User feedback about grasping force or slip of objects is lacking in current myoelectric forearm prostheses, resulting in a high number of prosthesis abandonment, because a high level of concentration is required to hold an object. Several approaches to provide force feedback to the user via vibrotactile stimulation have been described in literature, but none of them have investigated the optimal stimulation parameters. This study describes an evaluation of three modulation techniques to provide force feedback. Furthermore, the same modulation techniques to provide slip feedback were evaluated, which has not been described before. The performance in virtual object holding tasks was significantly improved in most cases compared to the non-feedback situation, but at the cost of an increased task duration.