Using Nonlinear Kinematic Parameters as a Means of Predicting Motion Sickness in Real-Time in Virtual Environments.

OBJECTIVE: This article presents two studies (one simulation and one pilot) that assess a custom computer algorithm designed to predict motion sickness in real-time. BACKGROUND: Virtual reality has a wide range of applications; however, many users experience visually induced motion sickness. Previous research has demonstrated that changes in kinematic (behavioral) parameters are predictive of motion sickness. However, there has not been research demonstrating that these measures can be utilized in real-time applications. METHOD: Two studies were performed to assess an algorithm designed to predict motion sickness in real-time. Study 1 was a simulation study that used data from Smart et al. (2014). Study 2 employed the algorithm on 28 new participants' motion while exposed to virtual motion. RESULTS: Study 1 revealed that the algorithm was able to classify motion sick participants with 100% accuracy. Study 2 revealed that the algorithm could predict if a participant would become motion sick with 57% accuracy. CONCLUSION: The results of the present study suggest that the motion sickness prediction algorithm can predict if an individual will experience motion sickness but needs further refinement to improve performance. APPLICATION: The algorithm could be used for a wide array of VR devices to predict likelihood of motion sickness with enough time to intervene.

Parsing attentional processes involved in the elicitation of the N2pc component.

The elicitation of the N2pc event-related potential component is commonly thought to be related to attentional processes involved in the selection of lateralized target information. However, it has recently been suggested that this component may reflect the localization of visual information in preparation of selection processes. This hypothesis specifically proposes that processes responsible for localization, rather than the selection of target identity elicit the N2pc component. The present study sought to explore this hypothesis by using a paradigm in which a cue stimulus could initiate the localization process before the onset of a target in a lateralized rapid serial visual presentation stream. Results indicate that processing of a cue, designed to initiate localization in the absence of processing required for target identity selection, is sufficient to elicit the N2pc component. Further, the N2pc elicited by solo targets in this paradigm was not observed when targets were preceded by the spatially informative cue stimuli. These results support the localization hypothesis and may reconcile mixed results from previous research by addressing specific properties of cue stimuli.

Staying Alert? Neural Correlates of the Association Between Grit and Attention Networks.

Recent research has demonstrated that heightened motivational levels promote enhanced attention capabilities. However, the relation between attentional systems and the trait-based ability to sustain a motivational state long-term is less understood. Grit refers to one's ability and willingness to pursue long-term goals despite setbacks. This report presents the results of two studies conducted to examine the relation between facets of Grit-Consistency and Perseverance and attention networks, assessed using the Attention Network Test (ANT). Across both studies Grit-Perseverance was related to performance on the ANT. In Study 1, Grit-Perseverance was negatively related to alerting indicating that individuals who were high on Perseverance were more likely to show a smaller alerting effect. In particular, Grit-Perseverance was negatively correlated with reaction times in the no cue trials. In Study 2, we assessed ERP components associated with attention networks. Individuals with higher scores on Grit-Perseverance were more likely to demonstrate smaller mean difference in N1 amplitudes for double cue relative to no cue trials, suggesting an attenuated alerting effect. Our findings indicate that individuals high on Grit-Perseverance may have enhanced sustained attention. Specifically individuals with high Grit-Perseverance appear to exhibit a more efficient alerting system in the no cue trials. Implications of high levels of Grit on cognitive performance are discussed.

Effects of depression and selective serotonin reuptake inhibitor use on adherence to highly active antiretroviral therapy and on clinical outcomes in HIV-infected patients.

OBJECTIVES: To determine the impact of depression on highly active antiretroviral therapy (HAART) adherence and clinical measures and investigate if selective serotonin reuptake inhibitors (SSRIs) improve these measures. DESIGN: Retrospective cohort study. METHODS: In 2 large health maintenance organizations, we measured the effects of depression (with and without SSRI use) on adherence and changes in viral and immunologic control among HIV-infected patients starting a new HAART regimen. HAART adherence, HIV RNA levels, and changes in CD4 T-cell counts through 12 months were measured. RESULTS: A total of 3359 patients were evaluated; 42% had a depression diagnosis, and 15% used SSRIs during HAART. Depression without SSRI use was associated with significantly decreased odds of achieving > or =90% adherence to HAART (odds ratio [OR] = 0.81, 95% confidence interval [CI]: 0.70 to 0.98; P = 0.03). Depression was associated with significantly lower odds of an HIV RNA level <500 copies/mL (OR = 0.77, 95% CI: 0.62 to 0.95; P = 0.02). Depressed patients compliant with SSRI medication (>80% adherence to SSRI) had HAART adherence and viral control statistically similar to nondepressed HIV-infected patients taking HAART. Comparing depressed with nondepressed HIV-infected patients, CD4 T-cell responses were statistically similar; among depressed patients, those compliant with SSRI had statistically greater increases in CD4 cell responses. CONCLUSIONS: Depression significantly worsens HAART adherence and HIV viral control. Compliant SSRI use is associated with improved HIV adherence and laboratory parameters.

Attentional disengagement dysfunction following mTBI assessed with the gap saccade task.

Concussion, or mild traumatic brain injury (mTBI), leads to a number of cognitive, attentional, and sensorimotor deficits that can last a surprisingly long time after the initial injury. We have previously shown that the ability to orient visuospatial attention is deficient in participants with mTBI within 2 days of their injury, but then recovers to normal levels within a week. Orienting attention requires disengagement from the point of fixation, movement of attention to the location of interest, and re-engagement at that location. Deficits in any or all of these processes could lead to the difficulties with orienting attention that we have observed in mTBI. To address this issue, we tested participants with mTBI using a gap saccade task. Because this task manipulates the temporal gap between the offset of the fixation target and the appearance of the peripheral saccade target, it isolates the contribution of the disengagement process to saccadic reaction time. We found that participants with mTBI had significantly longer saccadic reaction times than controls when the temporal gap was short but not when it was long. This gap-dependent difference in saccadic reaction time was present within 2 days of the injury and resolved within 1 week. This pattern of results suggests that as the contribution of the disengagement process is reduced, so too is the extent of the reaction time deficit in the participants with mTBI. Taken together, this is consistent with the idea that the deficits in orienting visuospatial attention in participants with mTBI are fully accounted for by difficulties with the initial disengagement process.

The contribution of the human PPC to the orienting of visuospatial attention during smooth pursuit.

Smooth pursuit eye movements function to stabilize the retinal image of small moving targets. In order for those targets to be foveated, however, they must first be "captured" by an attentional mechanism which then interacts with the oculomotor system. Cortical sites involved with producing smooth pursuit overlap with areas known to be involved in directing visuospatial attention, particularly the posterior parietal cortex (PPC). The goal of the current study was to characterize the contributions made by the left and right posterior parietal cortices (lPPC and rPPC) to the interaction between visuospatial attention and the generation of smooth pursuit eye movements. Transcranial magnetic stimulation (TMS) was used to temporarily disrupt each area at different times around target motion onset in a pursuit task that explicitly manipulated the covert orienting of attention. TMS over the lPPC, rPPC and a control site (the vertex) evoked a similar pattern of results, in that the earlier TMS delivery times caused a reduced pursuit latency compared to baseline measures, while TMS immediately prior to target motion onset resulted in latencies slower than baseline. In addition, however, TMS over the lPPC and rPPC (but not the vertex) preferentially influenced the generation of contralateral pursuit, with the lPPC doing so in a relatively time-independent manner, and the rPPC doing so in a time-dependent manner. This pattern of results implies that both the left and right PPC are directly involved in the interaction between attention and smooth pursuit preparation.

The contribution of the human FEF and SEF to smooth pursuit initiation.

Smooth pursuit eye movements function to keep moving targets foveated. Behavioral studies have shown that pursuit is particularly effective for predictable target motion. There is evidence that both the frontal eye field (FEF) and supplementary eye field (SEF) (also known as the dorsomedial frontal cortex) contribute to pursuit control. The goal of the current experiment was to determine whether these 2 areas made different contributions to the initiation of pursuit in response to predictable compared with unpredictable target motion. Transcranial magnetic stimulation (TMS) was used in 5 healthy human participants to temporarily disrupt each area around the time of target motion onset. TMS over the FEF delayed contraversive pursuit markedly more than ipsiversive pursuit and this direction-dependent difference was more deeply modulated during pursuit of unpredictable than predictable target motion. By contrast, TMS over the SEF resulted in a much more muted modulation of pursuit latency that was similar across both predictable and unpredictable conditions. Taken together, we conclude that the human FEF, but not the SEF, makes a significant contribution to the processing required during the preparation of contraversive pursuit responses to unpredictable target motion and this contribution is less vital during pursuit to predictable target motion.

Cancelling planned actions following mild traumatic brain injury.

Mild traumatic brain injury (mTBI) leads to a variety of attentional, cognitive, and sensorimotor deficits. An important aspect of behavior that intersects each of these functions is the ability to cancel a planned action. Thus, the purpose of this study was to determine the effects of mTBI on the ability to perform a countermanding saccade task. In this task, participants were asked to generate a saccade to a target appearing in peripheral vision, but to inhibit saccade execution if an auditory stop signal was presented. The delay between the appearance of the peripheral target and the presentation of the auditory stop signal was varied between 0 and 125ms. We found that the change in the probability of cancelling the saccade as a function of this delay was no different between participants with mTBI tested within 2 days of their injury and matched controls. However, saccadic reaction times and the stop signal reaction time were unexpectedly faster in the participants with mTBI and, furthermore, they inaccurately inhibited saccades during 15% of the trials with no stop signal. Taken together, this data suggests that the ability to cancel planned actions is subtly yet adversely affected by mTBI.

The influence of mild traumatic brain injury on the temporal distribution of attention.

The purpose of this study was to examine whether the temporal dynamics of attention was deficient in participants who have recently experienced mild traumatic brain injury (mTBI). For this purpose the rapid serial visual presentation (RSVP) task was used and the performance of participants with mTBI was compared to that of controls matched for age, gender, education, and activity type. In the RSVP task a stream of rapidly presented letters is displayed with target and probe letters separated by varying durations. The participant is required to identify the target letter and determine whether the probe letter was present or not. Previous research has shown that healthy participants display an attentional blink: they fail to detect the probe letter when it appears within approximately 500 ms of the target letter. We found that participants with mTBI had a normal attentional blink-it was neither greater in magnitude nor longer in duration than that displayed by the control participants. However, the participants with mTBI did show evidence of attentional competition-making more errors in identifying the target letter when the probe letter was presented-that was not present in the control participants. Taken together, these results suggest that the temporal constraints of attention are subtly but systematically affected by mTBI.

Tracking the recovery of visuospatial attention deficits in mild traumatic brain injury.

The goal of the current investigation was to probe the deficits in the alerting, orienting and executive components of visuospatial attention in individuals who have recently suffered a mild traumatic brain injury (mTBI) and to assess the rate and degree of recovery for each of these components over a month post-injury. A group design was employed to assess and compare the performance of participants (12 males, 8 females; mean age: 21 +/- 1.74 years) identified with mTBI relative to control subjects matched for gender, age, height, weight and activity level. Participants performed the attentional network test, designed to isolate the constituents of attention into alerting, orienting and executive components. Reaction times (RTs) and response accuracy were the main dependent variables. The results showed that the orienting and executive components were significantly affected by mTBI immediately after the injury, whereas the alerting component was not. Furthermore, participants with mTBI recovered from the deficits in the orienting component of attention within a week of their injury, whereas the deficits in the executive component remained throughout the month post-injury. In addition, the RT cost to generate accurate compared with inaccurate responses was significantly larger in participants with mTBI than in controls, and this difference was maintained throughout the 1 month testing period. These findings indicate that the regions of the brain associated with the orienting and executive components of visuospatial attention may be most susceptible to neural damage resulting from mTBI. Moreover, the lack of recovery in the executive component indicates that the degree and time course for recovery may be regionally specific.

Eye-hand interactions differ in the human premotor and parietal cortices.

In order to successfully look at and reach for a visual target the central nervous system must perform a complex sensorimotor transformation. How this transformation is mapped onto relevant brain structures has become the subject of much recent investigation. In the present paper we examined the contribution of the human premotor cortex (PMC) to this transformation process during a task requiring coordinated eye and hand movements. For this purpose, we made use of single-pulse transcranial magnetic stimulation (TMS) to temporarily disrupt the processing occurring in the PMC during task performance. Subjects made open-loop pointing movements accompanied by saccades of the same size or two or three times larger. Under normal circumstances without TMS, the pointing movement amplitude increased with saccade amplitude. When TMS was applied over the PMC 100-200 ms after target presentation, the influence of saccade amplitude on the pointing movement amplitude was increased. This is the opposite effect to that observed in a previous study [Journal of Neurophysiology 84 (200) 1677-1680] when TMS was applied over the posterior parietal cortex (PPC) during the same task. We suggest that this pattern of results is consistent with the coding of the reach plan in eye-centered coordinates in the PPC and limb-centered coordinates in the PMC.

The allocation of attention during smooth pursuit eye movements.

The spatial-temporal allocation of attention during smooth pursuit eye movements is poorly understood. In this chapter we review evidence showing that attention contributes to both saccades and smooth pursuit. We then discuss results from our own recent studies using a dual-task paradigm in which subjects pursued a moving stimulus and pressed a button when targets appeared in the periphery. The results from these studies are consistent with the hypothesis that the allocation of attention is biased to a location just in front of the pursuit stimulus and that this bias can be altered by pursuit velocity.

Cortical frames of reference for eye-hand coordination.

To reach for an object the brain must transform visual input from the eye into motor output of the arm. Recent neurophysiological experiments have shown that this transformation maps onto a network of brain areas including the posterior parietal (PPC) and premotor (PMC) cortices. In this chapter, we review evidence from our own experiments which demonstrate that this network can only partially complete the transformation when the eye and limb movement amplitudes are dissociated. We also discuss the effects of disrupting either the PPC or PMC using transcranial magnetic stimulation (TMS) on the ability to carry out the transformation successfully.