Distractor-interference reduction is dimensionally constrained

ABSTRACT

The dimension-weighting account predicts that if observers search for a target standing out from the background in a particular dimension, they cannot readily ignore a distractor standing out in the same dimension. This prediction is tested here by asking two groups of observers to search for an orientation target or a luminance target, respectively, and presenting an additional distractor defined in either the respectively same dimension or the other dimension. Notably, in this cross-over design, the physically identical distractors served both as same- and different-dimension distractors, depending on target condition. While same-dimension distractors gave rise to massive interference, different-dimension distractors caused much weaker (though still substantial) interference. This result is most readily explained by the dimension-weighting account: different-dimension distractors are considerably down-weighted but not fully suppressed. Furthermore, same- and different dimension distractors delayed response times even when considering only the fastest (down to 2.5%) of trials, indicating that interference is exerted consistently on each trial, rather than probabilistically on some trials. Our results put strong constraints on models of distractor handling in visual search.

KEYWORDS:

• Attentional capture
• distractor handling
• dimension-weighting account
• additional-singleton task
• visual search

Acknowledgement

We thank Ulla Scheler and Pia Schmidt for assistance in data collection.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 This was confirmed by a control experiment in which 12 observers searched for either a 45°-tilted target among 12°-tilted non-targets or for a 98%-intensity target among 59%-intensity non-targets That is, roles were changed in that the previous distractors became targets and the previous targets became non-targets. Target condition (orientation vs. luminance) was blocked and the order of blocks was balanced across participants. The goal was to determine whether the contrast between these two objects was sufficient to produce efficient search (i.e., flat slopes of the function relating response times to the number of non-targets). Set-size was manipulated between 7 and 19 according to the design developed by Liesefeld et al. (2016, Experiments 2 and 3), which was adapted to the present study in that participants had to indicate the position of the notch (classification task) instead of deciding whether a target was present or absent. Results proved that both searches were highly efficient (−1 ms/item for orientation searches and 3 ms/item for luminance searches), indicating that the respective objects are sufficiently dissimilar to produce reliable pop-out (see Liesefeld et al., 2016, for details on the theoretical background).

Additional information

Funding

This work was supported by Deutsche Forschungsgemeinschaft [grant number MU 773/14-1,MU 773/16-1]; Graduate School of Systemic Neurosciences, Munich Center for Neurosciences – Brain & Mind; LMU Munich’s Institutional Strategy LMUexcellent within the framework of the German Excellence Initiative.