Date Published: February 28, 2018
Publisher: Public Library of Science
Author(s): Natalie Russo, Carl Erick Hagmann, Rosemary Andrews, Conner Black, Magenta Silberman, Nicole Shea, Jordan Suchow.
Stimulus sets are valuable tools that can facilitate the work of researchers designing experiments. Images of faces, and line drawings of objects have been developed and validated, however, pictures of animals, that do not contain backgrounds, have not been made available. Here we present image agreement and quality ratings for a set of 640 color images of animals on a transparent background, across 60 different basic categories (e.g. cat, dog, frog, bird), some with few, and others with many exemplars. These images were normed on 302 participants. Image agreement was measured both with respect to the proportion of participants that provided the same name as well as the H-statistic for each image. Image quality was measured both overall, and with respect to the accuracy of participants’ naming of the basic category. Word frequency of each basic and superordinate category based on the English Lexicon Project (Balota, et al., 2007) and the HAL database (Kucera & Francis, 1976) are provided as are Age of Acquisition (Kuperman, Stadthagen-Gonzalez, & Brysbaert, 2012) data.
The development of sets of stimulus images for experimental research has often been a lab by lab endeavor. When these stimulus sets are standardized, they can be a powerful resource for other scientists to use in experimental settings. Stimulus sets of line drawings [1–3], faces [4,5] and objects [6–8] and corpora of images (e.g. SUN database and ImageNet) have proven extremely useful to the scientific community. These have been used for studies that range from examining amygdala responses to medication in depressed patients , studies of object categorization in children  and adults , validations of memory models  psycholinguistic studies  and studies examining computer vision [14,15] and machine learning . These normed and validated stimulus sets often garner thousands of citations, suggesting that the scientific community values the sharing of stimulus resources.
There are some limitations of the stimulus set and the norming procedure. First, although the maximum size of the images presented was 500*500 pixels, some of the images were smaller than this during the presentation. Images were all clearly visible, but the effect of size on agreement is unclear. Second, the animals were not limited in their orientation in that some of them were presented in top view, while others were presented in profile. The orientation of each image is also made available for the stimulus set, but the relationship between stimulus orientation and ratings is unknown.