The Influence of Induced Emotions on Distance and Size Perception and on the Grip Scaling During Grasping

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.

Keywords: distance; emotion; grasping; perception; size; visual feedback.

Figure 1

Stimuli and layout of the setup of Experiment 1. (A) Toy rats, toy squirrels and wooden blocks with wooden plaques (target objects) resting on them. (B) At the beginning of each trial, the goggles were closed. Participants were asked to hold down the start button before the task. After the experimenter opened the goggles, participants indicated the perceived distance (up) or the perceived size (bottom) of the target object. For both distance and size estimation, the goggles were closed as soon as the participants released the start button (i.e., open-loop) to prevent any online visual feedback during the estimation.

Figure 2

Results of Experiment 1. (A,B) show the data of emotional arousal scores. (C,E) show the size estimation and distance estimation results. Error bars represent within-subjects 95% CIs (Loftus and Masson, 1994; Masson, 2003). (D,F) show the correlation between the relative distance/size estimation and the relative emotion scores across participants.

Figure 3

Setup and procedure for Experiment 2. Participants first held down the start button with the thumb and index finger of their right hand. The experimenter pressed a button to open the goggles when the inducer and the target object were positioned. Participants were asked to release the start button and reach out to grasp the target object along its long side naturally and accurately as soon as the goggles were opened. In the open-loop condition, the goggles were closed as soon as the start button was released, and therefore there was no online visual feedback during the execution of grasping movement. In the closed-loop condition, the goggles were open for 2s allowing a full view of the target object and the grasping hand during grasping.

Figure 4

The results in Experiment 2. (A) The reaction time in the control conditions (gray blocks and brown blocks) and the experimental conditions (toy rats and toy squirrels) when participants had no visual feedback (open-loop) or had visual feedback (closed-loop) during the execution of grasping. (B) The correlation between the normalized positive emotional scores and the normalized reaction time in the closed-loop condition across individuals. Note, although there seems an outlier, the correlation was still strong after the “outlier” was removed. In other words, the correlation could not be attributed to the existence of the “outlier.” (C) The peak grip apertures (PGAs) during grasping in the control conditions (gray blocks and brown blocks) and the experimental conditions (toy rats and toy squirrels) when participants had no visual feedback (open-loop) or had visual feedback (closed-loop) during the execution of grasping. (D) The correlation between the normalized negative emotional scores and the normalized peak grip aperture in the open-loop condition across individuals.

Figure 5

Results of Experiment 3. (A) Size estimation when paper-wrapped toys were used as inducers. (B) Peak grip aperture when paper-wrapped toys were used as inducers in open-loop condition. (C) Peak grip aperture when paper-wrapped toys were used as inducers in closed-loop condition.