Academic journal article Perception and Psychophysics

No Overall Right-Left Prevalence for Horizontal and Vertical Simon Effects

Academic journal article Perception and Psychophysics

No Overall Right-Left Prevalence for Horizontal and Vertical Simon Effects

Article excerpt

The present study confirmed that there is no overall right-left prevalence effect for Simon tasks, in which stimulus location is irrelevant, when (1) the stimulus and response sets vary along both horizontal and vertical dimensions simultaneously, (2) the stimulus set varies along both dimensions, but the response set varies along only one dimension, and (3) the stimuli and responses vary in one of four possible locations and responses are made by a unimanual joystick movement. In all experiments, Simon effects of similar magnitude were evident for both the horizontal and the vertical dimensions. The findings suggest that the right-left prevalence effect observed with two-dimensional location-relevant tasks is not due to stronger overall automatic activation of horizontal codes but to different translation efficiencies in intentional response selection processes.

Stimulus-response compatibility (SRC) is a major factor contributing to the speed with which response selection occurs. SRC is usually studied in choice reaction tasks for which subjects make assigned responses to attributes of the stimuli, such as their locations or colors. In a typical two-choice spatial SRC task, a left or right keypress is made in response to a stimulus in a left or right location (e.g., Shaffer, 1965). Performance is better with a spatially compatible mapping of stimuli to responses (i.e., left stimulus to left response and right stimulus to right response) than with an incompatible mapping (i.e., left stimulus to right response and right stimulus to left response). For tasks in which responding is based on a nonspatial stimulus attribute (e.g., color), performance is still better when the stimulus and the response locations correspond than when they do not (Simon & Small, 1969), a phenomenon known as the Simon effect (see Lu & Proctor, 1995, and Simon, 1990, for reviews).

SRC effects are obtained regardless of whether both the stimulus and the response sets are arrayed along the horizontal or the vertical dimension. For SRC proper, the horizontal and the vertical compatibility effects are of similar magnitude (Nicoletti & Umiltà, 1984; Vu, Proctor, & Pick, 2000). Thus, when measured in isolation, there does not seem to be an inherent advantage for the horizontal or the vertical dimension. In contrast, when the stimulus and the response sets vary along both the horizontal and the vertical dimensions simultaneously (e.g., when the locations are endpoints of the major diagonals of imaginary squares), a right-left prevalence effect is often obtained for SRC proper: The SRC effect is larger for the horizontal dimension than for the vertical dimension (e.g., Nicoletti & Umiltà, 1984, 1985; Nicoletti, Umiltà, Tressoldi, & Marzi, 1988).

Vu and Proctor (2001, 2002) showed that right-left prevalence is not due to an inherent advantage of the horizontal dimension over the vertical dimension but, rather, to the fact that in many situations, the stimulus or the response environment (e.g., responding with the left and the right hands) provides a salient frame of reference for horizontal coding. In fact, Vu and Proctor demonstrated that top-bottom prevalence could be obtained when the stimulus or the response environment was made to favor the vertical dimension. Moreover, they showed that the largest difference in SRC effects for the two dimensions occurred when the same dimension was salient for both the stimulus set and the response set.

Rubichi, Nicoletti, Pelosi, and Umiltà (2004) confirmed Vu and Proctor's (2001, 2002) findings that the salience of the response dimension is important in determining the relative magnitude of the compatibility effects for the horizontal and the vertical dimensions. In Rubichi et al.'s (2004) study, the stimuli varied along both dimensions simultaneously, as in previous studies, but the responses were arrayed along only one dimension at a time, with response keys operated by horizontal effectors (i. …

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