in maintaining and enhancing the capacity to model the world by minimizing model complexity and thereby maximizing both statistical and thermodynamic efficiency. This perspective suggests that consciousness corresponds to the embodied process of inference, realized through the generation of virtual realities (in both sleep and wakefulness). In short, our premise or hypothesis is that the waking brain engages with the world to predict the causes of sensations, while in sleep the brain’s generative model is actively refined so that it generates more efficient predictions during waking. We review the evidence in support of this hypothesis – evidence that grounds consciousness in biophysical computations whose neuronal and neurochemical infrastructure has been disclosed by sleep research.

Cognitive Dynamics: From Attractors to Active Inference

This paper combines recent formulations of self-organization and neuronal processing to provide an account of cognitive dynamics from basic principles. We start by showing that inference (and autopoiesis) are emergent features of any (weakly mixing) ergodic random dynamical system. We then apply the emergent dynamics to action and perception in a way that casts action as the fulfillment of (Bayesian) beliefs about the causes of sensations. More formally, we formulate ergodic flows on global random attractors as a generalized descent on a free energy functional of the internal states of a system. This formulation rests on a partition of states based on a Markov blanket that separates internal states from hidden states in the external milieu. This separation means that the internal states effectively represent external states probabilistically. The generalized descent is then related to classical Bayesian (e.g., Kalman-Bucy) filtering and predictive coding-of the sort that might be implemented in the brain. Finally, we present two simulations. The first simulates a primordial soup to illustrate the emergence of a Markov blanket and (active) inference about hidden states. The second uses the same emergent dynamics to simulate action and action observation.

Reid's Foundation for the Primary/Secondary Quality Distinction

Reid offers an under-appreciated account of the primary/secondary quality distinction. He gives sound reasons for rejecting the views of Locke, Boyle, Galileo and others, and presents a better alternative, according to which the distinction is epistemic rather than metaphysical. Primary qualities, for Reid, are qualities whose intrinsic natures can be known through sensation. Secondary qualities, on the other hand, are unknown causes of sensations. Some may object that Reid's view is internally inconsistent, or unacceptably relativistic. However, a deeper understanding shows that it is consistent, and relative only to normal humans. To acquire this deeper understanding, one must also explore the nature of dispositions, Reid's rejection of the theory of ideas, his distinction between sensation and perception, and his distinction between natural and acquired perceptions.

Replies to My Three Critics

Christopher Hookway correctly suggests that I am extremely uneasy about the oft-stated claim that epistemic judgments are normative. The issue is potentially important because a great many self-proclaimed internalists argue against externalism by claiming that the externalist cannot account for certain alleged normative aspects of our epistemic judgments. Thus, for example, some philosophers would argue against the reliabilist's construal of epistemic justification by appealing to evil thought experiments. We can compare two believers, each of whom has identical experience of the world, but where the subjective experience has radically different causes. The one believer is the victim of a powerful deceiver who amuses himself by inducing radically false beliefs about a non-existent material world. The other is a believer lucky enough to inhabit precisely the world of objects our common sense takes to be the causes of sensations. Can we really maintain that the demon-induced beliefs are any less justified than the world beliefs? To characterize a belief as unjustified is to criticize the belief, is to blame the subject for having the belief-justification is a normative notion. But the demon victim is blameless. The demon victim believes just what anyone else would and should believe given the available evidence. Reliabilists and tracking theorists, however, seem committed to the view that the demon victim's beliefs (produced by a massively unreliable process) are unjustified, while perceptual beliefs in the world are justified (produced, we may suppose, by generally reliable processes, processes that track effectively the relevant facts). The argument has certainly been influential. Indeed, the most notable reliabilist was clearly worried by the problem in his seminal paper What is Justified Belief? Indeed, he was so worried that in his book Epistemology and Cognition he took a disastrous detour into normal worlds reliabilism in

Hobbes's Causal Account of Sensation

Hobbes's Causal Account of Sensation JEFFREY BARNOUW I. Introduction If Hobbes's theory of sensation is notorious for its crudity,~ this is largely because it is scarcely known and rather subtle. The main purpose of this paper is to present an interpretation of Hobbes's account of sensation that should show it to be penetrating and plausible. I say "interpretation" because what Hobbes wrote makes considerable demands on our understanding and offers certain occasions for misunderstanding . Nonetheless, 1 believe his meaning is clear when one reads with a sense of what he was after. A secondary purpose of the paper is to suggest ramifications of Hobbes's conception of sense in the analysis of processes of thought and motivation. It will be shown that his grasp of sensation is such that he necessarily includes aspects of his analysis of memory and desire in his treatment of sensation, for sense itself presupposes memory and desire in the broadest sense, that is, experience and conation. Sense, for Hobbes, is not an immediacy of presence or contact, then, but involves generalized reference to the past in the service of an open anticipatory reference to the future. Hobbes's causal account of sensation cannot be understood apart from the context articulated by experience and conation. This does not mean, however, that Hobbes reduced sensation to a function of comprehensive epistemological or psychological theories . His writings show that the question, What is sensation? is primary for him. 2 In Chapter 25, "Of Sense and Animal Motion," which introduces the concluding part of De corpore, Hobbes writes, I have given to this part the title of PHYSlCS, or the Phenomena of Nature. Now such things as appear, or are shown to us by nature, we call phenomena or appearances. Of all the phenomena or appearances which are near us, the most admirable is apparition itself, x6 d~aiveo0at; namely, that some natural bodies have in themselves the patterns almost of all things.... 3 JD. W. Hamlyn writes, "Hobbes's forthrightness . . . leads to little in the way of subtlety, and he shows no sign of appreciating the fact that there are vast problems in the translation of the phenomena of perception into completely mechanical terms'" (Sensation and Perception: A History of the Philosophy of Perception [London: Routledge & Kegan Pual, 1961], p. 57). A parallel but richer example of this attitude is found in R. S. Peters and H. Tajfel, "Hobbes and HuI1--Metaphysicians of Behavior," in M. Cranston and R. S. Peters, eds., Hobbes and Rousseau: A Collection of Critical Essays (New York: Anchor Books, 1972). 2Toward the conclusion of his prose autobiography Hobbes relates, as a turning point of his own interest, that he once found himself among learned men who were discussing "the cause of sensation," when one scornfully asked, "Quid esset sensus," and found, amazingly, that none could answer (Opera Philosophica, ed. Sir William Molesworth, 5 vols. [London: John Bohn, 1839], 1:xx. Cf. n. 8 below.). 3The English Works of Thomas Hobbes, ed. Sir William Molesworth, 11 vols. (London: John Bohn, 1839), 1:38f. [ll5] 116 HISTORY OF PHILOSOPHY This remarkable passage contains a germ of the monadology; in his view of sensation or appearance as the pattern which some natural (animal) bodies have of a vast variety of other natural bodies, Hobbes imaginatively captures the marvel of sensation even more strikingly than Leibniz. How are we to locate the point of view implied in the last sentence quoted? At one and the same time it reflects a "perspective of sensation" grasping what nature shows to us and a "perspective of science" viewing sensation within nature. This mingling of internal and external points of view is characteristic of Hobbes. It no doubt seemed natural to him, and rightly so. It would be a mistake to take this mingling as philosophical naivet6 on his part, or as bad thinking. He had, after all, the counterexample of Descartes before him, whose assertion of the separation and incommensurability of thinking and extension as distinct substances he rejected explicitly and with insight. 4 Much misreading of Hobbes is due to the pervasive presupposition of a version of Cartesian dualism on the part of his critics. One result...

THE NATURE OF THE OBJECTIVE CAUSE OF SENSATION.—PART II. TASTE

Journal Article THE NATURE OF THE OBJECTIVE CAUSE OF SENSATION.—PART II. TASTE Get access JOHN BERRY HAYCRAFT JOHN BERRY HAYCRAFT Search for other works by this author on: Oxford Academic PubMed Google Scholar Brain, Volume 10, Issue 2-3, July 1887, Pages 145–163, https://doi.org/10.1093/brain/10.2-3.145 Published: 01 July 1887

Societies and Academies

EDINBURGH Royal Society, July 19.—Mr. Robert Gray, Vice-President, in the chair.—The Right Hon. Lord Rayleigh communicated a paper on the colours of thin plates. He has laid down on Maxwell's triangle of colours a curve representing the variation of the colours of thin plates as the thickness of the plates increases.—Prof. Dr. Fr. Meyer communicated a paper on algebraic knots.—Prof. Tait described Amagat's “manomètre à pistons libres.”—Prof. C. G. Knott communicated a paper on the electrical properties of hydrogenised palladium. This paper contains the results of experiments on the resistance and thermo-electric properties of hydrogenium or hydrogenised palladium. Up to a temperature of about 200° C. no special peculiarity is noticeable; but at that temperature, or a little higher, hydrogen begins to escape from the wire, and this causes the particular specimen of hydrogenium to recover partially, if not wholly, its pure palladium characteristics. It is known that the resistance of a palladium wire charged with hydrogen at ordinary atmospheric temperatures increases at a rate almost strictly proportional to the amount of charge. The fame law seems to hold at all temperatures up to 150° C., and in such a way that the total increase of resistance of a given palladium wire for a given rise of temperature is nearly the same at all charges; or the temperature-coefficient for any particular specimen of hydrogenised wire is practically inversely proportional to the resistance as compared with the resistance of the wire in its pure uncharged state. Just before the hydrogen begins to escape, the resistance begins to increase somewhat more rapidly than at lower temperatures; and this peculiarity is more marked in the specimens of higher charge. When once the hydrogen begins to escape, the resistance begins to fall off rapidly as the temperature rises to 300° C. At this temperature the wire cannot be distinguished from pure palladium. In the thermo-electric experiments, peculiar irregularities appear at the higher temperatures, which seem to be due to the fact that the hydrogenium wire is unequally heated, and that the hydrogen, which is almost completely driven out of the heated portion of the wire, returns partially as the wire is cooled down again. In all cases at temperatures below 150° C., the current is from pure palladium to hydrogenium through the hot junction, is probably proportional to the difference of temperature in each case, and is greater for the greater charge. Thermo-electrically, fully saturated hydroge nium lies between iron and copper at ordinary atmospheric temperatures. On the thermo-electric diagram the hydrogeniums of different charge are represented (up to a temperature of 150° C.) by a series of straight lines parallel to palladium, whose thermoelectric powers at 0° C. range roughly from −600 (pure palladium) to + 1400 (saturated hydrogenium) expressed in C.G.S. units. (Compare Everett's “Units and Physical Constants,” p. 151.) In other words, the electromotive force in a circuit of palladium:and saturated hydrogenium, the temperatures of the junctions being o° C. and 100° C., is 20 X 104 C.G.S. units, or.002 volts. The thermo-electric peculiarities of hydrogenium may be prettily shown by the following simple experiment. Let a palladium wire, by immersion to half its length in the electrolytic cell, be hydrogenised throughout that half length. Attach the ends of this seeming single uniform wire to the terminals of a galvanometer, and let a flame be allowed to play gently at the central point of the wire. A large current is at once obtained, which grows to a maximum, and then diminishes to zero as the tem perature rises to a red heat. There is no such current during cooling. This spurious neutral point is due to the hydrogen being driven out of the heated portion, partly, no doubt, into the contiguous colder portions. By following up with the flame the ever-shifting point of separation between the charged and uncharged portions, we may repeat the experiment indefinitely until the hydrogen is all driven out of the wire, or until the odistribution of hydrogen has become fairly uniform.—Mr. Thomas Andrews communicated a paper on the electro-chemical reactions between metals and fused salts.—Mr. H. N. Dickson communicated a paper on the hygrometry of Ben Nevis and the Scottish Marine Station.—Mr. J. T. Morrison read a paper on the temperature of Loch Lomond and Loch Katrine during winter and spring; also, a note on the surface temperature near a tidal race.—Mr. John Aitken gave further remarks on dew.— Prof. J. B. Haycraft gave a communication on the nature of the objective cause of sensation.

AN EXPERIMENTAL ENQUIRY INTO THE NATURE OF THE OBJECTIVE CAUSE OF SENSATION

Journal Article AN EXPERIMENTAL ENQUIRY INTO THE NATURE OF THE OBJECTIVE CAUSE OF SENSATION Get access JOHN B. HAYCRAFT, M.B., B.SC., F.R.S.E. JOHN B. HAYCRAFT, M.B., B.SC., F.R.S.E. Professor of Physiology, Mason College, Birmingham Search for other works by this author on: Oxford Academic PubMed Google Scholar Brain, Volume 8, Issue 2, July 1885, Pages 191–209, https://doi.org/10.1093/brain/8.2.191 Published: 01 July 1885

Sound and Light

I SHOULD like to learn if the following phenomenon is well known and alluded to in scientific writings. While lying awake a few mornings ago, with my eyelids closed, I was startled by a railway whistle. At the same instant I perceived a blaze of light on a dark ground seemingly a few yards off. I made inquiry of my wife (who is of a much more nervous temperament than I) if she had ever observed such a coincidence, and was informed that in her case it is not a very unfrequent occurrence. I likewise reported the circumstance to some scientific friends, but they had neither read nor heard of noise being the occasioning cause of sensation of colour.