Navon paper broken down from Uni of Notts

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School of Psychology
University of Nottingham

Navon’s (1977) Study of Global vs. Local Perceptual
Processing

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School of Psychology
University of Nottingham

The Title


Forest Before Trees: The Precedence of Global Features in Visual
Perception

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School of Psychology
University of Nottingham

The Abstract
“The idea that global structuring of a visual scene precedes analysis of local features is suggested, discussed and tested. In the first two experiments subjects were asked to respond to an auditorily presented name of a letter while looking at a visual stimulus that consisted of a large character (the global level) made out of small characters (the local level). The subjects’ auditory discrimination responses were subject to interference only by the global level and not by the local one. In Experiment 3 subjects were presented with large characters made out of small ones and they had to recognize either just the large characters or just the small ones. Whereas the identity of the small characters had no effect on recognition of the large ones, global cues which conflicted with the local ones did inhibit the responses to the local level. In
Experiment 4 subjects were asked to judge whether pairs of simple patterns of geometrical forms which were presented for a brief duration were the same or different. The patterns within a pair could differ either at the global or the local level. It was found that global differences were detected more often than local differences.” (pg. 353, Cognitive Psychology, 9, 1977)
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School of Psychology
University of Nottingham

The Introduction




Navon structured his introduction using subheadings:
• Definitional Framework
• The Principle of Global Precedence
• Functional Importance of Global-to-Local Processing
• Some Empirical Evidence
Subheadings are generally used for longer research reports.
• Generally you will not need them.

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School of Psychology
University of Nottingham

Definitional Framework


This section begins:
“The interpreted contents of a scene can be viewed as a hierarchy of subscenes interrelated by spatial relationships (Winston, 1973;
Palmer, 1975)”




Having introduced the area Navon provides more technical/theoretical detail He uses references to other work to show that this is not a new idea
(he’s avoiding plagiarism)

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School of Psychology
University of Nottingham

The Principle of Global Precedence (1)


The opening lines of Navon’s introduction are:
“Do we perceive a visual scene feature-by-feature? Or is the process instantaneous and simultaneous as some Gestalt psychologists believed? Or is it somewhere in between?”



By doing this he immediately ‘sets the scene’ for the reader.

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School of Psychology
University of Nottingham

The Principle of Global Precedence (2)


At the end of this section he states:
“The idea put forward in this paper is that perceptual processes are temporally organized so that they proceed from global structuring towards more and more fine-grained analysis.”



Navon makes very clear what his general theoretical claim is.

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School of Psychology
University of Nottingham

Functional Importance of Global-to-Local Processing


Navon presents an argument about why this may be important to the cognitive system:
“In most real situations the task of the human perceptual processor is not just to account for given input but also to select which part of the surrounding stimulation is worth receiving, attending to, and processing….suggest that a multipass system, in which finegrained processing is guided by prior cursory processing, may be superior to a system that tries to find a coherent structure for all pieces of data simultaneously” (pg. 355, Cognitive Psychology, 9,
1977)

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School of