Unraveling the Time-course of Perceptual Categorization: Does Fastest Mean First?

Unraveling the Time-course of Perceptual Categorization: Does Fastest Mean First? Michael L. Mack (michael.mack@vanderbilt.edu) Vanderbilt University, Psychology Department 301 Wilson Hall, Nashville, TN 37203 USA Alan C. -N. Wong (alan.wong@vanderbilt.edu) Vanderbilt University, Psychology Department 301 Wilson Hall, Nashville, TN 37203 USA Isabel Gauthier (isabel.gauthier@vanderbilt.edu) Vanderbilt University, Psychology Department 301 Wilson Hall, Nashville, TN 37203 USA James W. Tanaka (jtanaka@uvic.ca) University of Victoria, Department of Psychology A189 Cornett Building, Victoria, BC Canada Thomas J. Palmeri (thomas.j.palmeri@vanderbilt.edu) Vanderbilt University, Psychology Department 301 Wilson Hall, Nashville, TN 37203 USA Abstract Perceptual categorization at the basic level is faster than categorization at more superordinate or subordinate levels (Rosch et al, 1976). For categories of perceptual expertise, this basic-level advantage is attenuated such that subordinate levels are categorized as fast as the basic level (Tanaka & Taylor, 1991). But, what does it mean to be fastest? One explanation is that levels of abstraction that are categorized faster are processed first. We tested this fastest means first hypothesis by contrasting the time-course of basic- and subordinate- level categorization for novice and expert categories with a signal-to-respond task. Results indicated no qualitative differences in the time courses of perceptual decisions for novice and expert categories, nor was there evidence for a basic-level stage preceding a subordinate-level stage. Simulations with an extant object categorization model investigated how seemingly qualitative differences between novice and expert categorization can be accounted for with quantitative changes to model parameters over learning. Together, the behavioral data and simulation results suggest that fastest does not necessarily mean first in perceptual categorization. Keywords: categorization; basic level; time-course; cognitive modeling Introduction The human visual system allows us to rapidly and accurately recognize objects in the world around us. At a glance, we can detect that an object is there, categorize what kind of object it is, and identify the object with a unique name. An important and long-standing question about object processing concerns when these different levels of abstraction become available to the perceiver. Given an image of a dog, how much time is required before we know that the image contains an object, or that this object is an animal, a dog, or a golden retriever? Some of these perceptual decisions are made more quickly than others (Rosch, Mervis, Gray, Johnson, & Boyes-Braem, 1976). But does fastest mean first? Are certain perceptual decisions made prior to others during visual object recognition (Palmeri, Wong, & Gauthier, 2004; see also Grill-Spector & Kanwisher, 2005)? Rosch et al. (1976) found that participants were faster at verifying objects at a basic level (e.g., dog) than more superordinate (e.g., animal) or subordinate (e.g., Poodle) levels of abstraction. While this basic-level advantage is robustly found across many object categories, situations exist where this effect is significantly attenuated. For example, with objects of perceptual expertise (Tanaka & Taylor, 1991), subordinate-level categorization occurs as quickly and as accurately as basic-level categorization. This finding has sometimes been characterized as an entry-level shift (Jolicoeur, Gluck, & Kosslyn, 1984); for novice categories, the basic level is the entry level, but for expert categories, more subordinate levels become the entry level. But what does it mean for a particular level of abstraction to be the “entry” level? One simple and straightforward possibility is illustrated in Figure 1. In this box-and-arrow model, objects from novice categories, after low-level visual processing, are categorized first at the basic level (the entry level) before being categorized at more subordinate levels. Basic-level categorization is faster than subordinate-level categorization because basic-level categorization occurs before subordinate-level categorization – fastest means first. But for objects from expert categories, there is an entry level shift, whereby objects are categorized at subordinate levels of abstraction without first being categorized at the basic level.