Response inhibition refers to an ability to cancel or restrain an advantage response or habitual behavior, and it is an important ability for individuals to adapt to the environment. In recent years, the research of emotional effect on response inhibition has been increasing, but whether emotional cues facilitate or impair response inhibition was inconclusive. Based on existing evidence, the influence of emotional cues on response inhibition is related to the position of emotional cues in a response inhibition task. When the emotional cue enhances attention of a stop signal, the response inhibition is improved, whereas inhibition is impaired when the emotional cue is unrelated to the inhibition task. Most studies in the field have focused on the effects of emotional cues on response inhibition when the cues were in the priming, background and go trial positions, but fewer studies investigated the effect when emotional cues are as stop signals. Based on the summary, we predict emotional stop signals enhances inhibition in healthy group. In addition, clinical group such as patients with schizophrenia often show impairment in response inhibition. However, the patients with schizophrenia usually have normal emotional response when perceiving an emotional stimulus, therefore emotional stop signals may improve response inhibition in patients with schizophrenia. The two research questions were investigated in the present study. First, the influence of emotional stop signal on response inhibition was examined, and a benefit was predicted. Second, we examined whether patients with schizophrenia would also show benefit of emotional stop signals on response inhibition.
There were three studies. In series of three experiments in Study 1, the effect of emotional facial stop signals on response inhibition was examined in university students. In Experiment 1 (N=48), participants were asked to judge whether the shape was a circle or a square and made responses, and they need to stop response whenever they saw a face (i.e., stop signal). The four types of faces were happy, anger, sadness, or neutral, and the hair, ears and color of the face were removed to reduce interference unrelated to emotion. In Experiment 2 (N=30), more faces of different identities were included to avoid emotional adaptation of frequently repeated faces. In Experiment 3(N = 30), the ears, hair and colors of the faces were kept to improve the ecological validity of emotional faces. Across the three experiments, there was no significant effect of emotional faces on response inhibition.
In Study 2, a similar stop signal task was used except that emotional pictures were used as stop signals to reduce the cultural difference in facial perception. All the participants were healthy university students. In Experiment 4 (N = 25), participants were asked to judge whether a square was linear or curvy and made responses, and they had to stop response when they saw a picture inside the square. The picture cues were negative, neutral or positive. Negative cues impaired the inhibition while positive cues had no effect. In Experiment 5 (N = 27), the inter-stimuli-interval was shortened in the stop signal task to make it compatible with clinical studies, and it replicated the findings in Experiment 4. In Experiment 6 (N = 24), the negative pictures with violent content in previous experiments were replaced with the pictures without such content to prepare for clinical research, the new pictures had lower arousal ratings and failed to show any significant influence on response inhibition. In Experiment 7 (N = 23), the block design in previous experiment was changed to mixed design with positive, negative and neutral picture cues appearing alternately in the same block. Surprisingly, the negative emotional pictures facilitated response inhibition, and positive pictures still had no effect on response inhibition.
In Study 3, the influence of emotional cues on response inhibition was examined in patients with schizophrenia. A total of 36 patients with schizophrenia from community and 36 healthy controls matched in gender, age and education years attended the experiment. The task was same as the paradigm that showed a benefit of negative stop signals on response inhibition. The negative emotional pictures facilitated response inhibition in patients with schizophrenia to the same extent as to healthy controls. In both groups, positive pictures had no effect on inhibition. Despite benefit of negative stop cues, patients with schizophrenia still had worse performance of inhibition compared to health controls. Moreover, patients with schizophrenia had lower response accuracy of response trials after the stop trials in the condition negative cues, indicating the benefit of negative cues for response inhibition has a cost on cognitive resources.
In sum, present study systematically examined the effect of emotional stop signals on response inhibition in healthy group and patients with schizophrenia. There were three main findings. First, the findings of Study 1 and 2 in healthy undergraduates indicates that the influence of negative picture stop signals on response inhibition depends on arousal level of the picture cues and experiment design. In block design, highly arousal pictures impaired response inhibition whereas moderately arousal negative pictures had no effect. In mixed design, moderately arousal negative pictures facilitated response inhibition. Secondly, in both block and mixed design, positive stop signals had no effect on response inhibition. Finally, negative pictures facilitated inhibition in patients with schizophrenia to a similar extent as to healthy controls, but the impairment of inhibition still occurred in conditions of negative cues.
The studies of the influence of emotional stop cues on response inhibition are limited. The findings of present study indicate that emotional stop signal may facilitate or impair response inhibition, which depends on the experiment design and the arousal of emotional cues. These findings suggest that the effect of emotional cues on response inhibition are relatively complex, reflecting the intricate interaction between emotion and cognitive control. Moreover, the finding that moderately arousal negative stop signals improved response inhibition in patients with schizophrenia, may provide theoretical basis for clinical interventions in the future.