Reward delays quitting in visual search.

Reward motivates goal-directed behaviors, leading to faster reaction time (RT) and lower error rate in searching for a target in the reward condition than in the no-reward condition in target-discrimination tasks. However, it is unclear how reward influences target detection in which participants are required to judge whether a predesignated target is present or absent. Here, we asked participants to complete a target-detection search task in which the color of the search array indicated the reward availability of the current trial. Correct and faster (than a baseline) responses would be rewarded if the search array had the reward-related color. In Experiments 1A and 1B, the target was presented in 50% of the trials. Experiment 1B had the same design as Experiment 1A, except that different baselines were set for the target-present and target-absent conditions. In Experiment 2, the proportion of target presence was manipulated to be high (80%), moderate (50%), or low (20%) in different blocks of stimuli. Results showed that, across all the experiments, participants responded faster and made fewer errors in the reward than in the no-reward condition when the target was present. However, this facilitatory effect was reversed when the target was absent, showcasing a reward-induced interference. The signal detection analysis suggested that reward biased the report criterion to the "yes" response. These findings demonstrate that the impact of reward on goal-directed behavior can be detrimental and reward prolongs the search process by rendering participants reluctant to say "no" in visual search termination.

Reward makes the rhythmic sampling of spatial attention emerge earlier.

A growing body of evidence demonstrates a rhythmic characteristic of spatial attention, with the corresponding behavioral performance fluctuating periodically. Here, we investigate whether and how the rhythmic characteristic of spatial attention is affected by reward-an important factor in attentional selection. We adopted the classic spatial cueing paradigm with a time-resolved stimulus-onset-asynchrony (SOA) between the spatial cue and the target such that responses to the target in different phases could be examined. The color of the spatial cue was associated with either a high or low level of reward. Results showed that in the low-frequency band (<2 Hz) where classic exogenous spatial attention effects (i.e., facilitation and inhibition of return; IOR) appeared, reward enhanced the late IOR effect through facilitating behavioral responses to the target at the uncued location. Recurring lower alpha power (alpha inhibition) which fluctuated in a low-theta frequency (2-3 Hz) was observed at the cued location relative to the uncued location, irrespective of the reward level of the cue. Importantly, the recurring alpha inhibition emerged earlier (~120 ms) in the high-reward condition relative to the low-reward condition. We propose that the recurring alpha inhibition at the cued location implies a recurring attention sampling at the cued location and the expectation of a high reward makes the periodic attention sampling emerge earlier.

A value-driven McGurk effect: Value-associated faces enhance the influence of visual information on audiovisual speech perception and its eye movement pattern.

This study investigates whether and how value-associated faces affect audiovisual speech perception and its eye movement pattern. Participants were asked to learn to associate particular faces with or without monetary reward in the training phase, and, in the subsequent test phase, to identify syllables that the talkers had said in video clips in which the talkers' faces had or had not been associated with reward. The syllables were either congruent or incongruent with the talkers' mouth movements. Crucially, in some cases, the incongruent syllables could elicit the McGurk effect. Results showed that the McGurk effect occurred more often for reward-associated faces than for non-reward-associated faces. Moreover, the signal detection analysis revealed that participants had lower criterion and higher discriminability for reward-associated faces than for non-reward-associated faces. Surprisingly, eye movement data showed that participants spent more time looking at and fixated more often on the extraoral (nose/cheek) area for reward-associated faces than for non-reward-associated faces, while the opposite pattern was observed on the oral (mouth) area. The correlation analysis demonstrated that, over participants, the more they looked at the extraoral area in the training phase because of reward, the larger the increase of McGurk proportion (and the less they looked at the oral area) in the test phase. These findings not only demonstrate that value-associated faces enhance the influence of visual information on audiovisual speech perception but also highlight the importance of the extraoral facial area in the value-driven McGurk effect.

Reward expectation modulates multiple stages of auditory conflict control.

Although mounting evidence has shown that reward can improve conflict control in the visual domain, little is known about whether and how reward affects conflict processing in the auditory domain. In the present study, we adopted an auditory Stroop task in which the meaning of a sound word ('male' or 'female') could be either congruent or incongruent with the gender of the voice (male or female speaker), and the participants were asked to discriminate the gender of the voice (the phonetic task) or the meaning of the word (the semantic task). Importantly, an auditory cue signalling a potential reward or no-reward for the current trial was presented prior to the sound word. In both tasks, relative to the congruent sound word, response to the incongruent sound word was delayed, i.e., an auditory Stroop effect. However, this auditory Stroop effect was reduced following a reward cue relative to a no-reward cue. Event-related potentials (ERPs) showed a stronger contingent negativity variation (CNV, 1000-1500 ms) for the reward cue than for the no-reward cue. The conflict negativity Ninc (300-400 ms) was more negative-going for the incongruent word than for the congruent word, but this effect was significantly reduced in the reward condition. However, the late positive complex (LPC) showed at most a weak reward modulation. These findings suggest that reward expectation improves auditory conflict control by modulating different stages of conflict processing: promoting better attentional preparation for the upcoming target (CNV), and facilitating conflict detection (Ninc) on the presentation of the target.

Reward enhances cross-modal conflict control in object categorization: Electrophysiological evidence.

Cross-modal conflict arises when information from different sensory modalities are incompatible with each other. Such conflict may influence the processing of stimuli in the task-relevant modality and call for cognitive control to resolve this conflict. Here, we investigate how reward modulates cross-modal conflict control during object categorization. Participants categorized pictures as representing animate or inanimate objects while ignoring auditory stimuli. We manipulated the audiovisual congruency and performance-dependent reward (reward vs. no-reward). Behavioral results showed a significant cross-modal interference effect only in the no-reward condition, not in the reward condition. Neurally, we found that the frontocentral N2and theta band oscillations were larger in the incongruent condition than in the congruent condition, but only when there was no reward for performance. The converging behavioral and electrophysiological evidence demonstrates that reward enhances cognitive control in a cross-modal context and reduces cross-modal conflict.

Reward interacts with modality shift to reduce cross-modal conflict.

Previous studies have shown that reward can enhance cognitive control and reduce conflict in visual processing. Here we investigate (a) whether and how reward influences cross-modal conflict control and (b) how the shift of attention across modalities modulates the effect of reward on cross-modal conflict control. In four experiments, a cue indicating the reward availability of a given trial (reward vs. no reward) was presented prior to a target. The target was either a visual or an auditory letter, which was accompanied by a distracting letter from the other modality. The identity of the distracting letter was either the same as or different from the identity of the target letter (congruent vs. incongruent). When the cue modality was constant (Experiment 1) or changed across different experimental blocks (Experiment 3), the interference effect (i.e., the response time difference between incongruent and congruent trials) was smaller following a reward cue than a no-reward cue, suggesting that reward can reduce cross-modal conflict. In contrast, when the cue modality was changed trial-by-trial in an unpredictable way (Experiments 2 and 4), reward reduced cross-modal conflict only when the cue and the target were from different modalities and had a long stimulus onset asynchrony (SOA) between them but not when they shared the same modality or had a short SOA between them. These results suggest that reward can facilitate cross-modal conflict resolution, and this effect may critically depend on both the preparatory state between the cue and the target and timing to initiate cognitive control.

Independent effects of reward expectation and spatial orientation on the processing of emotional facial expressions.

The present study investigated the effect of reward expectation and spatial orientation on the processing of emotional facial expressions, using a spatial cue-target paradigm. A colored cue was presented at the left or right side of the central fixation point, with its color indicating the monetary reward stakes of a given trial (incentive vs. non-incentive), followed by the presentation of an emotional facial target (angry vs. neutral) at a cued or un-cued location. Participants were asked to discriminate the emotional expression of the target, with the cue-target stimulus onset asynchrony being 200-300 ms in Experiment 1 and 950-1250 ms in Experiment 2a (without a fixation cue) and Experiment 2b (with a fixation cue), producing a spatial facilitation effect and an inhibition of return effect, respectively. The results of all the experiments revealed faster reaction times in the monetary incentive condition than in the non-incentive condition, demonstrating the effect of reward to facilitate task performance. An interaction between reward expectation and the emotion of the target was evident in all the three experiments, with larger reward effects for angry faces than for neutral faces. This interaction was not affected by spatial orientation. These findings demonstrate that incentive motivation improves task performance and increases sensitivity to angry faces, irrespective of spatial orienting and reorienting processes.

Task relevance regulates the interaction between reward expectation and emotion.

In the present study, we investigated the impact of reward expectation on the processing of emotional facial expression using a cue-target paradigm. A cue indicating the reward condition of each trial (incentive vs. non-incentive) was followed by the presentation of a picture of an emotional face, the target. Participants were asked to discriminate the emotional expression of the target face in Experiment 1, to discriminate the gender of the target face in Experiment 2, and to judge a number superimposed on the center of the target face as even or odd in Experiment 3, rendering the emotional expression of the target face as task relevant in Experiment 1 but task irrelevant in Experiments 2 and 3. Faster reaction times (RTs) were observed in the monetary incentive condition than in the non-incentive condition, demonstrating the effect of reward on facilitating task concentration. Moreover, the reward effect (i.e., RTs in non-incentive conditions versus incentive conditions) was larger for emotional faces than for neutral faces when emotional expression was task relevant but not when it was task irrelevant. The findings suggest that top-down incentive motivation biased attentional processing toward task-relevant stimuli, and that task relevance played an important role in regulating the influence of reward expectation on the processing of emotional stimuli.

Attentional selection within and across hemispheres: implications for the perceptual load theory.

The perceptual load of a given task affects attentional selection, with the selection occurring earlier when the load is high and later when the load is low. Recent evidence suggests that local competitive interaction may underlie the perceptual load effect and determine to what extent a task-irrelevant distractor is processed. Here, we asked participants to search for a target bar among homogeneously oriented bars (the low load conditions) or heterogeneously oriented bars (the high load conditions) in the central display, while ignoring a congruent or incongruent flanker bar presented to the left or right side of the central display, or a bar presented at one of the six positions outer to the central display. Importantly, we differentiated conditions in which the target in the central display and the peripheral flanker was presented within the same hemifield or across different hemifields. Results showed a significant flanker effect for the low load condition, but not for the high load condition, when the target and the flanker were across hemifields. However, when the target and the flanker were presented within the same hemifield, there was no flanker effect for either low or high load conditions. These findings demonstrate that the ability to ignore the task-irrelevant distractor is affected by local competition within hemisphere and that the perceptual load theory needs to be supplemented with detailed analysis of cognitive processes and mechanisms underlying the consumption of attentional resources.