Measurement of Position Acuity in Strabismus and Amblyopia: Specificity of the Vernier VEP Paradigm

PURPOSE. An objective measure of positional acuity is desirable in the nonverbal clinical population. This study was conducted to investigate the specificity of the vernier VEP as a measure of positional acuity, evaluating the potential confound of asymmetric motion responses that may be present in some groups of patients. These motion responses could masquerade as position-specific responses, since they occur at the same response frequency as the vernier-related response. METHODS. Twelve observers with early-onset esotropia (EOE), 30 children with untreated amblyopia, and 15 control children underwent swept vernier VEP acuity testing accompanied by a swept motion control stimulus. The control condition was used to detect the presence of artifactual responses not related to position sensitivity. The patients with EOE were selected for high levels of motion asymmetry as documented with oscillating gratings presented monocularly. As a measure of motion confound (penetration), the proportion of first-harmonic responses recorded in the control condition was determined. RESULTS. The penetration rate in the vernier condition in each study group (EOE: 0.93%; amblyopes: 4.26%; normal subjects: 2.40%) and the entire group (2.85%) was acceptably low. The level of penetration was not significantly influenced by the presence of amblyopia. CONCLUSIONS. The vernier VEP paradigm, when applied in the manner described, can be interpreted as a measure of position sensitivity. The presence of motion asymmetry or untreated amblyopia does not affect the validity of vernier measurements made. (Invest Ophthalmol Vis Sci. 2005;46:4563-4570) DOI: 10.1167/iovs.05-0792 I t is well-known, on the one hand, that grating acuity systematically underestimates optotype acuity losses in amblyopia. 1-7 On the other hand, losses on vernier acuity more closely match the loss of optotype acuity than do losses on grating acuity. Visual evoked potentials (VEPs) provide another means of assessing visual function in nonverbal subjects. VEPs specific to vernier offsets have been measured in several studies. The steady state vernier VEP 26 -29 involves the periodic introduction and withdrawal of vernier offsets in a high-contrast square-wave grating target 26 A difficulty in applying the steady state vernier VEP in clinical populations is the possible presence of motion responses that are not symmetric. A clear example of asymmetric motion VEP responses occurs in patients with early-onset esotropia (EOE) in which the monocular response to rapidly oscillating gratings is dominated by odd-harmonic components that reflect the asymmetry of motion processing. 30 -35 A similar asymmetry is found in the monocular response of normal infants. This evidence suggests that a horizontally oriented carrier grating with vertically introduced vernier offsets offers a better choice of stimulus design. In this study, we examine the levels of motion contamination and confound of the steady state vernier VEP by recordings of patients with early-onset esotropia who first had a high level of motion asymmetry docuFrom th

Population Receptive Field Dynamics in Human Visual Cortex

Seminal work in the early nineties revealed that the visual receptive field of neurons in cat primary visual cortex can change in location and size when artificial scotomas are applied. Recent work now suggests that these single neuron receptive field dynamics also pertain to the neuronal population receptive field (pRF) that can be measured in humans with functional magnetic resonance imaging (fMRI). To examine this further, we estimated the pRF in twelve healthy participants while masking the central portion of the visual field. We found that the pRF changes in location and size for two differently sized artificial scotomas, and that these pRF dynamics are most likely due to a combination of the neuronal receptive field position and size scatter as well as modulatory feedback signals from extrastriate visual areas

The chronic pain skills study: Protocol for a randomized controlled trial comparing hypnosis, mindfulness meditation and pain education in Veterans

Objectives: To describe the protocol of a randomized controlled trial to evaluate the effectiveness and mechanisms of three behavioral interventions. Methods: Participants will include up to 343 Veterans with chronic pain due to a broad range of etiologies, randomly assigned to one of three 8-week manualized in-person group treatments: (1) Hypnosis (HYP), (2) Mindfulness Meditation (MM), or (3) Education Control (EDU). Projected outcomes: The primary aim of the study is to compare the effectiveness of HYP and MM to EDU on average pain intensity measured pre- and post-treatment. Additional study aims will explore the effectiveness of HYP and MM compared to EDU on secondary outcomes (i.e., pain interference, sleep, depression, anxiety and PTSD), and the maintenance of effects at 3- and 6-months post-treatment. Participants will have electroencephalogram (EEG) assessments at pre- and post-treatment to determine if the power of specific brain oscillations moderate the effectiveness of HYP and MM (Study Aim 2) and examine brain oscillations as possible mediators of treatment effects (exploratory aim). Additional planned exploratory analyses will be performed to identify possible treatment mediators (i.e., pain acceptance, catastrophizing, mindfulness) and moderators (e.g., hypnotizability, treatment expectations, pain type, cognitive function). Setting: The study treatments will be administered at a large Veterans Affairs Medical Center in the northwest United States. The treatments will be integrated within clinical infrastructure and delivered by licensed and credentialed health care professionals