  Understanding texts requires memory: the reader has to keep in mind enough
words to create meaning. This calls for a relation between the memory of the
reader and the structure of the text. To investigate this interaction, we first
identify a connectivity matrix defined by co-occurrence of words in the text. A
vector space of words characterizing the text is spanned by the principal
directions of this matrix. It is useful to think of these weighted combinations
of words as representing ``concepts''. As the reader follows the text, the set
of words in her window of attention follows a dynamical motion among these
concepts. We observe long range power law correlations in this trajectory. By
explicitly constructing surrogate hierarchical texts, we demonstrate that the
power law originates from structural organization of texts into subunits such
as chapters and paragraphs.
