Abstract: In an optical bistability system consisting of an optical cavity and four-level atoms positive and negative phase shifts of an intracavity optical mode can be observed under the action of control signal pulses tuned close to certain energy levels of the atoms. The bistability hysteresis curve can thus be shifted and switching between the "low" and high" transmission states obtained in a controlled manner. Based on the above effects we have realized all-optical storage and optical switching controlled with low light power. This mechanism may be of potential use for all-optical quantum information processing.