Resolving the controversy of the proportion validity effect: Volitional attention is not required, but may have an effect.

Response time (RT) is facilitated when a target appears at a cued (valid) location versus an uncued (invalid) location. Interestingly, this valid-versus-invalid RT difference increases as the percentage of valid trials increases. In the present study, we investigated the mechanism responsible for this proportion valid cueing effect (PVE). The PVE is thought to reflect changes in voluntary attentional allocation, with greater attention being committed endogenously to the cued location as the percentage of valid trials increases. However, recent research has suggested that the PVE may reflect a form of implicit learning between the cue and the target location that is developed outside of awareness, and that this determines how attention is allocated. This lack of convergence may be due to methodological differences in how voluntary processing has been inferred. To test this issue, we generated a method that would allow the measurement of different degrees of volitional attention. In addition, we manipulated whether participants were instructed to attend to the cue-target relationship and determined whether this explicit engagement of attention influenced the PVE. We found that for both peripheral and central cues, volitional control is not required for a PVE; however, volitional control can modulate a PVE that is produced by central cues. Thus, a PVE is not a reliable indicator of volitional control, but its sensitivity to volitional control varies across cues. The present data shed light on the mechanism subserving the PVE and lend support to the theory that different cues engage, to some degree, qualitatively different forms of visuospatial attention.