Dissociating stimulus information from internal representation - a case study in object recognition

Human object recognition is a function of both internal memory representati on(s) and stimulus input information. The role of the latter has been so fa r largely overlooked, and the nature of the representation is often directl y equated with recognition performance. We quantify stimulus information fo r three classes of objects in order of decreasing object complexity: unconn ected balls, balls connected with lines, and balls connected with cylinders . In an object discrimination task, subjects' performance improved with the decreasing object complexity. We show that input information also increase s with decreasing object complexity. Therefore, the results could potential ly be accounted for either by differences in the object representations lea rned for each class of objects, or by the increased information about the t hree-dimensional (3D) structure inherent in images of the less complex obje cts, or by both. We demonstrate that, when image information is taken into account, by computing efficiencies relative to a set of ideal observers, su bjects were more efficient in recognizing the less complex objects. This su ggests that differences in subjects' performance for different object class es is at least partly a function of the internal representations learned fo r the different object classes. We stress that this conclusion cannot be ac hieved without the quantitative analysis of stimulus input information. (C) 1998 Elsevier Science Ltd. All rights reserved.