Navon’s (1977) Study of Global vs. Local Perceptual
Processing
C81 MPA - Practical Methods
1
School of Psychology
University of Nottingham
The Title
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Forest Before Trees: The Precedence of Global Features in Visual
Perception
C81 MPA - Practical Methods
2
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)
C81 MPA - Practical Methods
3
School of Psychology
University of Nottingham
The Introduction
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•
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.
C81 MPA - Practical Methods
4
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)”
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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)
C81 MPA - Practical Methods
5
School of Psychology
University of Nottingham
The Principle of Global Precedence (1)
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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.
C81 MPA - Practical Methods
6
School of Psychology
University of Nottingham
The Principle of Global Precedence (2)
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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.”
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Navon makes very clear what his general theoretical claim is.
C81 MPA - Practical Methods
7
School of Psychology
University of Nottingham
Functional Importance of Global-to-Local Processing
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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)
