Abstract
Previous studies have shown that our perception of stimulus properties can be affected by the emotional nature of the stimulus. It is not clear, however, how emotions affect visually-guided actions toward objects. To address this question, we used toy rats, toy squirrels, and wooden blocks to induce negative, positive, and neutral emotions, respectively. Participants were asked to report the perceived distance and the perceived size of a target object resting on top of one of the three emotion-inducing objects; or to grasp the same target object either without visual feedback (open-loop) or with visual feedback (closed-loop) of both the target object and their grasping hand during the execution of grasping. We found that the target object was perceived closer and larger, but was grasped with a smaller grip aperture in the rat condition than in the squirrel and the wooden-block conditions when no visual feedback was available. With visual feedback present, this difference in grip aperture disappeared. These results showed that negative emotion influences both perceived size and grip aperture, but in opposite directions (larger perceived size but smaller grip aperture) and its influence on grip aperture could be corrected by visual feedback, which revealed different effects of emotion to perception and action. Our results have implications on the understanding of the relationship between perception and action in emotional condition, which showed the novel difference from previous theories.
Highlights
Simple effect analysis based on ANOVAs revealed that, the negative emotional arousal score for the toy rats was significantly higher than those for the wooden blocks (p < 0.001) and the toy squirrels (p < 0.001; Figure 2A)
The wooden blocks did not induce higher positive emotion arousal scores than the toy squirrels or higher negative emotional arousal scores than the toy rats, which suggests that when wooden object blocks were interleaved with toy rats and toy squirrel blocks, the wooden blocks could effectively prevent interactions between the toy rats and the toy squirrel blocks without introducing additional emotion effect
The main effect of toy types was not significant [F (1,21) = 2.084, p = 0.164], and the toy size was not significant [F (1,21) = 3.672, p = 0.069]. These results suggested that in these three conditions, the shape and size of neutral stimuli did not have an effect on the perception or the peak grip aperture (PGA), only the target object size would affect the estimation and grasping which excluded the uncertainty of previous results for the possible effect of stimuli size and shape
Summary
Even when people were not able to perceive the size or shape of the target object in their periphery visual field due to the crowding effect induced by the surrounding flankers, they could still scale their grip aperture to the size or shape of the target object (Chen et al, 2015a,b) This kind of dissociation between perception and action has been considered as evidence for the influential two-visual-stream theory proposed by Goodale and Milner (1992). In the closed-loop condition, participants were able to see their hands and the target during grasping which made online adjustment based on visual feedback available In this case, the kinematics of grasping depends on both the planning and online control of actions. Toy rats and toy squirrels used in experiments 1 and 2 were wrapped by white paper so that participants had no idea what were inside, and no positive or negative emotion was induced
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