Are there True Contradictions? A Critical Discussion of Graham Priest's, Beyond the limits of thought

The present article critically examines three aspects of Graham Priest's dialetheic analysis of very important kinds of limitations (the limit of what can be expressed, described, conceived, known, or the limit of some operation or other). First, it is shown that Priest's considerations focusing on Hegel's account of the infinite cannot be sustained, mainly because Priest seems to rely on a too restrictive notion of object. Second, we discuss Priest's treatment of the paradoxes in Cantorian set-theory. It is shown that Priest does not address the issue in full generality; rather, he relies on a reading of Cantor which implicitly attributes a very strong principle concerning quantification over arbitrary domains to Cantor. Third, the main piece of Priest's work, the so-called “inclosure schema”, is investigated. This schema is supposed to formalize the core of many well-known paradoxes. We claim, however, that formally the schema is not sound. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinematics of Goal-Directed Arm Movements in Neglect: Control of Hand Velocity

Do patients with unilateral neglect exhibit direction-specific deficits in the control of movement velocity when performing goal-directed arm movements? Five patients with left-sided neglect performed unrestrained three-dimensional pointing movements to visual targets presented at body midline, the left and right hemispace. A group of healthy adults and a group of patients with right-hemispheric brain damage but no neglect served as controls. Pointing was performed under normal room light or in darkness. Time-position data of the hand were recorded with an opto-electronic camera system. We found that compared to healthy controls, movement times were longer in both patient groups due to prolonged acceleration and deceleration phases. Tangential peak hand velocity was lower in both patient groups, but not significantly different from controls. Single peak, bell-shaped velocity profiles of the hand were preserved in all right hemispheric patients and in three out of five neglect patients. Most important, the velocity profiles of neglect patients to leftward targets did not differ significantly from those to targets in the right hemispace. In summary, we found evidence for general bradykinesia in neglect patients, but not for a direction-specific deficit in the control of hand velocity. We conclude that visual neglect induces characteristic changes in exploratory behavior, but not in the kinematics of goal-directed movements to objects in peripersonal space.     

Genes and family environment in familial clustering of cancer

Familial clustering of a disease is defined as the occurrence of the disease within some families in excess of what would be expected from the occurrence in the population. It has been demonstrated for several cancer types, ranging from rare cancers as the adenomatosis-coli-associated colon cancer or the Li-Fraumeni syndrome to more common cancers as breast cancer and colon cancer. Familial clustering, however, is merely an epidemiological pattern, and it does not tell whether genetic or environmental causes or both in combination are responsible for the familial clustering. Familial clustering may be due to genetic predisposition to the disease, but exposure to environmental factors — shared by members of some families, but not by members of other families — may also cause familial clustering and hence mimic genetic inheritance in the study of nuclear families. Based on assumptions regarding the individual steps in the biological process starting with exposure to carcinogens and ending with death from disseminated cancer we suggest that genetic and environmental factors may both be involved in most of these steps. The present paper focuses on research methodologies necessary to discriminate between the effect of genes and family environment in the development of cancer.     

Sind empirische Theorien falsifizierbar?

Die Frage: sind empirische Theorien falsifizierbar? ist natürlich trivialerweise zu verneinen, falls man Theorien nicht als Mengen von Aussagen, sonden z. B., wie Sneed/Stegmüller, als mengentheoretische Strukturen plus intendierte Anwendungsbereiche auffaßt. Daß die Antwort, zumindest dann, wenn man die Fragestellung auf bestimmte physikalische Theorien einschränkt, auch bei Zugrundelegung der sogenannten Aussagen-Konzeption (statement view) nicht anders lautet, ist hingegen schon weniger trivial — obgleich seit langem bekannt, spätestens nämlich seit Duhems berühmter Argumentation gegen die Möglichkeit eines experimentum crucis. Andererseits beruht eine der derzeit einflußreichsten methodologischen Theorien, die von Popper, gerade auf der gegenteiligen Behauptung. Erst jüngst noch hat Popper seine Falsifizierbarkeits-Annahme, vor allem gegen Kritiken von Lakatos und Putnam, zu verteidigen versucht; die gleiche Intention verfolgen auch zwei Aufsätze von Musgrave. Es erscheint mir daher angebracht, kurz auf das Problem der Falsifizierbarkeit von empirischen Theorien zurückzukommen. Vorweg noch zwei Bemerkungen zur Terminologie: 1) Ich verwende, ohne mich auf den Versuch einer genaueren Explikation einzulassen, den Begriff ?(physikalische) Theorie“ in dem für den statement view geläufigen Sinne, wonach eine (deterministische) Theorie aus einer Menge von allgemeinen (deterministischen Natur-)Gesetzen besteht. Es sei ausdrücklich darauf hingewiesen, daß dies wenigstens partiell dem sonst üblichen Sprachgebrauch zuwider läuft: die ?Theorie des Planetensystems“ und die ?Mondtheorie“, beispielsweise, sind keine Theorien im genannten Sinne, weil sie außer auf allgemeinen Naturgesetzen noch auf spezifischen nicht-gesetzesartigen Annahmen beruhen. Andrerseits dürfte diese Deutung des Begriffs ?Theorie“ zumindest mit derjenigen von Popper übereinstimmen. — 2) Daß eine Aussage bzw. Aussagenmenge T falsifizierbar ist, soll, wie bei Popper, bedeuten, daß Basissätze (wahre oder falsche) existieren, die zusammen mit T eine inkonsistente Satzmenge bilden; m.a.W.: falsifizierbar ist T ?in the simple logical sense of being logically incompatible with some basic statements. It has ‘potential falsifiers’“. Basissätze sind dabei, grob gesagt, als Darstellungen von Beobachtungs-Befunden aufzufassen; Genaueres interessiert hier nur insoweit, als es sich umraum-zeitlich singuläre (Existenz-) Sätze handeln muß. Entsprechend soll schließlich T als falsifiziert gelten, wenn es wahre bzw. anerkannte oder akzeptierte Basissätze gibt, die T widersprechen. (Poppers Forderung, daß diese Basissätze ein reproduzierbares Phänomen beschreiben, also eine — allgemeine — ?falsifizierende Hypothese“ bewähren müssen, kann im vorliegenden Zusammenhang außer Betracht bleiben).     

Personal names and the human right hemisphere: an illusory link?

Names are thought to be represented in the brain differently from common nouns. Although this idea is supported by both theoretical and empirical arguments, the brain areas that are relevant for the recognition of personal names-and in particular the extent of right hemisphere involvement-remain controversial. We investigated the hypothesis that, unlike common nouns, personal names are represented preferentially by the right hemisphere (D. Van Lancker, 1991; D. Van Lancker et al., 1991; C. Ohnesorge & D. Van Lancker, 1999). Participants performed lexical decisions to common nouns and pseudowords (Experiment 1) or familiarity decisions to personal names (Experiment 2), which were presented briefly to the left or right visual fields. Asymmetries were small or absent for both pseudowords and unfamiliar names. For familiar names, both reaction times and error rates revealed strong advantages for the right visual field/left hemisphere (RVF/LH), which were comparable to the asymmetries for nouns. Familiar personal names may be represented by brain systems that differ from those representing common nouns, but current evidence does not suggest a distinct contribution of the right hemisphere to these brain systems.     

Acquisition and use of mental operators: effects of type of practice

Planning interactions with the physical world requires knowledge about operations; in short, mental operators. Abstractness of content and directionality of access are two important properties to characterize the representational units of this kind of knowledge. Combining these properties allows four classes of knowledge units to be distinguished that can be found in the literature: (a) rules, (b) mental models or schemata, (c) instances, and (d) episodes or chunks. The influence of practicing alphabet-arithmetic operators in a prognostic, diagnostic, or retrognostic way (A + 2 = ?, A? = C, or ? + 2 = C, respectively) on the use of that knowledge in a subsequent test was used to assess the importance of these dimensions. At the beginning, the retrognostic use of knowledge was worse than the prognostic use, although identical operations were involved (A + 2 = ? vs. ? - 2 = A). This disadvantage was reduced with increased practice. Test performance was best if the task and the letter pairs were the same as in the acquisition phase. Overall, the findings support theories proposing multiple representational units of mental operators. The disadvantage for the retrognosis task was recovered in the test phase, and may be evidence for the importance of the order of events independent of the order of experience.