The roles of spatial frequency in category-level visual search of real-world scenes

Visual object recognition appears to be effortless and virtually instantaneous for humans. A number of previous investigations have suggested that visual perception follows a coarse-to-fine processing sequence in which low-spatial-frequency (LSF) information provides a coarse representation of an object for an initial guess and guides the fine processing of the object based on high-spatial-frequency (HSF) information. A category-level visual search of real-world scenes shares many aspects of processing mechanisms with object recognition. However, a key difference between them is the target template in visual search that is generally known in advance. In the present study, we investigated the role of spatial frequency information in the category-level visual search of real-world scenes with three behavioral experiments. In Experiment 1, we showed that the representation of the target template, which is held in short-term memory, had biased attention more towards LSF information than HSF information in the probe trials. In Experiments 2 and 3, we further demonstrated that the near-threshold LSF information could implicitly facilitate object recognition compared with HSF information, thereby providing supporting evidence that the LSF information of the target template implicitly facilitates target recognition and search performance. These findings support the role of the coarse-to-fine principle in rapid visual search performance of real-world scenes.