Daniel Ernst¹, Gernot Horstmann¹, Johan Hulleman², Jeremy Wolfe³; ¹Bielefeld University, ²The University of Manchester, ³Brigham and Women’s Hospital/Harvard Medical School

In visual search experiments, search trials are often blocked by difficulty. This enables observers (Os) to adjust their strategies to an expected level of difficulty. However, in natural search settings, observers may not be able to anticipate how difficult the next search will be; even when the search target remains constant. For instance, search for a cancer on one CT may be easier or harder than previous searches for that same cancer. Search strategies geared towards harder search may be suboptimal when the target is now more salient and this might lead to an increased number of miss errors. To test this, 25 Os searched for a circle among Landolt Cs (gap size of 0.09 degrees) in an initial block of 32 difficult search trials. Here, Os produced 37% miss errors. On trial 33, Os still searched for the same circle, but the gap size of the Landolt Cs was now 0.45 degrees. Normally, this new task would have been easy. However, when surprised by this easy search, Os failed to take advantage of the target’s higher salience and still produced 36% misses. For subsequent presentations of these easy search displays after the surprise trial, miss error rates dropped to 5%. The 36% of Os who responded “target-absent”, even though a salient target was present, can be said to have experienced a form of inattentional blindness (IB). Notice that, in contrast to traditional IB experiments, the missed IB stimulus here was no gorilla. It was the absolutely task-relevant, unaltered, and expected target of the search. The same target had already been searched for 32 times. Nevertheless, on the first trial when the distractors were unexpectedly changed to make the task easier, observers failed to adapt. We will discuss the relationship of this form of IB to more traditional versions.

Acknowledgements: Daniel Ernst was supported by grant ER 962/2-1; Johan Hulleman was supported by UKRI grant ES/X000443/1; Jeremy Wolfe was supported by grants NEI EY017001, NSF 2146617, NCI CA207490