Abstract
The brain needs to identify redundant sensory signals in order to integrate them optimally. The identification process, referred to as causal inference, depends on the spatial and temporal correspondence of the incoming sensory signals (‘online sensory causality evidence’) as well as on prior expectations regarding their causal relation. We here examine whether the same causal inference process underlies spatial integration of actions and their visual consequences. We used a basic cursor-control task for which online sensory causality evidence is provided by the correlated hand and cursor movements, and prior expectations are formed by everyday experience of such correlated movements. Participants made out-and-back movements and subsequently judged the hand or cursor movement endpoints. In one condition, we omitted the online sensory causality evidence by showing the cursor only at the movement endpoint. The integration strength was lower than in conditions where the cursor was visible during the outward movement, but a substantial level of integration persisted. These findings support the hypothesis that the binding of actions and their visual consequences is based on the general mechanism of optimal integration, and they specifically show that such binding can occur even if it is previous experience only that identifies the action consequence.
Highlights
IntroductionPart of the sensory input that the brain receives is redundant, meaning that the signals provide information on the same property of a physical object (e.g., the felt and seen size of a hand-held object) or event (e.g., the auditory and visually indicated location of a person speaking to you)
Part of the sensory input that the brain receives is redundant, meaning that the signals provide information on the same property of a physical object or event
Causal inference is believed to be a Bayesian process as well, meaning that it is based on causality information inherent to the sensory signals themselves as well as on causality information provided by prior experience and knowledge[9,10,11]
Summary
Part of the sensory input that the brain receives is redundant, meaning that the signals provide information on the same property of a physical object (e.g., the felt and seen size of a hand-held object) or event (e.g., the auditory and visually indicated location of a person speaking to you). This is nicely illustrated by a study in which participants were trained with an artificial relation between an object’s luminance and its stiffness over a one-hour experimental session[22] After this training, participants’ discrimination performance was reduced, indicating that participants started integrating these sources of information despite the absence of causality evidence in the incoming signals themselves. We found that the integration strength declined when the spatiotemporal hand-cursor cross-correlation during each movement was reduced by non-linearly transforming the cursor trajectory[25] These findings indicate that the brain integrates spatial information regarding an action (here of the hand) with spatial information regarding its visual consequence (here the motion of the cursor), and that spatiotemporal kinematic correlations provide online sensory causality evidence for this integration
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