Search efficiency as a function of target saliency: The transition from inefficient to efficient search and beyond

Heinrich René Liesefeld, Hermann J. Müller, Rani Moran, Marius Usher, Michael Zehetleitner

Research output: Contribution to journalArticlepeer-review


Searching for an object among distracting objects is a common daily task. These searches differ in efficiency. Some are so difficult that each object must be inspected in turn, whereas others are so easy that the target object directly catches the observer's eye. In 4 experiments, the difficulty of searching for an orientation-defined target was parametrically manipulated between blocks of trials via the target- distractor orientation contrast. We observed a smooth transition from inefficient to efficient search with increasing orientation contrast. When contrast was high, search slopes were flat (indicating pop-out); when contrast was low, slopes were steep (indicating serial search). At the transition from inefficient to efficient search, search slopes were flat for target-present trials and steep for target-absent trials within the same orientation-contrast block-suggesting that participants adapted their behavior on target-absent trials to the most difficult, rather than the average, target-present trials of each block. Furthermore, even when search slopes were flat, indicative of pop-out, search continued to become faster with increasing contrast. These observations provide several new constraints for models of visual search and indicate that differences between search tasks that were traditionally considered qualitative in nature might actually be due to purely quantitative differences in target discriminability.

Original languageEnglish
Pages (from-to)821-836
Number of pages16
JournalJournal of Experimental Psychology: Human Perception and Performance
Issue number6
StatePublished - 1 Jun 2016


  • Feature contrast
  • Feature search
  • Search efficiency
  • Slope ratio
  • Visual search


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