Global precedence

Images and other stimuli contain both local features (details, parts) and global features (the whole). Precedence refers to the level of processing (global or local) to which attention is first directed.Global precedence occurs when an individual more readily identifies the global feature when presented with a stimulus containing both global and local features. The global aspect of an object embodies the larger, overall image as a whole, whereas the local aspect consists of the individual features that make up this larger whole. Global processing is the act of processing a visual stimulus holistically. Although global precedence is generally more prevalent than local precedence, local preference also occurs under certain circumstances and for certain individuals. Global precedence is closely related to the Gestalt principles of grouping in that the global whole is a grouping of proximal and similar objects. Within global precedence, there is also the global interference effect, which occurs when an individual is directed to identify the local characteristic, and the global characteristic subsequently interferes by slowing the reaction time.

Global precedence was first studied using the Navon figure, where many small letters are arranged to form a larger letter that either does or does not match. Variations of the original Navon figure include both shapes and objects. Individuals presented with a Navon figure will be given one of two tasks. In one type of task, participants are told before the presentation of the stimulus whether to focus on a global or local level, and their accuracy and reaction times are recorded.

In another type of task, participants are first presented with a target stimulus, and later presented with two different visuals. One of the visuals matches the target stimulus on the global level, while the other visual matches the target stimulus on the local level. In this condition, experimenters note which of the two visuals, the global or local, is chosen to match the target stimulus.

In general, reaction time for identifying the larger letter is faster than for the smaller letters that make up the shape. Navon directed participants to focus either globally or locally to stimuli that were consistent, neutral, or conflicting on the global and local levels (see figures above). Reaction time for global identification was much faster than for local identification, showing global precedence. Additionally, global interference effect, which occurs when the global aspect is automatically processed even when attention is directed locally, causes slow reaction time. Navon's study global precedence and his stimuli, or variations of it, are still used in nearly all global precedence experiments.

When presented with a Navon figure, there is a slight local preference for Caucasians, but East Asians show an obvious global preference and are faster and more accurate at global processing. The inclination towards global precedence is also evident in second generation Asian-Australians, but the correlation is weaker than that of recent immigrants. This could stem from the physical environment of East Asian versus Western cities, as the level of visual complexity varies across these environments. The tendency of Caucasians to process information "analytically" and Asians "holistically" has also been attributed to differences in brain structure.

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