Effects of pre-cueing the target location on the set-size and eccentricity effects in visual search task

Purpose. Most studies that employ the visual search paradigm have not examined directly the role of covert attention, but rather inferred it from the pattern of results (e.g., set size effect). Recent findings, however, suggest that both the set size effect and the eccentricity effect (performance decreases as target eccentricity increases) may be due, to a large extent, to spatial resolution and lateral inhibition. To re-examine the role of covert attention, in this study we directly manipulated attention by peripherally pre-cueing the target location. Specifically, we explored the effects of pre-cueing the target location on the set-size and eccentricity effects. Methods. Eleven subjects participated in both feature (orientation) and conjunction (orientation x color) tasks, and were asked to detect a briefly (94 ms) presented target (a red vertical line) under three pre-cueing conditions: a) a valid cue indicating the target location (VA); b) an invalid cue indicating a non-target location (IV); and c) a neutral cue indicating that any location is possible (N). The target appeared from 1.4 to 7° of eccentricity, among 2 to 35 distractors. Both RT and error rate were recorded. Results. 1) Precueing the target location improved overall performance in both feature and conjunction searches, indicating that the attentional manipulation was successful. 2) Similar to previous studies, an eccentricity effect was found in both feature and conjunction tasks. However, in both tasks the effect was significantly reduced in the VA condition as compared to IV and N conditions, more so for features than for conjunctions. 3) A set-size effect was found only in conjunction search, and only the error rate was significantly reduced by pre-cueing. Conclusions. Directing attention to the target location reduced the effects of target eccentricity, suggesting that the attentional mechanism improves performance by enhancing the spatial resolution of the attended location. The larger reduction in feature search further supports the "early selection" view that covert attention can facilitate early perception. The inability of pre-cueing to eliminate the set-size effect call into question "serial-search" models that attribute a major role to covert attention in visual search.