In my opinion, increased productivity will usually lead to increased worker motivation because it should usually lead to increased worker pay. When workers are paid higher wages, they are likely to be more motivated.
Productivity leads to higher wages because it increases the quantity of products produced per worker hour. If that happens, each worker is producing more revenue for the firm and can be paid more. When this happens, workers will generally be happier and more motivated.
So, when productivity goes up, each worker is worth more to the company and is likely to be better paid and feel as if the company values him.