Effects of reward and attention have largely been considered as distinct phenomena, and they therefore have been investigated mainly in separate fields. However, it has been pointed out that most studies are not able to distinguish direct reward effects from effects of voluntary attentional enhancement (Maunsell, 2004). Previous studies have shown that attention and reward clearly interact: visual attention is more efficient when conditions or stimuli are motivationally significant (Engelmann and Pessoa, 2007) and rewarded stimulus aspects draw more attention (Krebs et al., 2010, 2013). These studies, however, have generally not been able to differentiate between more direct low-level influences of reward versus indirect strategic attentional effects, although some recent studies have shown that reward associations can have a direct impact on early stages of visual, cognitive, and oculomotor processes, without the mediation of strategic attention (Della Libera and Chelazzi, 2006; Hickey and van Zoest, 2012; Hickey et al., 2010). These early-stage effects are thought to rely on the direct association between task-relevant stimulus features and reward, and hence do not reflect preparatory or strategic effects that require a cue-target
