Project Details
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Compatibility effects between the physical size of stimulus objects and response locations.

Subject Area General, Cognitive and Mathematical Psychology
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 426561782
 
Final Report Year 2024

Final Report Abstract

The purpose of this project was to investigate the characteristics of a novel congruency effect between physical size (of stimuli) and spatial location (of responses). This so-called SSARC (spatial-size association of response codes) effect refers to the observation that participants respond faster and more accurately to small stimuli with their left hand and to large stimuli with their right hand than vice versa. The primary aims of the project were (a) to clarify important characteristics of the SSARC effect, (b) to determine similarities and differences between the SSARC and other congruency effects (e.g., SNARC, Simon), and (c) to develop and evaluate hypotheses about the origin of the effect. Investigations of stimulus-related determinants showed that relative stimulus size, with regard to the other elements in the stimulus set, and not absolute size, drives the SSARC effect. Investigations of response-related determinants produced several observations suggesting that the hands (as effectors) play a critical role for the SSARC effect. First, the effect does only occur with manual responses when response selection requires to choose between the two hands, but not when response selection requires to choose between two fingers of the same hand. Second, when the task requires to choose between hands, participants tend to code the responses in terms of hands, and not in terms of response positions, particularly in more demanding tasks. Finally, participants‘ handedness modulates the SSARC effect in that the effect is larger for right-handers. These findings contrast with the results of studies that have shown that relative (response) position – and not the effector – dominates response coding in both the SNARC and the Simon effect. In another study, we observed a correlation between individual strength differences (when the strength of the left and right hand were compared) and the size of the individual SSARC effect. In combination with other findings, this correlation supports a hypothesis about the origin of the SSARC effect according to which strength differences between hands have led to a habit of grasping larger objects with the dominant (mostly right) hand, while grasping smaller objects with the nondominant (mostly left) hand. This habit might have led to the SSARC effect. Notably, however, further investigations suggest that differences in object weight, which is usually correlated with size, do not seem to modulate the SSARC effect, or create a similar effect. Together, the results of our project suggest that the SSARC effect differs in several important characteristics from other, apparently similar, effects such as the SNARC or the Simon effect. This heterogeneity in turn suggests that different effects have different origins that might be rooted in different experiences. At the same time, the heterogeneity of the effects, and the evidence suggesting different origins of different effects, seem incompatible with the notion of a generalized, magnitude processing system in the brain as postulated in „A Theory of Magnitude“.

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