One of the key questions in cognitive neuroscience is how the brain selects relevant information from the abundance of sensory input. On the one hand, certain control mechanisms permit selecting relevant information according to a given task (e.g., finding a person wearing a green shirt in a crowd of people dressed in clothes of various colours). In this case, processing of green will be prioritized over other colours. At the same time, relevance might also be defined with respect to given action plans. For example, depending on whether one is to grasp a cup placed among many other cups and plates in a cupboard, or only point to it, different aspects of the cup will be prioritized. In grasping the cup, grip aperture is important, and hence, size of the cup and/or possibly orientation of its handle need to be processed with priority. In case of pointing, the cup’s location is the most important feature. Therefore, depending on what type of action is intended, processing should be focused on different sensory inputs. We propose that this is achieved by an action-related bias, or an intentional weighting mechanism (a term first introduced by Hommel et al., 2001). According to Hommel (2010), intentional weighting allows for providing perceptual information to open parameters of online action planning.
We investigated how intentional weighting related to natural actions influenced early attentional selection (e.g., Wykowska, Schubö, & Hommel, 2009; Wykowska, Hommel & Schubö, 2011). The experiments consisted of a visual search task combined with two actions: grasping and pointing. As such, the paradigm created two congruent perception-action pairs: size - grasping and luminance – pointing. It was assumed, in line with ideomotor theories (e.g., Greenwald, 1970; James, 1890; Prinz, 1997), that through lifelong experience with grasping, humans have learned that size is relevant for grasping whereas luminance (a feature allowing fast localization) is associated with pointing. Our results showed congruency effects: better performance in search when size was coupled with grasping (as compared to pointing), and better performance when luminance was combined with pointing (relative to grasping). These results argue in favour of perception being influenced by action and allow for a speculation that a mechanism which biases perception with respect to action planning is similar to the task-related bias. Therefore, intentional weighting might operate on perceptual dimensions (e.g., size, luminance) in such a way that dimensions which are relevant for a give action are weighted higher relative to irrelevant ones. Similarly, dimensions are weighted with respect to task-relevance or other factors (Found & Müller, 1996; Müller et al. 2003; Wolfe, 1994). In subsequent studies (Wykowska & Schubö, in prep.), we examined the ERP correlates of the intetional weighitng mechainsm. Results showed action-related modulation of the early sensory component P1 and the N2pc, which has been postulated as the marker of visual spatial attention.
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