Modeling the Dynamics of Visual Object Categorization
Novices are faster and more accurate to verify category membership at an intermediate level of abstraction, the so-called the basic or entry level (e.g., “bird”), than a superordinate (e.g., “animal”) or subordinate level (e.g., “Blue Jay”). One explanation for the relative speed of basic-level categorization is that categorization at this intermediate level is a prerequisite for more superordinate and subordinate categorizations – you need to know that it is a bird before you can tell whether it is an animal or a Blue Jay. An alternative explanation is that basic-level categorizations are fast because the basic level is more differentiated and informative, not that it happens first. We evaluated these two hypotheses by fitting the well-known drift-diffusion model of perceptual decision making to accuracy and response time data from a large sample of online participants, including both novices and individuals with varying levels of birding expertise. We identified these two hypotheses with differences in process parameters within the diffusion model: variability in non-decisional, perceptual processing time across category levels would indicate the former hypothesis, whereas variability in drift rate across category levels would indicate the latter hypothesis. We applied the diffusion model using a Bayesian hierarchical framework, which provides a powerful account of individual differences in the model parameters across conditions. Behaviorally, we replicated the basic-level advantage for novices in our online experiments. Theoretically, we found that variability in categorization speed across levels of categorization were well captured by variability in the drift rate across levels without any changes in the non-decisional, perceptual processing time across levels. Our results help to unravel the psychological processes that give rise to the behavioral pattern in speeded categorization and inform the understanding of individual differences in visual object categorization.