Are spatial and temporal attention independent?

Participants searched for one of two target letters in a rapid serial visual presentation (RSVP) sequence of 17 successive frames, each containing four letters arranged into a box around a central fixation point. In control trial blocks, the participants had no information about when or where one of the target letters would appear. In other trial blocks, visual cues were given to indicate with 100% validity either the spatial location of the target, the time at which it would be presented, or both where and when it would appear. The results showed that both types of cues were effective on their own in speeding target identification, and their effects combined additively when the cues were presented and used together. These results support a growing body of evidence indicating that early attentional selection of information in vision is independently attuned to spatial and temporal properties of the environment.