Coordination of Attention to Local and Global Features: Fractal Patterns in a Speeded-Categorization Task

Coordination of Attention to Local and Global Features: Fractal Patterns in a Speeded-Categorization Task Ramon D. Castillo (castilrn@mail.uc.edu) University of Cincinnati, Department of Psychology, 104 Dyer Hall, Cincinnati, OH 45221-0376, USA Heidi Kloos (heidi.kloos@uc.edu) University of Cincinnati, Department of Psychology, 125 Dyer Hall, Cincinnati, OH 45221-0376, USA Shana Vanderburgh (vandersm@mail.uc.edu) University of Cincinnati, Department of Psychology, 104 Dyer Hall, Cincinnati, OH 45221-0376, USA John G. Holden (john.holden@uc.edu) University of Cincinnati, Department of Psychology, 51Z0G Edwards1, Cincinnati, OH 45221-0376, USA findings on local/global processing, and then we turn to describing a method of measuring this coordination. Abstract How does the mind coordinate local and global features of a display to allow for adaptive functioning? To answer this question, we presented adults with a speeded categorization task in which they had to decide whether two stimuli match in a local element, in their global pattern, or in neither the local nor the global feature. The trial series of reaction times were then subjected to fractal analyses to capture the coordination that gives rise to performance. The assumption is that long- range correlations reveal themselves in pink-noise exponents, ones that are higher than white-noises exponents. To investigate the stability of fractal exponent, we manipulated both the local elements (to be either familiar or novel), and the order of trials (to be either random or blocked). Results show a significant deviation from white-noise, but only in familiar-elements condition in which trials were presented randomly. Implications for local/global research are discussed. Keywords: visual processing; categorization; analysis, detrended fluctuation analysis; pink noise. Local & Global Processing spectral Introduction How does the mind make senses of an ever changing array of light? This question has a long history, often addressed under the framework of local and global processing (e.g., Kimchi, 1990; Kimchi, Hadad, Behrmann, & Palmer, 2005; Kohler, 1969; Quinn, Burke & Rush, 1993). Indeed, a scene could be loosely divided into local elements and global patterns. And adaptive functioning needs both: the ability to integrate local elements into higher-order Gestalts, and the ability to segregate higher-order Gestalts into their component parts. In fact, processes of integration most likely must be coordinated fluidly with processes of segregation. The current paper is concerned with the question of this coordination. We first give a brief review of Traditionally, the emphasis has been on determining how attention to local aspects competes with the perception of global aspects, whether the stimuli pertain to faces, arbitrary items, or entire scenes. Navon’s (1977) well-known task is a good illustration of this emphasis. Stimuli involved small letters arranged spatially in such a way that they form a larger letter. The element letters either matched the Gestalt letter or not. And the task was to name a letter (either the element letter or the Gestalt letter) as fast as possible. The general finding suggests an asymmetry in competition: Perception of Gestalt features appears to interfere more with the perception of elemental features than vice versa. Consistent with the laws of perception outlined by Gestalt psychology, the organization of whole entities apparently takes priority over the separation into isolated elements. While subsequent research has supported the general finding of unidirectional competition between global and local processes (Dukette & Stiles, 1996; 2001), the issue might be more complex. Kimchi and her colleagues, for example, showed that the priority of global processes depends on the specific details of the stimuli used. When items consist of few elements (e.g., four triangles spatially arranged to form a square), the global preference disappears (e.g., Kimchi, 1990; Kimchi et al, 2005). It is only when items consist of many elements (e.g., twelve triangles spatially arranged to form a square) that global patterns take precedence. This pattern of findings was demonstrated in adults as well as children as young as 5 years of age; and it was replicated in speeded classification tasks, matching tasks, or visual searching task (Burack, Enns, Iarocci, & Randolph, 2000; Enns & Girgus, 1985). Together, these