Understanding Visual Processing After Occipital Stroke

N/AWithdrawnNCT06352086

University of Rochester

Overview

The purpose of this study is to investigate how visual orientation discrimination and metacognition (i.e., perceptual confidence) are affected by occipital stroke that causes hemianopia and quadrantanopia in adults. This research will provide insight as to how the residual visual system, which not directly damaged by the occipital stroke, processes orientation (assayed in terms of orientation discrimination) and metacognition (by measuring perceptual confidence for orientation discrimination). These measures will be used to refine computational models that attempt to explain how the brain copes with loss of primary visual cortex (V1) as a result of stroke. This knowledge is essential to devise more effective visual rehabilitation therapies for patients suffering from occipital strokes.

Study Type

OBSERVATIONAL

Conditions

Vision Loss Partial Vision; Loss, Both Eyes Hemianopia, Homonymous Hemianopia Quadrantanopia Stroke, Ischemic Stroke - Occipital Infarction

Eligibility

Sex: ALLMin age: 21 YearsMax age: 75 Years

Medical Language ↔ Plain English

Inclusion Criteria: * Residents of the United States or Canada * MRI and/or CT scans showing unilateral stroke or stroke-like damage to primary visual cortex or its immediate afferent white matter sustained 1-year or more prior to enrollment * Reliable visual field defects in both eyes as measured by Humphrey, Macular Integrity Assessment (MAIA), Goldmann, and/or equivalent perimetry. This deficit must be large enough to enclose a 5-deg diameter visual stimulus. * Ability to fixate on visual targets reliably for 1000ms (as demonstrated by visual fields, and verified in study participation) * Willing, able, and competent to provide informed consent * Cognitively able to understand and respond to written and oral instructions in English Exclusion Criteria: * Past or present ocular disease interfering with visual acuity * Corrected vision worse than 20/40 in either eye * Presence of damage to the dorsal Lateral Geniculate Nucleus * Diffuse, whole brain degenerative processes * Brain damage deemed by study staff to potentially interfere with testing ability or outcome measures * Documented history of traumatic brain injury * Documented history of drug/alcohol abuse * Current use neuroactive * Cognitive or seizure disorders * Subjects with one-sided attentional neglect

Outcomes

Primary Outcomes

Orientation discrimination threshold

Assessment of Static Orientation Discrimination. For each subject, the investigators will measure the ability to correctly identify the orientation of non-moving visual stimuli that vary in degree of angle tilt to the right or left of vertical. The investigators will measure the degree of angle tilt that can be reliably detected at a 72-75% correct level of performance. Tilt difference from vertical will vary between 80° (maximum) and 0.1° (minimum) based on subject performance and an adaptive staircase that will change tilt magnitude depending on subject performance, increasing the tilt (making the task easier) for each incorrect answers and decreasing tilt (making the task harder) after a number of correct answers in a row.

Time frame: Baseline

Perceptual Confidence in Orientation Discrimination

Assessment of Metacognition (i.e., perceptual confidence) in Orientation Discrimination. For each subject, the investigators will measure their confidence in identifying an object's tilt to the right or left of vertical. A running tally of 'response points' will be collected during the orientation testing. Points will be awarded for each response on a scale, with the highest points awarded for "correct discrimination \& high confidence", intermediate points awarded for "correct discrimination \& low confidence", followed by "incorrect discrimination \& low confidence" and with points subtracted for "incorrect discrimination \& high confidence". Total points will be recorded for each test, with the patient asked to accumulate the highest number of points they can during the task.

Time frame: Baseline