This article comes from Frontiers in Integrative Neuroscience, an attempt to examine the evolution of introspection in the Axial Age (first millennium BCE), studying the cultural record of the Greco-Roman and Judeo-Christian literary traditions.

One of the interesting and more readable books on this period in history (and it should be noted that some historians and anthropologists do not place as much emphasis on this period of time) is Karen Armstrong's The Great Transformation: The Beginning of Our Religious Traditions, but there is also Bruce Lero's From Earth Spirits to Sky Gods: The Socioecological Origins of Monotheism, Individualism, and Hyper-Abstract Reasoning, From the Stone Age to the Axial Iron Age (expensive but academically respected) and Robert Bellah's Religion in Human Evolution: From the Paleolithic to the Axial Age and The Axial Age and Its Consequences.

Back to the study. Their results offer these conclusions:

(a) it is possible to devise a consistent metric to quantify the history of a high-level concept such as introspection, cementing the path for a new quantitative philology and 
(b) to the extent that it is captured in the cultural record, the increased ability of human thought for self-reflection that the Axial Age brought about is still heavily determined by societal contingencies beyond the orality-literacy nexus.

 Below is the abstract and citation, followed by a brief section of the introduction.

A quantitative philology of introspection

Carlos G. Diuk¹, D. Fernandez Slezak², I. Raskovsky², M. Sigman³ and G. A. Cecchi⁴

• ¹Department of Psychology, Princeton Neuroscience Institute, Princeton University, Princeton, NJ, USA
• ²Department of Computer Science, University of Buenos Aires, Buenos Aires, Argentina
• ³Department of Physics, University of Buenos Aires, Buenos Aires, Argentina
• ⁴Computational Biology Center, T.J. Watson IBM Research Center, Yorktown Heights, NY, USA

The cultural evolution of introspective thought has been recognized to undergo a drastic change during the middle of the first millennium BC. This period, known as the “Axial Age,” saw the birth of religions and philosophies still alive in modern culture, as well as the transition from orality to literacy—which led to the hypothesis of a link between introspection and literacy. Here we set out to examine the evolution of introspection in the Axial Age, studying the cultural record of the Greco-Roman and Judeo-Christian literary traditions. Using a statistical measure of semantic similarity, we identify a single “arrow of time” in the Old and New Testaments of the Bible, and a more complex non-monotonic dynamics in the Greco-Roman tradition reflecting the rise and fall of the respective societies. A comparable analysis of the twentieth century cultural record shows a steady increase in the incidence of introspective topics, punctuated by abrupt declines during and preceding the First and Second World Wars. Our results show that (a) it is possible to devise a consistent metric to quantify the history of a high-level concept such as introspection, cementing the path for a new quantitative philology and (b) to the extent that it is captured in the cultural record, the increased ability of human thought for self-reflection that the Axial Age brought about is still heavily determined by societal contingencies beyond the orality-literacy nexus.

Full Citation: 
Diuk CG, Slezak DF, Raskovsky I, Sigman M and Cecchi GA (2012) A quantitative philology of introspection. Frontiers in Integrative Neuroscience; 6:80. doi: 10.3389/fnint.2012.00080

Here are the first few paragraphs from the introduction. The whole paper is open access and can be viewed online or downloaded as a PDF (follow the link above).

Introduction

The period in human history ranging from 800 BCE to 200 BCE marked a radical transformation in world civilizations, in particular those that constitute the Western tradition. Famously termed the Axial Age by Jaspers (1953), this period produced world religions and philosophies that are still pillars of modern culture. Many scholars have argued that one of the most prominent consequences of this transition was a change in consciousness, from a “homeostatic”, living-in-the-present form, to a self-reflective and time-expanding inner life (Schwartz, 1975; Eisenstadt, 1986; Armstrong, 2006). Studying two foundational texts of Western civilization, the Bible and the Homeric saga, Julian Jaynes (2000) argued that the change in conscious life that took place during the Axial Age is part of a larger introspection-increasing arc explicitly expressed in the textual narrative. The most cursory analysis of the Bible shows how the wrathful, interventionist god of the Old Testament, who expels Adam and Eve from the Garden of Eden (Genesis 6:22), is followed by the rich inner life of the New Testament, where Jesus asks the accusers of an adulterous woman to examine their own guilt (John 8:1). The striking differences between the Iliad and the Odyssey in the way the characters' behaviors are attributed, respectively, to divine intervention or to the individual's volition, have been pointed out in numerous studies (Dodds, 1951; Adkins, 1970; Onians, 1988; De Jong and Sullivan, 1994). The impulsive, irreflexive heroes of the Iliad, driven by passions insufflated into them by the gods, give way to the wily, cunning Odysseus who outsmarts Polifemo and leads his men to Scylla with a bad conscience.

It has been argued that these changes may reflect not just artistic or even cultural tendencies, but profound alterations in the mental structure of those who wrote, collected and assimilated the stories. Marshall McLuhan, in his seminal work on the relationship between semiotics, media and thought structures, argued for a materialistic effect of the type of medium (the linearity of written language, the holistic nature of the moving image) on the organization of thoughts (linear or integrative, respectively) (McLuhan, 1962). Given that one of the defining features of the Axial Age is the widespread adoption of the written word, it is reasonable to consider that the transitions from orality to literacy and from lower to higher introspection are fundamentally linked (Ong, 1982). Jaynes, moreover, proposed that the transition was also accompanied by a change from a mentality dominated by inner voices, issuing god-like commands necessary to maintain social cohesion, to one where the voices were replaced by a self-aware inner dialogue. Equally interesting and controversial from a neuroscientific perspective (Kuijsten, 2006; Cavanna et al., 2007), these ideas cannot be validated or refuted solely on the basis of philological and cultural studies. However, the “soft” hypothesis, as Daniel Dennett termed it, that within the Judeo-Greco-Christian tradition at least, there exists an “arrow of time” in the cultural narrative of the Axial Age representing increased concern with introspection can be put to the test in a quantifiable framework (Dennett, 1986; Jaynes, 2000).

The increasing availability of large text databases has facilitated the study of the statistical regularities embedded in language, including literary subtleties such as the analysis of a novel's plot, traditionally restricted to qualitative assessments (Moretti, 2005). Here we set out to develop a consistent analytic framework to measure the degree of introspection in extant texts spanning the Axial Age. With this tool, we tested the hypothesis of a “quantum leap” in the narrative during this transitional period, more generally, the possibility of measuring a cultural history of introspection.

We understand meaning in language as arising from the mutual dependencies of concepts, in a holistic fashion (Quine, 1951; Cancho and Sole, 2001; Sigman and Cecchi, 2002). Hence, our challenge is not merely to count the occurrence of a given word (for example, introspection) in a historical corpus but, instead, to measure the extent to which a concept, in its distributed semantic sense (as captured, for instance, in dictionaries, and thesauri), is represented in the text. Several methods have been introduced to identify regularities and obtain a notion of semantic proximity (Lund and Burgess, 1996; Patwardhan et al., 2003; Pedersen et al., 2004; Fellbaum, 2010). One of the more widely used resources is Latent Semantic Analysis (LSA) (Deerwester et al., 1990). LSA assumes that semantically related words will necessarily co-occur in texts with coherent topics. For a concept such as introspection to convey meaning, it must evoke a large array of related concepts or “images” in the mind. Conversely, semantically related words can convey the meaning of introspection without the word itself being present in a text. This is particularly relevant for our study of classical literature, as we do not expect words representing higher-order concepts such as introspection to be present in the Bible or Homer at all. That is, the use of semantic similarity analysis allows us to measure the relatedness of a classical text to a concept with no explicit word at the time.

Our goal in the present study is to quantify the incidence of introspective topics in Axial Age literature, and uncover its cultural history.