On the Scales of Photographic Abstraction

This article explores three key ways in which questions of abstraction have been and continue to be closely associated with photography: the tradition of photographs that desire to “be” abstract; the invisible but determining forms of abstraction central to capitalism and shaping of photography as a technical-historical form; and the technical-conceptual abstractions embedded in and structuring of photographic apparatuses. The exploration of these themes is pursued through analysis of Vilém Flusser’s philosophy of photography, Lambert Wiesing’s analysis of abstract photography and Allan Sekula’s critique of capitalist modes of equivalence and exchange as these impact on the photographic. These analyses are pursued through exploration of the issues, processes and operations of “scale”, “scaling” and “scalability” entailed in these three modes of abstraction and in their critical and theoretical reflection. The aim of this strategy is to outline and to analyse the complex web of abstractions that are central to photography and the modes of scale that are crucial to abstraction in this context. The article suggests that to encounter or to think about abstraction photographically is to operate within some modulation of scale and that this may in fact be the closest one can get to envisioning the complexity of abstraction in the photographic context

Physician Attitudes towards Pharmacological Cognitive Enhancement: Safety Concerns Are Paramount

The ethical dimensions of pharmacological cognitive enhancement have been widely discussed in academic circles and the popular media, but missing from the conversation have been the perspectives of physicians - key decision makers in the adoption of new technologies into medical practice. We queried primary care physicians in major urban centers in Canada and the United States with the aim of understanding their attitudes towards cognitive enhancement. Our primary hypothesis was that physicians would be more comfortable prescribing cognitive enhancers to older patients than to young adults. Physicians were presented with a hypothetical pharmaceutical cognitive enhancer that had been approved by the regulatory authorities for use in healthy adults, and was characterized as being safe, effective, and without significant adverse side effects. Respondents overwhelmingly reported increasing comfort with prescribing cognitive enhancers as the patient age increased from 25 to 65. When asked about their comfort with prescribing extant drugs that might be considered enhancements (sildenafil, modafinil, and methylphenidate) or our hypothetical cognitive enhancer to a normal, healthy 40 year old, physicians were more comfortable prescribing sildenafil than any of the other three agents. When queried as to the reasons they answered as they did, the most prominent concerns physicians expressed were issues of safety that were not offset by the benefit afforded the individual, even in the face of explicit safety claims. Moreover, many physicians indicated that they viewed safety claims with considerable skepticism. It has become routine for safety to be raised and summarily dismissed as an issue in the debate over pharmacological cognitive enhancement; the observation that physicians were so skeptical in the face of explicit safety claims suggests that such a conclusion may be premature. Thus, physician attitudes suggest that greater weight be placed upon the balance between safety and benefit in consideration of pharmacological cognitive enhancement

Invariant computations in local cortical networks with balanced excitation and inhibition

[Abstract] Cortical computations critically involve local neuronal circuits. The computations are often invariant across a cortical area yet are carried out by networks that can vary widely within an area according to its functional architecture. Here we demonstrate a mechanism by which orientation selectivity is computed invariantly in cat primary visual cortex across an orientation preference map that provides a wide diversity of local circuits. Visually evoked excitatory and inhibitory synaptic conductances are balanced exquisitely in cortical neurons and thus keep the spike response sharply tuned at all map locations. This functional balance derives from spatially isotropic local connectivity of both excitatory and inhibitory cells. Modeling results demonstrate that such covariation is a signature of recurrent rather than purely feed-forward processing and that the observed isotropic local circuit is sufficient to generate invariant spike tuning

Modelle der Repräsentation in der visuellen Hirnrinde

In dieser Dissertation wird die Verarbeitung visueller Informationen innerhalb der ersten Verarbeitungsstufen des visuellen Systems untersucht. Augenscheinlich bilden Zellen der primären visuellen Gehirnrinde (V1) eine Summe der Lichtintensitäten des gezeigten visuellen Stimulus, die in ihr rezeptives Feld fallen. Ein lineares Modell dieser Zellen hat den Vorteil, dass es einfach ist und eine Reihe von Eigenschaften der Zellfunktion erklärt. Jedoch zeigt sich, dass dieses Modell nicht ausreichend ist, um wichtige Nichlinearitäten der Zellantworten zu erklären, die eher intrakortikaler Natur zu sein scheinen. Zu diesem Forschungsgebiet existieren viele theoretische und experimentelle Studien. Jedoch sind die Mechanismen, die von der Integration der einzelnen Zelleneingänge bis zur finalen Zellantwort führen, immer noch unklar und werden auch heute noch sehr häufig in der Literatur diskutiert. Anhand von theoretischen Ansätzen und experimentellen Messungen soll durch diese Arbeit zum weiteren Verständnis neuronaler Netzwerkdynamiken beitragen werden. Im ersten Teil dieser Arbeit untersuchen wir mit Hilfe eines abstrakten „Correlation-Based-Learning“ (CBL) Modells, das lateralen Wettbewerb berücksichtigt, die Rolle von intrakortikaler Rekurrenz in der Entwicklung von Augendominanz und topographischen Karten. Dieser Mechanismus entspricht dem Effekt eines variablen Grades von intrakortikaler Interaktion, in dem sich Neurone gegenseitig auf kurzen Distanzen erregen und sich auf langen Distanzen hemmen. Dieser Ansatz ist durch eine nichtlineare Transferfunktion realisiert, dem ein Normalisierungsprozess folgt. Des Weiteren untersuchen wir den Effekt dieses Mechanismus an verschieden Orten der Augendominanz Karte. Diese ändert sich in vielen Spezies vom abwechselnden Streifenmuster zu fleckenförmigen Gebieten in der Peripherie des visuellen Kortizes. Wir untersuchen, bis zu welchem Grad diese Änderungen von Änderungen des „Cortical Magnification Factor“, als auch von Änderungen der Unterschiede in der relativen Differenz der Projektionen vom linken und rechten Auge abhängen. In einer letzen Untersuchung dieses ersten Teils untersuchen wir, welche Rolle eine nichtlineare Transferfunktion ohne den zusätzlichen Normalisierungsmechanismus auf die Entwicklung von Augendominanz und topographischen Karten hat. Im zweiten Teil dieser Arbeit präsentieren wir Ergebnisse elektrophysiologischer Messungen von Neuronen in der visuellen Gehirnrinde der Katze. Diese Messungen wurden an verschiedenen Positionen der Orientierungskarte gemacht. Zusätzlich zeigen wir anatomische Messungen, die Aufschluss über die räumliche laterale Ausbreitung der Eingänge zu diesen Neuronen bringen. Mit Hilfe einer mathematischen Analyse und Computersimulationen untersuchen wir weiterhin, welche Einschränkungen diese Messungen bzgl. des kortikalen „Arbeitspunktes“ (afferente vs. rekurrente Verarbeitung) machen. In einem einfachen „Superpositionsmodell“, welches das Zusammenspiel vom afferenten und erregenden rekurreten Antrieb beschreibt, zeigen wir, dass die experimentellen Ergebnisse nur dann erklärt werden können, wenn ein scharf „getuneter“ afferenter Input zusammen mit einem kortikalem Netzwerk von mittlerer Stärke verarbeitet wird. Des Weiteren untersuchen wir ein geometrisches Feuerratenmodell, mithilfe dessen wir die Orientierungsselektivität von erregenden und hemmenden Eingängen in neuronale Zellen und die Feuerrate als Funktion von einer großen Anzahl von Modellparametern berechnen können. Als abschließende Analyse untersuchen wir auch Parameteränderungen innerhalb eines biologisch realistischeren Netzwerkmodells, durch das wir zusätzlich die Orientierungsselektivität des Membranpotentials berücksichtigen können.We investigate the processing of visual input in the early visual system of mammals. Cells in the primary visual cortex (V1) often appear to compute a weighted sum of the light intensity distribution of the visual stimuli that fall on their receptive fields. A linear model of these cells has the advantage of simplicity and captures a number of basic aspects of cell function. On the other hand, it fails to account for important observed response nonlinearities which appear to have an intra-cortical origin. Much experimental and theoretical work has been published on this subject. However, the mechanisms that give rise to the integration of a cortical cell's input to its final response are still controversial and are still part of intense study and debate. In this manuscript, we illustrate the use of combined theoretical approaches and experimental measurements for understanding neuronal and circuit dynamics. Firstly, we use an abstract correlation-based learning (CBL) model to study the role of lateral interaction on the emergence of ocular dominance (OD) and topographic (TP) maps. In detail, this mechanism resembles the effect of a variable degree of intra-cortical competition in which neurons excite each other at short distances and inhibit each other at larger distances and is implemented through a nonlinear response function followed by divisive normalization mechanism. Furthermore, we explore the effect of this quantity at different locations of the OD map, which in many species dissolves in the periphery of the visual cortex. We investigate to what extent these OD pattern changes can be related - either as a cause or an effect - to changes in the cortical magnification factor as well as to changes in the relative strength of the projection from the left and the right eye. Secondly, we present electrophysiological measurements of the excitatory and inhibitory synaptic conductances in neurons at different orientation (OR) map positions - ranging from pinwheels to orientation domains - and anatomical measurements of the inputs to these neurons in the cat adult primary visual cortex. The local arrangement of cells with different response properties vary with spatial location in the OR map and influence information processing in local neuronal circuits. In a second step we investigate, using a combination of mathematical analysis and computer simulations, what constraints these experimental data imposes on the cortical "operating regime" (feed-forward, dominated inhibitory, dominated excitatory, intermediate recurrent or highly recurrent "marginal phase"). In a simple "superposition" model (describing the interplay of the afferent and the excitatory recurrent drive), we show that the experimental findings can only be explained if a sharply tuned feed-forward input is processed by a cortical network of intermediate recurrency. Using a geometrical firing rate network model we calculate the tuning curves of the total excitatory and inhibitory conductances and the output spike-rates as a function of a large range of model parameters

An fMRI study into emotional processing in Parkinson's disease: Does increased medial prefrontal activation compensate for striatal dysfunction?

Background Apart from a progressive decline of motor functions, Parkinson's disease (PD) is also characterized by non-motor symptoms, including disturbed processing of emotions. This study aims at assessing emotional processing and its neurobiological correlates in PD with the focus on how medicated Parkinson patients may achieve normal emotional responsiveness despite basal ganglia dysfunction. Methods Nineteen medicated patients with mild to moderate PD (without dementia or depression) and 19 matched healthy controls passively viewed positive, negative, and neutral pictures in an event-related blood oxygen level-dependent functional magnetic resonance imaging study (BOLD-fMRI). Individual subjective ratings of valence and arousal levels for these pictures were obtained right after the scanning. Results Parkinson patients showed similar valence and arousal ratings as controls, denoting intact emotional processing at the behavioral level. Yet, Parkinson patients showed decreased bilateral putaminal activation and increased activation in the right dorsomedial prefrontal cortex (PFC), compared to controls, both most pronounced for highly arousing emotional stimuli. Conclusions Our findings revealed for the first time a possible compensatory neural mechanism in Parkinson patients during emotional processing. The increased medial PFC activity may have modulated emotional responsiveness in patients via top-down cognitive control, therewith restoring emotional processing at the behavioral level, despite striatal dysfunction. These results may impact upon current treatment strategies of affective disorders in PD as patients may benefit from this intact or even compensatory influence of prefrontal areas when therapeutic strategies are applied that rely on cognitive control to modulate disturbed processing of emotions