Academic journal article Perception and Psychophysics

Conjunction Benefits and Costs Reveal Decision Priming for First-Order and Second-Order Features

Academic journal article Perception and Psychophysics

Conjunction Benefits and Costs Reveal Decision Priming for First-Order and Second-Order Features

Article excerpt

Across two experiments, decision priming was examined for conjunctions composed of first-order or first- and second-order stimulus features. Observers indicated the presence or absence of one or two features in a Gabor stimulus. When a pair of stimulus features differed in their speed of discrimination, responses indicating the presence of a conjunction were faster than those for the single feature for which discrimination was slowest (conjunction benefits). Also, responses indicating the absence of a conjunction were delayed if one of the features was present (conjunction costs). These results show that first- and second-order features can prime decisions about the presence of a conjunction and suggest that the two kinds of signals can be combined at a decision stage after the discrimination of stimulus properties has begun for each system.

Comparing decisions based on target stimuli defined by multiple features and those defined by single features has played an essential role in the development of many selective attention models (e.g., Bundesen, 2002; Cave, 1999; Cohen & Shoup, 2000; Duncan, 1984,1996; Lavie, 1995; Treisman & Gelade, 1980; Treisman & Sato, 1990; Wolfe, 1994). Evidence indicating differences in selection times and attentional capacity demands between multiple- and single-feature targets has typically been based on reaction time (RT) and accuracy measures. However, the question of how differences in discriminability and response mappings among features within these targets affect discrimination time and accuracy has been generally ignored. Furthermore, it is not known whether such differences affect targets composed of first-order features (defined by differences in mean luminance) and those composed of both first-order and second-order features (e.g., defined by contrast modulation without a change in mean luminance) similarly. Investigation of these factors can provide insight into how different classes of stimulus features are combined to render a decision concerning the presence or absence of a visual stimulus.

Founder and colleagues recently showed that the speed whh which one can accurately determine the presence or absence of a target defined by multiple first-order features is dependent on the discrimination speed and response mapping of features on the task-relevant stimulus dimensions (Founder, Bowd, & Herbert, 2000; Founder, Eriksen, & Bowd, 1998; Founder, Herbert, & Farris, 2004; Founder, Scheffers, Coles, Adamson, & Abad, 2000). They had observers judge the presence or absence of one or two target features within an object at a fixed and known spatial location. For example, the object was a letter that varied in hue (red or green) and shape (H or K) with the physical characteristics of the stimuli (e.g., size), making the shape of the letters slower to discriminate than their hue. They found that responses indicating the presence of the conjunction red X were faster than responses indicating the presence of the shape X alone. Thus, identifying whether two features are present in a stimulus can be faster than identifying whether the single feature, for which discrimination is slowest, is present This faster response to the presence of a conjunction is called a conjunction benefit. In addition, they found that responses indicating the absence of a conjunction redXwere faster than responses indicating the absence of the shape X alone, but only when all of the target features were absent in the former case. If one of the target features was present, responses indicating the absence of a conjunction were much slower, as compared with the case in which neither of the target features were present. These absent responses were particularly slow when the feature that was discriminated faster was the feature that was present (e.g., red). Slower responses indicating the absence of a conjunction when one of the target features is present is called a conjunction cost. …

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