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Attention: Navon 1977

Navon (1977). Forest before trees: The precedence of global features in visual perception. Cognitive Psychology, 9, 353-383. (doc)
This experiment asks participants to look for a particular letter (presented either as a large letter composed of other letters, or as the letters that make up the larger letter). For example, if the target were "a", both of these would be permissible:

AAAAAAA               EEEE
AAAAAAA              EE  EE
AA                  EE    EE
AA                  EE    EE
AAAAAAA             EE    EE
AAAAAAA             EE    EE

The experiment hopes to show that large-scale letters are recognized more quickly and easily than the smaller-scale letters that make them up.

Note that this particular experiment does not exactly replicate experiment 3 of Navon's paper, which involved H and S as targets. Subjects there were asked to report whether they saw an H or an S at a particular level (global or local) and the item of interest was how much the opposite target at the other level interfered with processing the actual target.


There are many different theories to explain how features and figures interact to produce visual perception. The Gestalt view is that all features are perceived and integrated at once. This view, however, is not consistent with the finding that people extract more information from images the longer they view those images. The interaction between top-down and bottom-up processing is not entirely clear.

The aim of this experiment was to show that the perceptual system processes every scene starting with the global features and progressing to the local features that compose them. In order to get at this processing, Navon attempted to find figures for which the global-local relation was immediately apparent. The letters composed of other letters were ideal because they were easily constructed and recognized as well as having hierarchically obvious features.

The experiment succeeded in showing the effect that global features take precedence over local features in speed of perception.

Stroop 1935
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Broadbent, D.E. Waves in the eye and ear. Journal of Sound and Vibration, 1975, 41, 113-125.

Campbell, F.W. The transmission of spatial information through the visual system. In F.O. Schmitt & F.G. Worden (Eds.), The neurosciences third study program. Cambridge, MA: MIT Press, 1974.

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Flavell, J.H., & Draguns, J. A microgenetic approach to perception and thought. Psychological Bulletin, 1957, 54, 197-217.

Helson, H., & Fehrer, E.V. The role of form in perception. Amercian Journal of Psychology, 1932, 44, 79-102.

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Johnson, N.F. On the function of letters in word identification: Some data and a preliminary model. Journal of Verbal Learning and Verbal Behavior, 1975, 14, 17-29.

Johnston, J.C., & McClelland, J.L. Perception of letters in words: Seek not and ye shall find. Science, 1974, 184, 1192-1194.

Mackworth, N.H., & Bruner, J.S. How adults and children search and recognize pictures. Human Development, 1970, 13, 149-177.

Meili-Dworetzki, G. The developments of perception in the Rorschach. In B. Klopfer (Ed.), Developments in the Rorschach technique. New York: Harcourt, Brace, & World, 1956, Vol. II.

Navon, D. Irrelevance of figural identity for resolving ambiguities in apparent motion. Journal of Experimental Psychology: Perception, 1976, 2, 130-138.

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Norman, D.A., & Bobrow, D.G. On the role of active memory processes in perception and cognition. In C.N. Cofer (Ed.), The structure of human memory. San Francisco: Freeman, 1976.

Palmer, S.E. Visual perception and world knowledge: Notes on a model of sensory-cognitive interaction. In D.A. Norman, D.E. Rumelhart, & the LNR Research Group, Explorations in Cognition. San Francisco: Freeman, 1975.

Palmer, S.E. The effects of contextual scenes on the identification of objects. Memory and Cognition, 1975a, 3, 519-526.

Pillsbury, W.B. A study in apperception. American Journal of Psychology, 1897, 8, 315-393.

Rayner, K. The perceptual span and peripheral cues in reading. Cognitive Psychology, 1975, 7, 65-81.

Reicher, G.M. Perceptual recognition as a function of meaningfulness of stimulus material. Journal of Experimental Psychology, 1969, 81, 274-280.

Rumelhart, D.E., & Siple, P. Process of recognizing tachistoscopically presented words. Psychological Review, 1974, 81, 99-118.

Stroop, J.R. Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 1935, 18, 643-662.

Warren, R.M. Perceptual restoration of missing speech sounds. Science, 1970, 167, 392-393.

Wheeler, D.D. Processes in word recognition. Cognitive Psychology, 1970, 1, 59-85.

Williams, L.G. The effect of target specification on objects fixed during visual search. Perception and Psychophysics, 1966, 1, 315-318.

Winer, B.J. Statistical principles in experimental design. New York: McGraw-Hill, 1971, 2nd ed.

Winston, P.H. Learning to identify toy block structures, In R.L. Solso (Ed.), Contemporary issues in cognitive psychology: The Loyola Symposium. Washington, D.C.: Winston, 1973.

Yarbus, A.L. Eye movements and vision. New York: Plenum, 1967.

The idea that global structuring of a visual scene preceded 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 at the local level. It was found that global differences were detected more often than local differences.


Brian MacWhinney