  A general framework is suggested to describe human decision making in a
certain class of experiments performed in a trading laboratory. We are in
particular interested in discerning between two different moods, or states of
the investors, corresponding to investors using fundamental investment
strategies, technical analysis investment strategies respectively. Our
framework accounts for two opposite situations already encountered in
experimental setups: i) the rational expectations case, and ii) the case of
pure speculation. We consider new experimental conditions which allow both
elements to be present in the decision making process of the traders, thereby
creating a dilemma in terms of investment strategy. Our theoretical framework
allows us to predict the outcome of this type of trading experiments, depending
on such variables as the number of people trading, the liquidity of the market,
the amount of information used in technical analysis strategies, as well as the
dividends attributed to an asset. We find that it is possible to give a
qualitative prediction of trading behavior depending on a ratio that quantifies
the fluctuations in the model.
