53 research outputs found
Toward an Ethics of AI Belief
Philosophical research in AI has hitherto largely focused on the ethics of
AI. In this paper we, an ethicist of belief and a machine learning scientist,
suggest that we need to pursue a novel area of philosophical research in AI -
the epistemology of AI, and in particular an ethics of belief for AI, i.e., an
ethics of AI belief. Here we take the ethics of belief, a field that has been
defined in various ways, to refer to a sub-field within epistemology. This
subfield is concerned with the study of possible moral, practical, and other
non-alethic dimensions of belief. And in this paper, we will primarily be
concerned with the normative question within the ethics of belief of what
agents - both human and artificial - ought to believe, rather than with
descriptive questions concerning whether certain beliefs meet various
evaluative standards such as being true, being justified or warranted,
constituting knowledge, and so on. We suggest four topics in extant work in the
ethics of (human) belief that can be applied to an ethics of AI belief:
doxastic wronging by AI; morally owed beliefs; pragmatic and moral encroachment
on AI beliefs; and moral responsibility for AI beliefs. We also indicate an
important nascent area of philosophical research in epistemic injustice and AI
that has not yet been recognized as research in the ethics of AI belief, but
which is so in virtue of concerning moral and practical dimensions of belief
Impaired reinforcement learning and Bayesian inference in psychiatric disorders: from maladaptive decision making to psychosis in schizophrenia
Computational modelling has been gaining an increasing amount of support from the
neuroscience community as a tool to assay cognition and computational processes in
the brain. Lately, scientists have started to apply computational methods from neuroscience
to the study of psychiatry to gain further insight into the mechanisms leading
to mental disorders. In fact, only recently has psychiatry started to move away from
categorising illnesses using behavioural symptoms in an attempt for a more biologically
driven diagnosis. To date, several neurobiological anomalies have been found
in schizophrenia and led to a multitude of conceptual framework attempting to link
the biology to the patients’ symptoms. Computational modelling can be applied to
formalise these conceptual frameworks in an effort to test the validity or likelihood
of each hypothesis. Recently, a novel conceptual model has been proposed to describe
how positive symptoms (delusions, hallucinations and thought disorder) and
cognitive symptoms (poor decision-making, i.e. “executive functioning”) might arise
in schizophrenia. This framework however, has not been tested experimentally or
against computational models. The focus of this thesis was to use a combination of
behavioural experiments and computational models to independently assess the validity
of each component that make up this framework.
The first study of this thesis focused on the computational analysis of a disrupted
prediction-error signalling and its implications for decision-making performances in
complex tasks. Briefly, we used a reinforcement-learning model of a gambling task
in rodents and disrupted the prediction-error signal known to be critical for learning.
We found that this disruption can account for poor performances in decision-making
due to an incorrect acquisition of the model of the world. This study illustrates how
disruptions in prediction-error signalling (known to be present in schizophrenia) can
lead to the acquisition of an incorrect world model which can lead to poor executive
functioning or false beliefs (delusions) as seen in patients.
The second study presented in this thesis addressed spatial working memory performances
in chronic schizophrenia, bipolar disorder, first episode psychosis and family
relatives of DISC1 translocation carriers. We build a probabilistic inference model
to solve the working memory task optimally and then implemented various alterations
of this model to test commonly debated hypotheses of cognitive deficiency
in schizophrenia. Our goal was to find which of these hypotheses accounts best for
the poor performance observed in patients. We found that while the performance at
the task was significantly different for most patients groups in comparison to controls,
this effect disappeared after controlling for IQ in one group. The models were
nonetheless fitted to the experimental data and suggest that working memory maintenance
is most likely to account for the poor performances observed in patients. We
propose that the maintenance of information in working memory might have indirect
implications for measures of general cognitive performance, as these rely on a correct
filtering of information against distractions and cortical noise.
Finally the third study presented in this thesis assessed the performance of medicated
chronic schizophrenia patients in a statistical learning task of visual stimuli
and measured how the acquired statistics influenced their perception. We find that
patient with chronic schizophrenia appear to be unimpaired at statistical learning
of visual stimuli. The acquired statistics however appear to induce less expectation-driven
‘hallucinations’ of the stimuli in the patients group than in controls. We find
that this is in line with previous literature showing that patients are less susceptible
to expectation-driven illusions than controls. This study highlights however the idea
that perceptual processes during sensory integration diverge from this of healthy controls.
In conclusion, this thesis suggests that impairments in reinforcement learning and
Bayesian inference appear to be able to account for the positive and cognitive symptoms
observed in schizophrenia, but that further work is required to merge these
findings. Specifically, while our studies addressed individual components such as
associative learning, working memory, implicit learning & perceptual inference, we
cannot conclude that deficits of reinforcement learning and Bayesian inference can
collectively account for symptoms in schizophrenia. We argue however that the studies
presented in this thesis provided evidence that impairments of reinforcement
learning and Bayesian inference are compatible with the emergence of positive and
cognitive symptoms in schizophrenia
Recommendations for Bayesian hierarchical model specifications for case-control studies in mental health
Hierarchical model fitting has become commonplace for case-control studies of
cognition and behaviour in mental health. However, these techniques require us
to formalise assumptions about the data-generating process at the group level,
which may not be known. Specifically, researchers typically must choose whether
to assume all subjects are drawn from a common population, or to model them as
deriving from separate populations. These assumptions have profound
implications for computational psychiatry, as they affect the resulting
inference (latent parameter recovery) and may conflate or mask true group-level
differences. To test these assumptions we ran systematic simulations on
synthetic multi-group behavioural data from a commonly used multi-armed bandit
task (reinforcement learning task). We then examined recovery of group
differences in latent parameter space under the two commonly used generative
modelling assumptions: (1) modelling groups under a common shared group-level
prior (assuming all participants are generated from a common distribution, and
are likely to share common characteristics); (2) modelling separate groups
based on symptomatology or diagnostic labels, resulting in separate group-level
priors. We evaluated the robustness of these approaches to variations in data
quality and prior specifications on a variety of metrics. We found that fitting
groups separately (assumptions 2), provided the most accurate and robust
inference across all conditions. Our results suggest that when dealing with
data from multiple clinical groups, researchers should analyse patient and
control groups separately as it provides the most accurate and robust recovery
of the parameters of interest.Comment: Machine Learning for Health (ML4H) at NeurIPS 2020 - Extended
Abstrac
The flavin reductase ActVB from Streptomyces coelicolor: characterization of the electron transferase activity of the flavoprotein form.
International audienceThe flavin reductase ActVB is involved in the last step of actinorhodin biosynthesis in Streptomyces coelicolor. Although ActVB can be isolated with some FMN bound, this form was not involved in the flavin reductase activity. By studying the ferric reductase activity of ActVB, we show that its FMN-bound form exhibits a proper enzymatic activity of reduction of iron complexes by NADH. This shows that ActVB active site exhibits a dual property with regard to the FMN. It can use it as a substrate that goes in and off the active site or as a cofactor to provide an electron transferase activity to the polypeptide
A two-component flavin-dependent monooxygenase involved in actinorhodin biosynthesis in Streptomyces coelicolor.
International audienceThe two-component flavin-dependent monooxygenases belong to an emerging class of enzymes involved in oxidation reactions in a number of metabolic and biosynthetic pathways in microorganisms. One component is a NAD(P)H:flavin oxidoreductase, which provides a reduced flavin to the second component, the proper monooxygenase. There, the reduced flavin activates molecular oxygen for substrate oxidation. Here, we study the flavin reductase ActVB and ActVA-ORF5 gene product, both reported to be involved in the last step of biosynthesis of the natural antibiotic actinorhodin in Streptomyces coelicolor. For the first time we show that ActVA-ORF5 is a FMN-dependent monooxygenase that together with the help of the flavin reductase ActVB catalyzes the oxidation reaction. The mechanism of the transfer of reduced FMN between ActVB and ActVA-ORF5 has been investigated. Dissociation constant values for oxidized and reduced flavin (FMNox and FMNred) with regard to ActVB and ActVA-ORF5 have been determined. The data clearly demonstrate a thermodynamic transfer of FMNred from ActVB to ActVA-ORF5 without involving a particular interaction between the two protein components. In full agreement with these data, we propose a reaction mechanism in which FMNox binds to ActVB, where it is reduced, and the resulting FMNred moves to ActVA-ORF5, where it reacts with O2 to generate a flavinperoxide intermediate. A direct spectroscopic evidence for the formation of such species within ActVA-ORF5 is reported
Intermolecular electron transfer in two-iron superoxide reductase: a putative role for the desulforedoxin center as an electron donor to the iron active site.
International audienceSuperoxide reductase (SOR) is a superoxide detoxification system present in some microorganisms. Its active site consists of an unusual mononuclear iron center with an FeN4S1 coordination which catalyzes the one-electron reduction of superoxide to form hydrogen peroxide. Different classes of SORs have been described depending on the presence of an additional rubredoxin-like, desulforedoxin iron center, whose function has remained unknown until now. In this work, we investigated the mechanism of the reduction of the SOR iron active site using the NADPH:flavodoxin oxidoreductase from Escherichia coli, which was previously shown to efficiently transfer electrons to the Desulfoarculus baarsii SOR. When present, the additional rubredoxin-like iron center could function as an electronic relay between cellular reductases and the iron active site for superoxide reduction. This electron transfer was mainly intermolecular, between the rubredoxin-like iron center of one SOR and the iron active site of another SOR. These data provide the first experimental evidence for a possible role of the rubredoxin-like iron center in the superoxide detoxifying activity of SOR
Acquisition of visual priors and induced hallucinations in chronic schizophrenia
Prominent theories suggest that symptoms of schizophrenia stem from learning deficiencies resulting in distorted internal models of the world. To test these theories further, we used a visual statistical learning task known to induce rapid implicit learning of the stimulus statistics. In this task, participants are presented with a field of coherently moving dots and are asked to report the presented direction of the dots (estimation task), and whether they saw any dots or not (detection task). Two of the directions were more frequently presented than the others. In controls, the implicit acquisition of the stimuli statistics influences their perception in two ways: (i) motion directions are perceived as being more similar to the most frequently presented directions than they really are (estimation biases); and (ii) in the absence of stimuli, participants sometimes report perceiving the most frequently presented directions (a form of hallucinations). Such behaviour is consistent with probabilistic inference, i.e. combining learnt perceptual priors with sensory evidence. We investigated whether patients with chronic, stable, treated schizophrenia (n = 20) differ from controls (n = 23) in the acquisition of the perceptual priors and/or their influence on perception. We found that although patients were slower than controls, they showed comparable acquisition of perceptual priors, approximating the stimulus statistics. This suggests that patients have no statistical learning deficits in our task. This may reflect our patients’ relative wellbeing on antipsychotic medication. Intriguingly, however, patients experienced significantly fewer (P = 0.016) hallucinations of the most frequently presented directions than controls when the stimulus was absent or when it was very weak (prior-based lapse estimations). This suggests that prior expectations had less influence on patients’ perception than on controls when stimuli were absent or below perceptual threshold
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