In this chapter, we discuss a selection of current views of the neural correlates of consciousness (NCC). We focus on the different predictions they make, in particular with respect to the role of prefrontal cortex (PFC) during visual experiences, which is an area of critical interest and some source of contention. Our discussion of these views focuses on the level of functional anatomy, rather than at the neuronal circuitry level. We take this approach because we currently understand more about experimental (...) evidence at this coarse level and because these results are appropriate for arbitrating between current theoretical frameworks. We discuss the Two-Visual-Systems Hypothesis (Milner & Goodale 1995; 2006), Local Recurrency (Lamme 2010; Lamme 2006), Higher Order (Lau 2008; Lau & Rosenthal 2011) and Global Workspace theories (Baars 1997; Baars 2005; Dehaene & Naccache 2001; Dehaene 2014). Despite the apparent stark differences between conscious and unconscious perceptual processing, available evidence suggests that their neural substrates must be largely shared. This indicates that the difference in neural activity between conscious and unconscious perceptual processing is likely to be subtle and highly specialized. We argue that current experimental evidence about the involvement of specific activity in prefrontal cortex supports the higher order neural theory of consciousness. In consequence, imaging techniques that focus only on marked differences between conscious and unconscious level of activity are likely to be insensitive to the relevant neural activity patterns that underlie conscious experiences. Finally, it follows from the evidence we discuss that the functional advantages of conscious over unconscious perceptual processing may be more limited than commonly thought. (shrink)

Arguably the most foundational principle in perception research is that our experience of the world goes beyond the retinal image; we perceive the distal environment itself, not the proximal stimulation it causes. Shape may be the paradigm case of such “unconscious inference”: When a coin is rotated in depth, we infer the circular object it truly is, discarding the perspectival ellipse projected on our eyes. But is this really the fate of such perspectival shapes? Or does a tilted coin retain (...) an elliptical appearance even when we know it’s circular? This question has generated heated debate from Locke and Hume to the present; but whereas extant arguments rely primarily on introspection, this problem is also open to empirical test. If tilted coins bear a representational similarity to elliptical objects, then a circular coin should, when rotated, impair search for a distal ellipse. Here, nine experiments demonstrate that this is so, suggesting that perspectival shapes persist in the mind far longer than traditionally assumed. Subjects saw search arrays of three-dimensional “coins,” and simply had to locate a distally elliptical coin. Surprisingly, rotated circular coins slowed search for elliptical targets, even when subjects clearly knew the rotated coins were circular. This pattern arose with static and dynamic cues, couldn’t be explained by strategic responding or unfamiliarity, generalized across shape classes, and occurred even with sustained viewing. Finally, these effects extended beyond artificial displays to real-world objects viewed in naturalistic, full-cue conditions. We conclude that objects have a remarkably persistent dual character: their objective shape “out there,” and their perspectival shape “from here.”. (shrink)

Introspection is a fundamental part of our mental lives. Nevertheless, its reliability and its underlying cognitive architecture have been widely disputed. Here, I propose a principled way to model introspection. By using time-tested principles from signal detection theory (SDT) and extrapolating them from perception to introspection, I offer a new framework for an introspective signal detection theory (iSDT). In SDT, the reliability of perceptual judgments is a function of the strength of an internal perceptual response (signal- to-noise ratio) which is, (...) to a large extent, driven by the intensity of the stimulus. In parallel to perception, iSDT models the reliability of introspective judgments as a function of the strength of an internal introspective response (signal-to-noise ratio) which is, to a large extent, driven by the intensity of conscious experiences. Thus, by modelling introspection after perception, iSDT can calibrate introspection’s reliability across a whole range of contexts. iSDT offers a novel, illuminating way of thinking about introspection and the cognitive processes that support it. (shrink)

Martin Buber believed that life's deepest truth lies in human relationships. In this classic work he puts this belief into practice, applying it to the concrete problems of contemporary society.

Metacognition is the capacity to evaluate the success of one's own cognitive processes in various domains; for example, memory and perception. It remains controversial whether metacognition relies on a domain-general resource that is applied to different tasks or if self-evaluative processes are domain specific. Here, we investigated this issue directly by examining the neural substrates engaged when metacognitive judgments were made by human participants of both sexes during perceptual and memory tasks matched for stimulus and performance characteristics. By comparing patterns (...) of fMRI activity while subjects evaluated their performance, we revealed both domain-specific and domain-general metacognitive representations. Multivoxel activity patterns in anterior prefrontal cortex predicted levels of confidence in a domain-specific fashion, whereas domain-general signals predicting confidence and accuracy were found in a widespread network in the frontal and posterior midline. The demonstration of domain-specific metacognitive representations suggests the presence of a content-rich mechanism available to introspection and cognitive control. (shrink)

Studying the neural correlates of conscious awareness depends on a reliable comparison between activations associated with awareness and unawareness. One particularly difficult confound to remove is task performance capacity, i.e. the difference in performance between the conditions of interest. While ideally task performance capacity should be matched across different conditions, this is difficult to achieve experimentally. However, differences in performance could theoretically be corrected for mathematically. One such proposal is found in a recent paper by Lamy, Salti and Bar-Haim [Lamy (...) D, Salti M, Bar-Haim Y. Neural correlates of subjective awareness and unconscious processing: an ERP study. J Cognitive Neurosci 2009,21:1435-46], who put forward a corrective method for an electroencephalography experiment. We argue that their analysis is essentially grounded in a version of High Threshold Theory, which has been shown to be inferior in general to Signal Detection Theory. We show through a series of computer simulations that their correction method only partially removes the influence of perfor- mance capacity, which can yield misleading results. We present a mathematical correction method based on Signal Detection Theory that is theoretically capable of removing performance capacity confounds. We discuss the limitations of mathemati- cally correcting for performance capacity confounds in imaging studies and its impact for theories about consciousness. (shrink)

Implementing corporate social responsibility (CSR) in supply chains is not a trivial task. In fact, many firms in recent years have publicly proclaimed that in order to keep their CSR commitments, they had to reduce reliance on external suppliers by vertically integrating their operations. Our aim in this article is to examine whether there is truly a relationship between a firm’s CSR performance and its level of vertical integration. Drawing on a multi-industry sample of 2,715 firm-year observations, and after addressing (...) endogeneity concerns, we demonstrate that firms with higher CSR performance tend to vertically integrate more (or, outsource less). We also demonstrate that this tendency is weaker for firms that have higher degrees of asset specificity or international diversification. Our core conclusion is that CSR performance and outsourcing are at odds, but firms can reconcile this tension by deepening their collaborations with suppliers. (shrink)

Consciousness and confidence seem intimately related. Accordingly, some researchers use confidence ratings as a measure of, or proxy for, consciousness. Rosenthal discusses the potential connections between the two, and rejects confidence as a valid measure of consciousness. He argues that there are better alternatives to get at conscious experiences such as direct subjective reports of awareness (i.e. subjects’ reports of perceiving something or of the degree of visibility of a stimulus). In this chapter, we offer a different perspective. Confidence ratings (...) in general, and metacognitive measures in particular, may offer important advantages over subjective ratings. The arguments we offer here are supported by empirical, practical and socio-strategic considerations. However, we do not suggest consciousness and confidence are interchangeable. We recognize the limitations of confidence ratings in some experimental designs and for some research questions. Nevertheless, we also address a potential conceptual link between consciousness and confidence that stems from Rosenthal’s very own work on mental quality space theory. (shrink)

This is the first book-length study of Descartes's metaphysics to place it in its immediate historical context, the Late Scholastic philosophy of thinkers such as Suárez against which Descartes reacted. Jorge Secada views Cartesian philosophy as an 'essentialist' reply to the 'existentialism' of the School, and his discussion includes careful analyses and original interpretations of such central Cartesian themes as the role of scepticism, intentionality and the doctrine of the material falsity of ideas, universals and the relation between sense (...) and understanding, causation and the proofs of the existence of God, the theory of substance, and the dualism of mind and matter. His study offers a picture of Descartes's metaphysics that is both novel and philosophically illuminating. (shrink)

To find the neural substrates of consciousness, researchers compare subjects’ neural activity when they are aware of stimuli against neural activity when they are not aware. Ideally, to guarantee that the neural substrates of consciousness—and nothing but the neural substrates of consciousness—are isolated, the only difference between these two contrast conditions should be conscious awareness. Nevertheless, in practice, it is quite challenging to eliminate confounds and irrelevant differences between conscious and unconscious conditions. In particular, there is an often-neglected confound that (...) is crucial to eliminate from neuroimaging studies: task performance. Unless subjects’ task performance is matched (and hence perceptual signal processing is matched), researchers risk finding the neural correlates of perception, rather than conscious perception. Here, we discuss the theoretical motivations for the performance matching framework and review empirical demonstrations of, and theoretical inferences derived from, obtaining differences in consciousness while controlling for task performance. We summarize signal detection theoretic modeling frameworks that explain how it is that we can derive performance-matched differences in consciousness without the effect being trivially driven by differences in criterion setting, and also provide principles for designing experimental paradigms that yield performance-matched differences in awareness. Finally, we address potential technical and theoretical issues that stem from matching performance across conditions of awareness, and we introduce the notion of “triangulation” for designing comprehensive experimental sets that can better reveal the neural substrates of consciousness. (shrink)

La conferencia “Das Ge-Stell”, “Lo dis-puesto”, ha sido recogida en el volumen 79 de la Edición integral (Martin Heidegger, Gesamtausgabe (GA), Bd. 79: Bremer und Freiburger Vorträge, Vittorio Klostermann, Frankfurt a. M., 1994. Vorträge 1949 und 1957 herausgegeben von Petra Jaeger). Es una de las conferencias pronunciadas en Bremen el año 1949 (Einblick in das was is, Mirada en lo que es. Bremer Vorträge 1949). “Das Ge-Stell”, se halla entre las páginas 24 y 45. Las otras conferencias de esta parte (...) del libro — Mirada en lo que es—, son “Das Ding”, “La cosa” (pp. 5-23), “Die Gefahr”, “El peligro” (pp. 46-67) y “Die Kehre”, “La vuelta” (p. 68-77). La otra parte se titula Grundsätze des Denkens, Principios del pensamiento2. (shrink)

Se espera que una revista científica cumpla la función de dar a conocer resultados de investigación, difundir escritos y nuevas ideas y, ahora más que antes, abrir espacios para un fructífero intercambio entre instituciones, bajo el lema de “internacionalización del conocimiento”. En honor a su compromiso como revista académica de filosofía, el presente número de Aoristo - International Journal of Phenomenology, Hermeneutics and Metaphysics, cumple con las tres misiones antes mencionadas, haciendo énfasis en la última.

De uma revista científica espera-se que cumpra a função de divulgar resultados de pesquisas, difundir trabalhos e novas ideias e, agora mais do que antes, franquear espaço para o frutífero intercâmbio entre instituições, sob o lema da internacionalização dos saberes. Honrando seu compromisso de periódico acadêmico de filosofia, o presente número de Aoristo - International Journal of Phenomenology, Hermeneutics and Metaphysics, atende às três mencionadas missões, fazendo ênfase na última.

One can expect a scientific journal to fulfill the purpose of disseminating research results, spreading works and new ideas and, now more than ever, franking space for the fruitful exchange among institutions under the dictum of the knowledge’s internationalization. Honoring its commitment as an academical philosophy journal, the present issue of the Aoristo - International Journal of Phenomenology, Hermeneutics and Metaphysics assumes the three afore mentioned missions, with emphasis on the last one.

In this paper, I reject that animal reasoning, negation in particular, necessarily involves the representation of absences, as suggested by Bermúdez (2003, 2006, 2007), since this would still work as a logical negation (unavailable for non-linguistic creatures). False belief, pretense, and communication experiments show that non-human animals (at least some primates) have difficulties representing absent entities or properties. I offer an alternative account resorting to the sub-symbolic similarity judgments proposed by Vigo & Allen (2009) and expectations: animal proto-negation takes place (...) through the incompatibility between an expected and the actual representation. Finally, I propose that the expectation paradigm be extrapolated to other experi-ments in cognitive psychology (both with pre-linguistic children and animals) in order to design fair experiments that test other minds considering their true abilities. (shrink)

We give characterizations for the sentences "Every $\Sigma^1_2$-set is measurable" and "Every $\Delta^1_2$-set is measurable" for various notions of measurability derived from well-known forcing partial orderings.

We investigate which filters onωcan contain towers, that is, a modulo finite descending sequence without any pseudointersection. We prove the following results:Many classical examples of nice tall filters contain no towers.It is consistent that tall analytic P-filters contain towers of arbitrary regular height.It is consistent that all towers generate nonmeager filters, in particular Borel filters do not contain towers.The statement “Every ultrafilter contains towers.” is independent of ZFC.Furthermore, we study many possible logical implications between the existence of towers in filters, (...) inequalities between cardinal invariants of filters $,${\rm{co}}{{\rm{f}}^{\rm{*}}}\left$,${\rm{no}}{{\rm{n}}^{\rm{*}}}\left$, and${\rm{co}}{{\rm{v}}^{\rm{*}}}\left$), and the existence of Luzin type families, that is, if${\cal F}$is a filter then${\cal X} \subseteq {[\omega ]^\omega }$is an${\cal F}$-Luzin family if$\left\{ {X \in {\cal X}:|X \setminus F| = \omega } \right\}$is countable for every$F \in {\cal F}$. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:.. MERELY A MAN OF LETTERS" an interview with Jorge Luis Borges* Philosophy and Literature: Why don't you tell us about some of the philosophers who have influenced your work and in whom you have been the most interested? Jorge Luis Borges: Well, I think that's an easy one. You might talk in terms of two: Berkeley and Schopenhauer. But I suppose Hume might be worked in (...) also, because, after all, Hume refutes Berkeley. Really, he comes from Berkeley—even if Berkeley comes from Locke. You might think of Locke, of Berkeley, and of Hume as being three links in an argument..... But I suppose that when someone refutes someone else in philosophy, he is carrying on the argument. P&L: And Schopenhauer? Borges: Schopenhauer is very different from Hume. Of course, Schopenhauer had his idea of the Will. That is not to be found in Hume.... The case of Berkeley was different. I suppose he thought of God as being aware of all things all the time, if I don't get him wrong. If we go away, does this room disappear? No, because God is thinking about it. Now, in the case of Schopenhauer, I was rereading Die Welt als Wille und Vorstellung, The World as Will and Idea, and I was rather taken aback, or baffled I should say, puzzled by something that keeps on recurring in Schopenhauer. Of course it may have been a slip of the pen, but as he goes back to it, and as he was a very careful writer, I wonder if it is a slip of the pen. For example, Schopenhauer begins by saying that the universe, the stars, the spaces in between, the planets, *On April 14, 1976, two editors of Philosophy and Literature, along with an interested colleague, interviewed Jorge Luis Borges at Michigan State University, where he held a position as visiting professor for the winter term. These remarks are edited from the transcript of that conversation. 337 338Philosophy and Literature this planet, those things, have no existence—except in the mind which perceives them. But then, to my surprise—and I suppose you can explain this to me, since you are philosophers and I am not—what Schopenhauer says is that all those things have no existence except in the brain. And that the universe—I remember these words, I don't think I'm inventing them now—"ist ein Gehirnphänomen," that the world is a cerebral phenomenon. Now, I was baffled. Because, of course, if you think of the universe, I suppose the brain is as much a part of the external world as the stars or the moon. The brain after all is a system of visual, of tactile, perceptions. He keeps on insisting on the brain. I don't think, for example, that Bishop Berkeley insists on the brain, or Hume, who would have insisted on the mind, consciousness. P&L: People sometimes say that they see Berkeley in stories like "Orbis Tertius." Borges: Yes, I suppose they do. Well, of course. But in that story I was led by literary means also. P&L: How do you distinguish the literary from the philosophical means in that story? Could you explain that? Borges: Very easily.... Encyclopedias have been my chief reading. I have always been interested in encyclopedias. I used to go to the Biblioteca National in Buenos Aires—and since I was so shy, I felt I could not cope with asking for a book, so I looked on the shelves for the Encyclopaedia Britannica. I would pick up any chance volume and I would read it. One night I was richly rewarded, because I read all about the Druses, Dryden and the Druids—a treasure trove, no?—all in the same volume, "Dr-." Then I came to the idea of how fine it would be to think of an encyclopedia... a very rigorous one of course, of an imaginary world, where everything should be linked. For example, you would have a language and then a literature, and then a history and so on. Then I thought I would write a story of a fancy encyclopedia. Of course that would require many different people to write it... (shrink)

The contributors to this volume argue that we can, and they offer a new way: the "participatory turn," which proposes that individuals and communities have an ...

When visual attention is directed away from a stimulus, neural processing is weak and strength and precision of sensory data decreases. From a computational perspective, in such situations observers should give more weight to prior expectations in order to behave optimally during a discrimination task. Here we test a signal detection theoretic model that counter-intuitively predicts subjects will do just the opposite in a discrimination task with two stimuli, one attended and one unattended: when subjects are probed to discriminate the (...) unattended stimulus, they rely less on prior information about the probed stimulus’ identity. The model is in part inspired by recent findings that attention reduces trial-by-trial variability of the neuronal population response and that they use a common criterion for attended and unattended trials. In five different visual discrimination experiments, when attention was directed away from the target stimulus, subjects did not adjust their response bias in reaction to a change in stimulus presentation frequency despite being fully informed and despite the presence of performance feedback and monetary and social incentives. This indicates that subjects did not rely more on the priors under conditions of inattention as would be predicted by a Bayes-optimal observer model. These results inform and constrain future models of Bayesian inference in the human brain. (shrink)

This article pretends to provide a reading of the Seventh Letter focused on the role that medical terminology plays in it. Leaving aside the unsolvable enigma of Plato’s authorship, the letter shows evident connections with fundamental topics from the “last” Plato, particularly in its political aspects. In many passages of the Seventh Letter, the figure of the philosopher as an educator appears covered with medical aspects, and the political situation is defined as a pathology that we must treat according to (...) a therapeutic methodology. (shrink)

El presente artículo argumenta que hay un desarrollo en la postura de Platón frente a la geometría. A partir del primer contacto con la geometría, Platón se sintió atraído hacia la geometría por sus sorprendentes resultados. Por tal motivo, en un primer momento, Platón presenta en el Menón y en el Teeteto a la geometría como una ciencia ejemplar y le pide a los interlocutores que imiten sus procesos. En un segundo momento, Platón en la República incluye a la geometría (...) dentro de la filosofía, hace que el método de la geometría fundamente a su máxima ciencia dialéctica, incluye a los entes geométricos dentro del edificio ontológico, y a la ciencia geométrica dentro de las disciplinas que el rey-filosofo debe estudiar para ascender a las ideas. En un tercer momento, en el Timeo, la geometría es la ciencia básica que utiliza el Demiurgo para componer al universo. (shrink)

In this essay I propose a model of philosophical conceptual analysis that might also serve as a common methodological basis for the various forms of applied philosophy. I elucidate the linguistic, the logical, and finally the social dimension of conceptual analysis, and I also try to show how it contributes to personal autonomy and conflict management.

Aristotle’s argument against Timaeus’ view of intellection as an endless circular motion can be divided into two main sections: a categorial one, which rests upon the impossibility of intertwining material and immaterial ingredients into a single (albeit twofold) substance; and a geometrical one, which highlights those features of circular magnitudes which render them unsuitable for performing intellectual tasks. This paper focuses on the first set of reasons that Aristotle puts forward, by stressing the productive philosophical outcome of this otherwise perplexing (...) doxographical survey. It is argued that Aristotle’s own notions of ‘contact’ and ‘unmoved mover’ are greatly indebted to his critical scrutiny of Timaeus’ cosmogony. Further, the paper holds that the version of ‘causal synonymy’ that Aristotle discovers in Timaeus’ εἰκὼς μûθος leads him to recast this principle, in order to avoid unwelcome ‘physiological’ consequences. In this way, Aristotle’s literal reading of Timaeus’ εἰκὼς μûθος emerges as a plausible interpretive stance. (shrink)

La filosofía de Jámblico ha supuesto todo un reto hermenéutico para sus lectores. En concreto, su concepción del _logos_ y su epistemología se clausuran si no las atendemos desde ópticas respetuosas con las prácticas y pensamientos propios de la época y de la tradición de la que nacen. Algunos autores han invalidado precisamente la propuesta jambliqueana al sostener que es una suerte de invitación al irracionalismo. Frente a tal lectura, autoras como C. V. Liefferinge se han apoyado en tesis presentes (...) en la filosofía de P. Hadot para defender que es posible abrirnos a la concepción de filosofía de Jámblico a través de su defensa del ritual y del símbolo. Por ello, en el presente estudio indagaremos en esta idea a fin de iluminar los núcleos de sentido ocultos de la hermenéutica de la racionalidad que emanan de la obra de Jámblico. Para ello sostendremos que su filosofía es, ante todo, una defensa de una forma de vida racional que se puede rastrear en sus raíces platónicas. (shrink)

In classical philosophy of time, present time mainly has been considered in its fleetingness: it is transition, in the Platonic meaning of the sudden or in the Aristotelian sense of discreet moment and isolated intensity that escapes possible perception. Through the idea of subjective constitution of time, Husserl’s phenomenology tries to spread the moment. He transcends the idea of linear and empty time in modern philosophy. Phenomenological description of time experience analyses the filled character of the moment that can be (...) detained in the performance of consciousness. As a consequence of the temporality of consciousness, he nevertheless remains in the temporal conception of presence. The phenomenology of Merleau-Ponty, however, is able to grasp the spacial meaning of presence. In his perspective of a phenomenology of perception, presence can be understood as a space surrounding the body, as a field of present things given in perception. Merleau-Ponty recovers the ancient sense of ‘praesentia’ as a fundamental concept of being in the world. (shrink)

Der Status quo in zeitgenossischen pluralistischen Gesellschaften konfrontiert die politische Philosophie mit dem Problem, eine Staatslegitimation zu formulieren, die fur alle Burger trotz konfligierender Interessen und Wertvorstellungen uberzeugend ist. Im ersten Teil wird Thomas Hobbes klassische Vertragstheorie, die Spieltheorie sowie James Buchanans okonomische Vertragstheorie kritisch diskutiert. Die im zweiten Teil entworfene kontextbezogene Vertragstheorie analysiert eine Gesellschaft, in der Egoisten, moderate Altruisten und moralische Idealisten interagieren. Sie zeigt, dass ein Verfassungsstaat fur fast alle Burger interessenkompatibel ist, weil er Interaktionsprobleme vermeidet, die (...) im Naturzustand, einem Sklavenstaat, einer Moraldiktatur und einem Minimalstaat auftreten wurden.". (shrink)

Brendle, J., H. Judah and S. Shelah, Combinatorial properties of Hechler forcing, Annals of Pure and Applied Logic 59 185–199. Using a notion of rank for Hechler forcing we show: assuming ωV1 = ωL1, there is no real in V[d] which is eventually different from the reals in L[ d], where d is Hechler over V; adding one Hechler real makes the invariants on the left-hand side of Cichoń's diagram equal ω1 and those on the right-hand side equal 2ω and (...) produces a maximal almost disjoint family of subsets of ω of size ω1; there is no perfect set of random reals over V in V[ r][ d], where r is random over V and d Hechler over V[r], thus answering a question of the first and second authors. (shrink)

Michel Foucault left us with an implicit reflection about the meaning of the work of the “master of life,” just as antique philosophy (Greco-Roman) practiced and made a problem of it. In Foucault’s studies about ancient philosophy, which will soon be available as a whole in a written edition, this f..

The distinction between agent-relative reasons and agent-neutral reasons is philosophically important, but there is no consensus on how to understand the distinction exactly. In this paper, I discuss several interpretations of the distinction that can be found in the literature: the Motivational Interpretation, the Scope Interpretation, and the Goal Interpretation, and argue that none of these interpretations is entirely convincing. I propose a novel interpretation of the distinction, which I call the Normative Force Interpretation, according to which the distinction between (...) agent-relative reasons and agent-neutral reasons concerns the normative force that these reasons can have for agents. (shrink)

This article examines Aristotle's views concerning the possibility of friendship between human beings and nonhuman animals. The suggestion that he denies this possibility is rejected. I reassess the textual evidence adduced by scholars in support of this reading, while adding new material for discussion. Central to the traditional reading is the assumption that animals, in Aristotle's view, cannot be friends in virtue of their cognitive limitations. I argue that Aristotle's account of animal cognition is perfectly consistent with the possibility of (...) friendship between human beings and nonhuman animals. (shrink)

This comprehensive reference volume features essays by some of the most distinguished scholars in the field. Provides a comprehensive "who's who" guide to medieval philosophers. Offers a refreshing mix of essays providing historical context followed by 140 alphabetically arranged entries on individual thinkers. Constitutes an extensively cross-referenced and indexed source. Written by a distinguished cast of philosophers. Spans the history of medieval philosophy from the fourth century AD to the fifteenth century.