Specific visual features can be attended to and processed with a higher priority by our brain, termed feature-based attention (FBA). Two potential mechanisms for FBA have been suggested: goal-driven attentional mediating and stimulus-driven feature priming. Some researchers argued that several reported top-down FBA effects might also involve the influence of feature priming. To clarify this confusion, we used an orientation discrimination task in which the target was tilted randomly from the horizontal or vertical axis and presented at one of four iso-eccentric positions. The target's orientation was precued from trial to trial by an oriented line (Experiment 1) or by a symbolic arrow presented peripherally (Experiment 2) or centrally (Experiments 3/4). The cue could be either valid or invalid according to the congruency of its indicating orientation with the target's nearest cardinal axis. Our results demonstrate that the discrimination speed was significantly faster following a valid than an invalid cue (validity effect) in the session with 80% cue validity when both response accuracy and speed were emphasized. Moreover, this validity effect could also be observed in the session with 50% cue validity using the line cue (Experiment 1), even though its magnitude was significantly reduced, which illustrates the impact of feature priming. However, we did not find the validity effect in the session with 50% cue validity using the symbolic cue (Experiments 2/3). These modulations on the magnitude of the validity effect should be ascribed to top-down attentional mediating that is independent of spatial attention (illustrated by Experiment 3). Importantly, when response accuracy was stressed over speed in Experiment 4, the accuracy was significantly higher following a valid than an invalid cue in the session with 80% cue validity but not in the session with 50% cue validity. Our findings indicate that both top-down attentional mediating and feature priming are important mechanisms for FBA.