Abstract
Real-world search difficulty is highly variable, but can be reliably anticipated sometimes (e.g. finding your car in an empty parking lot). During a difficult block of trials, performance decreases, but observers who hold more target detail in visual-working memory mitigate the performance decrement associated with difficult search (Schmidt, & Zelinsky, 2017). Given this, expected search difficulty may significantly drive performance. This study examined expected difficulty effects in simple stimuli (Landolt-C’s; Experiment 1) and real-world objects (RWO; Experiment 2). We recorded eye-movements as participants performed blocks of easy, moderate, or difficult search created by manipulating the number of target similar distractors. Observers localized previously cued targets within a semi-circular array of six items. Expectancy was assessed by examining the change in search performance between trials that matched the block difficulty level (Experiment 1: 83.33% & Experiment 2: 75.00% of trials), and trials that were easier or harder than expected. In both studies, increased search difficulty resulted in reduced accuracy, increased RT, and increased time spent fixating targets and distractors (all p<.05). Search guidance was at chance in Experiment 1 (p=.422), and above chance in Experiment 2, but decreased with increasing search difficulty (p<.001). Searching for simple stimuli and expecting an easy search, but performing a more difficult search, resulted in reduced accuracy, less time fixating targets and fixating distractors (all p<.01). Expecting a difficult search, but performing an easier search, resulted in more time fixating targets/distractors and increased RT (all p<.05). RWO’s replicated the easier than expected effects in RT and time spent fixating distractors, and additionally observed a decrease in target guidance (all p<.05). Overall, expectancy changes performance to make it more like the expected search difficulty. Consequently, these expectations should only change performance by some fractional difference between expected and actual difficulty.