Right-sided Stimuli Research Articles

Age-related changes in time perception: Effects of immersive virtual reality and spatial location of stimuli

The perception of time is subject to various environmental influences and exhibits changes across the lifespan. Studies on time perception have often been conducted using abstract stimuli and artificial scenarios, and recent claims for more naturalistic paradigms and realistic stimuli pose the question as to whether immersive virtual reality set-ups differently affect the timing abilities of older versus younger adults. Here, we tested the hypotheses that naturalistic 3D stimuli presented in immersive virtual reality (as opposed to abstract 2D stimuli presented on a computer screen) and the spatial location of those stimuli (left vs. right) affect the perceived time point of their occurrence.Our results demonstrate that a naturalistic presentation of stimuli leads to a bias towards earlier time points in younger, but not older participants. Furthermore, this bias was associated with lower scores of memory capacity. Contrary to our hypothesis that right-sided stimuli are perceived as later than left-sided stimuli, no spatial influences on temporal processing were observed. These results show that older and younger adults are differently affected by an increase in the realism and the immersiveness of experimental paradigms, and highlight the importance of task design in studies on human time perception.

Use of minimal working memory in visual comparison: An eye-tracking study.

In this study, we used a novel application of the previous paradigm provided by Pomplun to examine the eye movement strategies of using minimal working memory in visual comparison. This paradigm includes two tasks: one is a free comparison and the other is a single sequential comparison. In the free comparison, participants can freely view two horizontally presented stimuli until they judge whether the two stimuli are the same or not. In the single sequential comparison, participants can only view the left-side stimuli one time, and when their eyes cross the invisible boundary at the center of the screen, the left-side stimuli disappear and the right-side stimuli appear. Participants need to judge whether the right-side stimuli are the same as the disappeared left-side stimuli. Eye movement data showed significant differences between the single sequential comparison and free comparison tasks that suggests the use of minimal working memory in free comparison. Moreover, when the number of items was more than three, an average of 2.87 items would be processed in each view sequence. Participants also used the alternating left-right reference strategy that made the shortest scan path with the use of minimal working memory. The typical eye movement strategy in visual comparison and its theoretical significance were discussed.

Unilateral spatial neglect affected by right-sided stimuli in a three-dimensional virtual environment: A preliminary proof-of-concept study.

Seven patients with USN participated in this study, and two types of visual stimuli were created: the numbers and objects in the 3D virtual environment. To eliminate the visual stimuli on the right side, a moving slit was introduced in the virtual environment. During the experiment, patients were required to orally identify each object and number both in moving and nonmoving slit conditions. A statistical comparison of scores with and without the moving slit in the 3D virtual space indicated significant changes in the object stimuli condition; however, no statistically significant difference was observed in the number stimuli condition. Masking the right side within the 3D virtual space increased the number of objects that can be recognized on the left side by patients with USN. The results may allow interventions in a virtual reality environment that closely resembles the patient's real-life space.Clinical Relevance-Magnetic attraction is a symptom seen in patients in clinical practice, but there is no method of rehabilitation. The proposed moving slit method is expected to be effective because it enables attention guidance in a three-dimensional space.

Effects of variability in manually contoured spinal cord masks on fMRI co-registration and interpretation.

Functional magnetic resonance imaging (fMRI) of the human spinal cord (SC) is a unique non-invasive method for characterizing neurovascular responses to stimuli. Group-analysis of SC fMRI data involves co-registration of subject-level data to standard space, which requires manual masking of the cord and may result in bias of group-level SC fMRI results. To test this, we examined variability in SC masks drawn in fMRI data from 21 healthy participants from a completed study mapping responses to sensory stimuli of the C7 dermatome. Masks were drawn on temporal mean functional image by eight raters with varying levels of neuroimaging experience, and the rater from the original study acted as a reference. Spatial agreement between rater and reference masks was measured using the Dice Similarity Coefficient, and the influence of rater and dataset was examined using ANOVA. Each rater's masks were used to register functional data to the PAM50 template. Gray matter-white matter signal contrast of registered functional data was used to evaluate the spatial normalization accuracy across raters. Subject- and group-level analyses of activation during left- and right-sided sensory stimuli were performed for each rater's co-registered data. Agreement with the reference SC mask was associated with both rater (F(7, 140) = 32.12, P < 2 × 10-16, η2 = 0.29) and dataset (F(20, 140) = 20.58, P < 2 × 10-16, η2 = 0.53). Dataset variations may reflect image quality metrics: the ratio between the signal intensity of spinal cord voxels and surrounding cerebrospinal fluid was correlated with DSC results (p < 0.001). As predicted, variability in the manually-drawn masks influenced spatial normalization, and GM:WM contrast in the registered data showed significant effects of rater and dataset (rater: F(8, 160) = 23.57, P < 2 × 10-16, η2 = 0.24; dataset: F(20, 160) = 22.00, P < 2 × 10-16, η2 = 0.56). Registration differences propagated into subject-level activation maps which showed rater-dependent agreement with the reference. Although group-level activation maps differed between raters, no systematic bias was identified. Increasing consistency in manual contouring of spinal cord fMRI data improved co-registration and inter-rater agreement in activation mapping, however our results suggest that improvements in image acquisition and post-processing are also critical to address.

Assessing the spatial distribution of cervical spinal cord activity during tactile stimulation of the upper extremity in humans with functional magnetic resonance imaging

Dermatomal maps are a mainstay of clinical practice and provide information on the spatial distribution of the cutaneous innervation of spinal nerves. Dermatomal deficits can help isolate the level of spinal nerve root involvement in spinal conditions and guide clinicians in diagnosis and treatment. Dermatomal maps, however, have limitations, and the spatial distribution of spinal cord sensory activity in humans remains to be quantitatively assessed. Here we used spinal cord functional MRI to map and quantitatively compare the spatial distribution of sensory spinal cord activity during tactile stimulation of the left and right lateral shoulders (i.e. C5 dermatome) and dorsal third digits of the hands (i.e., C7 dermatome) in healthy humans (n ​= ​24, age ​= ​36.8 ​± ​11.8 years). Based on the central sites for processing of innocuous tactile sensory information, we hypothesized that the activity would be localized more to the ipsilateral dorsal spinal cord with the lateral shoulder stimulation activity being localized more superiorly than the dorsal third digit. The findings demonstrate lateralization of the activity with the left- and right-sided stimuli having more activation in the ipsilateral hemicord. Contradictory to our hypotheses, the activity for both stimulation sites was spread across the dorsal and ventral hemicords and did not demonstrate a clear superior-inferior localization. Instead, the activity for both stimuli had a broader than expected distribution, extending across the C5, C6, and C7 spinal cord segments. We highlight the complexity of the human spinal cord neuroanatomy and several sources of variability that may explain the observed patterns of activity. While the findings were not completely consistent with our a priori hypotheses, this study provides a foundation for continued work and is an important step towards developing normative quantitative spinal cord measures of sensory function, which may become useful objective MRI-based biomarkers of neurological injury and improve the management of spinal disorders.

Age-related changes in the allocation of spatially directed focal attention

ABSTRACT Objectives Leftward deviation on a horizontal line bisection test (pseudoneglect) might be induced by right hemispheric dominance for mediating spatial or global attention, or a hemispheric asymmetry in the ability to spatially disengage attention. With aging, this leftward bias is reduced, likely due to the aging-related deterioration of right hemisphere mediated functions (right hemi-aging) or hemispheric asymmetry reduction in old adults (HAROLD). Methods Forty-seven healthy adults divided into younger and older groups performed a modified Posner spatial-attentional task. Results Overall, younger individuals responded faster to left than right-sided imperative stimuli. In contrast, older participants did not reveal a right-left asymmetry to imperative stimuli. The younger group also revealed a strong inverse relationship between the reaction time to right valid cues and the leftward attentional bias while performing the line bisection task (pseudoneglect). Conclusions Our results provide support for both the right hemisphere spatial-attentional dominance hypothesis of pseudoneglect and the right hemi-aging hypotheses.

Impaired disengagement of attention and its relationship to emotional distress in infants at high-risk for autism spectrum disorder

ABSTRACTIntroduction: We provide data on visual orienting and emotional distress in infants at high and low risk for autism spectrum disorder (ASD). Method: Participants included 83 high-risk (HR) infants with an older sibling with ASD and 53 low-risk (LR) control infants with no family history of ASD. Infants were assessed on the gap-overlap task and a parent-completed temperament questionnaire at 6 and 12 months of age. At 36 months of age, an independent, gold standard diagnostic assessment for ASD was conducted. Results: HR infants subsequently diagnosed with ASD were distinguished at 12 months by an asymmetric disengage impairment (for left- vs. right-sided stimuli) that was associated with an increase in latencies between 6 and 12 months. Across groups, prolonged left-directed disengage latencies at 12 months were associated with emotional distress (high irritability and difficult to soothe). Conclusions: The asymmetry in our findings raises the question of whether the disengage problem in ASD is at base one of orienting or alerting attention. Our findings also raise the question of whether attention training might be a critical ingredient in the early treatment of ASD.

The Effect of Background Context on the Size–Time Illusion

Previous studies suggest that time perception may be altered by nontemporal stimulus properties, such as size and numerosity, where increases lead to a longer perception of time. These studies have led to the suggestion of a generalized magnitude system that processes abstract quantities. However, the majority of studies on this phenomenon have used simple stimuli, varying along one or two dimensions, and occurring in the same location. Here, we sought to explore the influence of the size–time illusion amongst complex visual scenes. Across five experiments, human participants judged the duration of two visual stimuli, of different sizes, appearing at different spatial locations for a range of sub-second durations. In half of the trials, these stimuli were overlaid on an image of a city street, with one stimulus presented farther away than the other. We found that larger stimuli were judged to be longer, but only when the larger stimulus was presented on the left side of space, and not when presented on the right or when the entire stimulus array was on the left. This effect extended to a marginal bias for left-sided stimuli to be judged as longer. However, we found that the size–time illusion for right-sided stimuli was reinstated when a background city context was presented, which may have been driven by an imposed effect of perceived distance. These results suggest that the size–time illusion is affected by the background context and location against which stimuli are presented, and provide important qualifications to theories of a common magnitude system.

The asymmetrical influence of increasing time-on-task on attentional disengagement

Increasing time-on-task leads to fatigue and, as shown by previous research, differentially affects the deployment of visual attention towards the left and the right visual space. In healthy participants, an increasing rightward bias is commonly observed with increasing time-on-task. Yet, it is unclear whether specific mechanisms involved in the spatial deployment of visual attention are differentially affected by increasing time-on-task.The aim of the present study was to investigate whether prolonged time-on-task would affect a specific mechanism of visuospatial attentional deployment, namely attentional disengagement, in an asymmetrical fashion. For this purpose, we administered to healthy participants a prolonged gap/overlap saccadic paradigm, with left- and right-sided target stimuli. This oculomotor paradigm allowed to quantify disengagement costs according to the direction of the subsequent attentional shifts, and to evaluate the temporal development of disengagement costs with increasing time-on-task.Our results show that, with increasing time-on-task, participants demonstrated significantly lower disengagement costs for rightward compared to leftward saccades. These effects were specific, since concurring side differences of saccadic latencies were found for overlap trials (requiring attentional disengagement), but not for gap trials (requiring no or less attentional disengagement). Moreover, the results were paralleled by a non-lateralised decrease in saccadic peak velocity with increasing time-on-task, a common finding indicating an increasing level of fatigue.Our findings support the idea that non-spatial attentional aspects, such as fatigue due to increasing time-on-task, can have a substantial influence on the spatial deployment of visual attention, in particular on its disengagement, depending on the direction of the subsequent attentional shift.

Hypnosis meets neuropsychology: Simulating visuospatial neglect in healthy participants

Neglect patients are not aware of stimuli in the contralesional space. We aimed to simulate neglect-like behaviour in healthy participants, by asking them to orient their visuospatial attention in two conditions: non-hypnotic suggestion and post-hypnotic suggestion. Results showed that directing visuospatial attention to one side of space caused neglect of stimuli in the opposite side of space, but only when participants were under post-hypnotic suggestion. Furthermore, directing visuospatial attention to the right side of space caused more neglect of left-sided stimuli than directing visuospatial attention to the left side of space did for right-sided stimuli. We propose that post-hypnotic suggestion can be a useful tool for (de)activating neurocognitive mechanisms underlying visuospatial awareness, a function that is fundamental for our survival. The use of post-hypnotic suggestion could be applied to the study of many domains of cognitive neurosciences (e.g., neurocognitive rehabilitation).

Absence of visual feedback abolishes expression of hemispatial neglect in self-guided spatial completion

BackgroundPatients with left neglect direct their attention too strongly to the right. Hypotheses hold that this is due to a failure to disengage attention from right-sided stimuli or to a...

Visual attention deficits in Alzheimer's disease: Relationship to HMPAO SPECT cortical hypoperfusion

Patients with Alzheimer's disease (AD) display a multiplicity of cognitive deficits in domains such as memory, language, and attention, all of which can be clearly linked to the underlying neuropathological alterations. The typical degenerative changes occur early on in the disease in the temporal–parietal lobes, with other brain regions, such as the frontal cortex, becoming more affected as the disease progresses. In light of the importance of the parietal cortex in mediating visuospatial attentional processing, in the present study, we investigated a deficit in covert orienting of visual attention and its relationship to cortical hypoperfusion in AD. We characterized the visual attentional profile of 21 AD patients, relative to that of 26 matched normal individuals, and then assessed the correspondence between behavior and hypoperfusion, as measured by regional cerebral blood flow using SPECT. Relative to controls, the AD group demonstrated a unilateral attentional deficit, with disproportionate slowing in reorienting attention to targets in the left compared to the right hemispace, especially following an invalid peripheral cue. Furthermore, even in the presence of bilateral pathology typical of AD, there was a positive correlation between this unilateral attentional disorder and the magnitude of the right superior parietal lobe hypoperfusion. The association of the altered attentional processing profile (i.e., greater difficulty disengaging attention from right-sided stimuli) with right-hemisphere-predominant hypoperfusion not only confirms the critical role of the right parietal lobe in covert attentional orienting but, more importantly, identifies a potential locus of the behavioral alterations in visuospatial processing in AD.

Dissecting the component deficits of perceptual imbalance in visual neglect: Evidence from horizontal–vertical length comparisons

IntroductionSigns of left unilateral neglect often occur after damage to the right hemisphere and entail a left–right imbalance in stimulus processing. Typically, neglect patients deviate rightward when bisecting lines. An underestimation of the left portion of the line and/or a right overestimation could explain this effect. MethodsHere we dissected their respective contribution by asking participants to compare a vertical segment to a horizontal segment, either on the left or on the right. We also tested whether neglect patients exhibited the symmetry law, whereby normal participants underestimate symmetrically bisected lines as compared to asymmetrically bisected lines. ResultsControls and patients underestimated symmetric figures. Depending on the degree of left–right horizontal competition, neglect patients underestimated left-sided stimuli or overestimated right-sided stimuli. ConclusionsWe concluded that two independent deficits contribute to neglect signs: a deficit in attentional orienting to the left, which can be worsened by left hemianopia, perhaps depending on impaired functioning of right-hemisphere attentional networks, and a tendency for attention to be captured by right-sided stimuli, possibly resulting from the activity of an isolated left hemisphere. Finally, the symmetry law was preserved in neglect patients, and thus appears to be driven by pre-attentive mechanisms.

Influences of negative BOLD responses on positive BOLD responses

Understanding possible interactions between blood oxygenation level-dependent (BOLD) responses is critical for model-based analyses and the interpretation of experiments that deal with stimuli presented close together in time. Such interactions are well documented in the case of successive positive BOLD responses. However, the influence that a stimulus-induced, negative BOLD response exerts on a subsequent positive BOLD response has yet to be investigated and is the focus of the current study. We performed functional magnetic resonance imaging on 10 healthy subjects during bilateral electrical median nerve stimulation using five different time intervals between left- and right-sided stimuli. We found an acute interruption of the ongoing negative BOLD response at the onset of the positive BOLD response. Different parameters characterizing the positive BOLD response were estimated. There was no impact of the preceding negative BOLD response on the parameters describing the subsequent positive BOLD response. These findings indicate that the underlying mechanisms for negative and positive BOLD responses do not engage parallel processes. We hypothesize that the negative BOLD response is caused by a decreased release of the same vasodilatative agents that evoke the positive BOLD response. Additionally, our results demonstrate that there is no need to adjust the model of a positive BOLD response due to a preceding negative BOLD response in the same brain area.

Stimulus affective valence reverses spatial compatibility effect.

In spatial compatibility tasks, the Reaction Time to right-side stimuli is shorter for right key responses (compatible condition) than for left key responses (incompatible condition) and vice-versa for left-side stimuli. Similar results have been found when the stimulus location is not relevant for response selection, such as in the Simon task. The Simon effect is the difference between the reaction times for non-corresponding and corresponding conditions. The Simon effect and its variants may be modulated by using emotional stimuli. However, until now, no work has studied how the affective valence of a stimulus influences spatial compatibility effects along the horizontal dimension. The present study investigated this issue by using small lateralized figures of soccer team players as stimuli. In the experiment, a compatible or incompatible response was chosen according to the team shirt. In one block, for the Favorite team, the volunteers had to press the key on the same side as the stimulus hemifield but the opposite-side key for the Rival team. In the other block, a reverse code had to be used. Fourteen right-handed volunteers were tested. Mean reaction times were subjected to analysis of variance with the following variables: Preference (Favorite/Rival), Hemifield (Left/Right), and Response Key (Left/Right). A three-way interaction was found (F1,13 = 6.60, p = .023), showing that the spatial compatibility effects depended on Preference. The Favorite team player elicited the usual spatial compatibility pattern, but for the Rival team player, the reverse effect was found, with incompatible responses being faster than compatible responses. We propose that this modulation may result from approach/avoidance reactions to the Favorite and Rival teams, respectively. Moreover, we suggest as a corollary that the classic spatial compatibility task is a powerful tool for investigating approach/avoidance effects.

Multisensory gain within and across hemispaces in simple and choice reaction time paradigms

Recent results on the nature and limits of multisensory enhancement are inconsistent when stimuli are presented across spatial regions. We presented visual, tactile and visuotactile stimuli to participants in two speeded response tasks. Each unisensory stimulus was presented to either the left or right hemispace, and multisensory stimuli were presented as either aligned (e.g. visual right/tactile right) or misaligned (e.g. visual right/tactile left). The first task was a simple reaction time (SRT) paradigm where participants responded to all stimulations irrespective of spatial position. Results showed that multisensory gain and coactivation were the same for spatially aligned and misaligned visuotactile stimulation. In the second task, a choice reaction time (CRT) paradigm where participants responded to right-sided stimuli only, misaligned stimuli yielded slower reaction times. No difference in multisensory gain was found between the SRT and CRT tasks for aligned stimulation. Overall, the results suggest that when spatial information is task-irrelevant, multisensory integration of spatially aligned and misaligned stimuli is equivalent. However, manipulating task requirements can alter this effect.

Alterations in visual and auditory processing in hemispatial neglect: An evoked potential follow-up study

Hemispatial neglect is common after cerebrovascular stroke in the right hemisphere. Cortical electrophysiological studies, especially investigations of both visual and auditory processing in subjects with neglect are sparse. Our purpose was to assess whether and to which extent subjects with neglect may show impairments in both visual and auditory processing. Thereby, we assessed the evolution of changes in sensory processing and neglect symptoms over a 6 month follow-up period. Twenty-one stroke subjects with hemispatial neglect were studied at baseline, 3 weeks later and at 6 months follow-up. At enrollment, 12 patients were in Acute/subacute and 9 were in the chronic stage of stroke. Visual and auditory evoked potentials (EP) were elicited with unilateral stimulations and electrophysiologic data were registered with high-density EEG. Primary visual and auditory cortex activations seen in EP components were analyzed at three time points in order to detect alterations. Both sensory modalities revealed differences between hemispheres in processing stimuli coming from a unilateral source. Amplitudes of visual and auditory EP components elicited by left-sided stimuli were smaller compared to those elicited by right-sided stimuli in the Acute/subacute group. The behavioral neglect was more severe in those who had smaller EP amplitudes (e.g. EP amplitude after the right auditory stimulus was significantly associated with total behavioral neglect score, r = 0.57). The main hemispheric differences diminished by the follow-up 6 months later along with the decreasing severity of neglect in the Acute/subacute group.

Representation and disconnection in imaginal neglect

Patients with neglect failure to detect, orient, or respond to stimuli from a spatially confined region, usually on their left side. Often, the presence of perceptual input increases left omissions, while sensory deprivation decreases them, possibly by removing attention-catching right-sided stimuli (Bartolomeo, 2007). However, such an influence of visual deprivation on representational neglect was not observed in patients while they were imagining a map of France (Rode et al., 2007). Therefore, these patients with imaginal neglect either failed to generate the left side of mental images (Bisiach & Luzzatti, 1978), or suffered from a co-occurrence of deficits in automatic (bottom-up) and voluntary (top-down) orienting of attention. However, in Rode et al.’s experiment visual input was not directly relevant to the task; moreover, distraction from visual input might primarily manifest itself when representation guides somatomotor actions, beyond those involved in the generation and mental exploration of an internal map (Thomas, 1999). To explore these possibilities, we asked a patient with right hemisphere damage, R.D., to explore visual and imagined versions of a map of France in three conditions: (1) ‘imagine the map in your mind’ (imaginal); (2) ‘describe a real map’ (visual); and (3) ‘list the names of French towns’ (propositional). For the imaginal and visual conditions, verbal and manual pointing responses were collected; the task was also given before and after mental rotation of the map by 180°. R.D. mentioned more towns on the right side of the map in the imaginal and visual conditions, but showed no representational deficit in the propositional condition. The rightward inner exploration bias in the imaginal and visual conditions was similar in magnitude and was not influenced by mental rotation or response type (verbal responses or manual pointing to locations on a map), thus suggesting that the representational deficit was robust and independent of perceptual input in R.D. Structural and diffusion MRI demonstrated damage to several white matter tracts in the right hemisphere and to the splenium of corpus callosum. A second right-brain damaged patient (P.P.), who showed signs of visual but not imaginal neglect, had damage to the same intra-hemispheric tracts, but the callosal connections were spared. Imaginal neglect in R.D. may result from fronto-parietal dysfunction impairing orientation towards left-sided items and posterior callosal disconnection preventing the symmetrical processing of spatial information from long-term memory.

Superstitious perception: Response-independent reinforcement and punishment as determinants of recurring eccentric interpretations

This study provided controlled observations of a potential mechanism for the determination of the repetitive, aberrant perceptions or interpretations of everyday events that figure prominently in a range of psychological disorders: the adventitious reinforcement of acts of cognition by the actual consequences of concurrent motor acts. Adults made a series of two-choice brightness discriminations; on 60% of trials, choosing the brighter stimulus produced a “correct” signal while errors produced an aversive sound. On 40% of trials, the choice stimuli did not in fact differ in brightness; the consequences of responding on these “identical stimuli” trials differed across blocks of trials. Thus, on these trials perceptual judgments were directly followed by events that they did not produce. When all choices on identical stimuli trials were punished with the “error” sound, subjects showed little preference for the left-side or right-side identical stimuli, but when all choices of identical stimuli were reinforced with the “correct” light, individual preferences for the left-side or the right-side stimuli substantially increased. As the consequences of responding on identical stimuli trials were independent of the stimuli chosen, these findings provide evidence for superstitious perception, the reinforcement of perceptual acts by events that do not depend upon their occurrence.

Distractibility and Alzheimer Disease: The “Neglected” Phenomenon

Patients with Alzheimer's disease (AD) might have bilateral attentional disorders, such as a reduced spatial attentional window, due to pathological changes in regions important for mediating spatial attention. AD patients may also be highly distractible with the presentation of unilateral novel stimuli or be impaired at disengaging and reallocating their attention with imperative stimuli. This study sought to test these hypotheses by asking AD patients and normal control subjects to bisect 72 horizontal lines of 3 different lengths in three conditions: no lateral stimuli, novel right or left lateral stimuli ('bottom-up'), and imperative left or right lateral stimuli ('top-down'). Regarding the bottom-up condition, no group differences emerged, but the AD patients had a greater rightward bias with short lines and a leftward bias with long lines, independent of distracting stimuli. In the top-down condition, when the patients with AD, versus controls, were presented with imperative stimuli on their left side, they demonstrated a greater attentional bias than when presented with right-sided stimuli. Thus AD patients have a reduced spatial attentional window and while they are not highly distracted by novel stimuli, after allocating their attention to left sided stimuli, they have a reduced capacity to spatially re-allocate their attention.