Detecting conjunctions of color and form in parallel. Mordkoff, J., T., Yantis, S., Egeth, H., E., Valen, K., V., Marra, R., Thakral, V., & Mcdowell, C. Perception & Psychophystcs, 48(2):157-568, 1990.
Detecting conjunctions of color and form in parallel [pdf]Paper  abstract   bibtex   
Certain theories of visual attention assume that at least one processing stage must be serial when the target of search is defined as the conjunction of two or more separable features. To explain why conjunction-search response times do not always form linearly increasing functions of display size, recent versions of this general model have posited the existence of an early parallel process that guides the serial stage toward display elements that are likely targets. Other models have relaxed the seriality assumption, allowing for a limited number of parallel decisions. In the three experiments reported here, a redundant-target detection task was used with conjunc-tively defined targets and display sizes of two (Experiment 1), one or two (Experiment 2), and six (Experiment 3). In all three experiments, strong evidence for parallel processing was observed. The implications for models of elementary visual processes are discussed. Experiments in visual search provide an important class of tools for exploring the processes subserving early vi-sion. For example, the analysis of response time as a func-tion of display size has furnished significant evidence con-cerning the properties of the rate-limiting process underlying visual search (Egeth, Jonides, & Wall, 1972; Treisman & Gelade, 1980). Two qualitatively different patterns of results are typically observed when the num-ber of display elements is varied from trial to trial. Which pattern is found depends on the nature of the target and nontarget stimuli. When search involves a target that differs from nontargets in a single salient feature (e.g., a vertical line among horizontal lines), then the search-time function remains essentially flat over wide ranges of display size, supporting the notion that targets are de-tected by a spatially parallel process. In contrast, when the target is defined by a conjunction of features, each of which is separately present among the nontarget ele-ments (e.g., a red X among red Os and black Xs), then search times increase linearly with display size, suggest-ing a serial, item-by-item search. This fundamental differ-This research was supported by grants from NASA (JRI NCA2-413) and NIMH (R01-MH43924) to Steven Yantis and by AFOSR (87-0180) to Howard Egeth. Preliminary reports were made at the 60th Annual Meeting of the Eastern Psychological Association and the 1st Annual Meetang of the American Psychologmal Society. Some results from Ex-periments 1 and 2 will also appear in J. Pomerantz and G. Lockhead, (Eds.), The Perception of Structure (Wasfungton, DC: The American Psychological Association).

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