Location-cued visual selection-Placeholder dots improve target identification

Visual cues help to select a target and attract attention to it. In the present study, a 50-ms exogenous cue was presented to select one of 80 tilted lines, and attention effects at various delays were measured as the time observers needed to identify this target. Like in earlier detection studies, there was a transient cuing effect; targets presented soon after the cue (delays of 50-300 ms) were identified particularly fast. This benefit was followed by a continuous decay of performance toward longer delays (measured up to 5 s), at which the necessary presentation time to identify the target was strongly increased. The decay was substantially reduced when placeholder dots were shown during the delay, at subsequent line positions. The simple presentation of a structured background in the form of random dots did not have this effect. When the presentation times for constant performance were taken to compute the presumed strength of underlying neural responses, the effect of placeholders was seen as a nearly constant addition to the cued target signals, with an additional transient peak about 100 ms after cue (and placeholders) onset.