  We present generalized dynamical models describing the sharing of
information, and the corresponding herd behavior, in a population based on the
recent model proposed by Egu\'{\i}luz and Zimmermann (EZ) [Phys. Rev. Lett. 85,
5659 (2000)]. The EZ model, which is a dynamical version of the herd formation
model of Cont and Bouchaud (CB), gives a reasonable model for the formation of
clusters of agents and for actions taken by clusters of agents. Both the EZ and
CB models give a cluster size distribution characterized by a power law with an
exponent -5/2. By introducing a size-dependent probability for dissociation of
a cluster of agents, we show that the exponent characterizing the cluster size
distribution becomes model-dependent and non-universal, with an exponential
cutoff for large cluster sizes. The actions taken by the clusters of agents
generate the price returns, the distribution of which is also characterized by
a model-dependent exponent. When a size-dependent transaction rate is
introduced instead of a size-dependent dissociation rate, it is found that the
distribution of price returns is characterized by a model-dependent exponent
while the exponent for the cluster-size distribution remains unchanged. The
resulting systems provide simplified models of a financial market and yield
power law behaviour with an easily tunable exponent.
