1,218 research outputs found
A silicon model of auditory localization
The barn owl accurately localizes sounds in the azimuthal plane, using interaural time difference as a cue. The time-coding pathway in the owl's brainstem encodes a neural map of azimuth, by processing interaural timing information. We have built a silicon model of the time-coding pathway of the owl. The integrated circuit models the structure as well as the function of the pathway; most subcircuits in the chip have an anatomical correlate. The chip computes all outputs in real time, using analog, continuous-time processing
Cognitive and Neural Map Representations in Schizophrenia
An ability to build structured cognitive maps of the world may lie at the heart of understanding cognitive features of schizophrenia. In rodents, cognitive map representations are supported by sequential hippocampal place cell reactivations during rest (offline), known as replay. These events occur in the context of local high frequency ripple oscillations, and whole-brain default mode network (DMN) activation. Genetic mouse models of schizophrenia also report replay and ripple abnormalities. Here, I investigate the behavioural and neural signatures of structured internal representations in people with a diagnosis of schizophrenia (PScz, n = 29) and matched control participants (n = 28) using magnetoencephalography (MEG). Participants were asked to infer correct sequential relationships between task pictures by applying a pre-learned task template to visual experiences containing these pictures. In Chapter 3 I show that, during a post-task rest session, controls exhibited fast spontaneous neural reactivation of task state representations that replayed inferred relationships. Replay was coincident with increased ripple power in hippocampus, which may be related to NMDAR availability (Chapter 4). PScz showed both reduced replay and augmented ripple power, convergent with genetic mouse models. These abnormalities were linked to impairments in behavioural acquisition of task structure, and to its subsequent representation in visually evoked neural responses. In Chapter 5 I explore the temporal coupling between replay onsets and DMN activation. I show an impairment in this association in PScz, which related to subsequent mnemonic maintenance of learned task structure, complementing previous reports of DMN abnormalities in the condition. Finally, in Chapter 6, using a separate verbal fluency task, I show that PScz exhibit evidence of reduced use of (semantic) associative information when sampling concepts from memory. Together, my results provide support for a hypothesis that schizophrenia is associated with abnormalities in neural and behavioural correlates of cognitive map representation
The self-organization of combinatoriality and phonotactics in vocalization systems
This paper shows how a society of agents can self-organize a shared vocalization system that is
discrete, combinatorial and has a form of primitive phonotactics, starting from holistic inarticulate
vocalizations. The originality of the system is that: (1) it does not include any explicit pressure for
communication; (2) agents do not possess capabilities of coordinated interactions, in particular they
do not play language games; (3) agents possess no specific linguistic capacities; and (4) initially
there exists no convention that agents can use. As a consequence, the system shows how a primitive
speech code may bootstrap in the absence of a communication system between agents, i.e. before the
appearance of language
Experimenting the variational definition of neural map computation
International audienc
The Self-Organization of Speech Sounds
The speech code is a vehicle of language: it defines
a set of forms used by a community to carry information.
Such a code is necessary to support the linguistic
interactions that allow humans to communicate.
How then may a speech code be formed prior to the
existence of linguistic interactions?
Moreover, the human speech code is discrete and compositional,
shared by all the individuals of a community but different
across communities, and phoneme inventories are characterized by
statistical regularities. How can a speech code with these properties form?
We try to approach these questions in the paper,
using the ``methodology of the artificial''. We
build a society of artificial agents, and detail a mechanism that
shows the formation of a discrete speech code without pre-supposing
the existence of linguistic capacities or of coordinated interactions.
The mechanism is based on a low-level model of
sensory-motor interactions. We show that the integration of certain very
simple and non language-specific neural devices
leads to the formation of a speech code that
has properties similar to the human speech code.
This result relies on the self-organizing properties of a generic
coupling between perception and production
within agents, and on the interactions between agents.
The artificial system helps us to develop better intuitions on how speech
might have appeared, by showing how self-organization
might have helped natural selection to find speech
An Investigation of the Effects of Categorization and Discrimination Training on Auditory Perceptual Space
Psychophysical phenomena such as categorical perception and the perceptual magnet effect indicate that our auditory perceptual spaces are warped for some stimuli. This paper investigates the effects of two different kinds of training on auditory perceptual space. It is first shown that categorization training, in which subjects learn to identify stimuli within a particular frequency range as members of the same category, can lead to a decrease in sensitivity to stimuli in that category. This phenomenon is an example of acquired similarity and apparently has not been previously demonstrated for a category-relevant dimension. Discrimination training with the same set of stimuli was shown to have the opposite effect: subjects became more sensitive to differences in the stimuli presented during training. Further experiments investigated some of the conditions that are necessary to generate the acquired similarity found in the first experiment. The results of these experiments are used to evaluate two neural network models of the perceptual magnet effect. These models, in combination with our experimental results, are used to generate an experimentally testable hypothesis concerning changes in the brain's auditory maps under different training conditions.Alfred P. Sloan Foundation and the National institutes of Deafness and other Communication Disorders (R29 02852); Air Force Office of Scientific Research (F49620-98-1-0108
From Holistic to Discrete Speech Sounds: The Blind Snow-Flake Maker Hypothesis
Sound is a medium used by humans to carry information.
The existence of this kind of
medium is a pre-requisite for language. It is organized
into a code, called speech, which
provides a repertoire of forms that is shared in each
language community. This code is necessary to support the linguistic
interactions that allow humans to communicate.
How then may a speech code be formed prior to the
existence of linguistic interactions?
Moreover, the human speech code is characterized by several
properties: speech is digital and compositional (vocalizations
are made of units re-used systematically in other syllables);
phoneme inventories have precise regularities as well as
great diversity in human languages; all the speakers of a
language community categorize sounds in the same manner,
but each language has its own system of categorization,
possibly very different from every other.
How can a speech code with these properties form?
These are the questions we will approach in the paper. We will
study them using the method of the artificial. We will
build a society of artificial agents, and study what mechanisms
may provide answers. This will not prove directly what mechanisms
were used for humans, but rather give ideas about what kind
of mechanism may have been used. This allows us to shape the
search space of possible answers, in particular by showing
what is sufficient and what is not necessary.
The mechanism we present is based on a low-level model of
sensory-motor interactions. We show that the integration of certain very
simple and non language-specific neural devices
allows a population of agents to build a speech code that
has the properties mentioned above. The originality is
that it pre-supposes neither a functional pressure for
communication, nor the ability to have coordinated
social interactions (they do not play language or imitation
games). It relies on the self-organizing properties of a generic
coupling between perception and production both
within agents, and on the interactions between agents
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