A godsend to the labor markets of the inner system, deja vu allows workers to repeat repetitive tasks without boredom or stress. Because of the influx of unskilled infugees, and despite the established industry of AI design, it has become economically favorable (at least in the inner system) to employ egos based on their basic intuitions and instincts, as opposed to learned skills. A typical ego is competitive in such tasks as pattern recognition (especially those involving faces) rapid character evaluations and arbitrary sorting problems.
The deja vu mental modification simply prevents the transfer of memory from short-term to long-term, while simultaneously interfering with the ego's sense of time. As a result, the ego cannot become bored and will not realize how much time has passed, allowing them to repeat a task for an indefinite length of time. Often, the mod is paired with a psychosurgically enforced focus on the presented task.
For example, an infugee might be indentured to spend 3 years in the wide-angle camera of a hotel lobby. This would render most egos insane, but with deja vu, the ego is simply told to watch for a small set of faces, and after a few minutes, they find that three years have passed and there indenture completed.