Introduction
The human visual perceptual processes begin from global processing to local processing (Navon, 1977, p.353). This is based on the principle of global precedence (Navon, 1977, p.354). It follows; visual perception (p.355) begins with recognition of global features before local features are recognized, processed and synthesized. Development of awareness of the global features (Navon, p.353) is critical to visual processing. Visual perception therefore follows a hierarchical order because visual processing depends on stimulus development (Navon, pp.355-6).
Testable hypothesis
The two testable hypotheses in the Navon study sought to test inevitability of global processing (Navon, p.368) hence confirming the principle of global precedence (Navon, p.353). The principle of global precedence affirms recognition of local features following visualization of global features. The second hypothesis was meant to test conflict between global cues and local cues (Navon, p.353). Through identification of rate of subject response to pairs of simple patterns, it was envisioned possible to identify priority of global or local visual perception.
The design of the study
The design of the study (Navon, p. 353, p.368) involved response of subjects to the auditory character. The study was designed to test processes through which visual perception develops. The study used a visual stimulus that consisted of large characters (representing the global level) that had been made up of small characters (representing the local level). The goal was to determine if the viewer would recognize the large characters first as opposed to recognition of the small characters that formed the large character. The character, large or small, that would have been recognized first would have helped to determine mechanism through which visual processing initiates and develops.
Findings of the study
The results presented an error percentage of 3.3% (Navon, p.369). The differences (p.370) were non-significant at 0.05 confidence level. The conflicting consistency (Navon, p.370) was significant when attention was directed at P<0.01. The mean latency in the conflicting trials for the local directed condition was determined to be higher compared to the global directed condition (Navon, p.370).
Discussion of the results
The results established that respondents have higher recognition for global features than local features. The subjects first recognized the large character (global level) before they recognized the small characters that formed the large character (local level). The subjects demonstrated increasing reliance on global features as opposed to local features. This implies, human perceptual processes proceed from the global level, intermediate levels or coarse-grained analysis and finally fine-grained analysis of local level is achieved (Navon, p.370). This proved first hypothesis on inevitability of global processing to be true. The findings established that if subjects have no specific feature to identify or attention is not directed, the viewer’s attention is drawn to the global features. The study established attention could be directed to local features if the subject has prior knowledge or awareness of global features. The subjects therefore cannot demonstrate capacity to control perceptual processing regardless of efforts to ignore scenes. This implies, for a subject to demonstrate local processing, the subject should have awareness of the global level (Navon, p.368). This confirmed word letter phenomenon hence higher level of visual perception has capacity to improve local level processing (Navon, p.357).
The recognition of letters H or S at global level [experiment 3(1)] indicated global level had higher priority (Navon, p.369). The differences observed in experiment 3(2) established subjects could allocate attention level to local level if they had prior awareness of global level. The variation in speed of response based on mean latencies (Navon, p.369-370) is indicator of global awareness influence on local level processing. This demonstrates that when people attend to global level, they have limited capacity to attend to local level (Hughes et al, 1984). It further shows attention is indivisible between two elements that are dependent. Based on mean latencies, local processing doesn’t interfere with global level processing but global level processing can interfere with local processing.
Conclusion
The human perceptual processing, therefore, develops from global processing (Robertson et al, 1993; Duncan, 1984). The global level has properties of the local level. Local-level processing involves the identification of individual entities (small letters that form the global level). This means global level processing is an important step towards human local processing (Rensink, O’Regan & Clark, 1997). This satisfies principle of global processing. Processing of local level is negatively influenced by global processing if a viewer doesn’t have global level awareness. This provides proof that visual perception is not instantaneous as implied by gestalt psychological theory.
References
Duncan, J. (1984). Selective attention and the organization of visual information. Journal of Experimental Psychology: General, 113, 501-51
Hughes, H.C., Layton, W.M., Baird, J.C., & Lester, L.S. (1984). Global precedence in visual pattern recognition. Perception & Psychophysics, 35, 361-371.
Navon, D. (1977). Forest before trees: The precedence of global features in visual perception. Cognitive Psychology, 9, 353-383.
Rensink, R.A., O’Regan, J.K., & Clark, J.J. (1997). To see or not to see: The need for attention to perceive changes in scenes. Psychological Science, 8, 368-373.
Robertson, L.C., Egly, R., Lamb, M.R., & Kerth, L. (1993). Spatial attention and cuing to global and local levels of hierarchical structure. Journal of Experimental Psychology: Human Perception and Performance, 19, 471-487.