Passive Control Condition Research Articles

"Everybody brush!": protocol for a parallel-group randomized controlled trial of a family-focused primary prevention program with distribution of oral hygiene products and education to increase frequency of toothbrushing.

BackgroundTwice daily toothbrushing with fluoridated toothpaste is the most widely advocated preventive strategy for dental caries (tooth decay) and is recommended by professional dental associations. Not all parents, children, or adolescents follow this recommendation. This protocol describes the methods for the implementation and evaluation of a quality improvement health promotion program.ObjectiveThe objective of the study is to show a theory-informed, evidence-based program to improve twice daily toothbrushing and oral health-related quality of life that may reduce dental caries, dental treatment need, and costs.MethodsThe design is a parallel-group, pragmatic randomized controlled trial. Families of Medicaid-insured children and adolescents within a large dental care organization in central Oregon will participate in the trial (n=21,743). Families will be assigned to one of three groups: a test intervention, an active control, or a passive control condition. The intervention aims to address barriers and support for twice-daily toothbrushing. Families in the test condition will receive toothpaste and toothbrushes by mail for all family members every three months. In addition, they will receive education and social support to encourage toothbrushing via postcards, recorded telephone messages, and an optional participant-initiated telephone helpline. Families in the active control condition will receive the kit of supplies by mail, but no additional instructional information or telephone support. Families assigned to the passive control will be on a waiting list. The primary outcomes are restorative dental care received and, only for children younger than 36 months old at baseline, the frequency of twice-daily toothbrushing. Data will be collected through dental claims records and, for children younger than 36 months old at baseline, parent interviews and clinical exams.ResultsEnrollment of participants and baseline interviews have been completed. Final results are expected in early summer, 2017.ConclusionsIf proven effective, this simple intervention can be sustained by the dental care organization and replicated by other organizations and government.Trial RegistrationTrial Registration: ClinicalTrials.gov NCT02327507; http://clinicaltrials.gov/ct2/show/NCT02327507 (Archived by WebCite at http://www.webcitation.org/6YCIxJSor).

Successful balance training is associated with improved multisensory function in fall-prone older adults

Balance maintenance relies on a complex interplay between many different sensory modalities. Although optimal multisensory processing is thought to decline with ageing, inefficient integration is particularly associated with falls in older adults. We investigated whether improved balance control, following a novel balance training intervention, was associated with more efficient multisensory integration in older adults, particularly those who have fallen in the past. Specifically, 76 healthy and fall-prone older adults were allocated to either a balance training programme conducted over 5weeks or to a passive control condition. Balance training involved a VR display in which the on-screen position of a target object was controlled by shifts in postural balance on a Wii balance board. Susceptibility to the sound-induced flash illusion, before and after the intervention (or control condition), was used as a measure of multisensory function. Whilst balance and postural control improved for all participants assigned to the Intervention group, improved functional balance was correlated with more efficient multisensory processing in the fall-prone older adults only. Our findings add to growing evidence suggesting important links between balance control and multisensory interactions in the ageing brain and have implications for the development of interventions designed to reduce the risk of falls.

A Comparison of the Attentional Effects of Single-Session Mindfulness Meditation and Fp-HEG Neurofeedback in Novices

The efficacy of mindfulness meditation (MM) relative to prefrontal hemoencephalography (Fp-HEG) neurofeedback (NFB) for enhancing attentional functioning and increasing Fp-HEG has not been studied. Moreover, few measures exist for assessing attentional capacities during MM. In the present study, we therefore randomized participants to MM (n = 23), NFB (n = 26), or a passive counting backward control condition (n = 21) and measured Fp-HEG at the frontal pole during a pretreatment baseline, during each of the 15-min interventions (MM, NFB, or control) and during subsequent performance of the Attentional Network Test (ANT). Meditation Breath Attention Scores (MBAS) were also assessed in the MM group as a measure of individual differences in the ability to sustain attention to breathing (i.e., to disengage from mind wandering) during MM, and a comparable Counting Backward Attention Score (CBAS) was assessed in the counting control group. Relative to baseline, Fp-HEG was reduced during interventions, as well as during ANT performance, across groups, with no significant differences between groups. NFB participants evidenced improved ANT accuracy relative to control, with MM not differing from NFB or control. Increased accuracy during the ANT was correlated with increasing Fp-HEG across groups. Within the MM group, increased MBAS were also associated with increased ANT accuracy as well as slower ANT orienting. CBAS were marginally higher than MBAS, indicating that sustaining attention to backward counting may have been easier than sustaining attention to breath sensation. We conclude that a single session of Fp-HEG may be effective in improving attention whereas the benefits of MM may require multiple sessions. We also infer that mindful concentration during meditation may be associated with general attentional capacities. Replication and longitudinal extension in larger samples are needed.

Making Working Memory Work: A Meta-Analysis of Executive-Control and Working Memory Training in Older Adults

This meta-analysis examined the effects of process-based executive-function and working memory training (49 articles, 61 independent samples) in older adults (> 60 years). The interventions resulted in significant effects on performance on the trained task and near-transfer tasks; significant results were obtained for the net pretest-to-posttest gain relative to active and passive control groups and for the net effect at posttest relative to active and passive control groups. Far-transfer effects were smaller than near-transfer effects but were significant for the net pretest-to-posttest gain relative to passive control groups and for the net gain at posttest relative to both active and passive control groups. We detected marginally significant differences in training-induced improvements between working memory and executive-function training, but no differences between the training-induced improvements observed in older adults and younger adults, between the benefits associated with adaptive and nonadaptive training, or between the effects in active and passive control conditions. Gains did not vary with total training time.

Longitudinal assessment of default-mode brain function in aging

Age-related changes in the default-mode network (DMN) have been identified in prior cross-sectional functional magnetic resonance imaging studies. Here, we investigated longitudinal change in DMN activity and connectivity. Cognitively intact participants (aged 49–79 years at baseline) were scanned twice, with a 6-year interval, while performing an episodic memory task interleaved with a passive control condition. Longitudinal analyses showed that the DMN (control condition > memory task) could be reliably identified at both baseline and follow-up. Differences in the magnitude of task-induced deactivation in posterior DMN regions were observed between baseline and follow-up indicating reduced deactivation in these regions with increasing age. Although no overall longitudinal changes in within-network connectivity were found across the whole sample, individual differences in memory change correlated with change in connectivity. Thus, our results show stability of whole-brain DMN topology and functional connectivity over time in healthy older adults, whereas within-region DMN analyses show reduced deactivation between baseline and follow-up. The current findings provide novel insights into DMN functioning that may assist in identifying brain changes in patient populations, as well as characterizing factors that distinguish between normal and pathologic aging.

Is skills training necessary for the primary prevention of marital distress and dissolution? A 3-year experimental study of three interventions.

Evidence in support of skill-based programs for preventing marital discord and dissolution, while promising, comes mainly from studies using single treatment conditions, passive assessment-only control conditions, and short-term follow-up assessments of relationship outcomes. This study overcomes these limitations and further evaluates the efficacy of skill-based programs. Engaged and newlywed couples (N = 174) were randomly assigned to a 4-session, 15-hr small-group intervention designed to teach them skills in managing conflict and problem resolution (PREP) or skills in acceptance, support, and empathy (CARE). These couples were compared to each other, to couples receiving a 1-session relationship awareness (RA) intervention with no skill training, and to couples receiving no treatment on 3-year rates of dissolution and 3-year trajectories of self-reported relationship functioning. Couples in the no-treatment condition dissolved their relationships at a higher rate (24%) than couples completing PREP, CARE, and RA, who did not differ on rates of dissolution (11%). PREP and CARE yielded unintended effects on 3-year changes in reported relationship behaviors. For example, wives receiving PREP showed slower declines in hostile conflict than wives receiving CARE, and husbands and wives receiving CARE showed faster declines in positive behaviors than husbands and wives receiving PREP. These findings highlight the potential value of cost-effective interventions such as RA, cast doubt on the unique benefits of skill-based interventions for primary prevention of relationship dysfunction, and raise the possibility that skill-based interventions may inadvertently sensitize couples to skill deficits in their relationships.

Selective transfer of visual working memory training on Chinese character learning

Previous research has shown a systematic relationship between phonological working memory capacity and second language proficiency for alphabetic languages. However, little is known about the impact of working memory processes on second language learning in a non-alphabetic language such as Mandarin Chinese. Due to the greater complexity of the Chinese writing system we expect that visual working memory rather than phonological working memory exerts a unique influence on learning Chinese characters. This issue was explored in the present experiment by comparing visual working memory training with an active (auditory working memory training) control condition and a passive, no training control condition. Training induced modulations in language-related brain networks were additionally examined using functional magnetic resonance imaging in a pretest-training-posttest design. As revealed by pre- to posttest comparisons and analyses of individual differences in working memory training gains, visual working memory training led to positive transfer effects on visual Chinese vocabulary learning compared to both control conditions. In addition, we found sustained activation after visual working memory training in the (predominantly visual) left infero-temporal cortex that was associated with behavioral transfer. In the control conditions, activation either increased (active control condition) or decreased (passive control condition) without reliable behavioral transfer effects. This suggests that visual working memory training leads to more efficient processing and more refined responses in brain regions involved in visual processing. Furthermore, visual working memory training boosted additional activation in the precuneus, presumably reflecting mental image generation of the learned characters. We, therefore, suggest that the conjoint activity of the mid-fusiform gyrus and the precuneus after visual working memory training reflects an interaction of working memory and imagery processes with complex visual stimuli that fosters the coherent synthesis of a percept from a complex visual input in service of enhanced Chinese character learning.

Acute effect of exercise on alcohol urges and attentional bias towards alcohol related images in high alcohol consumers

BackgroundShort bouts of exercise can reduce cravings, attentional bias (AB) and substance use among abstaining smokers and snackers. Only one study has shown reduced alcohol cravings following exercise but none have investigated the effects on attentional bias. The aim of the present study was to examine whether a single session of exercise reduces AB towards alcohol-related images and alcohol urges among high alcohol consumers. MethodsThe study involved 20 abstaining (for ≥3 days) alcohol drinkers, consuming more than weekly recommendations, with a mean age (SD) = 20.8 (0.8) years. Participants were initially randomised in a counterbalanced cross-over design to undertake either (1) 15 min of brisk walking or (2) 15 min of passive seating on different days. Participants completed an adapted dot probe task, with matched neutral and alcohol images randomly presented for either 200 ms or 1000 ms to respectively measure initial (IAB) or maintained attentional bias (MAB) pre- and post-treatment. The Alcohol Urge Questionnaire (AUQ) was administered before, immediately after, and 5 and 10 min post treatment. ResultsA two-way fully repeated measures ANOVA revealed a significant condition × time interaction for MAB F(1, 17) = 6.96, p = 0.017, and AUQ scores F(1.47, 27.96) = 60.19, p < 0.001. MAB was significantly reduced following the exercise compared with the control condition. Differences in AUQ between conditions were significant at all assessments post treatment. ConclusionsA short bout of exercise, compared with a passive control condition, may acutely reduce MAB to alcohol cues and alcohol urges, and thus may help with self-regulation of alcohol consumption.

Impact of aerobic exercise intensity on craving and reactivity to smoking cues.

Aerobic exercise can acutely reduce cigarette cravings during periods of nicotine deprivation. The primary aim of this study was to assess the differential effects of light and vigorous intensity aerobic exercise on cigarette cravings, subjective and physiological reactivity to smoking cues, and affect after overnight nicotine deprivation. A secondary aim was to examine cortisol change as a mediator of the effects of exercise on smoking motivation. 162 (55 female, 107 male) overnight nicotine-deprived smokers were randomized to one of three exercise conditions: light intensity, vigorous intensity, or a passive control condition. After each condition, participants engaged in a standardized cue reactivity assessment. Self-reported urges to smoke, affect, and salivary cortisol were assessed at baseline (i.e., before each condition), immediately after each condition, and after the cue reactivity assessment. Light and vigorous exercise significantly decreased urges to smoke and increased positive affect, relative to the control condition. In addition, those in the vigorous exercise condition demonstrated suppressed appetitive reactivity to smoking cues, as indexed by the startle eyeblink reflex. Although exercise intensity was associated with expected changes in cortisol concentration, these effects were not related to changes in craving or cue reactivity. Both light and vigorous exercise can reduce general cravings to smoke, whereas vigorous exercise appears especially well-suited for reducing appetitive reactions to cues that may precede smoking. Results did not support exercise-induced cortisol release as a mechanism for these effects.

The acute effects of exercise on cigarette cravings, withdrawal symptoms, affect, and smoking behaviour: systematic review update and meta-analysis

Smoking cessation is associated with cigarette cravings and tobacco withdrawal symptoms (TWS), and exercise appears to ameliorate many of these negative effects. A number of studies have examined the relationships between exercise, cigarette cravings, and TWS. The objectives of this study were (a) to review and update the literature examining the effects of short bouts of exercise on cigarette cravings, TWS, affect, and smoking behaviour and (b) to conduct meta-analyses of the effect of exercise on cigarette cravings. A systematic review of all studies published between January 2006 and June 2011 was conducted. Fifteen new studies were identified, 12 of which found a positive effect of exercise on cigarette cravings. The magnitude of statistically significant effect sizes for 'desire to smoke' and 'strength of desire to smoke' ranged from 0.4 to 1.98 in favour of exercise compared to passive control conditions, and peaked either during or soon after treatment. Effects were found up to 30min post-exercise. Cigarette cravings were reduced following exercise with a wide range of intensities from isometric exercise and yoga to activity as high as 80-85% heart rate reserve. Meta-analyses revealed weighted mean differences of -1.90 and -2.41 in 'desire to smoke' and 'strength of desire to smoke' outcomes, respectively. Measures of TWS and negative affect were reduced following light-moderate intensity exercise, but increased during vigorous exercise. Exercise can have a positive effect on cigarette cravings and TWS. However, the most effective exercise intensity to reduce cravings and the underlying mechanisms associated with this effect remain unclear.

The impact of auditory working memory training on the fronto-parietal working memory network

Working memory training has been widely used to investigate working memory processes. We have shown previously that visual working memory benefits only from intra-modal visual but not from across-modal auditory working memory training. In the present functional magnetic resonance imaging study we examined whether auditory working memory processes can also be trained specifically and which training-induced activation changes accompany theses effects. It was investigated whether working memory training with strongly distinct auditory materials transfers exclusively to an auditory (intra-modal) working memory task or whether it generalizes to a (across-modal) visual working memory task. We used adaptive n-back training with tonal sequences and a passive control condition. The memory training led to a reliable training gain. Transfer effects were found for the (intra-modal) auditory but not for the (across-modal) visual transfer task. Training-induced activation decreases in the auditory transfer task were found in two regions in the right inferior frontal gyrus. These effects confirm our previous findings in the visual modality and extents intra-modal effects in the prefrontal cortex to the auditory modality. As the right inferior frontal gyrus is frequently found in maintaining modality-specific auditory information, these results might reflect increased neural efficiency in auditory working memory processes. Furthermore, task-unspecific (amodal) activation decreases in the visual and auditory transfer task were found in the right inferior parietal lobule and the superior portion of the right middle frontal gyrus reflecting less demand on general attentional control processes. These data are in good agreement with amodal activation decreases within the same brain regions on a visual transfer task reported previously.

No temporal binding of action consequences to actions in a rhythmic context

Temporal binding (TB) refers to a subjective contraction of the time that elapses between an action and a delayed sensory consequence of it. The TB effect has been demonstrated primarily in tasks in which a key press triggers a tone after a short delay and in which participants judge the timing of one or both of these events relative to a visual reference (e.g., a rotating clock hand). In the present Experiments 1 and 2, musicians listened instead to an auditory "clock" (a metronome) and occasionally made a tap that triggered a delayed tone. The task was to judge whether that test tone fell before, on, or after the midpoint of the interval between two metronome tones. In a passive control condition, participants judged test tones but did not tap. The hypothesis was that the test tone would be perceived as occurring earlier in the active than in the passive condition. However, there was no difference in perceptual judgments. Experiment 3 used a visual metronome as the reference but again obtained negative results, despite greater uncertainty of judgments. It is suggested that TB of action consequences to actions does not occur when the reference signal is rhythmic because such a context enables participants (musicians, at least) to perceive and judge the actual time of occurrence of the action-triggered tone.

Effects of relaxation on psychobiological wellbeing during pregnancy: A randomized controlled trial

Prenatal maternal stress is associated with adverse birth outcomes and may be reduced by relaxation exercises. The aim of the present study was to compare the immediate effects of two active and one passive 10-min relaxation technique on perceived and physiological indicators of relaxation. 39 healthy pregnant women recruited at the outpatient department of the University Women's Hospital Basel participated in a randomized controlled trial with an experimental repeated measure design. Participants were assigned to one of two active relaxation techniques, progressive muscle relaxation (PMR) or guided imagery (GI), or a passive relaxation control condition. Self-reported relaxation on a visual analogue scale (VAS) and state anxiety (STAI-S), endocrine parameters indicating hypothalamic-pituitary-adrenal (HPA) axis (cortisol and ACTH) and sympathetic-adrenal-medullary (SAM) system activity (norepinephrine and epinephrine), as well as cardiovascular responses (heart rate, systolic and diastolic blood pressure) were measured at four time points before and after the relaxation exercise. Between group differences showed, that compared to the PMR and control conditions, GI was significantly more effective in enhancing levels of relaxation and together with PMR, GI was associated with a significant decrease in heart rate. Within the groups, passive as well as active relaxation procedures were associated with a decline in endocrine measures except epinephrine. Taken together, these data indicate that different types of relaxation had differential effects on various psychological and biological stress systems. GI was especially effective in inducing self-reported relaxation in pregnant women while at the same time reducing cardiovascular activity.

Evidence that boosters augment the long-term impact of implementation intentions on fruit and vegetable intake

The present study tests the efficacy of a single implementation intention to increase intake over a 6-month period, and investigates whether deploying a second implementation intention at 3 months can sustain the long-term impact, compared with passive and active control groups. Participants (N = 650) completed single-item and FFQ measures of behaviour and motivation at baseline before being randomised to one of six conditions in a between-persons design. Intention to treat analysis revealed that for the single-item measure: (1) a single implementation intention is an effective means of initiating fruit and vegetable increase over a 3-month period, but this effect is not sustained over 6 months; (2) administering a second implementation intention at 3 months was successful in increasing intake over 6 months, and acted as a booster on the initial impact; and (3) neither the passive nor active control condition had any impact on behaviour. However, no effects of the manipulations on fruit and vegetable intake were found when behaviour was assessed by the FFQ measure. Secondary analyses showed that reported increases in intake were not related to demand characteristics. The findings are discussed in relation to their conceptual and practical value.

Lipreading and Covert Speech Production Similarly Modulate Human Auditory-Cortex Responses to Pure Tones

Watching the lips of a speaker enhances speech perception. At the same time, the 100 ms response to speech sounds is suppressed in the observer's auditory cortex. Here, we used whole-scalp 306-channel magnetoencephalography (MEG) to study whether lipreading modulates human auditory processing already at the level of the most elementary sound features, i.e., pure tones. We further envisioned the temporal dynamics of the suppression to tell whether the effect is driven by top-down influences. Nineteen subjects were presented with 50 ms tones spanning six octaves (125-8000 Hz) (1) during "lipreading," i.e., when they watched video clips of silent articulations of Finnish vowels /a/, /i/, /o/, and /y/, and reacted to vowels presented twice in a row; (2) during a visual control task; (3) during a still-face passive control condition; and (4) in a separate experiment with a subset of nine subjects, during covert production of the same vowels. Auditory-cortex 100 ms responses (N100m) were equally suppressed in the lipreading and covert-speech-production tasks compared with the visual control and baseline tasks; the effects involved all frequencies and were most prominent in the left hemisphere. Responses to tones presented at different times with respect to the onset of the visual articulation showed significantly increased N100m suppression immediately after the articulatory gesture. These findings suggest that the lipreading-related suppression in the auditory cortex is caused by top-down influences, possibly by an efference copy from the speech-production system, generated during both own speech and lipreading.

How useful are the stages of change for targeting interventions? Randomized test of a brief intervention to reduce smoking.

To see whether the stages of change are useful for targeting a brief intervention to reduce smoking based on implementation intentions. A second objective was to rule out demand characteristics as an alternative explanation for the findings of intervention studies based on the transtheoretical model and implementation intentions. Participants (N = 350) were randomized to a passive control condition (questionnaire only), active control condition (questionnaire plus instruction to plan to quit), or experimental condition (questionnaire, plan to quit, form an implementation intention). Their behavior and psychosocial orientation to quit were measured at baseline and at 2-month follow-up. Theory of planned behavior variables, nicotine dependence, and quitting. Significantly more people quit smoking in the experimental condition than in the control conditions, and the planning instructions changed intention to quit and perceived control over quitting, but not behavior. Stage of change moderated these effects such that implementation intentions worked best for individuals who were in the preparation stage at baseline. Harnessing both motivational and volitional processes seems to enhance the effectiveness of smoking cessation programs, although further work is required to clarify inconsistencies in the literature using the stages of change.

Cervical spine manipulation alters sensorimotor integration: A somatosensory evoked potential study

ObjectiveTo study the immediate sensorimotor neurophysiological effects of cervical spine manipulation using somatosensory evoked potentials (SEPs). MethodsTwelve subjects with a history of reoccurring neck stiffness and/or neck pain, but no acute symptoms at the time of the study were invited to participate in the study. An additional twelve subjects participated in a passive head movement control experiment. Spinal (N11, N13) brainstem (P14) and cortical (N20, N30) SEPs to median nerve stimulation were recorded before and for 30min after a single session of cervical spine manipulation, or passive head movement. ResultsThere was a significant decrease in the amplitude of parietal N20 and frontal N30 SEP components following the single session of cervical spine manipulation compared to pre-manipulation baseline values. These changes lasted on average 20min following the manipulation intervention. No changes were observed in the passive head movement control condition. ConclusionsSpinal manipulation of dysfunctional cervical joints can lead to transient cortical plastic changes, as demonstrated by attenuation of cortical somatosensory evoked responses. SignificanceThis study suggests that cervical spine manipulation may alter cortical somatosensory processing and sensorimotor integration. These findings may help to elucidate the mechanisms responsible for the effective relief of pain and restoration of functional ability documented following spinal manipulation treatment.

Mental Simulation and the Achievement of Health Goals: The Role of Goal Difficulty

The present study examined whether performing mental simulation fosters the achievement of personal health-related goals. College students were asked to choose either an easy or a difficult health goal. In addition, they were either assigned to a process simulation condition (simulating the steps to the goal), an outcome simulation condition (simulating the achievement of the goal), or to a passive control condition. Results indicated that both types of mental simulation enhanced the achievement of health-related goals, and proved especially effective at difficult goals. Given an easy goal, it did not make a difference if participants had performed mental simulations or not. The effect of mental simulation on the achievement of difficult health goals was mediated by enhanced motivation.

Effects of a brisk walk on blood pressure responses to the Stroop, a speech task and a smoking cue among temporarily abstinent smokers

A review and meta-analysis by Hamer et al. (2006) showed that a single session of exercise can attenuate post-exercise blood pressure (BP) responses to stress, but no studies examined the effects among smokers or with brisk walking. Healthy volunteers (n=60), averaging 28 years of age and smoking 15 cigarettes daily, abstained from smoking for 2 h before being randomly assigned to a 15-min brisk semi-self-paced walk or passive control condition. Subject characteristics, typical smoking cue-elicited cravings and BP were assessed at baseline. After each condition, BP was assessed before and after three psycho-social stressors were carried out: (1) computerised Stroop word-colour interference task, (2) speech task and (3) only handling a lit cigarette. A two-way mixed ANCOVA (controlling for baseline) revealed a significant overall interaction effect for time by condition for both systolic blood pressure (SBP) and diastolic blood pressure (DBP). Univariate ANCOVAs (to compare between-groups post-stressor BP, controlling for pre-stressor BP) revealed that exercise attenuated systolic BP and diastolic BP responses to the Stroop and speech tasks and SBP to the lit cigarette equivalent to an attenuated SBP and DBP of up to 3.8 mmHg. Post-exercise attenuation effects were moderated by resting blood pressure and self-reported smoking cue-elicited craving. Effects were strongest among those with higher blood pressure and smokers who reported typically stronger cravings when faced with smoking cues. Blood pressure responses to the lit cigarette were not associated with responses to the Stroop and speech task. A self-paced 15-min walk can reduce smokers' SBP and DBP responses to stress, of a magnitude similar on average to non-smokers.

Functional Neuroanatomy of the Human Visual Fixation System

The regional cerebral blood flow correlates of the active fixation of an imagined target were studied in five healthy humans using the positron emission tomography activation paradigm. The fixation task was contrasted to a passive control condition, both tasks being performed in total darkness. Blood flow increases were observed in the frontal eye fields and supplementary eye fields and in the median cingulate gyrus. We suggest that the network of these activated regions mediates the interactions between ocular fixation, eye movements and directed visual attention.