| To successfully guide attention toward a relevant object, the observer must have information about the defining (or essential) features of that object. Often, the observer also has information about non-essential features of the target, the distractors, or both; however, such ancillary information is often not manipulated independently of the essential information, and so its role in top-down guidance is unclear. Accordingly, the present study was designed to assess whether ancillary information can influence the guidance of attention using a visual search task in which observers searched for one of two target letters within a central array while trying to ignore a peripheral distractor. In this study, the two target letters were distinguished from the non-target letters by their form and they were distinguished from the peripheral distractor by their spatial location, thereby making form and location essential. In addition, the color of the target and non-target letters matched the color of the distractor in one condition, but they mismatched the peripheral distractor in another condition, thereby making color ancillary to the task. This ancillary color information was provided about the distractor in Experiment 1 and it was provided about the target in Experiments 2, 3, and 4. The ability of ancillary color information to guide attention was measured by the amount of interference that was generated by incompatible distracters relative to neutral distracters. In addition, this guidance was investigated under both low (Experiments 1 and 2) and high (Experiments 3 and 4) levels of perceptual load. In the low load condition, guidance by ancillary color information was predicted to be reflected by a reduction in distractor interference in the color mismatch condition relative to the color match condition. However, the results of Experiment 1 and 2 suggested that such guidance did not occur under conditions of low load, regardless of whether ancillary color information was provided about the distractor or the target. In the high load condition, guidance by ancillary color information was predicted to be reflected by an increase in distractor interference in the color match condition relative to the color mismatch condition. The results were consistent with this prediction, as long as the salience of the distractor was controlled (as in Experiment 4). Altogether the present findings extend our understanding of the role of top-down information in the guidance of attention, while also establishing initial boundary conditions for these effects. Implications for major theories of attention such guided search and perceptual load are discussed. |
