312 research outputs found
MLDS: Maximum Likelihood Difference Scaling in R
No full textThe MLDS package in the R programming language can be used to estimate perceptual scales based on the results of psychophysical experiments using the method of difference scaling. In a difference scaling experiment, observers compare two supra-threshold differences (a,b) and (c,d) on each trial. The approach is based on a stochastic model of how the observer decides which perceptual difference (or interval) (a,b) or (c,d) is greater, and the parameters of the model are estimated using a maximum likelihood criterion. We also propose a method to test the model by evaluating the self-consistency of the estimated scale. The package includes an example in which an observer judges the differences in correlation between scatterplots. The example may be readily adapted to estimate perceptual scales for arbitrary physical continua.
Discursive ideologies: reading western rhetoric
No full textIncludes bibliographical references and index.In Discursive Ideologies, C.H. Knoblauch argues that European rhetorical theory comprises several distinct and fundamentally opposed traditions of discourse. Writing accessibly for the upper division student, Knoblauch resists the conventional narrative of a unified Western rhetorical tradition. He identifies deep ideological and epistemological differences that exist among strands of Western thought and that are based in divergent "grounds of meaningfulness." These conflicts underlie and influence current discourse about vital public issues.The Meaning of Meaning -- Magical Rhetoric -- Ontological Rhetoric -- Objectivist Rhetoric -- Expressivist Rhetoric -- Sociological Rhetoric -- Deconstructive Rhetoric -- Afterword: Critical Reflections
Representing an observer's matches in an alien color space
No full textA color space is constructed so that lights that have the same appearance for a given observer map into the same point. As such, a color space is specific to an observer, and a different observer requires a different space to represent the mapping between lights of identical appearance and points. Nevertheless, situations arise in which one would like to consider the properties of one observer with respect to a different observer but in the same space. Some examples include the evaluation of rod excitation in trichromatic color space, the relation between anomalous and normal trichromatic discrimination, the relation between the CIE 1931 and the Judd observers and the relation between human and camera observers. The object of this article is to examine the geometry of such situations
Representing an observer's matches in an alien color space
No full textA color space is constructed so that lights that have the same appearance for a given observer map into the same point. As such, a color space is specific to an observer, and a different observer requires a different space to represent the mapping between lights of identical appearance and points. Nevertheless, situations arise in which one would like to consider the properties of one observer with respect to a different observer but in the same space. Some examples include the evaluation of rod excitation in trichromatic color space, the relation between anomalous and normal trichromatic discrimination, the relation between the CIE 1931 and the Judd observers and the relation between human and camera observers. The object of this article is to examine the geometry of such situations
MLDS: Maximum Likelihood Difference Scaling in R
No full textThis introduction to the R package MLDS is a modified and updated version of Knoblauch and Maloney (2008) published in the Journal of Statistical Software. The MLDS package in the R programming language can be used to estimate perceptual scales based on the results of psychophysical experiments using the method of difference scaling. In a difference scaling experiment, observers compare two supra-threshold differ-ences (a,b) and (c,d) on each trial. The approach is based on a stochastic model of how the observer decides which perceptual difference (or interval) (a, b) or (c, d) is greater, and the parameters of the model are estimated using a maximum likelihood criterion. We also propose a method to test the model by evaluating the self-consistency of the esti-mated scale. The package includes an example in which an observer judges the differences in correlation between scatterplots. The example may be readily adapted to estimate perceptual scales for arbitrary physical continua
Del origen del vampiro a un vampiro entre emigrantes en Die Wahrheit über Vampire und knoblauch de Rafik Schami
No full textResumen:
El objetivo de este ensayo es analizar la figura del vampiro que Rafik Schami utiliza en su relato Die Wahrheit über Vampire und Knoblauch (La verdad sobre los vampiros y el ajo). Después de presentar los primeros documentos sobre vampiros escritos en lengua alemana, se intenta contextualizar al autor y su obra –y su representación en diversas formas discursivas- a la par de dar respuesta a los siguientes interrogantes: ¿Por qué elige Rafik Schami precisamente esta figura para su narración? ¿De qué fuentes y estrategias narrativas se sirve? ¿Cómo lo caracteriza y qué función tiene?
Palabras clave: Vampiro, Rafik Schami, Alemania, emigración.
Abstract:
The aim of this essay is to analyze the vampire in Rafik Schami’s Die Wahrheit über Vampire und Knoblauch. After presenting the first documents about vampires written in German it will contextualize the author and his work –and its representation in different cultural discourses- , trying to answer the following questions: Why does Schami choose the vampire for his story? What sources and narrative strategies does the author use? What are the characteristics and what is the function of Schami’s vampire?
Keywords: Vampire, Rafik Schami, Germany, migration
Del origen del vampiro a un vampiro entre emigrantes en Die Wahrheit über Vampire und knoblauch de Rafik Schami
No full textResumen:
El objetivo de este ensayo es analizar la figura del vampiro que Rafik Schami utiliza en su relato Die Wahrheit über Vampire und Knoblauch (La verdad sobre los vampiros y el ajo). Después de presentar los primeros documentos sobre vampiros escritos en lengua alemana, se intenta contextualizar al autor y su obra –y su representación en diversas formas discursivas- a la par de dar respuesta a los siguientes interrogantes: ¿Por qué elige Rafik Schami precisamente esta figura para su narración? ¿De qué fuentes y estrategias narrativas se sirve? ¿Cómo lo caracteriza y qué función tiene?
Palabras clave: Vampiro, Rafik Schami, Alemania, emigración.
Abstract:
The aim of this essay is to analyze the vampire in Rafik Schami’s Die Wahrheit über Vampire und Knoblauch. After presenting the first documents about vampires written in German it will contextualize the author and his work –and its representation in different cultural discourses- , trying to answer the following questions: Why does Schami choose the vampire for his story? What sources and narrative strategies does the author use? What are the characteristics and what is the function of Schami’s vampire?
Keywords: Vampire, Rafik Schami, Germany, migration
seanfw/dopamine-dist-wm: Dopamine working memory model code
No full textExample Jupyter notebooks to reproduce the main figures in
Froudist-Walsh, Sean, Daniel P. Bliss, Xingyu Ding, Lucija Jankovic-Rapan, Meiqi Niu, Kenneth Knoblauch, Karl Zilles, Henry Kennedy, Nicola Palomero-Gallagher, and Xiao-Jing Wang. "A dopamine gradient controls access to distributed working memory in the large-scale monkey cortex." Neuron (2021)
Über die Verwendung von MLDS in der Untersuchung der Tiefen- und Helligkeitswahrnehmung
No full textAn open question in vision research is how to measure the perceptual dimension evoked by the stimulus in a reliable way. Although a variety of psychophysical procedures are available, it is still a challenge to find methods that are efficient and avoid critical confounds, such as strategies triggered by difficult and unnatural tasks used by discrimination methods. In this doctoral thesis I propose the use of Maximum Likelihood Difference Scaling (MLDS, Maloney & Yang, 2003) as a reliable tool for measuring perception. MLDS is a method based on judgments of appearance of clearly visible stimulus differences in an easy and intuitive task, and it allows the estimation of perceptual scales in an efficient way.
Here I first use numerical simulations to test the accuracy and precision of the scales derived with MLDS, and I also tested the effect of violations of the model assumptions. The results of these simulations establish the validity of MLDS as a method for measuring appearance. Then, we evaluated MLDS experimentally in the domain of lightness perception. We measured perceptual lightness scales under different viewing conditions and we validate the derived scales empirically by predicting lightness matches that were derived in a classical asymmetric matching task. A large practical benefit of MLDS is that it renders the task easy for the subject and thus minimizing the potential influence of strategies. At the same time the perceptual scales provide a more direct estimate of internal variables against which theoretical models of appearance can be tested.
In a third part I study the relationship between MLDS and discrimination methods as suggested by Devinck & Knoblauch (2012). In simulations MLDS was more efficient than the traditional 2-AFC discrimination method while at the same time providing analogous sensitivity estimates. I also tested this equivalence experimentally in a slant-from-texture task, for which sensitivity has been previously studied in the literature. Here I found varying degrees of equivalence and it remains to be tested in the future whether these differences are due to true differences in the perceptual representation, or to violations of the model assumptions.
Together with the use of realistic stimuli, MLDS offers a reliable method to measure the perceptual dimension, and in that way enabling the testing of theoretical models of perceptual inference.Eine offene Frage in der visuellen Wahrnehmungsforschung ist, wie sich eine durch einen Stimulus evozierte Wahrnehmungsdimension reliabel messen lässt. Trotz einer Auswahl existierender psychophysischer Methoden, bleibt es eine Herausforderung effiziente Methoden zu finden, die kritische Konfundierungen verhindern, wie es zum Beispiel bei Diskriminationsaufgaben mit schwierigen und unnatürlichen Aufgaben der Fall sein kann. In dieser Dissertation stelle ich „Maximum Likelihood Difference Scaling" (MLDS, Maloney & Yang, 2003) als eine reliable Methode zur Messung von Wahrnehmungseindrücken vor. MLDS basiert auf der Bewertung deutlich sichtbarer Stimulusunterschiede in einer intuitiven und einfachen Aufgabe und ermöglicht die effiziente und reliable Schätzung perzeptueller Skalen.
In einem ersten Schritt wird MLDS als eine zuverlässig Methode zur Messung von Wahrnehmunseindrücken etabliert, indem ihre Genauigkeit und Präzision bestimmt wird sowie Verletzungen von Modellannahmen numerisch simuliert werden. In einem nächsten Schritt wird MLDS im Bereich der Helligkeitswahrnehmung experimentell evaluiert, indem gezeigt wird, dass MLDS erfolgreich Wahrnehmungsskalen für verschiedene visuelle Kontextbedingungen bestimmt. Die gemessenen Skalen weisen weitgehend Helligkeitskonstanz auf. MLDS erforderte dafür den Vergleich von Stimuli innerhalb eines visuellen Kontexts, was zu einer Vereinfachung der Aufgabe für die Versuchsperson sowie zur Vermeidung von Problemen geführt hat, welche mit Vergleichen über visuelle Kontextbedingungen hinweg in Verbindung gebracht werden. Zusätzlich hierzu, schien MLDS der Methode des asymmetrischen Vergleichs für die Bestimmung von Helligkeitskonstanz überlegen, da diese im Gegensatz zu MLDS nur ein indirektes Maß liefern kann und Wahrnehmungsskalen nicht direkt misst.
Der Zusammenhang zwischen MLDS und Diskriminanzverfahren wurde auch im Rahmen der Signalentdeckungstheorie untersucht, wie zuletzt von Devinck & Knoblauch (2012) vorgeschlagen. Simulationen haben gezeigt, dass MLDS effizienter ist und in der Sensitivitätsschätzung quantitativ ähnlich zu traditionellen „2-AFC" Diskriminanzverfahren, jedoch nur wenn alle Modellannahmen erfüllt waren. Diese Äquivalenz wurde zudem experimentell in einer „slant-from-texture" Aufgabe getestet, für die Sensitivitätsmaße bereits untersucht wurden. Ich fand unterschiedliche Abstufungen von Übereinstimmung, die entweder tatsächliche Unterschiede in der perzeptuellen Repräsentation oder eine Verletzung der Modellannahmen darstellen können.
Zusammen mit der Verwendung realistischer Stimuli bietet MLDS eine reliablere Methode zur Messung perzeptueller Dimensionen und ermöglicht so die Testung theoretischer Modelle perzeptueller Inferenz
Development and structure of cortical networks in the macaque
No full textLe travail effectué au cours de cette thèse se divise en trois. Pour la première partie, 12 injections de traceurs rétrogrades ont été effectuées chez le macaque cynomolgus à différentes excentricités visuelles de V1, V2, V4 et MT. Nous observons que, si les injections effectuées au sein des territoires correspondant aux représentations centrales (i.e fovéale) de l'hémi-champs visuel reçoivent préférentiellement des projections issues de la voie ventrale, les injections placées au sein des représentations périphériques marques préférentiellement les neurones d'aires connues pour faire partie de la voie dorsale. Les injections excentriques affichent une décroissance exponentielle des poids de connexion avec l'augmentation des distances, comme décrit précédemment (Markov et al. 2014). Ceci plaide en faveur de l'hypothèse que la règle exponentielle de distance (EDR en anglais) (Ercsey-Ravasz et al 2013) est assez puissante pour expliquer la formation des voies fonctionnelles du cortex visuel. De plus, cela suggère fortement que l'EDR s'applique à n'importe quel point du manteau cortical, indépendamment de toutes limites d'aires, et que, par conséquent, le cortex est mieux décrit comme une gradient continu de propriétés progressivement changeantes, au lieu d'une mosaïque de aires corticales bien définies. De plus, cela a de profondes implications concernant l'évolution biologique des aires corticales ainsi que du cortex dans son ensemble. En seconde partie, tractographie et traçage de voies furent comparés, via l'utilisation d'IRM de diffusion. Une analyse en tractographie fut effectuée, et la matrice de connectivité résultante comparée à celle obtenue par traçage de voies (Markov et al., 2014). Les résultats préliminaires de cette thèse tombent dans le même intervalle de succès de détection que les études précédentes : entre 70 et 77 % de la connectivité évaluée par tractographie est correcte (Azadbakht et al 2015, Calabrese et al 2015a, Donahue et al 2016). Cela met également en évidence un problème de spécificité des connexions détectées par la tractographie, qui ne parvient pas à reconnaître les connexions absentes avec précision, un problème particulièrement visible dans le contexte des aires visuelles de bas niveau, chez qui la connectivité est connue pour être très spécifique (Tigges et al 1973, Tigges et al 1974, Martinez-Millan & Hollander 1975, Kaas & Lin 1977, Wong-Riley 1978). En conclusion, les propriétés de connectivité du cortex ne devraient pas, à ce stade, être déduites la tractographie basée sur l'imagerie de diffusion. Pour la dernière partie, 6 injections ont été réalisées chez 3 animaux bilatéralement énucléés (3 dans le « Default Extrastriate Cortex » - DEC ; 1 dans V2 et 2 dans V4) afin d'évaluer comment la connectivité visuelle est affectée par la perte des afférences rétiniennes au thalamus. Comme rapportées antérieurement, des gyri anormaux sont observés sur l'operculum occipital, dont le territoire est dominé par la DEC, un cortex hybride entre cortex strié et extrastrié (Dehay et al 1996a, Dehay et al 1996b). De plus, l'anatomie du LGN est massivement perturbée. Les afférences en provenance du pulvinar et du LGN sont éparses et mal ciblées lors d'injections placées côte-à-côte. La connection du pulvinar au DEC est d'un ordre de grandeur supérieure à une connexion normale du pulvinar à V1, alors que la même comparaison pour le LGN est d'un ordre de grandeur inférieure. Ces changements en matière de connectivité s'amenuisent en allant plus haut au sein de la hiérarchie visuelle corticale. En effet, les changements les plus frappants se produisent dans V1 (aberrant gyri, DEC, ventralisation, etc.) alors que V4 semble être peu perturbé par l'absence d'afférences rétiniennes. Du point de vue du développement du système visuel, cela plaide pour un effet localisé des entrées thalamiques (i.e. seulement V1 et V2) ainsi que pour une absence d'effet domino en cascade compromettant l'ensemble du cerveauThe work performed during this thesis is three fold. In the first part, 12 injections of retrograde tracers were performed in cynomolgus macaques at different visual eccentricities in V1, V2, V4 and MT. We observe that, while injections performed in territories corresponding to the central (i.e. foveal) representation of the visual hemifield preferentially receive inputs from areas belonging to the ventral pathway, injections placed in peripheral representations preferentially labels neurons in areas known to be part of the dorsal pathway. Eccentric injections return an exponential decay of connexion strength with increasing distances, as previously described (Markov et al, 2014). This strongly argues in favour of the Exponential Distance Rule (EDR) being powerful enough to explain the formation of the functional streams of the visual cortex. Firstly, it strongly suggests that the EDR is applicable at any point of the cortical sheet regardless of area boundaries, and that therefore the cortex is better seen as a continuous sheet of gradually changing properties, instead of a mosaic of well-defined cortical areas. Secondly, it helps inform and refine our current definition of an area towards a more comprehensive one which includes topological location. Finally, it has deep implications regarding the evolution of cortical areas as well as the cortex as a whole. In the second part, a comparison was attempted between tractography and tract tracing, with the high definition diffusion MRI scan of one macaque brain. Tractography was computed on it, and the resulting connectivity matrix compared to tract tracing (Markov et al, 2014). The preliminary results obtained in this thesis fall in the same range of detection success than previous studies: between 70 and 77 % of the connectivity assessed by dMRI-based tractography is correct using the same Receiver Operating Charateristic (ROC) approach (Azadbakht et al 2015, Calabrese et al 2015a, Donahue et al 2016). It also highlights a problem of specificity of connexions detected by tractography. It fails to accurately discriminate empty connexions (i.e. absent) as empty, a problem especially salient in the context of early visual areas, the connectivity of which is known to be very specific (Tigges et al 1973, Tigges et al 1974, Martinez-Millan & Hollander 1975, Kaas & Lin 1977, Wong-Riley 1978). Overall, caution is for now warranted and connectivity properties should not at this point be inferred on diffusion MRI based tractography. In the last part, 6 injections were performed in 3 bilaterally enucleated animals (3 in the Default Extrastriate Cortex - DEC, 1 in V2 and 2 in V4) in order to assess how the visual connectivity is impacted by the loss of retinal inputs to the thalamus. As previously reported, abnormal gyri are observed on the operculum, whose territory is now dominated by the DEC, a hybrid cortex combining histological and histochemical feature of striate and exstrastiate cortex (Dehay et al 1996a, Dehay et al 1996b). Also, the LGN anatomy is massively perturbed, losing its heterogeneity of strictly defined layers for a homogeneous structure. Inputs from the pulvinar and the LGN were found to be unfocused, scattered and unsegregated in side-by-side injections. The pulvinar input to the DEC was found to be an order of magnitude higher than a normal pulvinar-to-V1 connexion, when the same comparison for the LGN was found to be an order of magnitude lower. These changes in connectivity appear to diminish in importance as one goes up the visual hierarchy. Indeed the most striking changes are in V1 (aberrant gyri, DEC, ventralisation, etc.) whereas V4 appears to be seemingly unperturbed by the absence of retinal inputs. Regarding the development of the visual system, this fact argues for a localised effect of the thalamic inputs (i.e. only V1 and V2) and an absence of domino-effect cascade that would perturb the entirety of the brain, despite the quite drastic enucleation proces
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