Binocular cues in the perception of distance of a point source of light

The ability to make egocentric distance estimates of a single point source of light, seen in darkness and without the cues of changing size and luminance, was investigated in sixteen observers. The attenuation required to maintain constant luminance, when the target was viewed from different distances, was shown to follow the inverse square law providing the angle subtended by the light was less than 20 s arc. Distance changes were also simulated by means of a split mirror which produced vergence cues, or by test lenses to provide accommodation cues. Over the range 0.5 to 9.2 m distance estimates were surprisingly accurate, although there was some overestimation of near and underestimation of far distances. Most observers made good judgements when only convergence cues were varied, whereas no observers made consistently good judgements when only accommodation cues were varied. The difficulties are discussed in terms of the accommodation-convergence link. When distance was simulated by changing convergence and accommodation cues, estimates were not as good as when real distance was changed. Since good estimates were made with brief target exposures, these judgements were not based on subsequent convergence or accommodation changes. It is suggested that the metric or reference against which the apparently absolute judgements were made was the efferent demand signal associated with a 'resting' position of convergence in darkness.     

Rabbi and Magister: Overlapping intellectual models of the twelfth-century renaissance

Elka Klein’s writings have illuminated reciprocal and distinctive characteristics of the social and intellectual lives of Jewry in Iberia and by comparison Northern Europe during the High Middle Ages. This article honors her insights, by comparing the development of biblical hermeneutics at the Abbey of St. Victor in Paris and in the writings of Abraham ibn Ezra. Hugh of St. Victor’s introduction to the study of Scripture, Didascalicon, provides a program for the individual student to integrate all branches of human knowledge into the search for Divine Wisdom that may be found only in Scripture. The innovation in Hugh’s program is the emphasis on the “literal” or “historical” sense of Scripture as the solid basis for the development of theological study. Grammar and rhetoric were stepping stones that led the young theologians to higher levels of Divine Wisdom. The introduction to Abraham ibn Ezra’s commentary on the Pentateuch constitutes a parallel point of orientation for twelfth-century Jewish readers. A close reading of ibn Ezra’s prologue maps the hermeneutical approaches that different communities – Christian, rabbinic Jewish, and Karaite – utilized in their expositions of the Pentateuch. After critiquing each community, ibn Ezra offers his own approach that builds an overall framework for correct interpretation on the foundation of grammar and the rabbinic oral tradition. From this perspective, the article demonstrates that during this period Jews and Christians, both in Iberia and Northern Europe, focused on harmonizing reason and revelation. Both communities used grammar as the primary criterion for evaluating the accumulation of traditional sources. Both approaches intended to develop students, who were capable of understanding that “reason is the angel that mediates between God and humanity.”     

A Type of Non-Causal Explanation1

There is a type of explanation frequently employed in the sciences, particularly the quantitative ones, that I intend to focus on. It seeks to understand some phenomenon or regularity that occurs in a type of system S by deriving an equation describing that phenomenon or regularity from a set of equations that govern S. I want to propose a way of understanding such explanations.