Prof. Ohad Ben-Shahar

What is the order of processing in scene gist recognition? Following the seminal studies by Rosch (1978) and Tversky and Hemmenway (1983) it has been assumed that basic-level categorization is privileged over the superordinate level because the former maximizes both within-category similarity and between-category variance. However, recent research has begun to challenge this view (Oliva & Torralba, 2001; Joubert, Rousselet, Fize, & Fabre-Thorpe, 2007; Loschky & Larson, 2010). Here we study these directions more fundamentally by investigating the perceptual relations between scene categories in a way that allows us to identify the order of processing of scene categories across taxonomic levels. We introduce the category discrimination paradigm where we briefly present two real scene stimuli simultaneously and ask human observers whether they belong to the same basic-level category or not (i.e., same/different task). As we show, analysis of the obtained data reveals a hierarchical perceptual structure between different scene categories and a corresponding hierarchical structure at the perceptual processing level. In particular, we show a new type of evidence to suggest that the decision whether the scene is manmade or natural is made first, and only then more complicated decisions are taken (such as whether a manmade scene is indoor or outdoor) among a smaller set of viable candidate categories. We argue that this hierarchical structure improves performance and efficiency in both biological and artificial gist recognition systems.