The effect of feature discriminability on the intertrial inhibition of focused attention

Abstract

Identifying the shape of a colour oddball is faster when the distractor colour is viewed in the preceding target-absent trial and slower when the target colour is previewed, an intertrial effect known as the distractor previewing effect (DPE). We tested the effect of feature discriminability on the DPE. In Experiment 1, we determined the interitem discriminability of two colour pairs and two shape pairs. In Experiments 2 and 3, we measured DPEs with these set of target–distractor discriminability pairs. Our results showed that when the defining features allow for efficient parallel search, the a priori degree of interitem discriminability did not modulate the DPE. The results suggest the DPE does not arise as a strictly bottom-up modulation of saliency of the search-relevant features but reflects an attentional bias aimed at preventing attention from revisiting recently rejected “search features”. The underlying mechanism of this attentional bias is discussed.

Keywords:

• Distractor previewing effect (DPE)
• Inhibition
• Focused attention
• Visual search
• Feature discriminability

Acknowledgements

We thank Palav Shah for running experiments and our reviewers for their thoughtful comments of our previous versions of this manuscript. Some of the data were presented at 2006 VSS annual meeting, Sarasota, Florida, 2006. This work was partially supported by two grants from the NSF to AL (awards nos. 0527361 and 07-46586 CAR).

Notes

¹To address the concerns that the between-subjects design might have lowered the power of our experiment and therefore undermined the theoretical significance of our null result, we ran an additional experiment with both red/green and fuchsia/pink conditions tested within subjects. Ten participants searched for an odd-coloured diamond and identified the missing corner, with some blocks of trials using the red/green colour pair in the displays and others using the fuchsia/pink colour pair. Comparable DPEs in the red/green (75 ms) and fuchsia/pink (91 ms) conditions were found, t(9) = 1.48, p>.17. The results of the 2 (preview type: Target or distractor previewed)×2 (defining feature: Red/green or fuchsia/pink) ANOVAs also mimicked the pattern of results in Experiment 2. The preview type affected the RTs, F(1, 9) = 89.93, p<.01, but not accuracies, F(1, 9) = 2.89, p>.12, indicating the presence of the DPE. The defining feature discriminability also affected the RTs, F(1, 9) = 26.61, p<.01, but not accuracies, F(1, 56) = 2.36, p>.15, with RTs in the red/green condition being 113 ms faster than in the fuchsia/pink condition. Importantly, the interaction between preview type and defining feature was not significant on either RTs or accuracies, both Fs < 2.19, ps>.17, suggesting that the magnitude of the DPE was independent of the target/distractor colour discriminability.

²Note that the PoPs were calculated on the basis of a much reduced number of observations per condition, so we only present these trends as suggestive, rather than conclusive, of a relation between these two effects. More testing is required before a conclusion can be reached.