1. the blocking of learning or of memory retrieval by the learning or remembering of other conflicting material. Interference has many sources, including prior learning (see proactive interference), subsequent learning (see retroactive interference), competition during recall (see output interference), and presentation of other material (see interpolated task).

2. the mutual effect on meeting of two or more light, sound, or other waves, the overlap of which produces a new pattern of waves. The term is used most frequently with reference to waves of the same or similar frequency, whose interference may be either constructive or destructive. In the former, the waves are in phase and the wave motions are reinforced, which results in alternating areas of increased and decreased wave amplitude (e.g., as light and dark lines or louder and softer sound); in the latter, the waves are out of phase and the wave motions are decreased or cancelled.

3. the distortion of a signal due to the presence of noise.

4. see language transfer.