Research Online at MacEwan :: Browsing by Author "Striemer, Christopher"

Browsing by Author "Striemer, Christopher"

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Affective blindsight in the absence of input from face processing regions in occipital-temporal cortex
(2017) Striemer, Christopher; Whitwell, Robert L.; Goodale, Melvyn
Previous research suggests that the implicit recognition of emotional expressions may be carried out by pathways that bypass primary visual cortex (V1) and project to the amygdala. Some of the strongest evidence supporting this claim comes from case studies of “affective blindsight” in which patients with V1 damage can correctly guess whether an unseen face was depicting a fearful or happy expression. In the current study, we report a new case of affective blindsight in patient MC who is cortically blind following extensive bilateral lesions to V1, as well as face and object processing regions in her ventral visual stream. Despite her large lesions, MC has preserved motion perception which is related to sparing of the motion sensitive region MT+ in both hemispheres.
Can intention override the “automatic pilot”?
(2010) Striemer, Christopher; Yukovsky, Julia; Goodale, Melvyn
Previous research has suggested that the visuomotor system possesses an “automatic pilot” which allows people to make rapid online movement corrections in response to sudden changes in target position. Importantly, the automatic pilot has been shown to operate in the absence of visual awareness, and even under circumstances in which people are explicitly asked not to correct their ongoing movement. In the current study, we investigated the extent to which the automatic pilot could be “disengaged” by explicitly instructing participants to ignore the target jump (i.e., “NO-GO”), by manipulating the order in which the two tasks were completed (i.e., either “GO” or NO-GO first), and by manipulating the proportion of trials in which the target jumped. The results indicated that participants made fewer corrections in response to the target jump when they were asked not to correct their movement (i.e. NO-GO), and when they completed the NO-GO task prior to the task in which they were asked to correct their movement when the target jumped (i.e., the GO task). However, increasing the proportion of jumping targets had only a minimal influence on performance. Critically, participants still made a significant number of unintended corrections (i.e., errors) in the NO-GO tasks, even under explicit instructions not to correct their movement if the target jumped. Overall these data suggest that, while the automatic pilot can be influenced to some degree by top-down strategies and previous experience, the pre-potent response to correct an ongoing movement cannot be completely disengaged.
Cerebellar lesions disrupt spatial and temporal visual attention
(2021) Craig, Brandon T.; Morrill, Adam; Danckert, James; Anderson, Britt; Striemer, Christopher
The current study represents the first comprehensive examination of spatial, temporal and sustained attention following cerebellar damage. Results indicated that, compared to controls, cerebellar damage resulted in a larger cueing effect at the longest SOA – possibly reflecting a slowed the onset of inhibition of return (IOR) during a reflexive covert attention task, and reduced the ability to detect successive targets during an attentional blink task. However, there was little evidence to support the notion that cerebellar damage disrupted voluntary covert attention or the sustained attention to response task (SART). Lesion overlay data and supplementary voxel-based lesion symptom mapping (VLSM) analyses indicated that impaired performance on the reflexive covert attention and attentional blink tasks were related to damage to Crus II of the left posterior cerebellum. In addition, subsequent analyses indicated our results are not due to either general motor impairments or to damage to the deep cerebellar nuclei. Collectively these data demonstrate, for the first time, that the same cerebellar regions may be involved in both spatial and temporal visual attention.
Cerebellar tDCS alters the perception of optic flow
(2021) Nankoo, Jean-François; Madan, Christopher R.; Medina, Omar; Makepeace, Tyler; Striemer, Christopher
Studies have shown that the cerebellar vermis is involved in the perception of motion. However, it is unclear how the cerebellum influences motion perception. tDCS is a non-invasive brain stimulation technique that can reduce (through cathodal stimulation) or increase neuronal excitability (through anodal stimulation). To explore the nature of the cerebellar involvement on large-field global motion perception (i.e., optic flow-like motion), we applied tDCS on the cerebellar midline while participants performed an optic flow motion discrimination task. Our results show that anodal tDCS improves discrimination threshold for optic flow perception, but only for left-right motion in contrast to up-down motion discrimination. This result was evident within the first 10 min of stimulation and was also found post-stimulation. Cathodal stimulation did not have any significant effects on performance in any direction. The results show that discrimination of optic flow can be improved with tDCS of the cerebellar midline and provide further support for the role of the human midline cerebellum in the perception of optic flow.
Covert face priming reveals a ‘true face effect’ in a case of congenital prosopagnosia
(2009) Striemer, Christopher; Gingerich, Trevor; Striemer, Danielle; Dixon, Mike
Previous research indicates that individuals with congenital prosopagnosia (CP) fail to demonstrate significant priming from faces to related names in covert recognition tasks. The interpretation has been that CP precludes the ability to acquire face representations. In the current study we replicated this important finding, but also show a significant ‘true face effect’ in a CP patient, where face primes that matched the probe names facilitated reaction times compared to unrelated face primes. These data suggest that some individuals with CP may possess degraded face representations that facilitate the priming of a person’s identity, but not semantic associates.
Deficits in peripheral visual attention in patients with optic ataxia
(2007) Striemer, Christopher; Blangero, Annabelle; Rossetti, Yves; Boisson, Dominique; Rode, Gilles; Vighetto, Alain; Pisella, Laure; Danckert, James
Previous research has suggested that optic ataxia – a deficit in reaching in peripheral vision, can be isolated from Balint’s syndrome as it is primarily a visuomotor disorder, independent of perceptual or attentional deficits. Yet, almost no research has examined the attentional abilities of these patients. We examined peripheral visual attention in two patients with unilateral optic ataxia. Results indicated that both patients were slower to respond to targets in their ataxic visual field, irrespective of cuing condition (i.e., validly, invalidly, and no cue conditions), consistent with an overall decrease in the salience of stimuli in the ataxic field. Attentional deficits in peripheral vision are therefore an important factor to consider when examining visuomotor control deficits in optic ataxia.
Deficits in reflexive covert attention following cerebellar injury
(2015) Striemer, Christopher; Cantelmi, David; Cusimano, Michael; Danckert, James; Schweizer, Tom
Traditionally the cerebellum has been known for its important role in coordinating motor output. Over the past 15 years numerous studies have indicated that the cerebellum plays a role in a variety of cognitive functions including working memory, language, perceptual functions, and emotion. In addition, recent work suggests that regions of the cerebellum involved in eye movements also play a role in controlling covert visual attention. Here we investigated whether regions of the cerebellum that are not strictly tied to the control of eye movements might also contribute to covert attention. To address this question we examined the effects of circumscribed cerebellar lesions on reflexive covert attention in a group of patients (n = 11) without any gross motor or oculomotor deficits, and compared their performance to a group of age-matched controls (n = 11). Results indicated that the traditional RT advantage for validly cued targets was significantly smaller at the shortest (50 ms) SOA for cerebellar patients compared to controls. Critically, a lesion overlap analysis indicated that this deficit in the rapid deployment of attention was linked to damage in Crus I and Crus II of the lateral cerebellum. Importantly, both cerebellar regions have connections to non-motor regions of the prefrontal and posterior parietal cortices—regions important for controlling visuospatial attention. Together, these data provide converging evidence that both lateral and midline regions of the cerebellum play an important role in the control of reflexive covert visual attention.
Differential influences of prism adaptation on reflexive and voluntary covert attention
(2006) Striemer, Christopher; Sablatnig, Jeffery; Danckert, James
Recent research has demonstrated some beneficial effects in patients with neglect using rightward shifting prismatic lenses. Despite a great deal of research exploring this effect, we know very little about the cognitive mechanisms underlying prism adaptation in neglect. We examined the possibility that prism adaptation influences visual attention by having healthy participants complete either a reflexive or a voluntary covert visual attention cuing paradigm before and after adaptation to leftward, rightward, or sham (no shift) prisms. The results for reflexive orienting demonstrated that a subset of participants with large cuing effects prior to prism adaptation were faster to reorient attention away from an invalid cue on the side of space opposite the prismatic shift post adaptation. For voluntary orienting, left prisms increased the efficiency of voluntary attention in both left and right visual space in participants with a small cuing effect prior to prism adaptation. In contrast, right prisms decreased the efficiency of voluntary attention in both left and right space for participants with a large cuing effect prior to prism adaptation. No significant effects were observed in the sham prisms groups. These results suggest that prism adaptation may exert a variety of influences attentional orienting mechanisms.
Individual differences in inhibitory control: the associations between the “automatic pilot,” executive function, and executive attention
(2023) Otte, Branden; Striemer, Christopher
Research has demonstrated that the visuomotor system can rapidly correct ongoing movements following abrupt changes in a target's location. These “online corrections” can precede conscious awareness, and can occur even when participants are instructed not to correct. This “automatic pilot” is controlled by the dorsal visual stream, which plays a critical role in visually guided actions. These inadvertent corrections commonly occur during the Automatic Pilot Task – a procedure sensitive to errors in movement inhibition. Response inhibition is a component of executive function, which is governed, in part, by the right inferior frontal cortex, and a series of fronto-basal-ganglia networks. Response inhibition, however, is not a unitary construct, and has various facets. It is currently unclear whether the mechanisms that inhibit automatic movement corrections in the dorsal stream share common cognitive and neural substrates with other aspects of executive attention or executive function. Therefore, this study will investigate whether unintended corrections in the Automatic Pilot Task are related to other measures of executive attention, such as the Sustained Attention to Response Task (SART) and the Cognitive Failures Questionnaire (CFQ), as well as measures of executive function such as the Adult ADHD Self-Report Scale (ASRS), and the Behaviour Rating Inventory of Executive Function for Adults (BRIEF-A). If the mechanisms that inhibit the “automatic pilot” share common substrates with executive attention and executive control, then increases in unintended corrections in the Automatic Pilot Task should be associated with increased errors on the SART, and poorer scores on the ASRS, CFQ, and BRIEF-A.
Lateralization of facial emotion recognition in the human cerebellum: a transcranial direct current stimulation (tDCS) study
(2023) Slade, Sophia A.; Striemer, Christopher
The cerebellum, one of the oldest structures in the nervous system, is well-known for the important role it plays in the coordination and timing of movement. However, there has been a paradigm shift with recent clinical, neuroimaging, and experimental research suggesting that the cerebellum also plays a role in higher-order cognitive functions such as attention and emotion. The substantial increase in research regarding the cerebellum's ability for emotional processing has indicated that it may be particularly adept at recognizing and processing negative facial expressions (e.g., fear, anger, sadness). Previous research using functional brain imaging and patients with cerebellar brain injuries provide some evidence of cerebellar lateralization, with the left cerebellum being more specialized for processing emotions than the right. To examine this, we delivered transcranial direct current stimulation (tDCS) over the left cerebellum of 67 healthy participants, randomly assigned to a tDCS condition (anodal, cathodal, or sham), and had them complete a facial emotion recognition task pre-tDCS, during-tDCS, and post-tDCS. Anodal and cathodal cerebellar tDCS did not significantly alter participant reaction time and accuracy. Participants did get faster, less variable, and more accurate over time, especially for positive emotions (happy), compared to negative emotions (angry and sad). However, due to relatively limited research examining the role of the cerebellum in emotion processes, and the limitations of the current study, we cannot say for certain why there were no effects of tDCS.
Neglected time: impaired temporal perception of multisecond intervals in unilateral neglect
(2007) Danckert, James; Ferber, Susanne; Pun, Carson; Broderick, Carol; Striemer, Christopher; Rock, Sherry; Stewart, Dwight
Recent neuroimaging and neuropsychological studies have suggested that the right hemisphere, particularly frontal regions, is important for the perception of the passage of time. We examined the ability to estimate durations of up to 60 sec in a group of eight patients with unilateral neglect. When estimating multisecond intervals, neglect patients grossly underestimated all durations. On average, healthy controls (HC) demonstrated reasonably accurate estimates of all durations tested. Although the right hemisphere lesioned control patients without neglect also tended to underestimate durations, these underestimations were significantly better than the performance of the neglect group. These findings suggest a pivotal role for a right hemisphere fronto-parietal network in the accurate perception of multisecond durations. Furthermore, these findings add to a growing body of literature suggesting that neglect cannot be understood simply in terms of a bias in orienting attention to one side of space. Additional deficits of the kind demonstrated here are likely to be crucial in determining the nature and extent of the loss of conscious awareness for contralesional events.
Overlapping neural circuits for visual attention and eye movements in the human cerebellum
(2015) Striemer, Christopher; Chouinard, Philippe; Goodale, Melvyn; De Ribaupierre, Sandrine
Previous research in patients with cerebellar damage suggests that the cerebellum plays a role in covert visual attention. One limitation of some of these studies is that they examined patients with heterogeneous cerebellar damage. As a result, the patterns of reported deficits have been inconsistent. In the current study, we used functional neuroimaging (fMRI) in healthy adults (N=14) to examine whether or not the cerebellum plays a role in covert visual attention. Participants performed two covert attention tasks in which they were cued exogenously (with peripheral flashes) or endogenously (using directional arrows) to attend to marked locations in the visual periphery without moving their eyes. We compared BOLD activation in these covert attention conditions to a number of control conditions including: the same attention tasks with eye movements, a target detection task with no cueing, and a self-paced button-press task. Subtracting these control conditions from the covert attention conditions allowed us to effectively remove the contribution of the cerebellum to motor output. In addition to the usual fronto-parietal networks commonly engaged by these attention tasks, lobule VI of the vermis in the cerebellum was also activated when participants performed the covert attention tasks with or without eye movements. Interestingly, this effect was larger for exogenous compared to endogenous cueing. These results, in concert with recent patient studies, provide independent yet converging evidence that the same cerebellar structures that are involved in eye movements are also involved in visuospatial attention.
Prism adaptation magnitude has differential influences on perceptual vs. manual responses
(2016) Striemer, Christopher; Russell, Karyn; Nath, Priya
Previous research has indicated that rightward prism adaptation can reduce symptoms of spatial neglect following right brain damage. In addition, leftward prism adaptation can create “neglectlike” patterns of performance in healthy adults on tasks that measure attention and spatial biases. Although a great deal of research has focused on which behaviours are influenced by prism adaptation, very few studies have focused directly on how the magnitude of visual shift induced by prisms might be related to the observed aftereffects, or the effects of prisms on measures of attentional and spatial biases. In the current study we examined these questions by having groups of healthy adult participants complete manual line bisection and landmark tasks prior to and following adaptation to either 8.5° (15 diopter; n=22) or 17° (30 diopter; n=25) leftward shifting prisms. Our results demonstrated a significantly larger rightward shift in straight-ahead pointing (a measure of prism aftereffect) following adaptation to 17°, compared to 8.5° leftward shifting prisms. In addition, only 17° leftward shifting prisms resulted in a significant rightward shift in line bisection following adaptation. However, there was a significant change in performance on the landmark task pre vs. post adaptation in both the 8.5° and 17° leftward shifting prisms groups. Interestingly, correlation analyses indicated that changes in straight-ahead pointing pre vs. post adaptation were positively correlated with changes in performance on the manual line bisection task, but not the landmark task. These data suggest that larger magnitudes of prism adaptation seem to have a greater influence on tasks that require a response with the adapted hand (i.e., line bisection), compared to tasks that only require a perceptual judgment (i.e., the landmark task). In addition, these data provide further evidence that the effects of prisms on manual and perceptual responses are not related to one-another.
Prism adaptation reduces the disengage deficit in right brain damage patients
(2007) Striemer, Christopher; Danckert, James
Recent research has shown that prism adaptation alleviates some of the symptoms of neglect. Although prism adaptation can aid patients with neglect, the mechanisms underlying these benefits remain largely unknown. One way in which prisms may work is by altering attentional orienting mechanisms known to be impaired in neglect. To investigate this hypothesis we tested four right brain damaged patients (two with neglect) on a reflexive covert attention task before and after rightward prism adaptation and compared them to a group of healthy controls who underwent sham prism adaptation. Results demonstrated that rightward prism adaptation reduced both the rightward attentional bias, and the disengage deficit in patients with right brain damage irrespective of the presence of neglect.
Programs for action in superior parietal cortex: a triple‐pulse TMS investigation
(2011) Striemer, Christopher; Chouinard, Philippe; Goodale, Melvyn
Converging evidence from neurological patients and functional brain imaging studies strongly supports the notion that the posterior parietal cortex (PPC), especially in the left hemisphere, plays a critical role in both the programming (i.e., setting the initial movement parameters of the reach) and the online control of goal-directed reaching movements. Importantly, however, there is no clear consensus on how different subregions within the PPC contribute to the programming and online control of reaching. In the current study, we investigated the role of the inferior (IPL) and superior (SPL) parietal lobules in reach programming using MRI-guided event-related transcranial magnetic stimulation (TMS). Specifically, we applied triple-pulse (tp) TMS to either the left IPL or the left SPL at different time points during reaching movements either at target onset (programming) or at movement onset (online control) while participants (n=16) made pointing movements to targets in the periphery without visual feedback of the moving hand. Stimulating the SPL but not the IPL resulted in a significant increase in endpoint errors when tp-TMS was applied during the programming phase compared to the online control phase. In short, these data demonstrate that the SPL plays a critical role in real-time movement programming.
‘‘Real-time’’ obstacle avoidance in the absence of primary visual cortex
(2009) Striemer, Christopher; Chapman, Craig; Goodale, Melvyn
When we reach toward objects, we easily avoid potential obstacles located in the workspace. Previous studies suggest that obstacle avoidance relies on mechanisms in the dorsal visual stream in the posterior parietal cortex. One fundamental question that remains unanswered is where the visual inputs to these dorsal-stream mechanisms are coming from. Here, we provide compelling evidence that these mechanisms can operate in ‘‘real-time’’ without direct input from primary visual cortex (V1). In our first experiment, we used a reaching task to demonstrate that an individual with a dense left visual field hemianopia after damage to V1 remained strikingly sensitive to the position of unseen static obstacles placed in his blind field. Importantly, in a second experiment, we showed that his sensitivity to the same obstacles in his blind field was abolished when a short 2-s delay (without vision) was introduced before reach onset. These findings have far-reaching implications, not only for our understanding of the time constraints under which different visual pathways operate, but also in relation to how these seemingly ‘‘primitive’’ subcortical visual pathways can control complex everyday behavior without recourse to conscious vision.
Spatial working memory deficits represent a core challenge for rehabilitating neglect
(2013) Striemer, Christopher; Ferber, Susanne; Danckert, James
Left neglect following right hemisphere injury is a debilitating disorder that has proven extremely difficult to rehabilitate. Traditional models of neglect have focused on impaired spatial attention as the core deficit and as such, most rehabilitation methods have tried to improve attentional processes. However, many of these techniques (e.g., visual scanning training, caloric stimulation, neck muscle vibration) produce only short-lived effects, or are too uncomfortable to use as a routine treatment. More recently, many investigators have begun examining the beneficial effects of prism adaptation for the treatment of neglect. Although prism adaptation has been shown to have some beneficial effects on both overt and covert spatial attention, it does not reliably alter many of the perceptual biases evident in neglect. One of the challenges of neglect rehabilitation may lie in the heterogeneous nature of the deficits. Most notably, a number of researchers have shown that neglect patients present with severe deficits in spatial working memory (SWM) in addition to their attentional impairments. Given that SWM can be seen as a foundational cognitive mechanism, critical for a wide range of other functions, any deficit in SWM memory will undoubtedly have severe consequences. In the current review we examine the evidence for SWM deficits in neglect and propose that it constitutes a core component of the syndrome. We present preliminary data which suggest that at least one current rehabilitation method (prism adaptation) has no effect on SWM deficits in neglect. Finally, we end by reviewing recent work that examines the effectiveness of SWM training and how SWM training may prove to be a useful avenue for future rehabilitative efforts in patients with neglect.
The effects of cerebellar transcranial direct current stimulation (tDCS) on sustained attention
(2017) Botha, Nadia; Striemer, Christopher
Although the cerebellum is primarily known for its role in motor coordination and motor learning, recent research indicates that it is also involved in cognitive functions such as attention. The current study used a mild brain stimulation technique – transcranial direct current stimulation (tDCS) to further investigate the involvement of the cerebellum in sustained attention using two different sustained attention tasks. Specifically, we were interested in the effects of stimulation to the left lateral cerebellum on the sustained attention to response task (SART), in which participants (currently n=12) must respond (via button press) to the digits 1-9, but not 3, presented in a random continuous sequence on a computer screen. In addition, participants also completed the attentional blink task in which they must detect the presence of either one or two targets within a rapid serial visual presentation. For each task participants completed 3 sessions: sham (no stimulation), cathodal (-), and anodal (+) stimulation. Preliminary results for each task will be presented for this ongoing study.
The effects of cerebellar transcranial direct current stimulation (tDCS) on voluntary covert attention
(2017) Botha, Nadia; Striemer, Christopher
Although the cerebellum is primarily known for its role in motor coordination and motor learning, recent research indicates that it is also involved in cognitive functions such as attention. The current study used a mild brain stimulation technique – transcranial direct current stimulation (tDCS), to further investigate the involvement of the cerebellum in attention. Specifically, we were interested in the effects of stimulation to the left lateral cerebellum on a voluntary covert attention task. Voluntary covert attention refers to an intentional shifting of attention without moving one’s eyes (e.g. paying attention to an object in your periphery). Participants completed 3 sessions: sham (no stimulation), cathodal (-), and anodal (+) stimulation. In this exploratory study, our main interest was to demonstrate a modulation of performance on the attention task following cerebellar tDCS. Therefore, any difference in performance on the attention task following either cathodal or anodal stimulations compared to sham were of interest. Consistent with previous findings, the results show that participants were faster compared to invalidly cued targets; however, these effects were not systematically altered by tDCS. We argue that the absence of any effects of tDCS on voluntary covert attention could be related to the stimulation parameters used, or the sensitivity of the behavioural tasks employed.
The influence of prism adaptation on perceptual and motor components of neglect: a reply to Saevarsson and Kristjansson
(2013) Striemer, Christopher; Danckert, James
In a recent opinion paper we argued that prism adaptation (PA) primarily influences motor behaviors and spatial attention in neglect, but may have very little influence on perceptual biases (Striemer and Danckert, 2010b). Furthermore, we also suggested that the effects of PA on motor behaviors and spatial attention in neglect may arise via interactions with the dorsal “vision for action” pathway (Milner and Goodale, 2006), and the “dorsal attention network” that is important for allocating attention to specific locations in space (Corbetta and Shulman, 2002). Thus, we view alterations in shifts of attention following PA as being closely related to changes in motor behaviors (e.g., eye movements) following PA (i.e., the premotor theory of attention; Rizzolatti et al., 1987).

Browsing by Author "Striemer, Christopher"

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