Temporal Order Judgment Research Articles

Object Stability, Attention, and Temporal Order Judgments

Object Stability, Attention, and Temporal Order Judgments

Scene construction processes in the anterior hippocampus during temporal episodic memory retrieval.

Although the hippocampus has been implicated in both the temporal organization of memories and association of scene elements, some theoretical accountsposit that the role of the hippocampus in episodic memory is largely atemporal. In this study, we set out to explore this discrepancy by identifying hippocampal activity patterns related to scene construction while participants performed a temporal order memory task. Participants in the fMRI scanner were shown a sequence of photographs, each consisting of a central object and a contextual background scene. On each retrieval trial, participants were shown a pair of the original photographs (FULL), objects from the scenes without the background (OBJ), or background contexts without the main foreground object (BACK). In the temporal order judgment (TOJ) task, participants judged the temporal order of the pair of scenes; in the Viewing trials, two identical scenes were shown without any task. First, we found that the anterior hippocampus-particularly the CA1 and subiculum-showed similar patterns of activation between the BACK and OBJ conditions, suggesting that scene construction occurred spontaneously during both TOJ and Viewing. Furthermore, neural markers of scene construction in the anterior hippocampus did not apply to incorrect trials, showing that successful temporal memory retrieval was functionally linked to scene construction. In the cortex, time-processing areas, such as the supplementary motor area and the precuneus, and scene-processing areas, such as the parahippocampal cortex, were activated and functionally connected with the hippocampus. Together, these results support the view that the hippocampus is concurrently involved in scene construction and temporal organization of memory and propose a model of hippocampal episodic memory that takes both processes into account.

Independent-channels models of temporal-order judgment revisited: A model comparison

The perception of temporal order or simultaneity of stimuli is almost always explained in terms of independent-channels models, such as perceptual-moment, triggered-moment, and attention-switching models. Independent-channels models generally posit that stimuli are processed in separate peripheral channels and that their arrival-time difference at a central location is translated into an internal state of order (simultaneity) if it reaches (misses) a certain threshold. Non-monotonic and non-parallel psychometric functions in a ternary-response task provided critical evidence against a wide range of independent-channels models. However, two independent-channels models have been introduced in the last decades that can account for such shapes by considering misreports of internal states (response-error model) or by assuming that simultaneity and order judgments rely on distinct sensory and decisional processes (two-stage model). Based on previous ideas, we also consider a two-threshold model, according to which the same arrival-time difference may need to reach a higher threshold for order detection than for successiveness detection. All three models were fitted to various data sets collected over a period of more than a century. The two-threshold model provided the best balance between goodness of fit and parsimony. This preference for the two-threshold model over the two-stage model and the response-error model aligns well with several lines of evidence from cognitive modeling, psychophysics, mental chronometry, and psychophysiology. We conclude that the seemingly deviant shapes of psychometric functions can be explained within the framework of independent-channels models in a simpler way than previously assumed.

Visuotactile integration in individuals with fibromyalgia.

Our brain constantly integrates afferent information, such as visual and tactile information, to perceive the world around us. According to the maximum-likelihood estimation (MLE) model, imprecise information will be weighted less than precise, making the multisensory percept as precise as possible. Individuals with fibromyalgia (FM), a chronic pain syndrome, show alterations in the integration of tactile information. This could lead to a decrease in their weight in a multisensory percept or a general disruption of multisensory integration, making it less beneficial. To assess multisensory integration, 15 participants with FM and 18 pain-free controls performed a temporal-order judgment task in which they received pairs of sequential visual, tactile (unisensory conditions), or visuotactile (multisensory condition) stimulations on the index and the thumb of the non-dominant hand and had to determine which finger was stimulated first. The task enabled us to measure the precision and accuracy of the percept in each condition. Results indicate an increase in precision in the visuotactile condition compared to the unimodal conditions in controls only, although we found no intergroup differences. The observed visuotactile precision was correlated to the precision predicted by the MLE model in both groups, suggesting an optimal integration. Finally, the weights of the sensory information were not different between the groups; however, in the group with FM, higher pain intensity was associated with smaller tactile weight. This study shows no alterations of the visuotactile integration in individuals with FM, though pain may influence tactile weight in these participants.

Perceived Audio-Visual Simultaneity Is Recalibrated by the Visual Intensity of the Preceding Trial.

A vital heuristic used when making judgements on whether audio-visual signals arise from the same event, is the temporal coincidence of the respective signals. Previous research has highlighted a process, whereby the perception of simultaneity rapidly recalibrates to account for differences in the physical temporal offsets of stimuli. The current paper investigated whether rapid recalibration also occurs in response to differences in central arrival latencies, driven by visual-intensity-dependent processing times. In a behavioural experiment, observers completed a temporal-order judgement (TOJ), simultaneity judgement (SJ) and simple reaction-time (RT) task and responded to audio-visual trials that were preceded by other audio-visual trials with either a bright or dim visual stimulus. It was found that the point of subjective simultaneity shifted, due to the visual intensity of the preceding stimulus, in the TOJ, but not SJ task, while the RT data revealed no effect of preceding intensity. Our data therefore provide some evidence that the perception of simultaneity rapidly recalibrates based on stimulus intensity.

Differences in audiovisual temporal processing in autistic adults are specific to simultaneity judgments.

Research has shown that children on the autism spectrum and adults with high levels of autistic traits are less sensitive to audiovisual asynchrony compared to their neurotypical peers. However, this evidence has been limited to simultaneity judgments (SJ) which require participants to consider the timing of two cues together. Given evidence of partly divergent perceptual and neural mechanisms involved in making temporal order judgments (TOJ) and SJ, and given that SJ require a more global type of processing which may be impaired in autistic individuals, here we ask whether the observed differences in audiovisual temporal processing are task and stimulus specific. We examined the ability to detect audiovisual asynchrony in a group of 26 autistic adult males and a group of age and IQ-matched neurotypical males. Participants were presented with beep-flash, point-light drumming, and face-voice displays with varying degrees of asynchrony and asked to make SJ and TOJ. The results indicated that autistic participants were less able to detect audiovisual asynchrony compared to the control group, but this effect was specific to SJ and more complex social stimuli (e.g., face-voice) with stronger semantic correspondence between the cues, requiring a more global type of processing. This indicates that audiovisual temporal processing is not generally different in autistic individuals and that a similar level of performance could be achieved by using a more local type of processing, thus informing multisensory integration theory as well as multisensory training aimed to aid perceptual abilities in this population.

Spatial attention in mental arithmetic: A literature review and meta-analysis.

We review the evidence for the conceptual association between arithmetic and space and quantify the effect size in meta-analyses. We focus on three effects: (a) the operational momentum effect (OME), which has been defined as participants' tendency to overestimate results of addition problems and underestimate results of subtraction problems; (b) the arithmetic cueing effect, in which arithmetic problems serve as spatial cues in target detection or temporal order judgment tasks; and (c) the associations between arithmetic and space observed with eye- and hand-tracking studies. The OME was consistently found in paradigms that provided the participants with numerical response alternatives. The OME shows a large effect size, driven by an underestimation during subtraction while addition was unbiased. In contrast, paradigms in which participants indicated their estimate by transcoding their final estimate to a spatial reference frame revealed no consistent OME. Arithmetic cueing studies show a reliable small to medium effect size, driven by a rightward bias for addition. Finally, eye- and hand-tracking studies point to replicable associations between arithmetic and eye or hand movements. To account for the complexity of the observed pattern, we introduce the Adaptive Pathways in Mental Arithmetic (APiMA) framework. The model accommodates central notions of numerical and arithmetic processing and helps identifying which pathway a given paradigm operates on. It proposes that the divergence between OME and arithmetic cueing studies comes from the predominant use of non-symbolic versus symbolic stimuli, respectively. Overall, our review and findings clearly support an association between arithmetic and spatial processing.

Reduced Visuospatial Attention in Personal Space is Not Limited to the Affected Limb in Complex Regional Pain Syndrome.

Alterations in spatial attention have been reported in people with chronic pain and may be relevant to understanding its cortical mechanisms and developing novel treatments. There is conflicting evidence as to whether people with Complex Regional Pain Syndrome (CRPS) have reduced visuospatial attention to their affected limb and/or its surrounding space, with some evidence that these deficits may be greater in personal (bodily) space. We aimed to test the competing hypotheses of whether the visuospatial attentional bias is specific to the personal space of the affected limb or generalizes to the personal space of other parts of the affected side of the body. Using visual Temporal Order Judgement tasks, we measured spatial attention in the personal space of the hands and feet of patients with upper (n=14) or lower (n=14) limb CRPS and pain-free controls (n=17). Participants judged the order of two light flashes presented at different temporal offsets on each of their hands or feet. Slower processing of the flash on one side relative to the other reflects reduced attention to that side of space. Controls prioritized stimuli on the non-dominant (left) relative to dominant side, consistent with the well-documented normal leftward bias of attention (ie "pseudoneglect"). Regardless of the location (upper or lower limb) of the pain or visual stimuli, people with CRPS showed no such asymmetry, representing reduced attention to the affected side (compared to the greater attention of controls to their non-dominant side). More severe CRPS symptoms were associated with a greater tendency to deprioritize stimuli on the affected side. Our findings suggest that relative visuospatial bias in CRPS is generalized to the personal space of the affected side of the body, rather than being specific to the personal space of the CRPS-affected limb.

Spatial tactile localization depends on sensorimotor binding: preliminary evidence from virtual reality.

Our brain continuously maps our body in space. It has been suggested that at least two main frames of reference are used to process somatosensory stimuli presented on our own body: the anatomical frame of reference (based on the somatotopic representation of our body in the somatosensory cortex) and the spatial frame of reference (where body parts are mapped in external space). Interestingly, a mismatch between somatotopic and spatial information significantly affects the processing of bodily information, as demonstrated by the "crossing hand" effect. However, it is not clear if this impairment occurs not only when the conflict between these frames of reference is determined by a static change in the body position (e.g., by crossing the hands) but also when new associations between motor and sensory responses are artificially created (e.g., by presenting feedback stimuli on a side of the body that is not involved in the movement). In the present study, 16 participants performed a temporal order judgment task before and after a congruent or incongruent visual-tactile-motor- task in virtual reality. During the VR task, participants had to move a cube using a virtual stick. In the congruent condition, the haptic feedback during the interaction with the cube was provided on the right hand (the one used to control the stick). In the incongruent condition, the haptic feedback was provided to the contralateral hand, simulating a sort of 'active' crossed feedback during the interaction. Using a psychophysical approach, the point of subjective equality (or PSE, i.e., the probability of responding left or right to the first stimulus in the sequence in 50% of the cases) and the JND (accuracy) were calculated for both conditions, before and after the VR-task. After the VR task, compared to the baseline condition, the PSE shifted toward the hand that received the haptic feedback during the interaction (toward the right hand for the congruent condition and toward the left hand for the incongruent condition). This study demonstrated the possibility of inducing spatial biases in the processing of bodily information by modulating the sensory-motor interaction between stimuli in virtual environments (while keeping constant the actual position of the body in space).

The less complex temporal patterns of resting‑state EEG activity, the lower the visual temporal order threshold.

Speech understanding, watching a movie, listening to music etc., requires perception of the temporal order of at least two incoming events. A history of performing these tasks may be reflected in spontaneous brain activity. Here, we examined the relationship between the complexity (temporal dynamics) of resting‑state EEG (rsEEG) signal, assessed using the multivariate MultiScale Entropy (mMSE) algorithm, and the perception of event ordering, indexed by a visual temporal order threshold (TOT), i.e., the minimum duration necessary to correctly identify the before‑after relation between two stimuli. Healthy adolescents and young adults performed a psychophysical task measuring the TOT and underwent an eyes‑closed rsEEG study. The features of mMSE vectors, namely the area under curve (AUC) that represents total signal complexity, as well as the MaxSlope and the AvgEnt, corresponding to the entropy at fine‑ and coarse‑grained timescales, respectively, were obtained for the central (midline), anterior, middle and posterior channel sets. The greater the AUC and AvgEnt values in the central, left and right posterior areas, and the higher AUC in the right middle region, the higher the TOT. The most significant relationships were found for the midline electrodes (Fz, Cz, Pz, Oz). There were no significant correlations between the MaxSlope values and the TOT. To the best of our knowledge, this is the first study demonstrating that spontaneous EEG signal complexity is associated with the temporal order perception of two stimuli presented in rapid succession. Our findings may indicate that low total and coarse entropy levels of rsEEG signal are beneficial for visual temporal order judgments.

A common timing mechanism across different millisecond domains: evidence from perceptual and motor tasks

Temporal information processing (TIP) constitutes a complex construct that underlies many cognitive functions and operates in a few hierarchically ordered time domains. This study aimed to verify the relationship between the tens of milliseconds and hundreds of milliseconds domains, referring to perceptual and motor timing, respectively. Sixty four young healthy individuals participated in this study. They underwent two auditory temporal order judgement tasks to assess their performance in the tens of milliseconds domain; on this basis, groups of high-level performers (HLP) and low-level performers (LLP) were identified. Then, a maximum tapping task was used to evaluate performance in the hundreds of milliseconds domain. The most remarkable result was that HLP achieved a faster tapping rate and synchronised quicker with their “internal clock” during the tapping task than did LLP. This result shows that there is a relationship between accuracy in judging temporally asynchronous stimuli and ability to achieve and maintain the pace of a movement adequate to one’s internal pacemaker. This could indicate the strong contribution of a common timing mechanism, responsible for temporal organisation and coordination of behaviours across different millisecond domains.

Does cross-modal correspondence modulate modality-specific perceptual processing? Study using timing judgment tasks.

Cross-modal correspondences refer to associations between stimulus features across sensory modalities. Previous studies have shown that cross-modal correspondences modulate reaction times for detecting and identifying stimuli in one modality when uninformative stimuli from another modality are present. However, it is unclear whether such modulation reflects changes in modality-specific perceptual processing. We used two psychophysical timing judgment tasks to examine the effects of audiovisual correspondences on visual perceptual processing. In Experiment 1, we conducted a temporal order judgment (TOJ) task that asked participants to judge which of two visual stimuli presented with various stimulus onset asynchronies (SOAs) appeared first. In Experiment 2, we conducted a simultaneous judgment (SJ) task that asked participants to report whether the two visual stimuli were simultaneous or successive. We also presented an unrelated auditory stimulus, simultaneously or preceding the first visual stimulus, and manipulated the congruency between audiovisual stimuli. Experiment 1 indicated that the points of subjective simultaneity (PSSs) between the two visual stimuli estimated in the TOJ task shifted according to the audiovisual correspondence between the auditory pitch and visual features of vertical location and size. However, these audiovisual correspondences did not affect PSS estimated using the SJ task in Experiment 2. The different results of the two tasks can be explained through the response bias triggered by audiovisual correspondence that only the TOJ task included. We concluded that audiovisual correspondence would not modulate visual perceptual timing and that changes in modality-specific perceptual processing might not trigger the congruency effects reported in previous studies.

Virtual reality as a tool to explore multisensory processing before and after engagement in physical activity.

This pilot study employed a non-randomized control trial design to explore the impact of physical activity within a virtual reality (VR) environment on multisensory processing among community-dwelling older adults. The investigation compared both chronic (over 6 weeks) and acute effects of VR-based physical activity to a reading control group. The evaluation metrics for multisensory processing included audiovisual response time (RT), simultaneity judgments (SJ), sound-induced flash illusion (SIFI), and temporal order judgments (TOJ). A total of 13 older adults were provided with VR headsets featuring custom-designed games, while another 14 older adults were assigned to a reading-based control group. Results indicated that acute engagement in physical activity led to higher accuracy in the SIFI task (experimental group: 85.6%; control group: 78.2%; p = 0.037). Additionally, both chronic and acute physical activity resulted in quicker response times (chronic: experimental group = 336.92; control group = 381.31; p = 0.012; acute: experimental group = 333.38; control group = 383.09; p = 0.006). Although the reading group showed a non-significant trend for greater improvement in mean RT, covariate analyses revealed that this discrepancy was due to the older age of the reading group. The findings suggest that immersive VR has potential utility for enhancing multisensory processing in older adults. However, future studies must rigorously control for participant variables like age and sex to ensure more accurate comparisons between experimental and control conditions.

Temporal correspondence in perceptual organization: Reciprocal interactions between temporal sensitivity and figure-ground segregation.

How do visual representations account for time? Is it the case that they represent time by themselves possessing temporal properties (temporal mirroring) or by atemporal markers/tags (temporal tagging)? This question has been asked for the past 5 decades and more, in neuroscience, philosophy, and psychology. To address this debate, we designed a study to test temporal correspondence. We tested whether a temporal property (flicker frequency) could influence figure-ground segregation, and in turn, reciprocally, whether a figure-ground segregation would alter a temporal property (here, temporal resolution). We manipulated flicker frequency of dots on either side of an ambiguous edge in Experiment 1 and asked participants to indicate the figural region. In Experiment 2, we measured temporal sensitivity using a temporal order judgment (TOJ) task in both figural and ground regions. We showed temporal correspondence by showing specifically that figure-ground segregation depends on flicker frequency differences between two regions in ambiguous displays, where slow-flickering regions are seen as figural (Experiment 1). Reciprocally, in Experiment 2, we showed that participants performed a temporal-order judgment task better when the task had to be performed on a region seen as background compared with the same region seen as a figure. We show how relatively slower flickering regions are seen as figural, and correspondingly, seeing a region as figural is associated with a poorer temporal resolution. Our results collectively allow us to demonstrate a tight temporal correspondence in figure-ground perception, which could be explained using the parvocellular and magnocellular pathways, the two major retino-geniculo-cortical pathways.

Motion-Binding Property Contributes to Accurate Temporal-Order Perception in Audiovisual Synchrony.

Temporal perception in multisensory processing is important for an accurate and efficient understanding of the physical world. In general, it is executed in a dynamic environment in our daily lives. In particular, the motion-binding property is important for correctly identifying moving objects in the external environment. However, how this property affects multisensory temporal perception remains unclear. We investigate whether the motion-binding property influences audiovisual temporal integration. The study subjects performed four types of temporal-order judgment (TOJ) task experiments using three types of perception. In Experiment 1, the subjects conducted audiovisual TOJ tasks in the motion-binding condition, between two flashes, and in the simultaneous condition, in which the two flashes are perceived as simultaneous stimuli without motion. In Experiment 2, subjects conducted audiovisual TOJ tasks in the motion-binding condition and the short and long successive interval condition, in which the two stimuli are perceived as successive with no motion. The results revealed that the point of subjective simultaneity (PSS) and the just-noticeable difference (JND) in the motion-binding condition differed significantly from those in the simultaneous and short and long successive interval conditions. Specifically, the PSS in the motion-binding condition was shifted toward a sound-lead stimulus in which the PSS became closer to zero (i.e., physical simultaneity) and the JND became narrower compared to other conditions. This suggests that the motion-binding property contributes to accurate temporal integration in multisensory processing by precisely encoding the temporal order of the physical stimuli.

Perceived timing of postural instability onset

BackgroundThis study investigates the perceived onset of postural instability, a critical aspect of balance. Prior research using Temporal Order Judgment (TOJ) tasks revealed that postural perturbations must occur significantly earlier than an auditory reference stimulus for individuals to perceive them as simultaneous. However, there are methodological concerns with this previous work, particularly an unbalanced stimulus onset asynchrony (SOA) distribution. Research questionDoes the point of subjective simultaneity (PSS) between postural perturbation onset and an auditory reference stimulus differ between SOA distributions unequally (distribution 1) and equally (distribution 2) distributed around true simultaneity (0 ms)? MethodsA repeated measures design was employed, presenting two different SOA distributions to 10 participants using a TOJ task during both distribution 1 (88 trials) and distribution 2 (72 trials) SOA distributions. Paired t-tests were used to determine if there was a significant difference between the PSS of distribution 1 and 2. One-sample t-tests were also performed on the PSS values of both conditions in comparison to 0 ms (defined as true simultaneity) to determine if perceptual responses were delayed. ResultsDistribution 1 led to a perceived delay of postural instability onset by 20.34 ms, while distribution 2 resulted in a perceived delay of the auditory stimulus of 3.52 ms. However, neither condition was significantly different from each other nor from true simultaneity. SignificanceThese findings suggest that the perception of postural instability onset is not slow, contrary to previous beliefs, and emphasize the importance of controlling methodological parameters when examining sensory cues. This understanding will help inform falls prevention strategies.

Spatial attention modulates auditory dominance in audiovisual order judgment.

Auditory dominance in audiovisual temporal order judgment is shown here to be modulated by exogenous orienting of attention to a spatial cue independent of the cue modality. The visual stimulus has to lead the auditory one further in advance for cued relative to uncued locations in order for the two to be perceived simultaneously, possibly suggesting an inhibitory function of spatial attention on temporal processing.

The Influence of Personal Harmony Value on Temporal Order Perception.

Empirical studies have demonstrated that self-relevant information affects temporal order perception. Therefore, the question arises of whether personal values-which are the core components of the self-influence temporal order perception. To explore this problem, we chose harmony, one of the most common values in Chinese culture, as the starting point. First, the harmony scale was used to measure the harmony values of the participants, and the participants were divided into high- and low-harmony groups. The validity of the grouping was then verified using an implicit-association test. Furthermore, two temporal order judgment (TOJ) tasks were used to explore the impact of harmony values on temporal order perception. The results revealed that in both TOJ tasks, participants in the high-harmony group tended to perceive harmonious stimuli before non-harmonious stimuli, while the effect was not found in the low-harmony group. We conclude that harmony values affect temporal order perception, and only if the values are important to the individual.

Prestimulus α/β power in temporal-order judgments: individuals differ in direction of modulation but show consistency over auditory and visual tasks.

The processing of incoming sensory information can be differentially affected by varying levels of α-power in the electroencephalogram (EEG). A prominent hypothesis is that relatively low prestimulus α-power is associated with improved perceptual performance. However, there are studies in the literature that do not fit easily into this picture, and the reasons for this are poorly understood and rarely discussed. To evaluate the robustness of previous findings and to better understand the overall mixed results, we used a spatial TOJ task in which we presented auditory and visual stimulus pairs in random order while recording EEG. For veridical and non-veridical TOJs, we calculated the power spectral density (PSD) for 3 frequencies (5 Hz steps: 10, 15, and 20 Hz). We found on the group level: (1) Veridical auditory TOJs, relative to non-veridical, were associated with higher β-band (20 Hz) power over central electrodes. (2) Veridical visual TOJs showed higher β-band (10, 15 Hz) power over parieto-occipital electrodes (3) Electrode site interacted with TOJ condition in the β-band: For auditory TOJs, PSD over central electrodes was higher for veridical than non-veridical and over parieto-occipital electrodes was lower for veridical than non-veridical trials, while the latter pattern was reversed for visual TOJs. While our group-level result showed a clear direction of prestimulus modulation, the individual-level modulation pattern was variable and included activations opposite to the group mean. Interestingly, our results at the individual-level mirror the situation in the literature, where reports of group-level prestimulus modulation were found in either direction. Because the direction of individual activation of electrodes over auditory brain regions and parieto-occipital electrodes was always negatively correlated in the respective TOJ conditions, this activation opposite to the group mean cannot be easily dismissed as noise. The consistency of the individual-level data cautions against premature generalization of group-effects and suggests different strategies that participants initially adopted and then consistently followed. We discuss our results in light of probabilistic information processing and complex system properties, and suggest that a general description of brain activity must account for variability in modulation directions at both the group and individual levels.

Characterizing biased visuospatial perception in complex regional pain syndrome.

Patients suffering from complex regional pain syndrome (CRPS) are increasingly shown to be affected by cognitive difficulties. While these cognitive symptoms were initially described as limited to the perception, representation and use of the body, that is, the somatic space, they were recently shown to also extend to the perception of extra-somatic space. CRPS patients seem indeed to pay less attention to visual stimuli occurring in the same side of space as their affected limb and especially those occurring close to that limb. The aim of the present study was to more precisely characterize these visuospatial biases, by investigating whether they may be dependent on the visually perceived proximity between the visual stimuli and the affected limb. Upper-limb CRPS patients and matched control participants performed temporal order judgements on visual stimuli, one presented in either side of space, while they could either see their hands near the visual stimuli or not. Visuospatial biases were not modulated by the availability of visual feedback about the hands. However, secondary analyses revealed that these biases depended on the type of rehabilitation program that the patients followed: whereas patients who did not follow any specific program presented significant biases to the detriment of visual stimuli in the affected side of space, patients who did follow a CRPS-specialized program did not. Patients' cognitive strategies will be important to consider when studying inter-individual differences in the cognitive symptomatology and associated cognitive-based rehabilitation procedures in CRPS. The existence of biases in visuospatial perception in Complex Regional Pain Syndrome has been reported but not always systematically replicated. We show that these biases might depend on the type of general rehabilitation program that the patients follow. Patients' individual cognitive strategies will be important to consider when studying the cognitive symptomatology of CRPS.