Are all real‐world objects created equal? Estimating the “set‐size” of the search target in visual working memory

Abstract Are all real‐world objects created equal? Visual search difficulty increases with the number of targets and as target‐related visual working memory (VWM) load increases. Our goal was to investigate the load imposed by individual real‐world objects held in VWM in the context of search. Measures of visual clutter attempt to quantify real‐world set‐size in the context of scenes. We applied one of these measures, the number of proto‐objects, to individual real‐world objects and used contralateral delay activity (CDA) to measure the resulting VWM load. The current study presented a real‐world object as a target cue, followed by a delay where CDA was measured. This was followed by a four‐object search array. We compared CDA and later search performance from target cues containing a high or low number of proto‐objects. High proto‐object target cues resulted in greater CDA, longer search RTs, target dwell times, and reduced search guidance, relative to low proto‐object targets. These findings demonstrate that targets with more proto‐objects result in a higher VWM load and reduced search performance. This shows that the number of proto‐objects contained within individual objects produce set‐size like effects in VWM and suggests proto‐objects may be a viable unit of measure of real‐world VWM load. Importantly, this demonstrates that not all real‐world objects are created equal.