Overt Visual Attention Research Articles

Dual-tasking impacts gait, cognitive performance, and gaze behavior during walking in a real-world environment in older adult fallers and non-fallers.

Everyday walking often involves simultaneous performance of a cognitive task in environments with competing auditory and visual stimuli. Previous research has not evaluated task performance in these situations, where older adults are known to fall, limiting our understanding of how older adults adjust their gait, visual scanning (gaze), and cognitive processing to avoid falls (or not). The purpose of this study was to examine the effect of dual-task walking in a high-distraction real-world environment on cognitive performance, gait performance, and gaze behavior in older adult fallers relative to non-fallers. Fourteen community-dwelling, older adult fallers (76.6±9.1years, 11 females) and 15 community-dwelling, older adult non-fallers (77.4±7.6years, 11 females) participated. Participants performed single-task walking, single-task cognitive (seated category naming), and dual-task walking (category naming + walking) trials for 1min each in a real-world environment (busy hospital lobby). Gait speed, stride length variability, stride duration variability, gaze fixation duration on 6 areas of interest (AOIs), and percentage of time fixating on 6 AOIs were recorded during single- and dual-task walking trials. Number of correct responses, time to first response, and mean subsequent response time (measure of rate of decline of response retrieval throughout trial) were determined for single-task cognitive and dual-task walking trials. Two-way MANCOVAs and MANOVAs were used to compare the effects of fall status and task condition on gait and cognitive variables. Hierarchical linear regression models were used to assess predictors of gaze behavior variables. Compared to single-task, during dual-task trials, participants walked 0.21m/s slower, had 1.5 fewer verbal responses, and a 2823ms shorter mean subsequent response time, indicating a faster declining rate of retrieval during the cognitive task. Additionally, during dual-task walking, participants fixated their gaze on Far People (AOI) for a significantly smaller percentage of time and on the Near Walking Path (AOI) for a significantly greater percentage of time than during single-task walking. During all trials, being a non-faller predicted a longer average fixation duration on the Far Environment (AOI) than for fallers. Environmental busyness, baseline gait speed, and baseline executive function impacted gaze behavior. All participants exhibited dual-task decrements in gait and cognitive performance and changes in gaze behavior from single- to dual-task walking. Perhaps of more importance, non-fallers appear to have had more freedom to divert their gaze to less relevant environmental stimuli while walking, and two measures of fall risk impacted patterns of gaze behavior differently. Thus, overt visual attention during walking in real-world environments should be further explored in relation to fall risk.

Attention allocation is a possible mediator of cultural variations in spontaneous trait and situation inferences: Eye-tracking evidence

Two studies sought to replicate previous work on cultural differences in the co-occurrence of spontaneous trait (STI) and situation (SSI) inferences, and to examine possible mediators at the individual level. Both studies replicated previous findings of cultural differences. European Americans made more STIs relative to SSIs than did Asian American or Japanese participants. However Experiment 1 found no evidence from the Analysis-Holism Scale (AHS) that self-reported cognitive style mediates this effect, although expected cultural differences on the AHS did occur. Experiment 2 found strong evidence that a bias in overt visual attention to actors relative to situations at encoding, measured with an eye-tracker, does predict a bias in STIs relative to SSIs. It also showed expected cultural differences in overt visual attention bias to actors relative to situations. These divergent results should sharpen conceptions of the role of holistic versus analytic cognition in the cross-cultural literature. They also provide the first evidence of possible mediators of STI and SSI within the false recognition paradigm. The role of visual attention in the production of perceptual and cognitive inferences is discussed.

Effects of an Unexpected and Expected Event on Older Adults' Autonomic Arousal and Eye Fixations During Autonomous Driving.

Driving cessation for some older adults can exacerbate physical, cognitive, and mental health challenges due to loss of independence and social isolation. Fully autonomous vehicles may offer an alternative transport solution, increasing social contact and encouraging independence. However, there are gaps in understanding the impact of older adults’ passive role on safe human–vehicle interaction, and on their well-being. 37 older adults (mean age ± SD = 68.35 ± 8.49 years) participated in an experiment where they experienced fully autonomous journeys consisting of a distinct stop (an unexpected event versus an expected event). The autonomous behavior of the vehicle was achieved using the Wizard of Oz approach. Subjective ratings of trust and reliability, and driver state monitoring including visual attention strategies (fixation duration and count) and physiological arousal (skin conductance and heart rate), were captured during the journeys. Results revealed that subjective trust and reliability ratings were high after journeys for both types of events. During an unexpected stop, overt visual attention was allocated toward the event, whereas during an expected stop, visual attention was directed toward the human–machine interface (HMI) and distributed across the central and peripheral driving environment. Elevated skin conductance level reflecting increased arousal persisted only after the unexpected event. These results suggest that safety-critical events occurring during passive fully automated driving may narrow visual attention and elevate arousal mechanisms. To improve in-vehicle user experience for older adults, a driver state monitoring system could examine such psychophysiological indices to evaluate functional state and well-being. This information could then be used to make informed decisions on vehicle behavior and offer reassurance during elevated arousal during unexpected events.

Blue blood, red blood. How does the color of an emotional scene affect visual attention and pupil size?

The function of color in the processing of emotional scenes is not entirely clear. While there are studies showing that color matters in terms of the capture of covert attention by emotional stimuli, the impact of color on fixation patterns, reflecting overt attention, is unresolved. Studies on the role of color in evoking emotional response have also produced mixed results. Here, we aimed to explore how image color and content influence pupillary response and the engagement of overt visual attention. In the first experiment, we examined the pupillary reaction to neutral images (intact and phase scrambled) in three color variants (natural, abnormal, and grayscale). In the second experiment, we investigated the pupillary changes and fixation pattern in response to images of different valence (neutral, positive, and negative), again in three color versions. The results showed that pupillary responses were influenced by both content and the color of the images. The pupillary response to phase-scrambled images did not differ between the color versions. Intact neutral and positive images, but not negative ones, evoked smaller pupil responses if they were presented in abnormal colors rather than natural ones. The initial capture of attention by emotional content depended on the color version, whereas holding of attention was affected solely by the emotional valence. Thus, color changes the physiological response to images, particularly low-arousing ones, and modulates the initial engagement of attention by image content.

Does visual attention to the instructor in online video affect learning and learner perceptions? An eye-tracking analysis

An increasing number of instructional videos online integrate a real instructor on the video screen. So far, the empirical evidence from previous studies has been limited and conflicting, and none of the studies have explored how learners' allocation of visual attention to the on-screen instructor influences learning and learner perceptions. Therefore, this study aimed to disentangle a) how instructor presence in online videos affects learning, learner perceptions (i.e., cognitive load, judgment of learning, satisfaction, situational interest), and visual attention distribution and b) to what extent visual attention patterns in instructor-present videos predict learning and learner perceptions. Sixty college students each watched two videos on Statistics, one on an easy topic and the other one on a difficult topic, with each in one of the two video formats: instructor-present or instructor-absent. Their eye movements were simultaneously registered using a desktop-mounted eye tracker. Afterwards, participants self-reported their cognitive load, judgment of learning, satisfaction, and situational interest for both videos, and feelings toward seeing the instructor for the instructor-present videos. Learning from the two videos was measured using retention and transfer questions. Findings indicated instructor presence a) improved transfer performance for the difficult topic, b) reduced cognitive load for the difficult topic, c) increased judgment of learning for the difficult topic, and d) enhanced satisfaction and situational interest for both topics. Most participants expressed a positive feeling toward the instructor. Results also showed the instructor attracted a considerable amount of overt visual attention in both videos, and the amount of attention allocated to the instructor positively predicted participants’ satisfaction level for both topics.

Eye tracking use in researching driver distraction: A scientometric and qualitative literature review approach

Many factors affect road safety, but research constantly shows that drivers are the major cause of critical situations that could potentially lead to a traffic accident in road traffic. Visual information is a crucial part of input information into the driving process; therefore, distractions of overt visual attention can potentially have a large impact on driving safety. Modern eye tracking technology enables researchers to gain precise insight into the direction and movement of a driver’s gaze during various distractions. As this is an evolving and currently very relevant field of road safety research, the present paper sets out to analyse the current state of the research field and the most relevant publications that use eye tracking for research of distractions to a driver’s visual attention. With the use of scientometrics and a qualitative review of the 139 identified publications that fit the inclusion criteria, the results revealed a currently expanding research field. The narrow research field is interdisciplinary in its core, as evidenced by the dispersion of publication sources and research variables. The main research gaps identified were performing research in real conditions, including a wider array of distractions, a larger number of participants, and increasing interdisciplinarity of the field with more author cooperation outside of their primary co-authorship networks.

Degree of Language Experience Modulates Visual Attention to Visible Speech and Iconic Gestures During Clear and Degraded Speech Comprehension.

Visual information conveyed by iconic hand gestures and visible speech can enhance speech comprehension under adverse listening conditions for both native and non‐native listeners. However, how a listener allocates visual attention to these articulators during speech comprehension is unknown. We used eye‐tracking to investigate whether and how native and highly proficient non‐native listeners of Dutch allocated overt eye gaze to visible speech and gestures during clear and degraded speech comprehension. Participants watched video clips of an actress uttering a clear or degraded (6‐band noise‐vocoded) action verb while performing a gesture or not, and were asked to indicate the word they heard in a cued‐recall task. Gestural enhancement was the largest (i.e., a relative reduction in reaction time cost) when speech was degraded for all listeners, but it was stronger for native listeners. Both native and non‐native listeners mostly gazed at the face during comprehension, but non‐native listeners gazed more often at gestures than native listeners. However, only native but not non‐native listeners' gaze allocation to gestures predicted gestural benefit during degraded speech comprehension. We conclude that non‐native listeners might gaze at gesture more as it might be more challenging for non‐native listeners to resolve the degraded auditory cues and couple those cues to phonological information that is conveyed by visible speech. This diminished phonological knowledge might hinder the use of semantic information that is conveyed by gestures for non‐native compared to native listeners. Our results demonstrate that the degree of language experience impacts overt visual attention to visual articulators, resulting in different visual benefits for native versus non‐native listeners.

Conditioned anticipatory outcome searching in humans

Two experiments used eye tracking to examine visual searching for expected outcomes in humans during an associative-learning task. In both, participants learned to press keys on a keyboard to activate weapons to repel invading spaceships in the presence of predictive “sensors.” In both experiments, eye tracking showed that participants came to direct their overt visual attention to the portions of the screen where the spaceship would arrive during the presentation of the sensor in a cue-specific manner. Participants also directed attention to the weapon that was used to repel the spaceship. The same results were observed regardless of whether participants were responding on the keyboard, or not (Experiment 2). Pupil dilations occurred to the appearance of the spaceship from the first trial and occurred to the predictive sensor stimuli on later trials in both experiments, suggesting that they might be conditioned responses. In Experiment 2 participants again looked for the expected outcome, but dilations to the predictive stimuli were shown to be an artifact of responding and not due to conditioning. The discussion involves the implications for investigating attention to predictive stimuli using eye trackers, roles of context in behavior, and the utility of outcome searching and pupil dilations as indexes of learning.

A human behavior model of multi-agent attention based on actor–observer switching for asynchronous motion tasks with limited field of view

This paper presents an overt visual attention approach for multi-agent systems and asynchronous motion tasks with limited field of view based on human behavior. In a first step, results from a study on human temporal attention switching during a formation task are presented. Three temporally switching human behaviors (observer, actor, idler) are identified and characterized towards distributions of attention foci. In a second step, based on these results, a behavior switching attention strategy is proposed. The strategy is evaluated in simulations of various formation task scenarios illustrating the effectiveness of the approach.

Visual scanning behavior during distracted walking in healthy young adults

BackgroundAn epidemic of pedestrian accidents when walking while texting suggests that people are less aware of their surroundings during distracted walking, and highlights the importance of visual scanning for pedestrian safety. Quantitative examination of visual scanning during distracted walking is still lacking. Research questionIs visual scanning behavior altered by distracted walking in healthy young adults? MethodsWe compared visual scanning behavior in 20 young adults during usual (single-task) walking, walking while performing a letter-fluency task, and walking while texting. Visual scanning behavior was measured by fixation count and dwell time percentage in specific areas of interest. Dual-task effects on gait speed, letter fluency, texting speed and accuracy, and situational awareness were also examined. ResultVisual scanning behavior differed between the three walking conditions. During dual-task letter fluency, participants had significantly more non-walking path fixations than either of the other two conditions (i.e., more frequent, broader visual scanning). Conversely, during dual-task texting, gaze was focused predominantly on the phone, with little visual scanning of the walking path and surrounding environment. When walking without texting or talking, gaze was directed equally to far walking path and surrounding environment. SignificanceTexting while walking is associated with a considerable reduction in overt visual attention to the walking path and surrounding areas. Whether this translates to reduced conscious awareness of environmental stimuli remains unclear. Performing a verbal task while walking was associated with more frequent, wider visual scanning behavior, which may be specific to the nature of the verbal task in this study.

Examining sensory ability, feature matching and assessment-based adaptation for a brain–computer interface using the steady-state visually evoked potential

Purpose: We investigated how overt visual attention and oculomotor control influence successful use of a visual feedback brain-computer interface (BCI) for accessing augmentative and alternative communication (AAC) devices in a heterogeneous population of individuals with profound neuromotor impairments. BCIs are often tested within a single patient population limiting generalization of results. This study focuses on examining individual sensory abilities with an eye toward possible interface adaptations to improve device performance.Methods: Five individuals with a range of neuromotor disorders participated in four-choice BCI control task involving the steady state visually evoked potential. The BCI graphical interface was designed to simulate a commercial AAC device to examine whether an integrated device could be used successfully by individuals with neuromotor impairment.Results: All participants were able to interact with the BCI and highest performance was found for participants able to employ an overt visual attention strategy. For participants with visual deficits to due to impaired oculomotor control, effective performance increased after accounting for mismatches between the graphical layout and participant visual capabilities.Conclusion: As BCIs are translated from research environments to clinical applications, the assessment of BCI-related skills will help facilitate proper device selection and provide individuals who use BCI the greatest likelihood of immediate and long term communicative success. Overall, our results indicate that adaptations can be an effective strategy to reduce barriers and increase access to BCI technology. These efforts should be directed by comprehensive assessments for matching individuals to the most appropriate device to support their complex communication needs.Implications for RehabilitationBrain computer interfaces using the steady state visually evoked potential can be integrated with an augmentative and alternative communication device to provide access to language and literacy for individuals with neuromotor impairment.Comprehensive assessments are needed to fully understand the sensory, motor, and cognitive abilities of individuals who may use brain-computer interfaces for proper feature matching as selection of the most appropriate device including optimization device layouts and control paradigms.Oculomotor impairments negatively impact brain-computer interfaces that use the steady state visually evoked potential, but modifications to place interface stimuli and communication items in the intact visual field can improve successful outcomes.

Cultural and Developmental Influences on Overt Visual Attention to Videos

Top-down influences on observers’ overt attention and how they interact with the features of the visual environment have been extensively investigated, but the cultural and developmental aspects of these modulations have been understudied. In this study we investigated these effects for US and Yucatec Mayan infants, children, and adults. Mayan and US participants viewed videos of two actors performing daily Mayan and US tasks in the foreground and the background while their eyes were tracked. Our region of interest analysis showed that viewers from the US looked significantly less at the foreground activity and spent more time attending to the ‘contextual’ information (static background) compared to Mayans. To investigate how and what visual features of videos were attended to in a comprehensive manner, we used multivariate methods which showed that visual features are attended to differentially by each culture. Additionally, we found that Mayan and US infants utilize the same eye-movement patterns in which fixation duration and saccade amplitude are altered in response to the visual stimuli independently. However, a bifurcation happens by age 6, at which US participants diverge and engage in eye-movement patterns where fixation durations and saccade amplitudes are altered simultaneously.

Gain/Loss Framing Effects on Learning in Economic Decision Making Investigated with Eye Tracking

Previous research has revealed a domain-based bias when people estimate payout likelihoods for probabilistic choice options that minimize losses versus those that maximize gains (Kuhnen, 2015). For...

Evaluation of the Psychometric Properties of the Gap‐Overlap Task in 10‐Month‐Old Infants

Understanding the development of attention is key to understanding cognitive maturation. The gap‐overlap task can be administered at all ages and is widely used to study the development of overt visual attention. However, studies using the gap‐overlap task report different measures and little is known about the tasks’ psychometric properties, especially in infants. We tested the 1‐week test–retest reliability of two frequently used gap‐overlap measures of attentional disengagement in 10‐month‐old infants; the gap effect as measured by the difference between the gap and overlap condition and the gap effect as measured by the difference between the gap and baseline condition. Sixty‐seven infants performed the gap‐overlap task twice, of which 45 infants had sufficient data quality for further analyses. Test–retest reliability of the overlap‐gap gap effect was higher (r = .50) than the baseline‐gap gap effect (r = .29). Moreover, the shared variance between overlap and baseline saccadic reaction times was moderate to high across sessions. In light of these results and the methodological challenges and limitations of infant research, we consider the overlap‐gap gap effect to be a good measure to study the development of attentional disengagement in infants and suggest the exclusion of the baseline condition in future studies.

Adding Shape to Saliency: A Proto-object Saliency Map for Predicting Fixations during Scene Viewing

Traditional saliency models predict fixations during scene viewing by computing local contrast between low-level color, intensity and orientation features; the higher the summed contrast the greater the probability of fixation. Evidence also suggests that high-level properties of objects are predictive of fixation locations. We attempt fixation prediction from proto-objects (POs), a mid-level representation existing between features and objects. Using our previously-reported proto-object model (Yu et. al., 2014, JoV), we segmented 384 images of real-world scenes into proto-objects, fragments of visual space, at multiple resolutions (feature-space bandwidths). We then built from these segmentations a saliency map by computing feature contrast between each proto-object and its local neighbors using intensity, color, orientation, and now, size and shape features. Center-surround size contrast was computed by comparing pixel area between a given proto-object and each "surrounding" neighbor. To compute shape contrast we first normalized a proto-object and a neighbor to have the same area, aligned them based on maximum area-overlap, then counted the number of pixels in the overlapping area (divided by the union of the areas), with a smaller overlap over neighbors coding a higher contrast. Doing this relative to each proto-object, then combining contrast signals across features and resolutions, generates a proto-object saliency map, which we used to predict the fixation behavior of 12 participants freely viewing the same scenes (each for 3 seconds) in anticipation of a memory test. We found that our proto-object saliency map predicted fixations as well or better than an Itti-Koch saliency model, and was nearly as predictive as the upper-limit defined by a Subject model obtained using the leave-one-out method. We conclude that size and shape features, quantified in terms of proto-objects, are used to guide overt visual attention, and that saliency-based models of fixation prediction need to recognize the importance of these mid-level visual features. Meeting abstract presented at VSS 2016

The µ-opioid system promotes visual attention to faces and eyes.

Paying attention to others' faces and eyes is a cornerstone of human social behavior. The µ-opioid receptor (MOR) system, central to social reward-processing in rodents and primates, has been proposed to mediate the capacity for affiliative reward in humans. We assessed the role of the human MOR system in visual exploration of faces and eyes of conspecifics. Thirty healthy males received a novel, bidirectional battery of psychopharmacological treatment (an MOR agonist, a non-selective opioid antagonist, or placebo, on three separate days). Eye-movements were recorded while participants viewed facial photographs. We predicted that the MOR system would promote visual exploration of faces, and hypothesized that MOR agonism would increase, whereas antagonism decrease overt attention to the information-rich eye region. The expected linear effect of MOR manipulation on visual attention to the stimuli was observed, such that MOR agonism increased while antagonism decreased visual exploration of faces and overt attention to the eyes. The observed effects suggest that the human MOR system promotes overt visual attention to socially significant cues, in line with theories linking reward value to gaze control and target selection. Enhanced attention to others' faces and eyes represents a putative behavioral mechanism through which the human MOR system promotes social interest.

Can’t Take My Eyes Off of You: Eye Tracking Reveals How Ruminating Young Adolescents Get Stuck

Rumination, a cognitive process that involves passively, repetitively focusing on negative feelings and their meaning, is a transdiagnostic risk factor for psychopathology. Research with adults has suggested that attentional control difficulties may underlie rumination, but questions remain about the nature of these processes. Furthermore, the relationship between attentional control and rumination in youth has received little empirical examination. In the present study, 92 youth (ages 9–14; 72% girls; 74% Caucasian) reported on their trait rumination and internalizing symptoms. They also completed a 1,500 ms emotional-faces dot-probe task while their eye movements were measured to examine overt visual attention with high temporal precision. Youth’s rumination was associated with greater dwell on emotional faces but not with initial orientation. These findings suggest that rumination is associated with increased attention to emotional information during the later stages of selective attention rather than earlier orienting to emotional cues. Implications for prevention and treatment of psychopathology are discussed.

Gaze behavior when approaching an intersection: Dwell time distribution and comparison with a quantitative prediction

The allocation of overt visual attention is investigated in a multi-task and dynamical situation: driving. The Expectancy–Value model of attention allocation stipulates that visual exploration depends on the expectancy and the value of the task-related information available in each Area Of Interest (AOI). We consider the approach to an intersection as a multi-task situation where two subtasks are involved: vehicle control and interactions with other drivers. Each of these subtasks is associated with some specific visual information present in the associated AOIs: the driver’s lane and the intersecting road at the intersection. An experiment was conducted in a driving simulator, coupled with a head-mounted eye-tracker. The intersecting road’s AOI’s Expectancy was manipulated with the traffic density, and its Value was manipulated with the priority rule before the intersection (stop, yield, and priority). The distribution of visual attention and the dynamics of visual exploration were analyzed on 20 participants, taking into account the dwell time in the AOIs associated to the driving subtasks, and the gaze transitions between the AOIs. The results suggest that visual attention to intersecting roads varied with the priority rule, and impacted the visual attention associated with the vehicle control subtask. In addition, a quantitative model was used to improve the understanding of the Expectancy and Value factors. The comparison of the data with the model’s predictions enables quantifying the observed differences between the experimental factors. Finally, the results associated with the traffic density are discussed in relation to the nature of the relevant information while approaching the intersection.

Using Experts' Eye Movements to Influence Scanning Behaviour in Novice Drivers

In many areas, experts often exhibit specialised eye movement behaviour which allows for more efficient task execution than novices. In some areas (e.g. Radiology), showing this pattern of eye movement behaviour to novices can help cue overt visual attention to more relevant areas; which allows for more efficient task completion. We present a study which investigated the effects of eye movement cueing in a dynamic task - that of driving. The aim was to investigate whether a more efficient visual search pattern (e.g. increased scanning of the road, increased use of mirrors) could be induced in novice drivers if they are shown eye movements of expert drivers, when driving in a simulated environment. One group of participants (eye movement condition) were asked to drive a set of courses in a driving simulator programme whilst their eye movements were tracked. After one week, this group was shown two five minute videos of an expert's drive with the corresponding eye movements overlaid. Participants were then asked to drive the three courses again whilst their eye movements were tracked. Another group of participants (control) were asked to complete similar drives (one week a part also) but were not shown eye movements. After the second driving session, those in the eye movement condition exhibited increased horizontal scanning of the road, larger saccade sizes and showed an increased use of their mirrors as measured by total dwell time and total fixation counts. The control group showed no such improvement in visual strategies. These beneficial eye movement patterns were retained after a six month follow-up. The results show that eye movement cueing can be used to train more efficient search strategies in a dynamic task such as driving. The current results highlight a possible training intervention which could be introduced to educate early-stage drivers. Meeting abstract presented at VSS 2015. Language: en

Loneliness and hypervigilance to social cues in females: an eye-tracking study.

The goal of the present study was to examine whether lonely individuals differ from nonlonely individuals in their overt visual attention to social cues. Previous studies showed that loneliness was related to biased post-attentive processing of social cues (e.g., negative interpretation bias), but research on whether lonely and nonlonely individuals also show differences in an earlier information processing stage (gazing behavior) is very limited. A sample of 25 lonely and 25 nonlonely students took part in an eye-tracking study consisting of four tasks. We measured gazing (duration, number of fixations and first fixation) at the eyes, nose and mouth region of faces expressing emotions (Task 1), at emotion quadrants (anger, fear, happiness and neutral expression) (Task 2), at quadrants with positive and negative social and nonsocial images (Task 3), and at the facial area of actors in video clips with positive and negative content (Task 4). In general, participants tended to gaze most often and longest at areas that conveyed most social information, such as the eye region of the face (T1), and social images (T3). Participants gazed most often and longest at happy faces (T2) in still images, and more often and longer at the facial area in negative than in positive video clips (T4). No differences occurred between lonely and nonlonely participants in their gazing times and frequencies, nor at first fixations at social cues in the four different tasks. Based on this study, we found no evidence that overt visual attention to social cues differs between lonely and nonlonely individuals. This implies that biases in social information processing of lonely individuals may be limited to other phases of social information processing. Alternatively, biased overt attention to social cues may only occur under specific conditions, for specific stimuli or for specific lonely individuals.