When we perform a visual search we know what we are looking for and determine where it is. A representation of the object in our working memory, the 'search-template', is compared to the items in the scene until a match is found. So far it is unknown whether observers can search for multiple items at the same time. Here we compare the performance of subjects between a task in which they search for one of two target-items in a stream of visual objects and a task with only a single target. We find that search is effectively limited to one item at a time. This limitation occurs for simple and complex objects and even if the subjects have to look for two features from different domains. We conclude that matching has a fundamental capacity-limitation as the visual input can be matched to only one search-template at a time.
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