Browsing by Author "Striemer, Christopher"
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Item Affective blindsight in the absence of input from face processing regions in occipital-temporal cortex(2017) Striemer, Christopher; Whitwell, Robert L.; Goodale, MelvynPrevious 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.Item Assessment and recovery of visually guided reaching deficits following cerebellar stroke(2023) Robles, Chella M.; Anderson, Britt; Dukelow, Sean P.; Striemer, ChristopherThe cerebellum is known to play an important role in the coordination and timing of limb movements. The present study focused on how reach kinematics are affected by cerebellar lesions to quantify both the presence of motor impairment, and recovery of motor function over time. In the current study, 12 patients with isolated cerebellar stroke completed clinical measures of cognitive and motor function, as well as a visually guided reaching (VGR) task using the Kinarm exoskeleton at baseline (~2 weeks), as well as 6, 12, and 24-weeks post-stroke. During the VGR task, patients made unassisted reaches with visual feedback from a central ‘start’ position to one of eight targets arranged in a circle. At baseline, 6/12 patients were impaired across several parameters of the VGR task compared to a Kinarm normative sample (n=307), revealing deficits in both feed-forward and feedback control. The only clinical measures that consistently demonstrated impairment were the Purdue Pegboard Task (PPT; 9/12 patients) and the Montreal Cognitive Assessment (6/11 patients). Overall, patients who were impaired at baseline showed significant recovery by the 24-week follow-up for both VGR and the PPT. A lesion overlap analysis indicated that the regions most commonly damaged in 5/12 patients (42% overlap) were lobule IX and Crus II of the right cerebellum. A lesion subtraction analysis comparing patients who were impaired (n=6) vs. unimpaired (n=6) on the VGR task at baseline showed that the region most commonly damaged in impaired patients was lobule VIII of the right cerebellum (40% overlap). Our results lend further support to the notion that the cerebellum is involved in both feedforward and feedback control during reaching, and that cerebellar patients tend to recover relatively quickly overall. In addition, we argue that future research should study the effects of cerebellar damage on visuomotor control from a perception-action theoretical framework to better understand how the cerebellum works with the dorsal stream to control visually guided action.Item Can intention override the “automatic pilot”?(2010) Striemer, Christopher; Yukovsky, Julia; Goodale, MelvynPrevious 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.Item Cerebellar lesions disrupt spatial and temporal visual attention(2021) Craig, Brandon T.; Morrill, Adam; Danckert, James; Anderson, Britt; Striemer, ChristopherThe 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.Item Cerebellar tDCS alters the perception of optic flow(2021) Nankoo, Jean-François; Madan, Christopher R.; Medina, Omar; Makepeace, Tyler; Striemer, ChristopherStudies 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.Item Covert face priming reveals a ‘true face effect’ in a case of congenital prosopagnosia(2009) Striemer, Christopher; Gingerich, Trevor; Striemer, Danielle; Dixon, MikePrevious 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.Item 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, JamesPrevious 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.Item Deficits in reflexive covert attention following cerebellar injury(2015) Striemer, Christopher; Cantelmi, David; Cusimano, Michael; Danckert, James; Schweizer, TomTraditionally 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.Item Differential influences of prism adaptation on reflexive and voluntary covert attention(2006) Striemer, Christopher; Sablatnig, Jeffery; Danckert, JamesRecent 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.Item Direction of visual shift and hand congruency enhance spatial realignment during visuomotor adaptation(2023) Striemer, Christopher; Morrill, AdamAlthough prism adaptation has been studied extensively for over 100 years to better understand how the motor system adapts to sensory perturbations, very few studies have systematically studied how the combination of the hand used to adapt, and the direction of visual shift, might influence adaptation. Given that sensory inputs and motor outputs from the same side are processed (at least initially) in the same hemisphere, we wondered whether there might be differences in how people adapt when the hand used and the direction of visual shift were congruent (e.g., adapting to rightward shifting prisms with the right hand),compared to incongruent (e.g., adapting to rightward shifting prisms with the left hand). In Experiment 1we re-analyzed a previously published dataset (Striemer, Enns, & Whitwell, 2019)in which healthy adults (n=17) adapted to 17° leftward or rightward optically displacing prisms using their left or right hand (tested in separate sessions, counterbalanced). Our results revealed a “congruency effect” such that adaptation aftereffects were significantly larger for reaches performed without visual feedback (i.e., straight-ahead pointing) when the direction of prism shift and the hand used were congruent, compared to incongruent. We replicated this same congruency effect in Experiment 2 in a new group of participants(n=25). We suggest that a better understanding of the cognitive and neural mechanisms underlying the congruency effect will allow researchers to build more precise models of visuomotor learning, and may lead to the development of more effective applications of prism adaptation for the treatment of attentional disorders following brain damage.Item The effects of cerebellar transcranial direct current stimulation (tDCS) on sustained attention(2017) Botha, Nadia; Striemer, ChristopherAlthough 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.Item The effects of cerebellar transcranial direct current stimulation (tDCS) on voluntary covert attention(2017) Botha, Nadia; Striemer, ChristopherAlthough 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.Item Individual differences in inhibitory control: the associations between the “automatic pilot,” executive function, and executive attention(2023) Otte, Branden; Striemer, ChristopherResearch 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.Item The influence of prism adaptation on perceptual and motor components of neglect: a reply to Saevarsson and Kristjansson(2013) Striemer, Christopher; Danckert, JamesIn 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).Item Lateralization of facial emotion recognition in the human cerebellum: a transcranial direct current stimulation (tDCS) study(2023) Slade, Sophia A.; Striemer, ChristopherThe 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.Item Left cerebellar lesions may be associated with an increase in spatial neglect-like symptoms(2023) Verbitsky, Ryan; Anderson, Britt; Danckert, James; Dukelow, Sean; Striemer, ChristopherEach cerebellar hemisphere projects to the contralateral cerebral hemisphere. Previous research suggests a lateralization of cognitive functions in the cerebellum that mirrors the cerebral cortex, with attention/visuospatial functions represented in the left cerebellar hemisphere, and language functions in the right cerebellar hemisphere. Although there is good evidence supporting the role of the right cerebellum with language functions, the evidence supporting the notion that attention and visuospatial functions are left lateralized is less clear. Given that spatial neglect is one of the most common disorders arising from right cortical damage, we reasoned that damage to the left cerebellum would result in increased spatial neglect-like symptoms, without necessarily leading to an official diagnosis of spatial neglect. To examine this disconnection hypothesis, we analyzed neglect screening data (line bisection, cancellation, figure copying) from 20 patients with isolated unilateral cerebellar stroke. Results indicated that left cerebellar patients (n=9) missed significantly more targets on the left side of cancellation tasks compared to a normative sample. No significant effects were observed for right cerebellar patients (n=11). A lesion overlap analysis indicated that Crus II (78% overlap), and lobules VII and IX (66% overlap) were the regions most commonly damaged in left cerebellar patients. Our results are consistent with the notion that the left cerebellum may be important for attention and visuospatial functions. Given the poor prognosis typically associated with neglect, we suggest that screening for neglect symptoms, and visuospatial deficits more generally, may be important for tailoring rehabilitative efforts to help maximize recovery in cerebellar patients.Item 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, DwightRecent 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.Item Overlapping neural circuits for visual attention and eye movements in the human cerebellum(2015) Striemer, Christopher; Chouinard, Philippe; Goodale, Melvyn; De Ribaupierre, SandrinePrevious 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.Item Prism adaptation magnitude has differential influences on perceptual vs. manual responses(2016) Striemer, Christopher; Russell, Karyn; Nath, PriyaPrevious 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.Item Prism adaptation reduces the disengage deficit in right brain damage patients(2007) Striemer, Christopher; Danckert, JamesRecent 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.