  Financial markets are subject to long periods of polarized behavior, such as
bull-market or bear-market phases, in which the vast majority of market
participants seem to almost exclusively choose one action (between buying or
selling) over the other. From the point of view of conventional economic
theory, such events are thought to reflect the arrival of ``external news''
that justifies the observed behavior. However, empirical observations of the
events leading up to such market phases, as well events occurring during the
lifetime of such a phase, have often failed to find significant correlation
between news from outside the market and the behavior of the agents comprising
the market. In this paper, we explore the alternative hypothesis that the
occurrence of such market polarizations are due to interactions amongst the
agents in the market, and not due to any influence external to it. In
particular, we present a model where the market (i.e., the aggregate behavior
of all the agents) is observed to become polarized even though individual
agents regularly change their actions (buy or sell) on a time-scale much
shorter than that of the market polarization phase.
